Modelling the Anthropocene

[AbruptSLR]

The linked references discusses the level of modeling effort recommended to reduce uncertainty of projecting future changes in the ENSO due to internal variability:

Xiao-Tong Zheng, Chang Hui & Sang-Wook Yeh (2017), "Response of ENSO amplitude to global warming in CESM large ensemble: uncertainty due to internal variability", Climate Dynamics, pp 1–17, https://doi.org/10.1007/s00382-017-3859-7

https://rd.springer.com/article/10.1007%2Fs00382-017-3859-7?utm_content=bufferc17f2&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "El Niño–Southern Oscillation (ENSO) is the dominant mode of variability in the coupled ocean-atmospheric system. Future projections of ENSO change under global warming are highly uncertain among models. In this study, the effect of internal variability on ENSO amplitude change in future climate projections is investigated based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project. A large uncertainty is identified among ensemble members due to internal variability. The inter-member diversity is associated with a zonal dipole pattern of sea surface temperature (SST) change in the mean along the equator, which is similar to the second empirical orthogonal function (EOF) mode of tropical Pacific decadal variability (TPDV) in the unforced control simulation. The uncertainty in CESM-LE is comparable in magnitude to that among models of the Coupled Model Intercomparison Project phase 5 (CMIP5), suggesting the contribution of internal variability to the intermodel uncertainty in ENSO amplitude change. However, the causations between changes in ENSO amplitude and the mean state are distinct between CESM-LE and CMIP5 ensemble. The CESM-LE results indicate that a large ensemble of ~15 members is needed to separate the relative contributions to ENSO amplitude change over the twenty-first century between forced response and internal variability."

[AbruptSLR]

The linked reference uses a climate model to help quantify the impact of "Earth greening" on global warming & found that global land-surface warming was decreased by about 12% (over the past 30 years) due to this consideration.  This makes me wonder what will happen if/when "Earth greening" moves in the negative direction due to climate and land use stresses on vegetation:

Zhenzhong Zeng et. al. (2017), "Climate mitigation from vegetation biophysical feedbacks during the past three decades", Nature Climate Change  7, 432–436, doi:10.1038/nclimate3299

http://www.nature.com/nclimate/journal/v7/n6/full/nclimate3299.html?foxtrotcallback=true

Abstract: "The surface air temperature response to vegetation changes has been studied for the extreme case of land-cover change; yet, it has never been quantified for the slow but persistent increase in leaf area index (LAI) observed over the past 30 years (Earth greening). Here we isolate the fingerprint of increasing LAI on surface air temperature using a coupled land–atmosphere global climate model prescribed with satellite LAI observations. We find that the global greening has slowed down the rise in global land-surface air temperature by 0.09 ± 0.02 °C since 1982. This net cooling effect is the sum of cooling from increased evapotranspiration (70%), changed atmospheric circulation (44%), decreased shortwave transmissivity (21%), and warming from increased longwave air emissivity (−29%) and decreased albedo (−6%). The global cooling originated from the regions where LAI has increased, including boreal Eurasia, Europe, India, northwest Amazonia, and the Sahel. Increasing LAI did not, however, significantly change surface air temperature in eastern North America and East Asia, where the effects of large-scale atmospheric circulation changes mask local vegetation feedbacks. Overall, the sum of biophysical feedbacks related to the greening of the Earth mitigated 12% of global land-surface warming for the past 30 years."

[AbruptSLR]

The linked comparison study provides insights into issues such as those raised by Sherwood et al (2014).  While the reference makes no definitive conclusions, it does highlight the importance of correctly modeling slow response feedback mechanisms associated with the ocean heat uptake (particularly in the (Equatorial Pacific) since 1750:

Kuan-Man Xu et al (9 September 2017), "Differences in the hydrological cycle and sensitivity between multiscale modeling frameworks with and without a higher-order turbulence closure", JAMES, DOI: 10.1002/2017MS000970

http://onlinelibrary.wiley.com/doi/10.1002/2017MS000970/full

Abstract: "Current conventional global climate models (GCMs) produce a weak increase in global-mean precipitation with anthropogenic warming in comparison with the lower tropospheric moisture increases. The motive of this study is to understand the differences in the hydrological sensitivity between two multiscale modeling frameworks (MMFs) that arise from the different treatments of turbulence and low clouds in order to aid to the understanding of the model spread among conventional GCMs. We compare the hydrological sensitivity and its energetic constraint from MMFs with (SPCAM-IPHOC) or without (SPCAM) an advanced higher-order turbulence closure. SPCAM-IPHOC simulates higher global hydrological sensitivity for the slow response but lower sensitivity for the fast response than SPCAM. Their differences are comparable to the spreads of conventional GCMs. The higher sensitivity in SPCAM-IPHOC is associated with the higher ratio of the changes in latent heating to those in net atmospheric radiative cooling, which is further related to a stronger decrease in the Bowen ratio with warming than in SPCAM. The higher sensitivity of cloud radiative cooling resulting from the lack of low clouds in SPCAM is another major factor in contributing to the lower precipitation sensitivity. The two MMFs differ greatly in the hydrological sensitivity over the tropical lands, where the simulated sensitivity of surface sensible heat fluxes to surface warming and CO2 increase in SPCAM-IPHOC is weaker than in SPCAM. The difference in divergences of dry static energy flux simulated by the two MMFs also contributes to the difference in land precipitation sensitivity between the two models."

Edit, see also:

Sherwood, S.C., Bony, S. and Dufresne, J.-L., (2014) "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; Volume: 505, pp 37–42, doi:10.1038/nature12829

http://www.nature.com/nature/journal/v505/n7481/full/nature12829.html

Fasullo, J.T. and Trenberth, K.E., (2012), "A Less Cloudy Future: The Role of Subtropical Subsidence in Climate Sensitivity", Science, vol. 338, pp. 792-794, 2012. http://dx.doi.org/10.1126/science.1227465.

http://www.sciencemag.org/content/338/6108/792

[AbruptSLR]

The unusually high Pacific trade winds in recent decades is frequently associated with the faux hiatus; and the linked reference discusses bias in CMIP5 projections that resulted in under-predictions of the strength of these Pacific trade winds during the faux hiatus.

Jules B. Kajtar, Agus Santoso, Shayne McGregor, Matthew H. England & Zak Baillie (2017), "Model under-representation of decadal Pacific trade wind trends and its link to tropical Atlantic bias", Climate Dynamics", doi:10.1007/s00382-017-3699-5

https://link.springer.com/article/10.1007/s00382-017-3699-5

Abstract: "The strengthening of the Pacific trade winds in recent decades has been unmatched in the observational record stretching back to the early twentieth century. This wind strengthening has been connected with numerous climate-related phenomena, including accelerated sea-level rise in the western Pacific, alterations to Indo-Pacific ocean currents, increased ocean heat uptake, and a slow-down in the rate of global-mean surface warming. Here we show that models in the Coupled Model Intercomparison Project phase 5 underestimate the observed range of decadal trends in the Pacific trade winds, despite capturing the range in decadal sea surface temperature (SST) variability. Analysis of observational data suggests that tropical Atlantic SST contributes considerably to the Pacific trade wind trends, whereas the Atlantic feedback in coupled models is muted. Atmosphere-only simulations forced by observed SST are capable of recovering the time-variation and the magnitude of the trade wind trends. Hence, we explore whether it is the biases in the mean or in the anomalous SST patterns that are responsible for the under-representation in fully coupled models. Over interannual time-scales, we find that model biases in the patterns of Atlantic SST anomalies are the strongest source of error in the precipitation and atmospheric circulation response. In contrast, on decadal time-scales, the magnitude of the model biases in Atlantic mean SST are directly linked with the trade wind variability response."

[6roucho]

AnruptSLR, how do you read so much and so widely? You're a machine!

[AbruptSLR]

AnruptSLR, how do you read so much and so widely? You're a machine!

As noted in the Adapting to the Anthropocene thread, by "... the recursive application of: deductive logic, inductive logic, the reduction of entropy, concentration/focus/effort/work and letting go of preconditioning ... "

[AbruptSLR]

Given the complex nature of climate change, I think that CMIP6 and similarly future modeling efforts would do well to follow the advice given in the linked reference to combine "… dynamical modeling with data-driven methodological approaches (i.e., neural networks and Granger causality) …".

