Selected Forcing Factor for Abrupt SLR from the Collapse of the WAIS

[AbruptSLR]

For those who have not accessed the Rose et al 2013 paper cited in my immediately prior post, I provide the following image from the simplified Rose et al 2013 model (forced with a simulated paleoclimate dominated by cycles of solar irradiance).  This figure shows that for this simplified model and this very light forcing levels, the Arctic Ice Cap effectively disappeared abruptly in about 200 years (from 5000 to 5200); which raises the question whether with our current worlds much stronger forcing levels; whether the atmospheric patterns will change rapidly to support a year-round sea ice free Arctic Ocean in the near future.  The caption for the figure is:

"Fig. 4. Evolution of sea surface conditions over the 8000 year Ridge simulation. The frames are 20-year averages every 100 years. Colors indicate annual mean sea surface temperature.  Shading indicates combined sea ice plus snow thickness at its maximum seasonal extent in March (northern hemisphere). Ice thickness is plotted where sea ice concentration exceeds 30%."

[AbruptSLR]

I have commented previously on the increasing risk of greater forcing from tundra wildfires, and the following quote from the linked article indicates that the forcing from the Northern Russian taiga wildfires are expected to double by 2100:

http://www.climatecentral.org/blogs/sunburn-in-siberia-heat-wave-leads-to-wildfires-16313

"Northern Russia has warmed more rapidly than many other places on the globe in recent decades, and according to NASA, researchers expect the number of taiga wildfires there to double by the end of the century."

[AbruptSLR]

The following reference by Hansen et al 2013 implies that climate sensitivity may well be higher than assumed by most current GCMs:

Hansen, J., Mki. Sato, G. Russell, and P. Kharecha, 2013: Climate sensitivity, sea level, and atmospheric CO2. Phil. Trans. R. Soc. A, in press.

"Cenozoic temperature, sea level and CO2 co-variations provide insights into climate sensitivity to external forcings and sea level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise paleoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity 3±1°C for 4 W/m2 CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e., 3-4°C for 4 W/m2 CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state-dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapor elevates the tropopause. Burning all fossil fuels, we conclude, would make much of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change."

[AbruptSLR]

The linked paper shows that climate sensitivity is likely higher than assumed in most prior GCM projections:

http://onlinelibrary.wiley.com/doi/10.1002/qj.2165/abstract;jsessionid=ED7BA33BAD69F5B1E7BCFD85EAC3DF89.d02t01

Previdi, M., B.G. Liepert, D. Peteet, J. Hansen, D.J. Beerling, A.J. Broccoli, S. Frolking, J.N. Galloway, M. Heimann, C. Le Quéré, S. Levitus, and V. Ramaswamy, 2013: Climate sensitivity in the Anthropocene. Q. J. R. Meteorol. Soc., 139, 1121-1131, doi:10.1002/qj.2165.

"Climate sensitivity in its most basic form is defined as the equilibrium change in global surface temperature that occurs in response to a climate forcing, or externally imposed perturbation of the planetary energy balance. Within this general definition, several specific forms of climate sensitivity exist that differ in terms of the types of climate feedbacks they include. Based on evidence from Earth's history, we suggest here that the relevant form of climate sensitivity in the Anthropocene (e.g. from which to base future greenhouse gas (GHG) stabilization targets) is the Earth system sensitivity including fast feedbacks from changes in water vapour, natural aerosols, clouds and sea ice, slower surface albedo feedbacks from changes in continental ice sheets and vegetation, and climate–GHG feedbacks from changes in natural (land and ocean) carbon sinks. Traditionally, only fast feedbacks have been considered (with the other feedbacks either ignored or treated as forcing), which has led to estimates of the climate sensitivity for doubled CO2 concentrations of about 3°C. The 2 X CO2 Earth system sensitivity is higher than this, being ∼4-6°C if the ice sheet/vegetation albedo feedback is included in addition to the fast feedbacks, and higher still if climate–GHG feedbacks are also included. The inclusion of climate–GHG feedbacks due to changes in the natural carbon sinks has the advantage of more directly linking anthropogenic GHG emissions with the ensuing global temperature increase, thus providing a truer indication of the climate sensitivity to human perturbations. The Earth system climate sensitivity is difficult to quantify due to the lack of palaeo-analogues for the present-day anthropogenic forcing, and the fact that ice sheet and climate–GHG feedbacks have yet to become globally significant in the Anthropocene. Furthermore, current models are unable to adequately simulate the physics of ice sheet decay and certain aspects of the natural carbon and nitrogen cycles. Obtaining quantitative estimates of the Earth system sensitivity is therefore a high priority for future work."

[AbruptSLR]

The linked reference (which offers a free pdf of the paper), indicates the risk of cleaning up air pollution in Asia (particularly China), and the trend to increase the size of deserts, on the risk of increasing global radiative forcing:

http://www.atmos-chem-phys.net/13/2939/2013/acp-13-2939-2013.html

Shindell, D.T., J.-F. Lamarque, M. Schulz, M. Flanner, C. Jiao, M. Chin, P.J. Young, Y.H. Lee, L. Rotstayn, N. Mahowald, G. Milly, G. Faluvegi, Y. Balkanski, W.J. Collins, A.J. Conley, S. Dalsoren, R. Easter, S. Ghan, L. Horowitz, X. Liu, G. Myhre, T. Nagashima, V. Naik, S.T. Rumbold, R. Skeie, K. Sudo, S. Szopa, T. Takemura, A. Voulgarakis, J.-H. Yoon, and F. Lo, 2013: Radiative forcing in the ACCMIP historical and future climate simulations. Atmos. Chem. Phys., 13, 2939-2974, doi:10.5194/acp-13-2939-2013.

"The Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) examined the short-lived drivers of climate change in current climate models. Here we evaluate the 10 ACCMIP models that included aerosols, 8 of which also participated in the Coupled Model Intercomparison Project phase 5 (CMIP5).
The models reproduce present-day total aerosol optical depth (AOD) relatively well, though many are biased low. Contributions from individual aerosol components are quite different, however, and most models underestimate east Asian AOD. The models capture most 1980–2000 AOD trends well, but underpredict increases over the Yellow/Eastern Sea. They strongly underestimate absorbing AOD in many regions.
We examine both the direct radiative forcing (RF) and the forcing including rapid adjustments (effective radiative forcing; ERF, including direct and indirect effects). The models' all-sky 1850 to 2000 global mean annual average total aerosol RF is (mean; range) -0.26 W/m2; -0.06 to -0.49 W/m2. Screening based on model skill in capturing observed AOD yields a best estimate of -0.42 W/m2; -0.33 to -0.50 W/m2, including adjustment for missing aerosol components in some models. Many ACCMIP and CMIP5 models appear to produce substantially smaller aerosol RF than this best estimate. Climate feedbacks contribute substantially (35 to -58%) to modeled historical aerosol RF. The 1850 to 2000 aerosol ERF is -1.17 W/m2; -0.71 to -1.44 W/m2. Thus adjustments, including clouds, typically cause greater forcing than direct RF. Despite this, the multi-model spread relative to the mean is typically the same for ERF as it is for RF, or even smaller, over areas with substantial forcing. The largest 1850 to 2000 negative aerosol RF and ERF values are over and near Europe, south and east Asia and North America. ERF, however, is positive over the Sahara, the Karakoram, high Southern latitudes and especially the Arctic.
Global aerosol RF peaks in most models around 1980, declining thereafter with only weak sensitivity to the Representative Concentration Pathway (RCP). One model, however, projects approximately stable RF levels, while two show increasingly negative RF due to nitrate (not included in most models). Aerosol ERF, in contrast, becomes more negative during 1980 to 2000. During this period, increased Asian emissions appear to have a larger impact on aerosol ERF than European and North American decreases due to their being upwind of the large, relatively pristine Pacific Ocean. There is no clear relationship between historical aerosol ERF and climate sensitivity in the CMIP5 subset of ACCMIP models. In the ACCMIP/CMIP5 models, historical aerosol ERF of about -0.8 to -1.5 W/m2 is most consistent with observed historical warming. Aerosol ERF masks a large portion of greenhouse forcing during the late 20th and early 21st century at the global scale. Regionally, aerosol ERF is so large that net forcing is negative over most industrialized and biomass burning regions through 1980, but remains strongly negative only over east and southeast Asia by 2000. Net forcing is strongly positive by 1980 over most deserts, the Arctic, Australia, and most tropical oceans. Both the magnitude of and area covered by positive forcing expand steadily thereafter."

