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jai mitchell

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Re: Conservative Scientists & its Consequences
« Reply #1900 on: September 03, 2017, 07:30:47 PM »
this one will be very useful

Combining observations and models to reduce uncertainty in the cloud response to global warming (258995)
Joel R Norris, University of California San Diego, La Jolla, CA, United States, Timothy Myers, University of California Los Angeles, Los Angeles, CA, United States and Seethala Chellappan, Scripps Institution of Oceanography, La Jolla, CA, United States
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AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1901 on: September 04, 2017, 05:23:30 PM »
I agree that one should use a sufficiently large scale.  However, cherry picking that scale to show the maximum trend, does you no great service.  The net gain in the 30 years prior to the start of your posted graph was almost 1000 Gt.  Add that to this year's expected 500 Gt gain, and the trend over the past half century is only half that stated on your plot.  Potential ice loss from Greenland is a real concern.  However, we should strive to state the current situation as accurately as possible.

Perhaps you should criticize NASA for the scales of the ice mass plots, and I think that you are doing yourself 'no great service', by implying that you believe that this plot will show a 500 Gt mass gain for Greenland by the end of 2017, as that is a ludicrous suggestion.  Provide a post of the linked NASA's GRACE plot a year from now and we will see who is being reasonable.

Edit: I hope that you are considering runoff in your evaluation of Greenland's net ice mass loss this year.

The linked article confirms that total mass loss in Greenland in 2017 will be approximately neutral:

Title: "Guest post: How the Greenland ice sheet fared in 2017"

https://www.carbonbrief.org/guest-post-greenland-ice-sheet-2017

Extract: "So far we’ve only discussed the surface processes. Incorporating the losses from calving gives us the “total mass budget” for the year.

Since at least 2002, the total mass budget has been substantially negative, with the Greenland ice sheet losing around 200-300bn tonnes of ice each year. This year, thanks partly to Nicole’s snow and partly to the relatively low amounts of melt in the summer, we estimate the total mass budget to be close to zero and possibly even positive.

We should emphasise that this is an educated estimate of the Greenland total mass budget. We will have to wait for further data to become available from various satellite datasets to estimate the actual calving losses. (Unfortunately, it’s not certain the ageing GRACE satellites, which show the trend in mass loss, will provide any more data. Their replacements are planned for launch later this year.)"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1902 on: September 06, 2017, 03:57:42 PM »
The linked reference confirms that AR5 significantly underestimated natural emissions of methane from wetlands worldwide, and recommends that policy makers shoulder the responsibility of taking corrective actions associated with AR5s shortcomings on this matter:

Zhen Zhang, et al (2017), "Emerging role of wetland methane emissions in driving 21st century climate change", PNAS, vol. 114 no. 36,  9647–9652, doi: 10.1073/pnas.1618765114

http://www.pnas.org/content/114/36/9647.short?utm_content=buffer165f2&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

"Significance
Conventional greenhouse gas mitigation policies ignore the role of global wetlands in emitting methane (CH4) from feedbacks associated with changing climate. Here we investigate wetland feedbacks and whether, and to what degree, wetlands will exceed anthropogenic 21st century CH4 emissions using an ensemble of climate projections and a biogeochemical methane model with dynamic wetland area and permafrost. Our results reveal an emerging contribution of global wetland CH4 emissions due to processes mainly related to the sensitivity of methane emissions to temperature and changing global wetland area. We highlight that climate-change and wetland CH4 feedbacks to radiative forcing are an important component of climate change and should be represented in policies aiming to mitigate global warming below 2°C."

Abstract: "Wetland methane (CH4) emissions are the largest natural source in the global CH4 budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO2, CH4 is strongly associated with climate feedbacks. However, due to the paucity of data, wetland CH4 feedbacks were not fully assessed in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The degree to which future expansion of wetlands and CH4 emissions will evolve and consequently drive climate feedbacks is thus a question of major concern. Here we present an ensemble estimate of wetland CH4 emissions driven by 38 general circulation models for the 21st century. We find that climate change-induced increases in boreal wetland extent and temperature-driven increases in tropical CH4 emissions will dominate anthropogenic CH4 emissions by 38 to 56% toward the end of the 21st century under the Representative Concentration Pathway (RCP2.6). Depending on scenarios, wetland CH4 feedbacks translate to an increase in additional global mean radiative forcing of 0.04 W·m−2 to 0.19 W·m−2 by the end of the 21st century. Under the “worst-case” RCP8.5 scenario, with no climate mitigation, boreal CH4 emissions are enhanced by 18.05 Tg to 41.69 Tg, due to thawing of inundated areas during the cold season (December to May) and rising temperature, while tropical CH4 emissions accelerate with a total increment of 48.36 Tg to 87.37 Tg by 2099. Our results suggest that climate mitigation policies must consider mitigation of wetland CH4 feedbacks to maintain average global warming below 2 °C."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

jai mitchell

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Re: Conservative Scientists & its Consequences
« Reply #1903 on: September 06, 2017, 05:52:30 PM »
with no climate mitigation, boreal CH4 emissions are enhanced by 18.05 Tg to 41.69 Tg, due to thawing of inundated areas during the cold season (December to May) and rising temperature, while tropical CH4 emissions accelerate with a total increment of 48.36 Tg to 87.37 Tg by 2099. Our results suggest that climate mitigation policies must consider mitigation of wetland CH4 feedbacks to maintain average global warming below 2 °C."