Fulvio Mazzocchi & Antonello Pasini (31 May 2017), "Climate model pluralism beyond dynamical ensembles", Wires: Climate Change, DOI: 10.1002/wcc.477

http://onlinelibrary.wiley.com/doi/10.1002/wcc.477/full

Abstract: "Using pluralist research strategies can be a profitable way to study complex systems. This contribution focuses on the approaches for studying the climate that make use of multiple different models, aiming to increase the reliability (in terms of robustness) of attribution results. This Opinion article argues that the traditional approach, which is based on ensemble runs of global climate models, only partially allows the application of a robustness scheme, owing to the difficulty to match or evaluate the conditions required for robustness (i.e., independence or heterogeneity among models). An alternative ‘multi-approach’ strategy is advanced, beyond dynamical modeling but still preserving the idea of model pluralism. Such a strategy, which uses a set of ensembles of different model types by combining dynamical modeling with data-driven methodological approaches (i.e., neural networks and Granger causality), seems to better match the condition of independence. In addition, neural networks and Granger causality lead to achievements in attribution studies that can complement those obtained by dynamical modeling."

[AbruptSLR]

The linked opinion piece describes actual and proposed systemic changes to CESM made in an effort to try to help modelers to gain a better understanding of the various Earth's Systems.  If this is done with sincerity it is a good idea; however, if managers/policy makers see that this affords them an opportunity to put their collective thumb on the modeling process/outcome then it is a bad idea:

Title: "When Less Is More: Opening the Door to Simpler Climate Models"

https://eos.org/opinions/when-less-is-more-opening-the-door-to-simpler-climate-models?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz092917

Extract: "Earth system models are resource intensive and complex. To cut through this complexity, the Community Earth System Model project will now be embracing a hierarchy of simpler climate models.
…
In a nutshell, ESMs may be good for simulating the climate system but may not be as valuable for understanding it. So we have now added a new set of tools within the Community Earth System Model (CESM) project: a hierarchy of simpler models to foster this understanding. Specifically, we are happy to announce that the next version of CESM will include two simple atmospheric models: a “dynamical core” and an “aquaplanet.”
…
We conclude by emphasizing one crucial point in Held’s proposal: Models in the hierarchy must be of lasting value. ESMs are constantly under development to promptly incorporate the latest findings or methods. However, we believe that at least some of the models in the hierarchy need to be forcefully shielded from the relentless cycle of model improving and updating. If those models are well chosen, their value will come precisely from the fact that they are not being updated. Because they remain unchanged, we will be able to understand them in great depth and thus close the gap between simulation and understanding—the ultimate motivation of this entire exercise."

[AbruptSLR]

The linked reference examines the output from CMIP5 projections to better differentiate between fast and slow components of the extratropical atmospheric circulation response to stepped radiative forcing.  I note that CMIP5 does not consider hosing from ice sheet mass loss & thus does not consider ice-climate feedback.  Nevertheless, the findings do indicate: (1) a fast response within 5 to 10 years of the stepped forcing; (2) an increase in ENSO activity (& increase in associated positive feedback mechanisms); and (3) an increase in Antarctic Amplification.  Hopefully, CMIP6 will consider freshwater hosing and ice-climate feedback.

Paulo Ceppi, Giuseppe Zappa, and Theodore G. Shepherd (28 September 2017), "Fast and slow components of the extratropical atmospheric circulation response to CO2 forcing", Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0323.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0323.1?utm_content=buffer2cb5c&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Poleward shifts of the extratropical atmospheric circulation are a common response to CO2 forcing in global climate models (GCMs), but little is known about the time dependence of this response. Here it is shown that in coupled climate models, the long-term evolution of sea surface temperatures (SSTs) induces two distinct time scales of circulation response to step-like CO2 forcing. In most Coupled Model Intercomparison Project phase 5 GCMs as well as in the multi-model mean, all of the poleward shift of the midlatitude jets and Hadley cell edge occurs in a fast response within 5 to 10 years of the forcing, during which less than half of the expected equilibrium warming is realized. Compared with this fast response, the slow response over subsequent decades to centuries features stronger polar amplification (especially in the Antarctic), enhanced warming in the Southern Ocean, an El Niño-like pattern of tropical Pacific warming, and weaker land-sea contrast. Atmosphere-only GCM experiments demonstrate that the SST evolution drives the difference between the fast and slow circulation responses, although the direct radiative effect of CO2 also contributes to the fast response. It is further shown that the fast and slow responses determine the long-term evolution of the circulation response to warming in the RCP4.5 scenario. The results imply that shifts in midlatitude circulation generally scale with the radiative forcing, rather than with global-mean temperature change. A corollary is that time slices taken from a transient simulation at a given level of warming will considerably overestimate the extratropical circulation response in a stabilized climate."

[AbruptSLR]

The linked article recommends that future climate change projections should account for the effects of future volcanic eruptions, and I note that this should include the eruption of halogen emitting volcanoes in the WAIS:

Title: "5 links between erupting volcanoes and climate change"

https://www.eenews.net/stories/1060062893

Extract: "The effects of volcanoes need to be accounted for in future climate change predictions, according to a study published in August in Nature Climate Change. As researchers make future predictions from climate models, they need to factor in major eruptions over the next century, said Ed Hawkins, a climatologist at the University of Reading. To accurately forecast how climate change will transform the planet, researchers must account for temporary periods of cooling that come from volcanoes, according to Hawkins.

"Including some eruptions makes the changes in global temperature more variable, but as the effects of eruptions are only temporary they will not counteract the warming from greenhouse gases over the next century," he wrote in an email."

[AbruptSLR]

The former ACME project is now the Energy Exascale Earth System Model (E3SM) Project

Title: "Energy Exascale Earth System Model"

https://climatemodeling.science.energy.gov/projects/energy-exascale-earth-system-model

Extract: "The Energy Exascale Earth System Model (E3SM) project, previously known as ACME, is central to ESM as well as many of the Climate and Environmental Sciences Division activities, as it is developing a computationally advanced coupled climate-energy model to investigate the challenges posed by the interactions of weather-climate scale variability with energy and related sectors. The E3SM model simulates the fully coupled Earth system at high-resolution (15-25km, including higher resolution within regionally refined areas) and is incorporating coupling with energy, water, land-use and related energy-relevant activities, with a focus on near-term hind-casts (1970-2015) for model validation and a near-term projection (2015-2050) as needed for energy sector planning."

[AbruptSLR]

While the linked reference's study of an Earth-like terra-planet may be of somewhat academic interest for newly discovered planets, the authors do note its possible relevance to an imaginary drop from present day conditions to the Snowball Earth state:

Kalidindi, S., Reick, C. H., Raddatz, T., and Claussen, M.: Two drastically different climate states on an Earth-like terra-planet, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-84, in review, 2017.

https://www.earth-syst-dynam-discuss.net/esd-2017-84/

Abstract. We study an Earth-like terra-planet with an overland recycling mechanism bringing fresh water back from higher latitudes to the lower latitudes. By performing model simulations for such a planet we find two drastically different climate states for the same set of boundary conditions and parameter values: A Cold and Wet (CW) state (present-day Earth-like climate) with dominant low-latitude precipitation and, a Hot and Dry (HD) state with only high-latitude precipitation. We notice that for perpetual equinox conditions, both climate states are stable below a certain threshold value of background soil albedo while above the threshold only the CW state is stable. Starting from the HD state and increasing background soil albedo above the threshold causes an abrupt shift from the HD state to the CW state resulting in a sudden cooling of about 35 °C globally which is of the order of the temperature difference between the present-day and the Snowball Earth state. In contrast to the Snowball Earth instability, we find that the sudden cooling in our study is driven by the cloud albedo feedback rather than the snow-albedo feedback. Also, when albedo in the CW state is reduced back to zero the terra-planet does not display a closed hysteresis. This is due to the high cloud cover in the CW state hiding the surface from solar irradiation. As a result, this reduction of background surface albedo has only a minor effect on the top of the atmosphere radiation balance, thereby making it impossible to heat the planet sufficiently strongly to switch back to the HD state. Additional simulations point to a similar abrupt transition from HD state to the CW state for non-zero obliquity which is the only stable state in this configuration. Our study also has implications for the habitability of Earth-like terra-planets. At the inner edge of the habitable zone, the higher cloud cover in the CW state cools the planet and may prevent the onset of a runaway greenhouse state. At the outer edge, the resupply of water at lower latitudes stabilizes the greenhouse effect and keeps the planet in the HD state and may prevent water from getting trapped at higher latitudes in frozen form. Overall, the existence of bi-stability in the presence of an overland recycling mechanism hints at the possibility of a wider habitable zone for Earth-like terra-planets at lower obliquities.