[sidd]

It is becoming clearer to me that climate sensitivity calculations over the next century should include albedo, permafrost sea level and vegetation feedback which were previously thought to occur or millenial scale. That is, the "slow" feedbacks are not so slow after all. To paraphrase Haldane, effective climate sensitivity is not only higher than we suppose, it might be higher than we can suppose. For we don't really know all the feedbacks that might be triggered.

Estamos jojidos, compadres.

[AbruptSLR]

Sidd,
I couldn't agree more with you about including "formerly slow" feedbacks calculating climate sensitivity, but we also need to consider radiative forcing distribution (see linked reference below).

As we are all posting on the Arctic Sea Ice, ASI, Forum we all understand that the polar amplification for the Arctic is currently stronger than for the Antarctic, and over the next few decades the Arctic amplification will likely get stronger still as the ASI area degrades rapidly.  Indeed, it is an underlying assumption in all of my SLR projections that strong Arctic amplification over the next few decades will help to trigger a similar degradation of Antarctic Sea Ice circa 2050 to 2060, that will both amplify Antarctic surface temperatures (due to albedo flip) and will promote ice mass loss by calving (due to the reduction in buttressing from sea ice).  The following linked article makes it clear that the scientific community believes that this "… interhemispheric temperature asymmetry (ITA) – is an emerging indicator of global climate change, …"  While the article focuses on meteorological changes associated with the ITA, such as the northward drift of tropical rainfall associated with the northern Hadley cell; it is worth stating the obvious other implications including: (a) as Asia cleans up its air pollution the ITA will become stronger still; (b) the stronger the current ITA is the sooner one can expect the ASI to degrade resulting in both a stronger ITA and a stronger mean global temperature increase; and (c) a portion of the current ITA is associated with internal variability and that within a few decades one can expect a natural shift to Antarctic heating.  Also, to continue stating the obvious, the large majority of posts that I have made indicate that I believe that the current heating of the Southern Ocean is occurring independently of the ITA, and is preconditioning the AIS (and the WAIS in particular) to accelerating collapse circa 2050; just when one can expect Antarctic amplification to accelerate sufficiently to promote such ice mass loss mechanisms as: (a) surface ice melting (feeding both runoff and basal melt water volumes); (b) melt pond collapse mechanisms for ice shelves; and (c) acceleration of the advection of warm CDW both under ice shelves (particularly the FRIS) and into advective subglacial cavities (particularly for PIG, Thwaites Glacier and Ferrigno Glaciers).  Such considerations emphasize that it not advisable to focus excessively on mean values (eg: mean global temperature rise; or mean Antarctic ice mass loss).  It is also valuable to remember that increased future storm surge due to ITA induced meteorological affects are superimposed on future SLR contributions from the AIS (both of which will be much worse after 2050):

http://journals.ametsoc.org/toc/clim/26/15

Friedman, Andrew R., Yen-Ting Hwang, John C. H. Chiang, Dargan M. W. Frierson, 2013: Interhemispheric Temperature Asymmetry over the Twentieth Century and in Future Projections. J. Climate, 26, 5419–5433. doi: http://dx.doi.org/10.1175/JCLI-D-12-00525.1

"Abstract
The temperature contrast between the Northern and Southern Hemispheres—the interhemispheric temperature asymmetry (ITA)—is an emerging indicator of global climate change, potentially relevant to the Hadley circulation and tropical rainfall. The authors examine the ITA in historical observations and in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5) simulations. The observed annual-mean ITA (north minus south) has varied within a 0.8°C range and features a significant positive trend since 1980. The CMIP multimodel ensembles simulate this trend, with a stronger and more realistic signal in CMIP5. Both ensembles project a continued increase in the ITA over the twenty-first century, well outside the twentieth-century range. The authors mainly attribute this increase to the uneven spatial impacts of greenhouse forcing, which result in amplified warming in the Arctic and northern landmasses. The CMIP5 specific-forcing simulations indicate that, before 1980, the greenhouse-forced ITA trend was primarily countered by anthropogenic aerosols. The authors also identify an abrupt decrease in the observed ITA in the late 1960s, which is generally not present in the CMIP simulations; it suggests that the observed drop was caused by internal variability. The difference in the strengths of the northern and southern Hadley cells covaries with the ITA in the CMIP5 simulations, in accordance with previous findings; the authors also find an association with the hemispheric asymmetry in tropical rainfall. These relationships imply a northward shift in tropical rainfall with increasing ITA in the twenty-first century, though this result is difficult to separate from the response to global-mean temperature change."

[AbruptSLR]

While I have focused on the hazards of the potential collapse of the AIS (particularly the WAIS) this century; that does not mean that the longer-term hazards of the complete de-glaciation of Antarctica do not merit discussion (as might be conceivable when two to three centuries if the current 3 meteorology circulation cells were to transform into single circulation cells in both the North and South Hemispheres); including discussion of the fact that when/if the planet absorbs more solar energy than it can release to maintain an equilibrium then the oceans would continue to evaporate into the atmosphere leading to a runaway greenhouse effect.  Recent research (see below) has estimated that it would take 30,000 parts per million of carbon dioxide equivalent (14,000 GtCarbon eq. or 282 W m−2) in the atmosphere to make it warm enough to trigger this runaway greenhouse.  As the level of carbon dioxide today is 400 parts per million and burning all of Earth's estimated recoverable fossil fuels would only raise it to 2,000 to 3,000 parts per million, it would seem that the risk of getting to 30,000 parts per million CO₂ eq, is unlikely, and thus most researchers (including Hansen) concur that a runaway scenario most likely would not happen for about a billion years when the sun brightens).

http://www.nature.com/ngeo/journal/v6/n8/full/ngeo1892.html

Low simulated radiation limit for runaway greenhouse climates; Colin Goldblatt, Tyler D. Robinson, Kevin J. Zahnle & David Crisp; Nature Geoscience, 6, pp 661–667, (2013), doi:10.1038/ngeo1892

"Abstract
The atmospheres of terrestrial planets are expected to be in long-term radiation balance: an increase in the absorption of solar radiation warms the surface and troposphere, which leads to a matching increase in the emission of thermal radiation. Warming a wet planet such as Earth would make the atmosphere moist and optically thick such that only thermal radiation emitted from the upper troposphere can escape to space. Hence, for a hot moist atmosphere, there is an upper limit on the thermal emission that is unrelated to surface temperature. If the solar radiation absorbed exceeds this limit, the planet will heat uncontrollably and the entire ocean will evaporate—the so-called runaway greenhouse. Here we model the solar and thermal radiative transfer in incipient and complete runaway greenhouse atmospheres at line-by-line spectral resolution using a modern spectral database. We find a thermal radiation limit of 282 W m−2 (lower than previously reported) and that 294 W m−2 of solar radiation is absorbed (higher than previously reported). Therefore, a steam atmosphere induced by such a runaway greenhouse may be a stable state for a planet receiving a similar amount of solar radiation as Earth today. Avoiding a runaway greenhouse on Earth requires that the atmosphere is subsaturated with water, and that the albedo effect of clouds exceeds their greenhouse effect. A runaway greenhouse could in theory be triggered by increased greenhouse forcing, but anthropogenic emissions are probably insufficient."