Those Boreal estimates seem low by about 10X (by 2099) under RCP 8.5  The wetlands CH4 seems high, as changes in precipitation regimes in current peat and rainforest locations should lead to significant drying and fire, not increased CH4 production. 
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AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1904 on: September 07, 2017, 05:58:13 PM »
The linked reference indicates that the proper definition of the pre-industrial baseline can add 0.2C to IPCC projections of GMSTA.  When one considers that CO2e (for a 100-year time frame) including the influence of ozone is currently over 530 ppm; and that the oceans have been stockpiling heat content since 1750 (which is has already triggered key slow response climate feedback mechanisms); one can appreciate that our situation is more dire than AR5 is indicating:

Schurer et al (2017), "Importance of the pre-industrial baseline for likelihood of exceeding Paris goals", Nature Climate Change 7, 563-567, doi:10.1038/nclimate3345

http://www.nature.com/nclimate/journal/v7/n8/full/nclimate3345.html?foxtrotcallback=true

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1905 on: September 08, 2017, 05:58:15 PM »
It seems to me that the year round Arctic mountain glacier feed recharging of major aquifers and base flow of lowland rivers cannot help but to impact such related matters as: sea ice formation, Arctic Ocean circulation patterns and permafrost degradation rates; more than previously assumed:

A. K. Liljedahl, A. Gädeke, S. O'Neel, T. A. Gatesman & T. A. Douglas (15 July 2017), "Glacierized headwater streams as aquifer recharge corridors, subarctic Alaska", Geophysical Research Letters, DOI: 10.1002/2017GL073834

http://onlinelibrary.wiley.com/doi/10.1002/2017GL073834/abstract;jsessionid=1DA678D531D181E116272B09748AC70E.f04t04?systemMessage=Wiley+Online+Library+will+be+unavailable+on+Saturday+and+Sunday+i.e+16th+and+17th+September+at+3%3A00+EDT+%2F+8%3A00+BST+%2F+12%3A30+IST+%2F+15%3A00+SGT+for+5+hours+and+3hours+for+essential+maintenance.+Apologies+for+any+inconvenience+caused+.

Abstract: "Arctic river discharge has increased in recent decades although sources and mechanisms remain debated. Abundant literature documents permafrost thaw and mountain glacier shrinkage over the past decades. Here we link glacier runoff to aquifer recharge via a losing headwater stream in subarctic Interior Alaska. Field measurements in Jarvis Creek (634 km2), a subbasin of the Tanana and Yukon Rivers, show glacier meltwater runoff as a large component (15–28%) of total annual streamflow despite low glacier cover (3%). About half of annual headwater streamflow is lost to the aquifer (38 to 56%). The estimated long-term change in glacier-derived aquifer recharge exceeds the observed increase in Tanana River base flow. Our findings suggest a linkage between glacier wastage, aquifer recharge along the headwater stream corridor, and lowland winter discharge. Accordingly, glacierized headwater streambeds may serve as major aquifer recharge zones in semiarid climates and therefore contributing to year-round base flow of lowland rivers."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1906 on: September 15, 2017, 04:41:46 PM »
Per the following op/ed piece: "Earth’s energy imbalance (EEI): the difference between incoming solar radiation and outgoing longwave (thermal) radiation." Furthermore, ocean heat content, OHC, is the dominate measure of EEI, and therefore should be reported in the output of CMIP6 as per the second cited reference Cheng et al (2017) the measured OHC of the upper 2,000 m of ocean since 1960 is actually 13% higher than assumed in CMIP5 {& the increase in OHC (including ice melt) is 18% than that for the upper 2,000 m].

Given the vital importance of this OHC with regard to 'slow response' feedback mechanisms such as the ice-climate feedback mechanism, the ESLD assumptions of CMIP5 and AR5 will likely extract a heavy price from future generations.

Title: "Taking the Pulse of the Planet"

https://eos.org/opinions/taking-the-pulse-of-the-planet?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz091517

Extract: "Ocean heat content and sea level rise measurements may provide a more reliable answer than atmospheric measurements

Since 2006, the Argo program of autonomous profiling floats has provided near-global coverage of the upper 2,000 meters of the ocean over all seasons [Riser et al., 2016]. In addition, climate scientists have been able to quantify the ocean temperature changes back to 1960 on the basis of the much sparser historical instrument record [Cheng et al., 2017].