[AbruptSLR]

The linked reference discusses a climate model of intermediate sophistication that represents an initial effort to model Earth Systems subject to changing from on climate state to another due to periodic climate attractors:

Valerio Lucarini and Tamás Bódai (2017), "Edge states in the climate system: exploring global instabilities and critical transitions", Nonlinearity 30 R32, https://doi.org/10.1088/1361-6544/aa6b11

http://iopscience.iop.org/article/10.1088/1361-6544/aa6b11/meta

Abstract: "Multistability is a ubiquitous feature in systems of geophysical relevance and provides key challenges for our ability to predict a system's response to perturbations. Near critical transitions small causes can lead to large effects and—for all practical purposes—irreversible changes in the properties of the system. As is well known, the Earth climate is multistable: present astronomical and astrophysical conditions support two stable regimes, the warm climate we live in, and a snowball climate characterized by global glaciation. We first provide an overview of methods and ideas relevant for studying the climate response to forcings and focus on the properties of critical transitions in the context of both stochastic and deterministic dynamics, and assess strengths and weaknesses of simplified approaches to the problem. Following an idea developed by Eckhardt and collaborators for the investigation of multistable turbulent fluid dynamical systems, we study the global instability giving rise to the snowball/warm multistability in the climate system by identifying the climatic edge state, a saddle embedded in the boundary between the two basins of attraction of the stable climates. The edge state attracts initial conditions belonging to such a boundary and, while being defined by the deterministic dynamics, is the gate facilitating noise-induced transitions between competing attractors. We use a simplified yet Earth-like intermediate complexity climate model constructed by coupling a primitive equations model of the atmosphere with a simple diffusive ocean. We refer to the climatic edge states as Melancholia states and provide an extensive analysis of their features. We study their dynamics, their symmetry properties, and we follow a complex set of bifurcations. We find situations where the Melancholia state has chaotic dynamics. In these cases, we have that the basin boundary between the two basins of attraction is a strange geometric set with a nearly zero codimension, and relate this feature to the time scale separation between instabilities occurring on weather and climatic time scales. We also discover a new stable climatic state that is similar to a Melancholia state and is characterized by non-trivial symmetry properties."

[Adam Ash]

Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes
https://www.nature.com/articles/s41467-017-01225-9

According to the current methodology, the temperature of the ocean depths, and the surface of the polar ocean, was some 15C (59F) higher 100 million years ago, compared to now.

These estimates have been challenged, however, by a joint team of researchers from the French National Center for Scientific Research (CNRS) and the Swiss Federal Institute of Technology in Lausanne (EPFL).

In their study, published in Nature Communications, the team posits that ocean temperatures may have remained relatively stable throughout this period, raising serious concerns about the current level of climate change being experienced by Mother Earth.

[sidd]

If that Bernard paper holds up, it answers the question as to why the polar oceans in Cretaceous and Paleogene were so much warmer. The answer is that they were not, and the equator to pole gradient was larger than supposed.

"Furthermore, the present study suggests that the vertical and latitudinal temperature gradients of the late Cretaceous and Paleogene oceans were likely not very different from the current ones."

Fig 4 tells the story. I attach.

sidd

[AbruptSLR]

Tropical-Extratropical telecommunications (particularly w.r.t. ENSO patterns) are of fundamental importance for understanding numerous feedback mechanisms including Arctic Amplification and Hansen's ice-climate feedback (especially w.r.t. WAIS stability):

Cristiana Stan, David M. Straus, Jorgen S. Frederiksen, Hai Lin, Eric D. Maloney & Courtney Schumacher
 (24 October 2017), "Review of Tropical-Extratropical Teleconnections on Intraseasonal Time Scales", Review of Geophysics, DOI: 10.1002/2016RG000538

http://onlinelibrary.wiley.com/doi/10.1002/2016RG000538/abstract

Abstract: "The interactions and teleconnections between the tropical and midlatitude regions on intraseasonal time scales are an important modulator of tropical and extratropical circulation anomalies and their associated weather patterns. These interactions arise due to the impact of the tropics on the extratropics, the impact of the midlatitudes on the tropics, and two-way interactions between the regions. Observational evidence, as well as theoretical studies with models of complexity ranging from the linear barotropic framework to intricate Earth system models, suggest the involvement of a myriad of processes and mechanisms in generating and maintaining these interconnections. At this stage, our understanding of these teleconnections is primarily a collection of concepts; a comprehensive theoretical framework has yet to be established. These intraseasonal teleconnections are increasingly recognized as an untapped source of potential subseasonal predictability. However, the complexity and diversity of mechanisms associated with these teleconnections, along with the lack of a conceptual framework to relate them, prevent this potential predictability from being translated into realized forecast skill. This review synthesizes our progress in understanding the observed characteristics of intraseasonal tropical-extratropical interactions and their associated mechanisms, identifies the significant gaps in this understanding, and recommends new research endeavors to address the remaining challenges."

[AbruptSLR]

The linked article indicates that in order to more accurately model the Atlantic Meridional Mode, cloud feedback needs to be positive:

Myers, T.A., Mechoso, C.R. & DeFlorio, M.J. (2017), "Importance of positive cloud feedback for tropical Atlantic interhemispheric climate variability", Clim Dy., https://doi.org/10.1007/s00382-017-3978-1

https://link.springer.com/article/10.1007%2Fs00382-017-3978-1?utm_content=buffer90766&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Over the tropical Atlantic during boreal spring, average interhemispheric differences in sea-surface temperature (SST) coincide with a coherent pattern of interannual climate variability often referred to as the Atlantic Meridional Mode. This includes anomalous SST and sea-level pressure roughly anti-symmetric about the equator, as well as cross-equatorial near-surface winds directed toward the warmer hemisphere. Within subtropical marine boundary layer cloud regions in both hemispheres, enhanced cloudiness associated with this variability is co-located with cool SST, a strong temperature inversion, and cold horizontal surface temperature advection, while reduced cloudiness is associated with the opposite meteorological conditions. This is indicative a positive cloud feedback that reinforces the underlying SST anomalies. The simulation of this feedback varies widely among models participating in phase 5 of the Coupled Model Intercomparison Project. Models that fail to simulate this feedback substantially underestimate the amplitudes of typical tropical Atlantic interhemispheric variability in cloudiness off of the equator, SST, and atmospheric circulation. Models that correctly reproduce a positive cloud feedback generally produce higher and more realistic amplitudes of variability, but with substantial scatter. Marine boundary layer clouds therefore appear to be a key element of springtime coupled atmosphere–ocean variability over the tropical Atlantic. A markedly more successful simulation of this variability in climate models may be obtained by better representing boundary layer cloud processes."

[AbruptSLR]

If that Bernard paper holds up, it answers the question as to why the polar oceans in Cretaceous and Paleogene were so much warmer. The answer is that they were not, and the equator to pole gradient was larger than supposed.

I think that the key take away message here is that current climate models have likely been calibrated to over predict the amount of heat energy that the oceans will absorb with continuing radiative forcing; which will leave more heat in the atmosphere resulting in more rapid increases in GMSTA (global mean surface temperature anomalies), which implies that ECS is likely towards the upper end of model projections.

[AbruptSLR]

If you want a model to indicate that you will succeed, all you have to do is to jack around with your assumption/input; and then claim plausible deniability when your projects don't match the future reality. 

Title: "Guest post: Who will deliver the negative emissions needed to avoid 2C warming?"

https://www.carbonbrief.org/guest-post-who-will-deliver-the-negative-emissions-needed-to-avoid-2c-warming

Extract: "“Negative emissions”, also known as “carbon dioxide removal” (CDR), refers to a group of approaches and technologies that take CO2 from the atmosphere and store it on land, underground or in the oceans.
…
Integrated Assessment Models (IAMs) also indicate that it is cheaper to have large-scale CDR in the future, than to have deeper mitigation now.

Love it or hate it, it may be that CDR is simply unavoidable if society wants to stabilise temperatures. If one can accept that we need CDR, the real debate becomes at what scale.

The land areas required for such large-scale CDR would be the size of India, or even larger."

[AbruptSLR]

The linked open access reference discusses improvements to modeling global soil carbon:

Kefeng Wang, Changhui Peng, Qiuan Zhu, Xiaolu Zhou, Meng Wang, Kerou Zhang & Gangsheng Wang (27 October 2017), "Modeling Global Soil Carbon and Soil Microbial Carbon by Integrating Microbial Processes into the Ecosystem Process Model TRIPLEX-GHG", JAMES, DOI: 10.1002/2017MS000920 

http://onlinelibrary.wiley.com/doi/10.1002/2017MS000920/full

Abstract: "Microbial physiology plays a critical role in the biogeochemical cycles of the Earth system. However, most traditional soil carbon models are lacking in terms of the representation of key microbial processes that control the soil carbon response to global climate change. In this study, the improved process-based model TRIPLEX-GHG was developed by coupling it with the new MEND (Microbial-ENzyme-mediated Decomposition) model to estimate total global soil organic carbon (SOC) and global soil microbial carbon. The new model (TRIPLEX-MICROBE) shows considerable improvement over the previous version (TRIPLEX-GHG) in simulating SOC. We estimated the global soil carbon stock to be approximately 1195 Pg C, with 348 Pg C located in the high northern latitudes, which is in good agreement with the well-regarded Harmonized World Soil Database (HWSD) and the Northern Circumpolar Soil Carbon Database (NCSCD). We also estimated the global soil microbial carbon to be 21 Pg C, similar to the 23 Pg C estimated by Xu et al. (2014). We found that the microbial carbon quantity in the latitudinal direction showed reversions at approximately 30°N, near the equator and at 25°S. A sensitivity analysis suggested that the tundra ecosystem exhibited the highest sensitivity to a 1°C increase or decrease in temperature in terms of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and mineral-associated organic carbon (MOC). However, our work represents the first step toward a new generation of ecosystem process models capable of integrating key microbial processes into soil carbon cycles."