Nevertheless, from a hazard assessment point of view it worth examining how high radiative forcing might go in the next 250 years assuming a RCP 9.5 50%CL base case (assuming both anthropogenic forcing and natural CO₂ from permafrost degradation for a total radiative forcing of about 12.5 W m−2 by 2250, see the first attached image)  combined with single meteorological circulation cells adding significant quantities of methane emissions from: (a) Arctic Ocean and Antarctic methane hydrates and (b) Arctic permafrost, as discussed below.
Russian scientists estimate that more than 1,000 billion tons of methane (in hydrate form) lie beneath the Siberian continental shelf, which implies that there should be over 2,000 billion tons of methane in hydrate form in all of the Arctic continental shelves, and scientists agree that Arctic sub-sea permafrost — with a temperature of 29° F to 30° F (-2 to -1 °C) — is closer to thawing than terrestrial permafrost, whose temperature can drop as low as 9.5° F (-12.5 °C).  As the Arctic sub-sea permafrost thaws it exposes the Arctic sub-sea gas hydrates to decomposition.  Furthermore, most researchers appear to neglect the fact that the majority of the Antarctic continental shelves were covered with glaciers during the LGM (last glacial maximum) and the Antarctic sub-sea permafrost must also be very close to (or likely already is) degrading which similar would expose another large quantities (probably on the order of 1,000 billion tons) of methane (in hydrate or free gas form).  While the collapse of the current AIS could cause another approximately 1,000 billion tons of methane to be subject to decomposition.
Thus (for the sake of simplicity) if we were to assume here the highest natural methane emission scenario calculated by Isaksen et al 2011 (see attached pdf and the second attached image) then the total radiative forcing from the high natural methane concentrations would be 5.4 W m−2; giving one possible high scenario radiative forcing value of 12.5 + 5.4 = 17.9 W m−2 by 2050, which is much lower than the 282 W m−2 value needed to cause a runaway scenario.

[AbruptSLR]

The linked reference confirms that warming from fossil fuel burning could be more intense and longer-lasting than previously thought:

http://www.pnas.org/content/early/2013/08/02/1222843110.abstract?sid=5a740205-4593-470a-8267-f984d04f3e42


Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions;
By: Richard E. Zeebe; August 5, 2013, doi: 10.1073/pnas.1222843110; PNAS

"Abstract
Climate sensitivity measures the response of Earth’s surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth’s climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO2 solubility, which in turn leads to higher atmospheric CO2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000–165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene–Eocene Thermal Maximum."

[AbruptSLR]

The following linked (with a free pdf) reference indicates that most climate sensitivity feedback mechanisms are non-linear (particularly with regard to the influence of water vapor); and thus from a hazard point of view it is not a good idea to over rely on climate sensitivity values based on assessments of paleo-conditions:

http://www.earth-syst-dynam.net/4/253/2013/esd-4-253-2013.html

Schaller, N., Cermak, J., Wild, M., and Knutti, R.: The sensitivity of the modeled energy budget and hydrological cycle to CO2 and solar forcing, Earth Syst. Dynam., 4, 253-266, doi:10.5194/esd-4-253-2013, 2013

"Abstract. The transient responses of the energy budget and the hydrological cycle to CO2 and solar forcings of the same magnitude in a global climate model are quantified in this study. Idealized simulations are designed to test the assumption that the responses to forcings are linearly additive, i.e. whether the response to individual forcings can be added to estimate the responses to the combined forcing, and to understand the physical processes occurring as a response to a surface warming caused by CO2 or solar forcing increases of the same magnitude. For the global climate model considered, the responses of most variables of the energy budget and hydrological cycle, including surface temperature, do not add linearly. A separation of the response into a forcing and a feedback term shows that for precipitation, this non-linearity arises from the feedback term, i.e. from the non-linearity of the temperature response and the changes in the water cycle resulting from it. Further, changes in the energy budget show that less energy is available at the surface for global annual mean latent heat flux, and hence global annual mean precipitation, in simulations of transient CO2 concentration increase compared to simulations with an equivalent transient increase in the solar constant. On the other hand, lower tropospheric water vapor increase is similar between simulations with CO2 and solar forcing increase of the same magnitude. The response in precipitation is therefore more muted compared to the response in water vapor in CO2 forcing simulations, leading to a larger increase in residence time of water vapor in the atmosphere compared to solar forcing simulations. Finally, energy budget calculations show that poleward atmospheric energy transport increases more in solar forcing compared to equivalent CO2 forcing simulations, which is in line with the identified strong increase in large-scale precipitation in solar forcing scenarios."

[AbruptSLR]

The linked reference provides information indicates that the recently observed increase plant growth in the Arctic tundra is not leading to more strong of carbon, but is leading to increased Arctic warming (both of which are bad news w.r.t. public safety):

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12129.html

Long-term warming restructures Arctic tundra without changing net soil carbon storage; By: Seeta A. Sistla, John C. Moore, Rodney T. Simpson, Laura Gough, Gaius R. Shaver & Joshua P. Schimel; 15 May 2013; Nature; doi:10.1038/nature12129

Abstract
"High latitudes contain nearly half of global soil carbon, prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures. Low temperatures suppress the activity of soil biota, retarding decomposition and nitrogen release, which limits plant and microbial growth. Warming initially accelerates decomposition, increasing nitrogen availability, productivity and woody-plant dominance. However, these responses may be transitory, because coupled abiotic–biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities, can develop. Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem. Warming increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity, but did not change total soil carbon or nitrogen stocks, thereby increasing net ecosystem carbon storage. Notably, the strongest effects were in the mineral horizon, where warming increased decomposer activity and carbon stock: a ‘biotic awakening’ at depth."

[AbruptSLR]

The article at the following website, supports my position that even if anthropogenic GHG emissions slowdown in the 2035 to 2045 timeframe, the acceleration of "slow" natural forcing mechanisms (such as the permafrost, albedo, methane, forest fires, etc), will likely keep the earth on a path similar to the RCP 8.5 (for which I base most of my ASLR projections presented elsewhere in the Antarctic folder):

http://thinkprogress.org/climate/2013/08/18/2484711/ipcc-report-more-certain-global-warming-is-caused-by-humans-impacts-speeding-up/

[AbruptSLR]

The referenced article (a free pdf can be found at the weblink); indicates that use of only an equilibrium climate sensitivity, ECS, value within a GCM is too simplistic to capture the influence of hydrologic cycle and its response to different types of forcing.  This implies that any GCM projections dependent on a simple ECS value should be given a greater range of uncertainty values; and Earth System Models should be calibrated to account for the different types of sensitivities to various types of forcings.

http://www.earth-syst-dynam-discuss.net/4/853/2013/esdd-4-853-2013.pdf


A simple explanation for the sensitivity of the hydrologic cycle to global climate change;
by: A. Kleidon and M. Renner; Earth Syst. Dynam. Discuss., 4, 853–868, 2013; www.earth-syst-dynam-discuss.net/4/853/2013/; doi:10.5194/esdd-4-853-2013

"Abstract
The global hydrologic cycle is likely to increase its strength with global warming. Climate models generally predict an increase in strength of 2.2%K−1, which is much weaker than what would be expected from the increase in saturation vapor pressure of 6.5%K−1. Furthermore, it has been reported that the sensitivity of the hydrologic cycle to surface temperature differences caused by solar radiation is about 50% greater than by an equivalent difference induced by the greenhouse effect. Here we show that these sensitivities can be derived analytically from an extremely simple surface energy balance model that is constrained by the assumption that vertical convective trans port within the atmosphere operates at maximum power. Using current climatic mean conditions, this model predicts a sensitivity of the hydrologic cycle of 2.2%K−1 to surface temperature induced by differences in the greenhouse effect, and a sensitivity of 3.2%K−1 for differences caused by absorbed solar radiation. These sensitivities can be explained by considering the changes in the surface energy balance in which the heating by solar radiation is partitioned equally into radiative and turbulent cooling at a state of maximum power of convective exchange. This explanation emphasizes the different roles that solar and terrestrial radiation play in the surface energy balance and hydrologic cycling that cannot be lumped together into a radiative forcing concept. We illustrate one implication of this explanation for the case of geoengineering, which aims to undo surface temperature differences by solar radiation management, but will nevertheless result in substantial differences in hydrologic cycling due to the difference in sensitivities. We conclude that the overall sensitivity of the hydrologic cycle to surface temperature can be understood and predicted by very simple physical considerations."

[AbruptSLR]

The following linked reference discusses the risk of decades-old carbon being emitted into the atmosphere due to global warming.  This could be a significant positive feedback factor (that has not been included in most models yet) if the world stays on the BAU path that it is currently following:

http://www.pnas.org/content/early/2012/06/07/1120603109.abstract


Warming accelerates decomposition of decades-old carbon in forest soils;
by: Francesca M. Hopkins, Margaret S. Torn, and Susan E. Trumbore; PNAS June 11, 2012; doi: 10.1073/pnas.1120603109


Abstract:

"Global climate carbon-cycle models predict acceleration of soil organic carbon losses to the atmosphere with warming, but the size of this feedback is poorly known. The temperature sensitivity of soil carbon decomposition is commonly determined by measuring changes in the rate of carbon dioxide (CO2) production under controlled laboratory conditions. We added measurements of carbon isotopes in respired CO2 to constrain the age of carbon substrates contributing to the temperature response of decomposition for surface soils from two temperate forest sites with very different overall rates of carbon cycling. Roughly one-third of the carbon respired at any temperature was fixed from the atmosphere more than 10 y ago, and the mean age of respired carbon reflected a mixture of substrates of varying ages. Consistent with global ecosystem model predictions, the temperature sensitivity of the carbon fixed more than a decade ago was the same as the temperature sensitivity for carbon fixed less than 10 y ago. However, we also observed an overall increase in the mean age of carbon respired at higher temperatures, even correcting for potential substrate limitation effects. The combination of several age constraints from carbon isotopes showed that warming had a similar effect on respiration of decades-old and younger (<10 y) carbon but a greater effect on decomposition of substrates of intermediate (between 7 and 13 y) age. Our results highlight the vulnerability of soil carbon to warming that is years-to-decades old, which makes up a large fraction of total soil carbon in forest soils globally."

[AbruptSLR]

The following linked reference indicates that the addition of forcings are generally non-linear resulting in larger radiative forcing than most models assume that are used to advise policymakers:

http://www.earth-syst-dynam.net/4/253/2013/esd-4-253-2013.html

The sensitivity of the modeled energy budget and hydrological cycle to CO2 and solar forcing by: N. Schaller, J. Cermak, M. Wild, and R. Knutti; Earth Syst. Dynam., 4, 253–266, 2013; www.earth-syst-dynam.net/4/253/2013/; doi:10.5194/esd-4-253-2013


"Abstract. The transient responses of the energy budget and the hydrological cycle to CO2 and solar forcings of the same magnitude in a global climate model are quantified in this study. Idealized simulations are designed to test the assumption that the responses to forcings are linearly additive, i.e. whether the response to individual forcings can be added to estimate the responses to the combined forcing, and to understand the physical processes occurring as a response to a surface warming caused by CO2 or solar forcing increases of the same magnitude. For the global climate model considered, the responses of most variables of the energy budget and hydrological cycle, including surface temperature, do not add linearly. A separation of the response into a forcing and a feedback term shows that for precipitation, this non-linearity arises from the feedback term, i.e. from the non-linearity of the temperature response and the changes in the water cycle resulting from it. Further, changes in the energy budget show that less energy is available at the surface for global annual mean latent heat flux, and hence global annual mean precipitation, in simulations of transient CO2 concentration increase compared to simulations with an equivalent transient increase in the solar constant. On the other hand, lower tropospheric water vapor increase is similar between simulations with CO2 and solar forcing increase of the same magnitude.  The response in precipitation is therefore more muted compared to the response in water vapor in CO2 forcing simulations, leading to a larger increase in residence time of water vapor in the atmosphere compared to solar forcing simulations.  Finally, energy budget calculations show that poleward atmospheric energy transport increases more in solar forcing compared to equivalent CO2 forcing simulations, which is in line with the identified strong increase in large-scale precipitation in solar forcing scenarios."

[AbruptSLR]

The following linked reference (followed by another link to a summary which, together with the two attached figures, is better than the abstract), that discusses the positive feedback caused by the acidification of the oceans reducing sulfur flux from the ocean which then results in more radiative forcing (see the second attached image) particularly over the Southern Ocean:

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1981.html

Global warming amplified by reduced sulphur fluxes as a result of ocean acidification; Katharina D. Six, Silvia Kloster, Tatiana Ilyina, Stephen D. Archer, Kai Zhang & Ernst Maier-Reimer; Nature Climate Change;  (2013); doi:10.1038/nclimate1981


http://www.mpimet.mpg.de/nc/en/communication/news/single-news/article/climate-change-ocean-acidification-amplifies-global-warming.html

Summary:

"Scientists at the Max Planck Institute for Meteorology (MPI-M), Dr. Katharina Six, Dr. Silvia Kloster, Dr. Tatiana Ilyina, the late Dr. Ernst Maier-Reimer and two co-authors from the US, demonstrate that ocean acidification may amplify global warming through the biogenic production of the marine sulfur component dimethylsulphide (DMS).

It is common knowledge that fossil fuel emissions of CO2 lead to global warming. The ocean, by taking up significant amounts of CO2, lessens the effect of this anthropogenic disturbance. The "price" for storing CO2 is an ongoing decrease of seawater pH (ocean acidification1), a process that is likely to have diverse and harmful impacts on marine biota, food webs, and ecosystems. Until now, however, climate change and ocean acidification have been widely considered as uncoupled consequences of the anthropogenic CO2 perturbation2. Recently, ocean biologists measured in experiments using seawater enclosures (mesocosms)3 that DMS concentrations were markedly lower in a low-pH environment (Figure 1).
When DMS is emitted to the atmosphere it oxidizes to gas phase sulfuric acid, which can form new aerosol particles that impact cloud albedo and, hence, cool the Earth's surface. As marine DMS emissions are the largest natural source for atmospheric sulfur, changes in their strength have the potential to notably alter the Earth's radiation budget. Based on the results from the mesocosm studies the researchers from the MPI-M have established relationships between pH changes and DMS concentrations in seawater. They projected changes in DMS emissions into the atmosphere in a future climate with enhanced ocean acidification using the MPI-M Earth system model4. In the journal Nature Climate Change it is demonstrated, that modeled DMS emissions decrease by about 18 (±3)% in 2100 compared to preindustrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS emissions induce a significant positive radiative forcing of which 83% (0.4 W/m2) can, in the model, be attributed to the impact of ocean acidification alone (Figure 2).
Compared to the Earth system response to a doubling of atmospheric CO2 this is tantamount to an equilibrium temperature increase between 0.23 and 0.48 K. Simply put, their research shows that ocean acidification has the potential to speed up global warming considerably.