[AbruptSLR]

The linked reference uses a ESM to study the impacts of freshwater hosing from the Greenland Ice Sheet.  While this is valuable information, studying the impacts of abrupt freshwater hosing from the WAIS would be even more useful:

Haijun Yang, Qin Wen, Jie Yao & Yuxing Wang (2017), "Bjerknes Compensation in Meridional Heat Transport under Freshwater Forcing and the Role of Climate Feedback", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0824.1

http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-16-0824.1

Abstract: "Using a coupled Earth climate model, freshwater forcing experiments are performed to study the Bjerknes compensation (BJC) between meridional atmosphere heat transport (AHT) and meridional ocean heat transport (OHT). Freshwater hosing in the North Atlantic weakens the Atlantic meridional overturning circulation (AMOC) and thus reduces the northward OHT in the Atlantic significantly, leading to a cooling (warming) in the surface layer in the Northern (Southern) Hemisphere. This results in an enhanced Hadley cell and northward AHT. Meanwhile, the OHT in the Indo-Pacific is increased in response to the Hadley cell change, partially offsetting the reduced OHT in the Atlantic. Two compensations occur here: compensation between the AHT and the Atlantic OHT, and that between the Indo-Pacific OHT and the Atlantic OHT. The AHT change undercompensates the OHT change by about 60% in the extratropics, while the former overcompensates the latter by about 30% in the tropics due to the Indo-Pacific change. The BJC can be understood from the viewpoint of large-scale circulation change. However, the intrinsic mechanism of BJC is related to the climate feedback of the Earth system. The authors’ coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy balance, and local climate feedback determines the extent of BJC, consistent with previous theoretical results. Even during the transient period of climate change, the BJC is well established when the ocean heat storage is slowly varying and its change is much weaker than the net local heat flux change at the ocean surface. The BJC can be deduced from the local climate feedback. Under the freshwater forcing, the overcompensation in the tropics is mainly caused by the positive longwave feedback related to clouds, and the undercompensation in the extratropics is due to the negative longwave feedback related to surface temperature change. Different dominant feedbacks determine different BJC scenarios in different regions, which are in essence constrained by local energy balance."

[Juan C. García]

Maybe we should have a topic for evaluating the different climate models. But I don't want to be the person that will open it, because I don't know enough about models.

Anyway, I believe that this news has not been include on this Forum and I find appropiate to included it here.

The most accurate climate change models predict the most alarming consequences, study finds

Washington Post

https://www.washingtonpost.com/news/energy-environment/wp/2017/12/06/the-most-accurate-climate-change-models-predict-the-most-alarming-consequences-study-claims/?wpisrc=nl_green&wpmm=1

[AbruptSLR]

The linked reference studies the IPO behavior focused on CMIP5 simulations and confirms the importance of correctly modeling the" Tropical-extratropical interactions via both an 'atmospheric bridge' and 'oceanic tunnel' mechanisms:

Benjamin J Henley et al (2017), "Spatial and temporal agreement in climate model
simulations of the Interdecadal Pacific Oscillation", Environ. Res. Lett. 12 044011, https://doi.org/10.1088/1748-9326/aa5cc8

http://iopscience.iop.org/article/10.1088/1748-9326/aa5cc8/pdf

Extract: "Tropical-extratropical interactions via an atmospheric ‘bridge’ (Newman et al 2016) and oceanic ‘tunnel’ (Farneti et al 2014) are likely component mechanisms that contribute to the decadal-scale variability evident in the IPO and PDO indices."

[AbruptSLR]

Maybe we should have a topic for evaluating the different climate models. But I don't want to be the person that will open it, because I don't know enough about models.

Anyway, I believe that this news has not been include on this Forum and I find appropiate to included it here.

The most accurate climate change models predict the most alarming consequences, study finds

Washington Post

https://www.washingtonpost.com/news/energy-environment/wp/2017/12/06/the-most-accurate-climate-change-models-predict-the-most-alarming-consequences-study-claims/?wpisrc=nl_green&wpmm=1

Juan,

I don't want to open a separate folder to compare different climate model projections (as it would be too difficult), but I concur that higher performance models project higher values of climate sensitivity as indicated by the following reposted information and images:

The first linked reference cites findings from an improved version of CESM that increases ESS from 4.1C to 5.6C.  If this is actually experienced this coming century, this is bad news for both people & the current biota:

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5

https://link.springer.com/article/10.1007%2Fs00382-017-3796-5?utm_content=bufferfdbc0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes."

&

The second linked reference provides satellite evidence that the CMIP5 projections substantially underestimate the positive feedback from precipitating clouds.  This is more evidence that consensus science has underestimated climate sensitivity:

J.-L. F. Li, Wei-Liang Lee, Yi-Hui Wang, Mark Richardson, Jia-Yuh Yu, E. Suhas, Eric Fetzer, Min-Hui Lo & Qing Yue (2016), "Assessing the Radiative Impacts of Precipitating Clouds on Winter Surface Air Temperatures and Land Surface Properties in GCMs Using Observations", JGR: Atmospheres, DOI: 10.1002/2016JD025175


http://onlinelibrary.wiley.com/doi/10.1002/2016JD025175/abstract


Abstract: "Using CloudSat-CALIPSO ice water, cloud fraction and radiation; CERES radiation and long-term station-measured surface air temperature (SAT), we identified a substantial underestimation of the total ice water path, total cloud fraction, land surface radiative flux, land surface temperature (LST) and SAT during Northern Hemisphere winter in CMIP5 models. We perform sensitivity experiments with the NCAR Community Earth System Model version 1 (CESM1) in fully coupled modes to identify processes driving these biases. We found that biases in land surface properties are associated with the exclusion of downwelling long-wave heating from precipitating ice during Northern Hemisphere winter. The land surface temperature biases introduced by the exclusion of precipitating ice radiative effects in CESM1 and CMIP5 both spatially correlate with winter biases over Eurasia and North America. The underestimated precipitating ice radiative effect leads to colder LST, associated surface energy-budget adjustments and cooler SAT. This bias also shifts regional soil moisture state from liquid to frozen, increases snow cover and depresses evapotranspiration (ET) and total leaf area index (TLAI) in Northern Hemisphere winter. The inclusion of the precipitating ice radiative effects largely reduces the model biases of surface radiative fluxes (more than 15 W m-2), SAT (up to 2-4 K), snow cover and ET (25-30%), compared with those without snow-radiative effects."

&

The third linked (open access) reference provides a comparison of the best 2014 version of Community Earth Systems Model run to date (CESM-H), and a standard ESM run (CESM-S) such as that used for AR5.  The article, the attached image (and caption) and extracts, make it very clear that while the CESM-H run is not perfect (i.e. there is still a reason to run ACME/E3SM), it is a substantial improvement about the AR5 generation of climate models, and it projects higher increases in mean global temperature increases, and less sea ice (see the figure 1) than the AR5 generation of projections.

R. Justin Small, Julio Bacmeister, David Bailey, Allison Baker, Stuart Bishop, Frank Bryan, Julie Caron, John Dennis, Peter Gent, Hsiao-ming Hsu, Markus Jochum, David Lawrence, Ernesto Muñoz, Pedro diNezio, Tim Scheitlin, Robert Tomas, Joseph Tribbia, Yu-heng Tseng, & Mariana Vertenstein, (December 2014), "A new synoptic scale resolving global climate simulation using the Community Earth System Model", JAMES, Volume 6, Issue 4, Pages 1065–1094, DOI: 10.1002/2014MS000363

http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014MS000363/

Abstract: "High-resolution global climate modeling holds the promise of capturing planetary-scale climate modes and small-scale (regional and sometimes extreme) features simultaneously, including their mutual interaction. This paper discusses a new state-of-the-art high-resolution Community Earth System Model (CESM) simulation that was performed with these goals in mind. The atmospheric component was at 0.25° grid spacing, and ocean component at 0.1°. One hundred years of “present-day” simulation were completed. Major results were that annual mean sea surface temperature (SST) in the equatorial Pacific and El-Niño Southern Oscillation variability were well simulated compared to standard resolution models. Tropical and southern Atlantic SST also had much reduced bias compared to previous versions of the model. In addition, the high resolution of the model enabled small-scale features of the climate system to be represented, such as air-sea interaction over ocean frontal zones, mesoscale systems generated by the Rockies, and Tropical Cyclones. Associated single component runs and standard resolution coupled runs are used to help attribute the strengths and weaknesses of the fully coupled run. The high-resolution run employed 23,404 cores, costing 250 thousand processor-hours per simulated year and made about two simulated years per day on the NCAR-Wyoming supercomputer “Yellowstone.”"