References:
1. Gattuso, J-P. & Hansson, L. in Ocean Acidification (eds Gattuso, J-P. & Hansson, L.) 1_20 (Oxford Univ. Press, 2011).
2. Doney, S. C., Fabry, V. J., Feely, R. A. & Kleypas, J. A. Ocean acidification: The other CO2 problem. Annu. Rev. Mar. Sci. 1,
dx.doi.org/10.1146/annurev.marine.010908.163834, 169-192 (2009).
3. Archer, S. D. et al. Contrasting responses of DMS and DMSP 102 to ocean acidification in Arctic waters. Biogeosciences 10, 103,
dx.doi.org/10.5194/bg-10-1893-2013 (2013).
4. Jungclaus, J. H. et al. Climate and carbon-cycle variability over the last millennium. Clim. Past 6, dx.doi.org/10.5194/cp-6-723-2010, 723-737 (2010)."

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The linked reference provides additional support for my position that the El Nino hiatus period is likely to end within a few years; which should accelerate ice mass loss from AIS:

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12534.html

Recent global-warming hiatus tied to equatorial Pacific surface cooling;
by: Yu Kosaka & Shang-Ping Xie; Nature; (2013); doi:10.1038/nature12534

Abstract:
"Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase."

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The following reference indicate that European forests are showing early signs of carbon saturation:

http://phys.org/news/2013-08-europe-forests-carbon-saturation.html

http://www.nature.com/nclimate/journal/v3/n9/full/nclimate1853.html


First signs of carbon sink saturation in European forest biomass; Gert-Jan Nabuurs, Marcus Lindner, Pieter J. Verkerk, Katja Gunia, Paola Deda, Roman Michalak & Giacomo Grassi; Nature Climate Change; 3, 792–796; (2013); doi:10.1038/nclimate1853

Abstract

"European forests are seen as a clear example of vegetation rebound in the Northern Hemisphere; recovering in area and growing stock since the 1950s, after centuries of stock decline and deforestation. These regrowing forests have shown to be a persistent carbon sink, projected to continue for decades, however, there are early signs of saturation. Forest policies and management strategies need revision if we want to sustain the sink."

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The following link leads to a free access pdf of: Bounding the role of Black Carbon in the Climate System: A Scientific Assessment.  Finding from this report are some of the most comprehensive that I could find:


http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50171/pdf

The model used in this study shows that BC is the second-most important agent of climate warming, after CO₂.  Overall, this study estimates a climate forcing value of +1.11 W m^-2. This represents a significant increase over past estimates, including that cited by the Intergovernmental Panel on Climate Change. This compares with the radiative forcing effect of +1.56 W m^-2 for CO₂ and +0.86 W m^-2 for CH₄.

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I believe that some will find the information, and pdf, at the following link for a Beginners Guide on the Recommended Concentration Pathways, RCP, from Skeptical Science, useful in understanding the input used in the GCM/RCM/LCM projections for SLR.  The creation of such scenarios absolves most modelers from taking responsibility for the accuracy of the input into their models, and as the RCP scenarios were developed by committees several years ago, they cannot possibly reflect the best thinking available today.  For example, the RCP scenarios do not properly account for methane emissions from permafrost degradation (nor properly for black carbon); which is a very serious omission for RCP 8.5, which best reflects the BAU case that the world has been following since well before AR3, and that we are likely (in my opinion) to be following well past 2050, at which point all of my ASLR projections to 2100 (posted in several places in the Antarctic folder) are likely to be valid:

http://www.skepticalscience.com/docs/RCP_Guide.pdf

http://www.skepticalscience.com/rcp-guide-part3-post.html

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The following abstract is taken from the proceedings of the following IGSOC sponsored symposia.  This abstract discusses the uncertainties and potential future impacts of Black Carbon, BC, on the absorption of solar radiance on snow and ice:

International Symposium on Changes in Glaciers and Ice Sheets: observations, modelling and environmental interactions; 28 July–2 August; Beijing, China; Contact: Secretary General, International Glaciological Society


http://www.igsoc.org/symposia/2013/beijing/proceedings/procsfiles/procabstracts_62.htm

Recently measured black carbon in the global snow and ice and the trends and implications for the climate
Ming JING
Corresponding author: Ming Jing
Corresponding author e-mail: petermingjing@hotmail.com
"Black carbon (BC) is thought to be a very important climate-warming agent during these years. Suspended as an aerosol in the atmosphere, it can shield the land surface and cool it, and in the meantime it will heat and warm the high and ambient air over land. Deposited in snow and ice surfaces, it can absorb incoming solar radiation and lower their albedos causing additional warming. In case of the reason for the complex role of BC in the climate, it has always been a highlight in the climate forcings since IPCC TAR. In the voice of request for reducing BC emission, the potential impacts of BC on the survival of ice bodies are still uncertain, including the current melting impact and potential trends. In this work, we will review the global distribution status of BC deposited in snow and ice, assess the impact of BC on the absorption of solar radiation in them, and presume the future trends of the impact of BC on them."

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Bruce Steele provided this link in the Consequences folder, but I thought that it was so significant that I thought that I would post it here:

http://www.egu.eu/news/76/tiny-plankton-could-have-big-impact-on-climate/

This article states:

""If the tiny plankton blooms, it consumes the nutrients that are normally also available to larger plankton species,” explains Ulf Riebesell, a professor of biological oceanography at the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany and head of the experimental team. This could mean the larger plankton run short of food.

Large plankton play an important role in carbon export to the deep ocean, but in a system dominated by the so-called pico- and nanoplankton, less carbon is transported out of surface waters. “This may cause the oceans to absorb less CO2 in the future,” says Riebesell.

The potential imbalance in the plankton food web may have an even bigger climate impact. Large plankton are also important producers of a climate-cooling gas called dimethyl sulphide, which stimulates cloud-formation over the oceans. Less dimethyl sulphide means more sunlight reaches the Earth’s surface, adding to the greenhouse effect. “These important services of the ocean may thus be significantly affected by acidification.”

Ecosystems in the Arctic are some of the most vulnerable to acidification because the cold temperatures here mean that the ocean absorbs more carbon dioxide. “Acidification is faster there than in temperate or tropical regions,” explains the coordinator of the European Project on Ocean Acidification (EPOCA), Jean-Pierre Gattuso of the Laboratory of Oceanography of Villefranche-sur-Mer of the French National Centre for Scientific Research (CNRS).

The increasing acidity is known to affect some calcifying organisms in the Arctic, including certain sea snails, mussels and other molluscs. But scientists did not know until now how ocean acidification alters both the base of the marine food web and carbon transport in the ocean. ..."


Obviously, it the oceans absorb less CO2 and emits less dimethyl sulphide, then global warming will occur faster than previously expected.  For additional related information, this article points to the free pdfs available on this topic from the following special issue of Biogenosciences

http://www.biogeosciences.net/special_issue120.html

While the previously cited research in the special issue of Biogeonscience focuses on the impacts on the Arctic; the situation in the Southern Ocean many pose an even larger risk within a few decades, not only because of the trend towards pico and nanoplankton; but also as the following article indicates, that if the wind speeds around the Southern Ocean continue to accelerate (say due to the increased atmospheric methane concentration over Antarctica) then the following linked article (with a free pdf), indicates that the carbon uptake in the Southern Ocean will also decrease because of this additional reason:


http://www.biogeosciences-discuss.net/10/15033/2013/bgd-10-15033-2013.html


Rodgers, K. B., Aumont, O., Mikaloff Fletcher, S. E., Plancherel, Y., Bopp, L., Boyer Montégut, C. de, Iudicone, D., Keeling, R. F., Madec, G., and Wanninkhof, R.: Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring, Biogeosciences Discuss., 10, 15033-15076, doi:10.5194/bgd-10-15033-2013, 2013


"Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry.

Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr−1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean."

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I have previously referred to a draft version of the following reference; but it is always good to have the links to the final paper, indicating greater likely climate sensitivity in the Antropocene:

http://onlinelibrary.wiley.com/doi/10.1002/qj.2165/full

Previdi, M., B.G. Liepert, D. Peteet, J. Hansen, D.J. Beerling, A.J. Broccoli, S. Frolking, J.N. Galloway, M. Heimann, C. Le Quéré, S. Levitus, and V. Ramaswamy, 2013: Climate sensitivity in the Anthropocene. Q. J. R. Meteorol. Soc., 139, 1121-1131, doi:10.1002/qj.2165.
Abstract
"Climate sensitivity in its most basic form is defined as the equilibrium change in global surface temperature that occurs in response to a climate forcing, or externally imposed perturbation of the planetary energy balance. Within this general definition, several specific forms of climate sensitivity exist that differ in terms of the types of climate feedbacks they include. Based on evidence from Earth's history, we suggest here that the relevant form of climate sensitivity in the Anthropocene (e.g. from which to base future greenhouse gas (GHG) stabilization targets) is the Earth system sensitivity including fast feedbacks from changes in water vapour, natural aerosols, clouds and sea ice, slower surface albedo feedbacks from changes in continental ice sheets and vegetation, and climate-GHG feedbacks from changes in natural (land and ocean) carbon sinks. Traditionally, only fast feedbacks have been considered (with the other feedbacks either ignored or treated as forcing), which has led to estimates of the climate sensitivity for doubled CO2 concentrations of about 3°C. The 2×CO2 Earth system sensitivity is higher than this, being ∼4-6°C if the ice sheet/vegetation albedo feedback is included in addition to the fast feedbacks, and higher still if climate-GHG feedbacks are also included. The inclusion of climate-GHG feedbacks due to changes in the natural carbon sinks has the advantage of more directly linking anthropogenic GHG emissions with the ensuing global temperature increase, thus providing a truer indication of the climate sensitivity to human perturbations. The Earth system climate sensitivity is difficult to quantify due to the lack of palaeo-analogues for the present-day anthropogenic forcing, and the fact that ice sheet and climate-GHG feedbacks have yet to become globally significant in the Anthropocene. Furthermore, current models are unable to adequately simulate the physics of ice sheet decay and certain aspects of the natural carbon and nitrogen cycles. Obtaining quantitative estimates of the Earth system sensitivity is therefore a high priority for future work."

[sidd]

Thanks for the Previdi(2013) reference. Seems like Hansen(2013)
Phil. Trans. R. Soc. A 2013 371, 20120294,  16 September 2013
for climate state dependent sensitivity, and implications of considering full earth system sensitivity (about twice the fast feedback sensitivity) is beginning to take hold. Look at the authors on the Previdi paper,  includes Hansen, LeQuere, Levitus and Ramaswamy.

sidd

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The linked reference indicates that there is considerable uncertainty in the amount of potential CO₂ contribution to the atmosphere from Soil Organic Carbon (SOC) particularly under RCP 8.5, and greater uncertainty means greater risk:

http://www.earth-syst-dynam-discuss.net/4/1035/2013/esdd-4-1035-2013.html


Nishina, K., Ito, A., Beerling, D. J., Cadule, P., Ciais, P., Clark, D. B., Falloon, P., Friend, A. D., Kahana, R., Kato, E., Keribin, R., Lucht, W., Lomas, M., Rademacher, T. T., Pavlick, R., Schaphoff, S., Vuichard, N., Warszawaski, L., and Yokohata, T.: Global soil organic carbon stock projection uncertainties relevant to sensitivity of global mean temperature and precipitation changes, Earth Syst. Dynam. Discuss., 4, 1035-1064, doi:10.5194/esdd-4-1035-2013, 2013


Abstract. Soil organic carbon (SOC) is the largest carbon pool in terrestrial ecosystems and may play a key role in biospheric feedback to elevated atmospheric carbon dioxide (CO2) in the warmer future world. We examined seven biome models with climate projections forced by four representative-concentration-pathways (RCPs)-based atmospheric concentration scenarios. The goal was to specify uncertainty in global SOC stock projections from global and regional perspectives. Our simulations showed that SOC stocks among the biome models varied from 1090 to 2650 Pg C even in historical periods (ca. 2000). In a higher forcing scenario (RCP8.5), inconsistent estimates of impact on the total SOC (2099–2000) were obtained from different model simulations, ranging from a net sink of 347 Pg C to a net source of 122 Pg C. In all models, the elevated atmospheric CO2 concentration in the RCP8.5 scenario considerably contributed to carbon accumulation in SOC. However, magnitudes varied from 93 to 264 Pg C by the end of the 21st century. Using time-series data of total global SOC estimated by biome biome model, we statistically analyzed the sensitivity of the global SOC stock to global mean temperature and global precipitation anomalies (ΔT and ΔP respectively) in each biome model using a state-space model. This analysis suggests that ΔT explained global SOC stock changes in most models with a resolution of 1–2 °C, and the magnitude of global SOC decomposition from a 2 °C rise ranged from almost 0 Pg C yr−1 to 3.53 Pg C yr⁻¹ among the biome models. On the other hand, ΔP had a negligible impact on change in the global SOC changes. Spatial heterogeneity was evident and inconsistent among the changes in SOC estimated by the biome models, especially in boreal to arctic regions. Our study revealed considerable climate change impact uncertainty in SOC decomposition among biome models. Further research is required to improve our understanding and ability to estimate biospheric feedback through SOC-relevant processes as well as vegetation processes.

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The following links to evidence that El Nino events will grow in intensity with global warming:

http://www.bbc.co.uk/news/science-environment-24494398

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The following link (with a free acess pdf)/citation/abstract indicate that the current climate change models greatly underestimate the amount of methane being released by thawing permafrost in the Canadian Arctic, according to Canada's National Institute of Scientific Research (INRS), as indicated by the following quote from Karita Negandhi, a student at INRS:

"We discovered that although the small shallow ponds we studied represent only 44 percent of the water-covered surface in a Bylot Island valley, they generate 83 percent of its methane emissions,"

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0078204

Small Thaw Ponds: An Unaccounted Source of Methane in the Canadian High Arctic Karita Negandhi, Isabelle Laurion, Michael J. Whiticar, Pierre E. Galand, and Connie Lovejoy; Journal PLOS; Nov 13, 2013; DOI: 10.1371/journal.pone.0078204

Abstract
"Thawing permafrost in the Canadian Arctic tundra leads to peat erosion and slumping in narrow and shallow runnel ponds that surround more commonly studied polygonal ponds. Here we compared the methane production between runnel and polygonal ponds using stable isotope ratios, 14C signatures, and investigated potential methanogenic communities through high-throughput sequencing archaeal 16S rRNA genes. We found that runnel ponds had significantly higher methane and carbon dioxide emissions, produced from a slightly larger fraction of old carbon, compared to polygonal ponds. The methane stable isotopic signature indicated production through acetoclastic methanogenesis, but gene signatures from acetoclastic and hydrogenotrophic methanogenic Archaea were detected in both polygonal and runnel ponds. We conclude that runnel ponds represent a source of methane from potentially older C, and that they contain methanogenic communities able to use diverse sources of carbon, increasing the risk of augmented methane release under a warmer climate."