Extracts: "The high-resolution CESM was run under “present-day” (year 2000) greenhouse gas conditions (fixed CO2 concentration of 367 ppm). This was chosen so that direct comparisons could be made with recent-era observations of fine-scale and large-scale phenomena. The prognostic carbon-nitrogen cycle was not used in this simulation.

In the following, this simulation will be referred to as CESM-High Resolution (CESM-H).
…
The interpretation of the model data employed in this paper is that the CESM-H and CESM-S are the best simulations available at their respective resolutions, for the same model version, and for year 2000 conditions."


Caption for the first image: "Time series of globally averaged quantities for 100 years of CESM-H (thick black line) and 166 years of CESM-S (thin gray line). (a) Top of atmosphere net radiation, positive incoming to Earth. Data are 10 year running mean. (b) Surface (including ocean, land, ice) temperature, 10 year running average. Sea ice area in (c) Northern Hemisphere and (d) Southern Hemisphere. (e) Atlantic Meridional Overturning Circulation (AMOC), 12 month running averages, (f) transport through Drake Passage due to Antarctic Circumpolar Current (ACC), annual values."

The following link provides public access to various model run outputs:

http://www.earthsystemgrid.org/

Also, Proistosescu & Huybers (2017) show that HadGEM2-ES indicate a range of ECS of from 6 to 8C (see the third & fourth images)

Cristian Proistosescu and Peter J. Huybers (05 Jul 2017), "Slow climate mode reconciles historical and model-based estimates of climate sensitivity", Science Advances, Vol. 3, no. 7, e1602821, DOI: 10.1126/sciadv.1602821

http://advances.sciencemag.org/content/3/7/e1602821

For other efforts to improve the state-of-the-art in ESM projections see also:

https://www.wcrp-climate.org/wgcm-overview
&
https://www.wcrp-climate.org/wgcm-cmip/wgcm-cmip6
&
https://eos.org/project-updates/a-more-powerful-reality-test-for-climate-models

Caption for fourth image: "Fig. 1. The Coupled Model Intercomparison Project Phase 5 (CMIP5) facilitates the comparison of results from various climate models. Shown here are relative error measures of different developmental tests of the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory (GFDL) model. Results are based on the global seasonal cycle climatology (1980–2005) computed from Atmospheric Model Intercomparison Project (AMIP) experiments. Rows and columns represent individual variables and models, respectively. The error measure is a spatial root-mean-square error (RMSE) that treats each variable separately. The color scale portrays this RMSE as a relative error by normalizing the result by the median error of all model results [Gleckler et al., 2008]. For example, a value of 0.20 indicates that a model’s RMSE is 20% larger than the median error for that variable across all simulations on the figure, whereas a value of –0.20 means the error is 20% smaller than the median error. The four triangles in grid square show the relative error with respect to the four seasons (in clockwise order, with December–January–February (DJF) at the top; MAM = March–April–May, JJA = June–July–August, and SON = September–October–November). The reference data sets are the default satellite and reanalysis data sets identified by Flato et al. [2013]. TOA = top of atmosphere, SW = shortwave, LW = longwave. Credit: Erik Mason/"
&
And for information on HadGEM3-GC3.1 see:

Title: "HadGEM3-GC3.1: The physical coupled model core of UKESM1 now frozen"

http://www.jwcrp.org.uk/documents/ukesm-jan17hadgem3.pdf

[AbruptSLR]

The linked AGU session entitled: "A32B: Climate Sensitivity and Feedbacks: Advances and New Paradigms I", indicates that values of ECS are increasing with global warming, and that it is unclear just how high the effective ECS will be by 2100:

https://agu.confex.com/agu/fm17/meetingapp.cgi/Session/31025

See also the following associated article:

Title: "More about Equilibrium Climate Sensitivity"

https://andthentheresphysics.wordpress.com/2017/12/14/more-about-equilibrium-climate-sensitivity/

Extract: "… Kate Marvel says in her summary it’s essentially that

You might think we could estimate this from observations: we’ve emitted carbon dioxide, and the temperature has risen. But the future may differ from the past, and there’s reason to think that the warming we’ve experienced so far is different from the warming to come."

[AbruptSLR]

The linked reference indicates that changing patterns of moisture transport for precipitation in the Arctic is more complex than most climate models currently indicate:

Gimeno-Sotelo, L., Nieto, R., Vázquez, M., and Gimeno, L.: The perfect pattern of moisture transport for precipitation for Arctic sea ice melting, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-122, in review, 2017.

https://www.earth-syst-dynam-discuss.net/esd-2017-122/
&
https://www.earth-syst-dynam-discuss.net/esd-2017-122/esd-2017-122.pdf

Abstract. We have identified the patterns of moisture transport for precipitation over the Arctic region, the Arctic Ocean, and its 13 main subdomains, which better fit with sea ice decline. For this purpose, we studied the different patterns of moisture transport for the case of high/low Arctic sea ice (ASI) extension linked to periods before/after the main change point (CP) in the extension of sea ice. The pattern consists of a general decrease in moisture transport in summer and enhanced moisture transport in autumn and early winter, with different contributions depending on the moisture source and ocean subregion. The pattern is not only statistically significant but also consistent with Eulerian fluxes diagnosis, changes in the frequency of circulation types, and known mechanisms of the effects of snowfall or rainfall on ice in the Arctic. The results of this paper also reveal that the assumed and partially documented enhanced poleward moisture transport from lower latitudes as a consequence of increased moisture from climate change seems to be less simple and constant than typically recognized in relation to enhanced Arctic precipitation throughout the year in the present climate.

[AbruptSLR]

The linked reference relates the emergent behavior of Arctic precipitation with Arctic Amplification, AA.  When AA increases sufficiently, I am concerned about the impact of future rainfall on numerous positive feedback mechanisms in the Arctic region:

Bruce T. Anderson et al. (27 December 2017), "Emergent behavior of Arctic precipitation in response to enhanced Arctic warming", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2017JD026799

http://onlinelibrary.wiley.com/doi/10.1002/2017JD026799/abstract?utm_content=bufferbe025&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Amplified warming of the high latitudes in response to human-induced emissions of greenhouse gases has already been observed in the historical record and is a robust feature evident across a hierarchy of model systems, including the models of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The main aims of this analysis are to quantify inter-model differences in the Arctic amplification (AA) of the global warming signal in CMIP5 RCP8.5 simulations and to diagnose these differences in the context of the energy and water cycles of the region. This diagnosis reveals an emergent behavior between the energetic and hydrometeorological responses of the Arctic to warming: in particular, enhanced AA and its associated reduction in dry static energy convergence is balanced to first order by latent heating via enhanced precipitation. This balance necessitates increasing Arctic precipitation with increasing AA while at the same time constraining the magnitude of that precipitation increase. The sensitivity of the increase, ~1.25 (W/m2)/K [~240 (km3/yr)/K], is evident across a broad range of historical and projected AA values. Accounting for the energetic constraint on Arctic precipitation, as a function of AA, in turn informs understanding of both the sign and magnitude of hydrologic cycle changes that the Arctic may experience."

[AbruptSLR]

The subject matter of the linked reference highlights the importance of correctly modeling the interplay between different ocean basins via the atmosphere:

Wei Zhang et al (27 December 2017), "Dominant Role of Atlantic Multi-decadal Oscillation in the Recent Decadal Changes in Western North Pacific Tropical Cyclone Activity", GRL, DOI: 10.1002/2017GL076397

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076397/abstract?utm_content=bufferd676e&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Over the 1997-2014 period, the mean frequency of western North Pacific (WNP) tropical cyclones (TCs) was markedly lower (~18%) than the period 1980-1996. Here we show that these changes were driven by an intensification of the vertical wind shear in the southeastern/eastern WNP tied to the changes in the Walker circulation, which arose primarily in response to the enhanced sea surface temperature (SST) warming in the North Atlantic, while the SST anomalies associated with the negative phase of the Pacific Decadal Oscillation (PDO) in the tropical Pacific and the anthropogenic forcing play only secondary roles. These results are based on observations and experiments using the Geophysical Fluid Dynamics Laboratory (GFDL) Forecast-oriented Low-ocean Resolution Coupled Climate Model (FLOR) coupled climate model. The present study suggests a crucial role of the North Atlantic SST in causing decadal changes to WNP TC frequency."

[AbruptSLR]

The linked reference provides information on land use scenarios for use with the Shared Socioeconomic Pathways, SSP, framework:

Stefan van der Esch, et al (2017), "Exploring future changes in land use and land condition and the impacts on food, water, climate change and biodiversity - Scenarios for the UNCCD Global Land Outlook"

PBL Netherlands Environmental Assessment Agency
The Hague, 2017
PBL publication number: 2076


http://www.pbl.nl/sites/default/files/cms/publicaties/pbl-2017-exploring-future-changes-in-land-use-and-land-condition-2076.pdf

[AbruptSLR]

Maybe climate models can be upgraded to better account for the impacts of human behavior/values on Earth Systems:

Gerten, D., Schönfeld, M., and Schauberger, B.: On deeper human dimensions in Earth system analysis and modelling, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-125, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2017-125/

Abstract. While humanity is altering planet Earth at unprecedented magnitude and speed, representation of the cultural driving factors and their dynamics in models of the Earth system is limited. In this review and perspectives paper, we argue that more or less distinct environmental value sets can be assigned to religion – a deeply embedded feature of human cultures, here defined as collectively shared belief in something sacred. This assertion renders religious theories, practices and actors suitable for studying cultural facets of anthropogenic Earth system change, especially regarding deeper, non-materialistic motivations that ask about humans' self-understanding in the Anthropocene epoch. We sketch a modelling landscape and outline some research primers, encompassing the following elements: (i) extensions of existing Earth system models by quantitative relationships between religious practices and biophysical processes, building on databases that allow for (mathematical) formalisation of such knowledge, (ii) design of new model types that specifically represent religious morals, actors and activities as part of coevolutionary human-environment dynamics, and (iii) identification of research questions of humanitarian relevance that are underrepresented in purely economic-technocratic modelling and scenario paradigms. While this analysis is by necessity heuristic and semi-cohesive, we hope that it will act as a stimulus for further, interdisciplinary and systematic research on the immaterial dimension of humanity's imprint on the Earth system, both qualitatively and quantitatively.

[AbruptSLR]

The linked article is '… the first article of a week-long series focused on climate modelling'.  It provides a very nice summary of the consensus science interpretation of climate models and their limitations.  Understanding such modeling fundamentals is essential before critiquing potential surprises (such as ice-climate feedback) that are not adequately addressed by consensus science:

Title: "Q&A: How do climate models work?"

https://www.carbonbrief.org/qa-how-do-climate-models-work

Extract: "In the first article of a week-long series focused on climate modelling, Carbon Brief explains in detail how scientists use computers to understand our changing climate…"

[AbruptSLR]

I think that the findings of the linked reference '… call for a deep reassessment of the way teleconnections are interpreted, and for a more rigorous way to evaluate causality and dependences between the different components of the climate system', because the current consensus science interpretation of these teleconnections is inadequate:

Vannitsem, S. and Ekelmans, P.: Causal dependences between the coupled ocean-atmosphere dynamics over the Tropical Pacific, the North Pacific and the North Atlantic, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-3, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-3/

Abstract. The causal dependences between the dynamics of three different coupled ocean-atmosphere basins, The North Atlantic, the North Pacific and the Tropical Pacific region, NINO3.4, have been explored using data from three reanalyses datasets, namely the ORA-20C, the ORAS4 and the ERA-20C. The approach is based on the Convergent Cross Mapping (CCM) developed by Sugihara et al. (2012) that allows for evaluating the dependences between observables beyond the classical teleconnection patterns based on correlations.

The use of CCM on these data mostly reveals that (i) the Tropical Pacific (NINO3.4 region) only influences the dynamics of the North Atlantic region through its annual climatological cycle; (ii) the atmosphere over the North Pacific is dynamically forcing the North Atlantic on a monthly basis; (iii) on longer time scales (interannual), the dynamics of the North Pacific and the North Atlantic are influencing each other through the ocean dynamics, suggesting a connection through the thermohaline circulation.

These findings shed a new light on the coupling between these three different important regions of the globe. In particular they call for a deep reassessment of the way teleconnections are interpreted, and for a more rigorous way to evaluate causality and dependences between the different components of the climate system.

[AbruptSLR]

Here is a link to the second article in the series on climate modeling:

Title: "Timeline: The history of climate modeling"

https://www.carbonbrief.org/timeline-history-climate-modelling

Extract: "The climate models used by scientists today rely on some of the world’s most advanced supercomputers. It can take dozens of highly skilled people to build and then operate a modern-day climate model."

[AbruptSLR]

Here is a link to a report on an Earth modeling framework:

Donges, J. F., Heitzig, J., Barfuss, W., Kassel, J. A., Kittel, T., Kolb, J. J., Kolster, T., Müller-Hansen, F., Otto, I. M., Wiedermann, M., Zimmerer, K. B., and Lucht, W.: Earth system modelling with complex dynamic human societies: the copan:CORE World-Earth modeling framework, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-126, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2017-126/

Abstract. Possible future trajectories of the Earth system in the Anthropocene are determined by the increasing entanglement of processes operating in the physical, chemical and biological systems of the planet, as well as in human societies, their cultures and economies. Here, we introduce the copan:CORE open source software library that provides a framework for developing, composing and running World-Earth models, i.e., models of social-ecological co-evolution up to planetary scales. It is an object-oriented software package written in Python designed for different user roles. It allows model end users to run parallel simulations with already available and tested models. Furthermore, model composers are enabled to easily implement new models by plugging together a broad range of model components, such as opinion formation on social networks, generic carbon cycle dynamics, or simple vegetation growth. For the sake of a modular structure, each provided component specifies a meaningful yet minimal collection of closely related processes. These processes can be formulated in terms of various process types, such as ordinary differential equations, explicit or implicit functions, as well as steps or events of deterministic or stochastic fashion. In addition to the already included variety of different components in copan:CORE, model developers can extend the framework with additional components that are based on elementary entity types, i.e., grid cells, individuals and social systems, or the fundamental process taxa environment, social metabolism, and culture. To showcase possible usage we present an exemplary World-Earth model that combines a variety of model components and interactions thereof. As the framework allows a simple activation and deactivation of certain components and related processes, users can test for their specific effects on modeling results and evaluate model robustness in a controlled way. Hence, copan:CORE allows developing process-based models of global change and sustainable development in planetary social-ecological systems and thus fosters a better understanding of crucial mechanisms governing the co-evolutionary dynamics between societies and the natural environment. Due to its modular structure, the framework enhances the development and application of stylized models in Earth system science but also climatology, economics, ecology, or sociology, and allows combining them for interdisciplinary studies at the interface between different areas of expertise.

[AbruptSLR]

The linked article on how to improve climate models is worth reading, but one still needs to read between the lines in order to really appreciate how far current climate models are erring on the side of least drama:

Title: "In-depth: Scientists discuss how to improve climate models"

https://www.carbonbrief.org/in-depth-scientists-discuss-how-to-improve-climate-models

Extract: "Prof Stefan Rahmstorf
Head of Earth systems analysis
Potsdam Institute for Climate Impact Research

I think a key challenge is non-linear effects, or tipping points."

[AbruptSLR]

Here is the fourth article in the series of five article on climate models:

Title: "Guest post: Why clouds hold the key to better climate models"

https://www.carbonbrief.org/guest-post-why-clouds-hold-key-better-climate-models

Extract: "And there are the things we could still do better:

•   Many of the ways cloud at low altitudes form, evolve and dissolve are not clearly understood and models do not appear to represent them very well.
•   The more detailed cloud resolving models need to be run over larger space and longer time domains to fully understand the benefits they bring
•   Ice clouds have been less well studied and considered so far
•   We need to maximise the information we can get from current and future satellite observations."

[AbruptSLR]

Here is a link to the 5th article on climate models.  Without considering any ice-climate feedback the CMIP5 models project more rainfall at high latitudes; which should accelerate polar amplification:

Title: "Explainer: What climate models tell us about future rainfall"

https://www.carbonbrief.org/explainer-what-climate-models-tell-us-about-future-rainfall

Extract: "Changes in average precipitation is much more difficult for climate models to predict than temperature. There are many parts of the world where models disagree whether there will be more or less rain and snow in the future. However, there are some regions, particularly the Mediterranean and southern Africa, where nearly all models suggest rainfall will decrease. Similarly, increases in rainfall are expected in high latitude areas, as well as much of South Asia."