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The following link/citation/abstract references research indicating that terrestrial ecosystems absorb about 11 billion tons less carbon dioxide every year as the result of the extreme climate events than they could if the events did not occur, the researchers write in the renowned journal Nature. This is equivalent to approximately a third of global CO2 emissions per year:


http://www.nature.com/nature/journal/v500/n7462/full/nature12350.html


"Climate extremes and the carbon cycle"; Reichstein M, Bahn M, Ciais P, Frank D, Mahecha MD, Seneviratne SI, Zscheischler J, Beer C, Buchmann N, Frank DC, Papale D, Rammig A, Smith P, Thonicke K, van der Velde M, Vicca S, Walz A, Wattenbach M.; Nature. 2013 Aug 15;500(7462):287-95. doi: 10.1038/nature12350.

Abstract

"The terrestrial biosphere is a key component of the global carbon cycle and its carbon balance is strongly influenced by climate. Continuing environmental changes are thought to increase global terrestrial carbon uptake. But evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected increase in terrestrial carbon uptake. Here we explore the mechanisms and impacts of climate extremes on the terrestrial carbon cycle, and propose a pathway to improve our understanding of present and future impacts of climate extremes on the terrestrial carbon budget."

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The linked reference indicates that terrestrial vegetation will stop acting as a carbon sink after a 4 degree C mean global surface temperature rise, while this high degree of climate sensitivity is not captured by most GCMs:

http://www.pnas.org/content/early/2013/12/12/1222477110

Andrew D. Friend, Wolfgang Lucht, Tim T. Rademacher, Rozenn Keribin, Richard Betts, Patricia Cadule, Philippe Ciais, Douglas B. Clark, Rutger Dankers, Pete D. Falloon, Akihiko Ito, Ron Kahana, Axel Kleidon, Mark R. Lomas, Kazuya Nishina, Sebastian Ostberg, Ryan Pavlick, Philippe Peylin, Sibyll Schaphoff, Nicolas Vuichard, Lila Warszawski, Andy Wiltshire, and F. Ian Woodward, 2013, "Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO₂", PNAS December 16, 2013, doi: 10.1073/pnas.1222477110

"Abstract
Future climate change and increasing atmospheric CO2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510–758 ppm of CO2), vegetation carbon increases by 52–477 Pg C (224 Pg C mean), mainly due to CO2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended."

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The linked reference provides the first evidence that as water vapor invades the stratosphere it is serving as source of a significant positive feedback mechanism (which in not fully modelled by most GCMs):

http://www.pnas.org/content/early/2013/09/26/1310344110.abstract?sid=8069b689-eb9f-44f1-8e4e-13e764b3d5fc

A. E. Dessler, M. R. Schoeberl, T. Wang, S. M. Davis, and K. H. Rosenlof, (2013), "Stratospheric water vapor feedback", PNAS, doi: 10.1073/pnas.1310344110
 
"Abstract
We show here that stratospheric water vapor variations play an important role in the evolution of our climate. This comes from analysis of observations showing that stratospheric water vapor increases with tropospheric temperature, implying the existence of a stratospheric water vapor feedback. We estimate the strength of this feedback in a chemistry–climate model to be +0.3 W/(m2⋅K), which would be a significant contributor to the overall climate sensitivity. One-third of this feedback comes from increases in water vapor entering the stratosphere through the tropical tropopause layer, with the rest coming from increases in water vapor entering through the extratropical tropopause."

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For further support of my point that radiative forcing is likely to raise mean global surface temperatures faster than previously assumed, the linked Christian Science Monitor article indicates how the International Energy Agency predicts a 3.5C increase by 2035.

See: http://www.csmonitor.com/World/Global-Issues/2010/1111/Global-temperature-to-rise-3.5-degrees-C.-by-2035-International-Energy-Agency

Such a likely rapid rise in mean global temperature clearly increases the probability of abrupt SLR this century.

[sidd]

should not take than CSM report or the IEA seriously. Birol is a showman, IEA exaggerated possible oil reserves for years. And CSM got the reporting wrong.

What the IEA actually said, and with which i disagree: in 35 years, given IEA numbers on future fossil carbon combustion, enough fossil carbon will be released to commit to _eventual_ surface temperature rise of 3.5C

_Not_ that 3.5 C rise will occur by 2035, but that enough carbon will be released by then to lock in eventual (century or millennium scale) rise of 3.5C

As i said, i disagree even with this watered down version of CSM version of IEA claim. IEA has been gloriously wrong in the past, and in my opinion, is wrong on this one also. Fossil carbon use will be nowhere close to their claims. For one thing, coal is dead, and the vultures are gathering. I am looking at financing reports and forget trying to get a loan for a new coal project, and forget trying to expand or upgrade exiting production or use. Banks are finally catching on, mainly because they find they cant lay off the risks like they used to. And existing credit arrangements with fossil companies are a)not being rolled over or b) extortionate rate increases are being imposed on all our favorite villains like Peabody and Massey c) New "special contingency" fees are being imposed on all coal or coal burning projects goin forward.


This report was from 2010, world is changing quickly

sidd

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Sidd,
Thank you very much for the correction.  It looks like I put too much blind faith in the CSM.  In an attempt to present more current and hopefully more reliable information, I provide the following link to the U.N. Environmental Programme November 2013 Emissions Gap Report:

http://www.unep.org/pdf/UNEPEmissionsGapReport2013.pdf

For those who want to focus on the actions that society can do to reduce emissions this report provides a state-of-the-art summary (highlighting the emissions gap between current pledges and that required to stay below 2 degrees C).  However, as I am less certain that society will make significant reductions from the business-as-usual, BaU, case, and as I believe that switching from coal to shale gas will not improve the CO2e emissions, I extract two BaU related projections in the following:
1.  Assuming that current pledges are honored (which may not be the case): "Global greenhouse gas emissions in 2020 are estimated at 59 GtCO2e per year (range: 56–60 GtCO2e per year) under a business-as-usual scenario – that is, a scenario that only considers existing mitigation efforts."
2.  In the attached image (the bottom panel only of Figure 3.1) the BaU case (with current pledges honored) is essentially represented by the purple bars (with 59 GtCO2e per year by 2020 and about 99 GtCO2e per year by 2100); which indicate that under this case mean global surface temperatures by 2100 will be well above 5 degrees C above 1990.

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The following link leads to an article that states that due to correct modeling of atmospheric/vapor updrafts, actual climate sensitivity is more positive than previously modeled (approximately 14 to 15% more positive due to this single feedback mechanism alone):

http://www.science20.com/news_articles/deeper_updrafts_new_cloud_simulation_leads_estimate_4%C2%B0c_rise_global_temperatures_2100-127058

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As the 14 to 15% increase in my immediate past post here, was too simplistic in that it only referred to the expected increase due to the discussed feedback mechanism as applied to the average climate sensitivity, I thought that I had better provide a link to the actual paper itself for clarification (as the prior low end estimate actually doubles while the high end estimate is not changed by this particular feedback mechanism):

Steven C. Sherwood, Sandrine Bony & Jean-Louis Dufresne; "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; 505, pp 37–42; (02 January 2014), doi:10.1038/nature12829

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

Abstract:
"Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming."