[AbruptSLR]

The linked reference discusses the: "Large Uncertainty in the Relative Rates of Dynamical and Hydrological Tropical Expansion"

William J. M. Seviour, Sean M. Davis, Kevin M. Grise & Darryn W. Waugh (19 January 2018), "Large Uncertainty in the Relative Rates of Dynamical and Hydrological Tropical Expansion", Geophysical Research Letters, DOI: 10.1002/2017GL076335 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076335/full

Abstract: "Climate models predict that the Hadley circulation will expand poleward in a warmer climate, a trend which may cause significant changes in global precipitation patterns. However, recent studies have disagreed as to how strongly changes in the Hadley circulation and changes in the hydrological cycle (specifically the latitude at which precipitation balances evaporation) are related. Here we analyze dynamical and hydrological measures of the Southern Hemisphere edge of the tropics using simulations from the fifth Coupled Model Intercomparison Project (CMIP5) and four reanalysis data sets. In simulations with an abrupt quadrupling of atmospheric CO2 concentrations, all models show a poleward expansion in both metrics. However, there is a large spread among models; the ratio of the hydrological to dynamical expansions varies from 0.6 to 1.4. We show that this model spread can be largely explained by differences in internal variability, which in turn is related to the mean state of models. Differences in mean states among reanalyses are similar to those of models, and so reanalyses do not help constrain uncertainty in model trends."

[AbruptSLR]

The linked reference helps to quantify the impacts of continuing climate change on fire activity in the Amazon:

Carlos H. R. Lima, Amir AghaKouchak & James T. Randerson (15 January 2018), "Unraveling the Role of Temperature and Rainfall on Active Fires in the Brazilian Amazon Using a Nonlinear Poisson Model", JGR – Biogeosciences, DOI: 10.1002/2017JG003836

http://onlinelibrary.wiley.com/doi/10.1002/2017JG003836/full

Extract: "Extreme droughts and high temperatures have become more frequent in the last two decades, increasing fire risk in the Amazon. The overarching goal of this study is to shed light on the influence of temperature and rainfall on fire occurrence for the 1998–2013 period. We use a Poisson regression to model satellite-based monthly fire counts across the Brazilian Amazon as a function of observed rainfall and temperature. Specifically, in the nonlinear regression framework we explore the fire count at month t as a function of the total monthly rainfall and monthly average of maximum daily temperatures at month t as well as lagged observations of these two predictors and of the fire counts. Our results indicate that the influence of temperature on fire counts can be larger than the effects of rainfall. Considering the temperature-fire relationship, the extra variance explained by rainfall is about 9%. Assuming average rainfall, we show that a 1°C increase in the monthly average of maximum daily temperatures results in a 30% increase in fire counts (19 fires per Mha more than the average), which translates into significant changes in the likelihood of fires within the Amazon. Our findings provide new insight about the role of temperature and rainfall in regulating fire occurrence in the Amazon, and the sensitivity of fire counts to relatively small changes in temperature highlights the vulnerability of the Amazon in a warming climate, where much higher temperatures are expected by the end of this century."

[AbruptSLR]

The linked reference uses a climate model to better evaluate the complexities of Agulhas leakage:

Jonathan V. Durgadoo, Siren Rühs, Arne Biastoch & Claus W. B. Böning (29 April 2017), "Indian Ocean sources of Agulhas leakage", JGR – Oceans, DOI: 10.1002/2016JC012676

http://onlinelibrary.wiley.com/doi/10.1002/2016JC012676/full

Abstract: "We examine the mean pathways, transit timescales, and transformation of waters flowing from the Pacific and the marginal seas through the Indian Ocean (IO) on their way toward the South Atlantic within a high-resolution ocean/sea-ice model. The model fields are analyzed from a Lagrangian perspective where water volumes are tracked as they enter the IO. The IO contributes 12.6 Sv to Agulhas leakage, which within the model is 14.1 ± 2.2 Sv, the rest originates from the South Atlantic. The Indonesian Through-flow constitutes about half of the IO contribution, is surface bound, cools and salinificates as it leaves the basin within 10–30 years. Waters entering the IO south of Australia are at intermediate depths and maintain their temperature-salinity properties as they exit the basin within 15–35 years. Of these waters, the contribution from Tasman leakage is 1.4 Sv. The rest stem from recirculation from the frontal regions of the Southern Ocean. The marginal seas export 1.0 Sv into the Atlantic within 15–40 years, and the waters cool and freshen on-route. However, the model's simulation of waters from the Gulfs of Aden and Oman are too light and hence overly influenced by upper ocean circulations. In the Cape Basin, Agulhas leakage is well mixed. On-route, temperature-salinity transformations occur predominantly in the Arabian Sea and within the greater Agulhas Current region. Overall, the IO exports at least 7.9 Sv from the Pacific to the Atlantic, thereby quantifying the strength of the upper cell of the global conveyor belt."

[AbruptSLR]

The linked reference uses output from three climate models to illustrates how rapidly changes in cloud cover can impact climate sensitivity:

Silvers, L. G., Paynter, D., & Zhao, M. (2018), "The diversity of cloud responses to twentieth century sea surface temperatures", Geophysical Research Letters, 45, https://doi.org/10.1002/2017GL075583

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075583/pdf

Abstract: "Low-level clouds are shown to be the conduit between the observed sea surface temperatures (SST) and large decadal fluctuations of the top of the atmosphere radiative imbalance. The influence of low-level clouds on the climate feedback is shown for global mean time series as well as particular geographic regions. The changes of clouds are found to be important for a midcentury period of high sensitivity and a late century period of low sensitivity. These conclusions are drawn from analysis of amip-piForcing simulations using three atmospheric general circulation models (AM2.1, AM3, and AM4.0).  All three models confirm the importance of the relationship between the global climate sensitivity and the eastern Pacific trends of SST and low-level clouds. However, this work argues that the variability of the climate feedback parameter is not driven by stratocumulus-dominated regions in the eastern ocean basins, but rather by the cloudy response in the rest of the tropics."

[AbruptSLR]

For those who are interested:

Modak, A., Bala, G., Caldeira, K. et al. (2018), "Does shortwave absorption by methane influence its effectiveness?", Clim Dyn., https://doi.org/10.1007/s00382-018-4102-x

https://rd.springer.com/article/10.1007%2Fs00382-018-4102-x?utm_content=buffer411f2&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "In this study, using idealized step-forcing simulations, we examine the effective radiative forcing of CH4 relative to that of CO2 and compare the effects of CH4 and CO2 forcing on the climate system. A tenfold increase in CH4 concentration in the NCAR CAM5 climate model produces similar long term global mean surface warming (~ 1.7 K) as a one-third increase in CO2 concentration. However, the radiative forcing estimated for CO2 using the prescribed-SST method is ~ 81% that of CH4, indicating that the efficacy of CH4 forcing is ~ 0.81. This estimate is nearly unchanged when the CO2 physiological effect is included in our simulations. Further, for the same long-term global mean surface warming, we simulate a smaller precipitation increase in the CH4 case compared to the CO2 case. This is because of the fast adjustment processes—precipitation reduction in the CH4 case is larger than that of the CO2 case. This is associated with a relatively more stable atmosphere and larger atmospheric radiative forcing in the CH4 case which occurs because of near-infrared absorption by CH4 in the upper troposphere and lower stratosphere. Within a month after an increase in CH4, this shortwave heating results in a temperature increase of ~ 0.8 K in the lower stratosphere and upper troposphere. In contrast, within a month after a CO2 increase, longwave cooling results in a temperature decrease of ~ 3 K in the stratosphere and a small change in the upper troposphere. These fast adjustments in the lower stratospheric and upper tropospheric temperature, along with the adjustments in clouds in the troposphere, influence the effective radiative forcing and the fast precipitation response. These differences in fast climate adjustments also produce differences in the climate states from which the slow response begins to evolve and hence they are likely associated with differing feedbacks. We also find that the tropics and subtropics are relatively warmer in the CH4 case for the same global mean surface warming because of a larger longwave clear-sky and shortwave cloud forcing over these regions in the CH4 case. Further investigation using a multi-model intercomparison framework would permit an assessment of the robustness of our results."

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Decadal climate change projections are making progress:

Erin Towler, Debasish PaiMazumder, and James Done (2018), "Towards the Application of Decadal Climate Predictions", JAMC, https://doi.org/10.1175/JAMC-D-17-0113.1

https://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-17-0113.1

Abstract: "Decadal prediction is a relatively new branch of climate science that bridges the gap between seasonal climate forecasts and multi-decadal to century climate change projections. This paper develops a three-step framework towards the potential application of decadal temperature predictions using the Community Climate System Model Version 4 (CCSM4). In step 1, we evaluate the predictions, finding that the temperature hindcasts show skill over some regions of the US and Canada. In step 2, we manipulate the predictions using two methods: a deterministic anomaly approach (like climate change projections) and a probabilistic tercile-based approach (like seasonal forecasts). In step 3, we translate the predictions by adding a delta (for the anomaly manipulation) and conducting a weighted resample (for the probabilistic manipulation), as well as using a new hybrid method. We demonstrate the framework predicting 2011-2015 using the 2010 initialized hindcast over two case study watersheds (Colorado and Ottawa). For the Colorado watershed, there was a noticeable shift towards higher temperatures, and the delta, weighted resample, and hybrid translations all did a better job capturing the observed temperatures than using climatology. For the Ottawa watershed, the observed temperatures over the period of prediction were only subtly different than climatology, therefore the differences between the translation methods was less noticeable. The advantages and disadvantages of the manipulation and translation approaches are discussed, as well as how their use will depend on the user context. We emphasize that skill should be tailored to particular applications and identify additional steps needed before the decadal temperature predictions can be readily incorporated into applications."

[AbruptSLR]

The linked reference indicates that using a GWP-20 value for methane in assessment models would result in a discount rate of 12.6%, which is much higher than is currently assumed in climate impact assessments.  As the reference states: "With increasing discount rates equivalent timescales decrease"; which implies that planner should expect climate damage sooner than currently expected if atmospheric methane concentrations remain high over the assessment period.

Sarofim, M. C. and Giordano, M. R.: A quantitative approach to evaluating the GWP timescale through implicit discount rates, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-6, in review, 2018

https://www.earth-syst-dynam-discuss.net/esd-2018-6/

Abstract. The 100-year Global Warming Potential (GWP) is the primary metric used to compare the climate impacts of different greenhouse gases (GHGs). The GWP relies on radiative forcing rather than damages, assumes constant future concentrations, and integrates over a timescale of 100 years without discounting: these choices lead to a metric which is transparent and simple to calculate, but have also been criticized. In this paper, we take a quantitative approach to evaluating the choice of time-horizon, accounting for many of these complicating factors. By calculating an equivalent GWP timescale based on discounted damages resulting from CH4 and CO2 pulses, we show that a 100-year timescale is consistent with a discount rate of 3.3 % (interquartile range of 2.7 % to 4.1 % in a sensitivity analysis). This range of discount rates is consistent with, or larger than, those usually considered for climate impact analyses. With increasing discount rates equivalent timescales decrease. We recognize the limitations of evaluating metrics by relying only on climate impact equivalencies without consideration of the economic and political implications of metric implementation.

[AbruptSLR]

While I think this reference ESLD, I provide it for completeness:

Judith L. Lean (22 February 2018), "Observation-based detection and attribution of 21st century climate change, WIREs Climate Change, DOI: 10.1002/wcc.511

http://onlinelibrary.wiley.com/doi/10.1002/wcc.511/abstract?utm_content=buffer99fa6&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Climate change detection and attribution have proven unexpectedly challenging during the 21st century. Earth’s global surface temperature increased less rapidly from 2000 to 2015 than during the last half of the 20th century, even though greenhouse gas concentrations continued to increase. A probable explanation is the mitigation of anthropogenic warming by La Niña cooling and declining solar irradiance. Physical climate models overestimated recent global warming because they did not generate the observed phase of La Niña cooling and may also have underestimated cooling by declining solar irradiance. Ongoing scientific investigations continue to seek alternative explanations to account for the divergence of simulated and observed climate change in the early 21st century, which IPCC termed a “global warming hiatus.” Amplified by media commentary, the suggestions by these studies that “missing” mechanisms may be influencing climate exacerbates confusion among policy makers, the public and other stakeholders about the causes and reality of modern climate change.
Understanding and communicating the causes of climate change in the next 20 years may be equally challenging. Predictions of the modulation of projected anthropogenic warming by natural processes have limited skill. The rapid warming at the end of 2015, for example, is not a resumption of anthropogenic warming but rather an amplification of ongoing warming by El Niño. Furthermore, emerging feedbacks and tipping points precipitated by, for example, melting summer Arctic sea ice may alter Earth’s global temperature in ways that even the most sophisticated physical climate models do not yet replicate."

[AbruptSLR]

Given the importance of the ENSO cycle on the dynamical aspects of climate change, I provide a link to a reference that discusses progress in improving predictions of El Nino events:

Nooteboom, P. D., Feng, Q. Y., López, C., Hernández-García, E., and Dijkstra, H. A.: Using Network Theory and Machine Learning to predict El Niño, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-13, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-13/

Abstract. The skill of current predictions of the warm phase of the El Niño Southern Oscillation (ENSO) reduces significantly beyond a lag of six months. In this paper, we aim to increase this prediction skill at lags up to one year. The new method to do so combines a classical Autoregressive Integrated Moving Average technique with a modern machine learning approach (through an Artificial Neural Network). The attributes in such a neural network are derived from topological properties of Climate Networks and are tested on both a Zebiak–Cane-type model and observations. For predictions up to six months ahead, the results of the hybrid model give a better skill than the CFSv2 ensemble prediction by the National Centers for Environmental Prediction (NCEP). Moreover, results for a twelve-month lead time prediction have a similar skill as the shorter lead time predictions.

[AbruptSLR]

The linked reference discusses improvements to the CESM w.r.t. the representation of anthropogenic carbon dioxide emissions:

Navarro, A., Moreno, R., and Tapiador, F. J.: Improving the representation of anthropogenic CO2 emissions in climate models: a new parameterization for the Community Earth System Model (CESM), Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-12, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-12/

Abstract. ESMs (Earth System Models) are important tools that help scientists understand the complexities of the Earth's climate. Advances in computing power have permitted the development of increasingly complex ESMs and the introduction of better, more accurate parameterizations of processes that are too complex to be described in detail. One of the least well-controlled parameterizations involves human activities and their direct impact at local and regional scales. In order to improve the direct representation of human activities and climate, we have developed a simple, scalable approach that we have named the POPEM module (POpulation Parameterization for Earth Models). This module computes monthly fossil fuel emissions at grid point scale using the modeled population projections. This paper shows how integrating POPEM parameterization into the CESM (Community Earth System Model) enhances the realism of global climate modeling, improving this beyond simpler approaches. The results show that it is indeed advantageous to model CO2 emissions and pollutants directly at model grid points rather than using the forcing approach. A major bonus of this approach is the increased capacity to understand the potential effects of localized pollutant emissions on long-term global climate statistics, thus assisting adaptation and mitigation policies.

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The linked reference discusses both present and future direct radiative forcing contributions from secondary organic aerosols, that have not yet been accounted for in climate models.

Tsigaridis, K. & Kanakidou, M. (2018), "The Present and Future of Secondary Organic Aerosol Direct Forcing on Climate", Curr Clim Change Rep., https://doi.org/10.1007/s40641-018-0092-3

https://rd.springer.com/article/10.1007%2Fs40641-018-0092-3

Abstract: "Secondary organic aerosols (SOA), a subset of organic aerosols that are chemically produced in the atmosphere, are included in climate modeling calculations using very simple parameterizations. Estimates on their shortwave forcing on climate span almost two orders of magnitude, being potentially comparable to sulfate direct forcing. In the longwave, a neglected part of the spectrum when it comes to SOA, the direct SOA forcing could exceed that of sulfate and black carbon, although in absolute values, it is much weaker than the shortwave forcing. Critical for these estimates is the vertical distribution of the climate active agents, pointing to SOA temperature-dependent volatility. Over the last few years, research also revealed the highly oxidized character of organic aerosol and its chemical aging in the atmosphere that partially leads to the formation of brown carbon, an absorbing form of organic aerosol. This review summarizes critical advances in the understanding of SOA behavior and properties relevant to direct climate forcing and puts them in perspective with regard to primary organic aerosol and brown carbon. These findings also demonstrate an emerging dynamic picture of organic aerosol that has not yet been integrated in climate modeling. The challenges for the coming years in order to reduce uncertainties in the direct organic aerosol climate impact are discussed. High priority for future model development should be given to the dynamic link between “white” and “brown” organic aerosol and between primary and secondary organic aerosol. The SOA temperature-dependent volatility parameterizations and wavelength-dependent refractive index should be also included."

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Antarctic models are steadily more sophisticated:

Naughten, K. A., Meissner, K. J., Galton-Fenzi, B. K., England, M. H., Timmermann, R., Hellmer, H. H., Hattermann, T., and Debernard, J. B.: Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4, Geosci. Model Dev., 11, 1257-1292, https://doi.org/10.5194/gmd-11-1257-2018, 2018.

https://www.geosci-model-dev.net/11/1257/2018/

Abstract. An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of warm water from offshore.

[morganism]

" We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event."

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?

https://arxiv.org/abs/1804.03748