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In regards to my post of Dec 31, 2013, the first attached image (from Sherwood et al, 2014) indicates that their analysis actually indicates that the most likely value for equilibrium climate sensitivity is greater than 4 degrees C.

While the second attached image (from Fasullo and Trenberth, 2012) indicates that the most likely value for equilibrium climate sensitivity is approximately 4.5 degrees C.

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The attached image from: Smil, V., 2014, "The Long Slow Rise of Solar and Wind", Scientific American, Volume 310, Number 1, pp 52 - 57, January 2014; indicates that it could easily take over 70 year for wind and solar energy to meet even 25% of the world's energy supply.  This implies that society is very likely to stay on a BAU radiative forcing pathway for many decades to come:

[AbruptSLR]

To provide context to my prior two posts, I would like to say that:
(a) As the atmospheric concentration of both black carbon and methane are currently well above that assumed in RCP 8.5 50% CL and as CO2 emissions are currently approximately tracking the RCP 8.5 50% CL; and
(b) It appears that the most likely quick response equilibrium climate sensitivity is between 4.25 and 4.5 degrees C:

These two factors will accelerate such slow climate sensitivity factors as: permafrost degradation, reductions of Arctic albedo; and reductions of the duration of northern hemisphere snow cover.  If so then as indicated in my reply #3 in this thread the combine effective climate sensitivity could easily increase to about 6 degrees C, this century.  If so then the mean global temperature increase by 2100 could be as high a 8 degrees C by the end of this century as indicates in my reply #10 of this thread.

[AbruptSLR]

It seems difficult to imagine that the US will really cut-back in total GHG warming potential when we are developing shale gas/oil faster than anyone imagined possible just a few years ago (see linked article):

http://www.sfgate.com/business/bloomberg/article/Unforeseen-U-S-Oil-Boom-Upends-Markets-as-5123980.php

[AbruptSLR]

In earlier replies in this thread, I discuss some of the risks of the transition of the atmospheric circulation patterns to those for an equable climate; and the evidence cited in those replies indicates that if the mean global surface temperature increase were to be above 8 degrees C by the end of this century, then the risk of such a transition is substantial.  Furthermore, the line of logic that I present in reply # 87 indicate the risk of the mean global surface temperature increase equaling, or exceeding 8 degrees C this century, is substantial.  While an abrupt transition to an equable climate would clearly accelerated ice mass loss from Antarctica, due to thermal inertia the SLR impacts associated with such an acceleration of Antarctic ice mass loss would occur much more slowly than would the atmospheric and hydrological impacts.
Sitting here, it seems likely than no national, or international, governmental body could find the impacts of an equable climate acceptable; which seems to imply that such governmental bodies would resort to the use of geo-engineering in an attempt to mitigate such impacts.  Unfortunately, current GCMs have a poor record wrt modeling equable climates and thus the potential risks associated with the implementation of such geo-engineering measures would be substantial, with potential consequences potentially as severe as those associated with an equable climate.

[AbruptSLR]

The article at the following link indicates that aging natural gas pipelines are leaking more than in the past and present a growing source of methane emitting into the atmosphere:

http://pubs.acs.org/doi/abs/10.1021/es404474x

[AbruptSLR]

I thought that I would post the attached atmospheric methane concentration from Mauna Loa for December 28, 2013; which indicates that since 2005 the atmospheric methane concentration has only increased (and is still increasing).

[AbruptSLR]

The information at the following link indicates that new research (to be published in Nature Geoscience) indicates that the hydrological cycle can/does amplify abrupt climate change:

http://www.exchangemagazine.com/morningpost/2014/week2/Friday/14011715.htm

As the hydrological cycle has been measured to be increasing at a rate that is approximately twice that of most of the GCM's referenced in AR5, society should not be surprised if abrupt climate change occurs during this century.

[AbruptSLR]

In their January 13 2014 forecast NOAA projects a transition from ENSO neutral to an mild El Nino condition by late summer of 2014 (see the pdf at the link and/or the attached image):

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

If this trend continues beyond the summer of 2014 then by the austral summer of 2014-2015 a strong El Nino condition could occur, which should accelerate ice mass loss from the WAIS.

[AbruptSLR]

The attached image (from NOAA January 7, 2014) shows that the PDO index has largely been negative since the end of the 1998 El Nino event; thus it is likely that beginning in 2015 the PDO will begin a period of positive index implying a return to a period of more frequent El Nino events:

[AbruptSLR]

Many commentators have noted that the retreat of Arctic Sea Ice may draw more shipping and more oil/gas development into the fragile Arctic Ocean; however, the linked article discusses the strong possibility that as the NH permafrost thaws farmers will move into this organic rich farmlands:

http://modernfarmer.com/2014/01/permafrost-farming-possible/

Note that these permafrost farms will accelerate the thawing of the permafrost, which could accelerate carbon emission from the organic currently frozen in the permafrost.

[steve s]

NH=?


New glossary entry needed?

[AbruptSLR]

steve s,

NH = Northern Hemisphere.  Sorry to be writing in a hurry, but I am traveling at the moment.

Best,
ASLR

[AbruptSLR]

Previously, researchers were uncertain about the effect of global warming on El Nino events; however, the following reference makes it very clear that the frequency of extreme El Nino events will at least double in frequency.  This clearly increases the recognized probability of ASLR this century:

Wenju Cai, Simon Borlace, Matthieu Lengaigne, Peter van Rensch, Mat Collins, Gabriel Vecchi, Axel Timmermann, Agus Santoso, Michael J. McPhaden, Lixin Wu, Matthew H. England, Guojian Wang, Eric Guilyardi & Fei-Fei Jin, (2014), "Increasing frequency of extreme El Niño events due to greenhouse warming", Nature Climate Change, doi:10.1038/nclimate2100
 
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2100.html

Abstract: "El Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as ‘the climate event of the twentieth century, and the 1982/83 extreme El Niño, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3) and 5 (CMIP5) multi-model databases, and a perturbed physics ensemble. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters, facilitating more occurrences of atmospheric convection in the eastern equatorial region."

[AbruptSLR]

I believe that the linked reference implies that radiative forcing is much more significant that solar irradiance for increasing mean global temperature.  If so, the world could warm faster during the anthropocene than during earlier epoch of the world:

http://link.springer.com/article/10.1007%2Fs10651-012-0226-z#page-1
 
Domenico Vitale, and Massimo Bilancia, "Role of the natural and anthropogenic radiative forcings on global warming: evidence from cointegration–VECM analysis"; Environmental and Ecological Statistics; September 2013, Volume 20, Issue 3, pp 413-444

"Abstract
Over the last few years there has been much debate about the hypothesis that anthropogenic emissions of CO2 and other greenhouse gases increase global temperature permanently. By using recent advances in time series econometrics, this paper tries to answer the question on how human activity affects Earth’s surface temperatures. Bearing in mind this goal, we estimated the long-run cointegration relations between global temperatures and changes in radiative forcings by a set of perturbing factors. We found that the temperature response to a doubling in radiative forcing of anthropogenic greenhouse gases is + 2.94 °C [95 % CI: + 1.91, + 3.97], in perfect accordance with prior research, and that the orthogonalized cumulated effect over a 100 year time period, in response to a unit increase of size of one standard deviation in greenhouse gas radiative forcing, is + 3.86 °C [95 % CI: + 0.03, + 6.54]. Conversely, the amplitude of solar irradiance variability is hardly sufficient to explain observed variations in the Earth’s climate. Our results show that the combined effect of stochastic trends attributable to anthropogenic radiative forcing variations are driving the Earth’s climate system toward an ongoing phase of global warming, and that such long-run movement is unlikely to be transient."