From these temperature measurements, scientists extract OHC. These analyses show that during 2015 and 2016, the heat stored in the upper 2,000 meters of the world ocean reached a new 57-year record high (Figure 1). This heat storage amounts to an increase of 30.4 × 1022 Joules (J) since 1960 [Cheng et al., 2017], equal to a heating rate of 0.33 Watts per square meter (W m−2) averaged over Earth’s entire surface—0.61 W m−2 after 1992. Improved measurements have revised these values upward by 13% compared with the results of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Rhein et al., 2013].

Studies show that taking the full ocean depth, ice melt, and other factors into account, Earth is estimated to have gained 0.40 ± 0.09 W m−2 since 1960 and 0.72 W m−2 since 1992 [Cheng et al., 2017]—18% higher than for the top 2,000-meter OHC alone.

The EEI has implications for the future and should be fundamental in guiding future energy policy and decisions; it is the heartbeat of the planet. Changes in OHC, the dominant measure of EEI, should be a fundamental metric along with SLR.

As we continue to scrutinize the fidelity of specific climate models, it is critical to validate their energetic imbalances as well as their depiction of GMST. The fact that the Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble mean accurately represents observed global OHC changes [Cheng et al., 2016] is critical for establishing the reliability of climate models for long-term climate change projections.

Consequently, we recommend that both the EEI and OHC be listed as output variables in the CMIP6 models, in addition to SLR and GMST. This vital sign informs societal decisions about adaptation to and mitigation of climate change [Trenberth et al., 2016]."

See also the associated reference:

Lijing Cheng, Kevin E. Trenberth, John Fasullo, Tim Boyer, John Abraham & Jiang Zhu (10 Mar 2017), "Improved estimates of ocean heat content from 1960 to 2015", Science Advances, Vol. 3, no. 3, e1601545, DOI: 10.1126/sciadv.1601545

http://advances.sciencemag.org/content/3/3/e1601545

Abstract: "Earth’s energy imbalance (EEI) drives the ongoing global warming and can best be assessed across the historical record (that is, since 1960) from ocean heat content (OHC) changes. An accurate assessment of OHC is a challenge, mainly because of insufficient and irregular data coverage. We provide updated OHC estimates with the goal of minimizing associated sampling error. We performed a subsample test, in which subsets of data during the data-rich Argo era are colocated with locations of earlier ocean observations, to quantify this error. Our results provide a new OHC estimate with an unbiased mean sampling error and with variability on decadal and multidecadal time scales (signal) that can be reliably distinguished from sampling error (noise) with signal-to-noise ratios higher than 3. The inferred integrated EEI is greater than that reported in previous assessments and is consistent with a reconstruction of the radiative imbalance at the top of atmosphere starting in 1985. We found that changes in OHC are relatively small before about 1980; since then, OHC has increased fairly steadily and, since 1990, has increasingly involved deeper layers of the ocean. In addition, OHC changes in six major oceans are reliable on decadal time scales. All ocean basins examined have experienced significant warming since 1998, with the greatest warming in the southern oceans, the tropical/subtropical Pacific Ocean, and the tropical/subtropical Atlantic Ocean. This new look at OHC and EEI changes over time provides greater confidence than previously possible, and the data sets produced are a valuable resource for further study."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1907 on: September 15, 2017, 05:24:11 PM »
The linked open access reference indicates that following a BAU pathway through 2050 could pose existential risks to large portion of the Earth's population by the end of this century:

Ramanathan, V., Molina, M.J., Zaelke, D., Borgford-Parnell, N.,
Xu, Y., Alex, K., Auffhammer, M., Bledsoe, P., Collins, W., Croes, B., Forman, F., Gustafsson, Ö,
Haines, A., Harnish, R., Jacobson, M.Z., Kang, S., Lawrence, M., Leloup, D., Lenton, T., Morehouse, T., Munk, W., Picolotti, R., Prather, K., Raga, G., Rignot, E., Shindell, D., Singh, A.K., Steiner, A., Thiemens, M., Titley, D.W., Tucker, M.E., Tripathi, S., & Victor, D., Well Under 2 Degrees Celsius: Fast Action Policies to Protect People and the Planet from Extreme Climate Change, 2017. Available at: http://www-ramanathan.ucsd.edu/about/publications.php and www.igsd.org/publications/

http://www.igsd.org/wp-content/uploads/2017/09/Well-Under-2-Degrees-Celsius-Report-2017.pdf

Extract: "A massive effort will be needed to stop warming at 2°C, and time is of the essence. With unchecked business-as-usual emissions, global warming has a 50% likelihood of exceeding 4ºC and a 5% probability of exceeding 6ºC in this century, raising existential questions for most, but especially the poorest three billion people.  A 4ºC warming is likely to expose as many as 75% of the global population to deadly heat."

See also:

Title: "Scripps says climate change may represent "existential" threat to humanity"

http://www.sandiegouniontribune.com/news/science/

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1908 on: September 15, 2017, 05:47:16 PM »
The linked article discusses the timing and outline for AR6.  It is my opinion that it will be 'a day late and a dollar short' w.r.t. to helping society to prevent a socio-economic collapse in the 2050-2060 timeframe:

Title: "Guest post: What will be in the next IPCC climate change assessment"

https://www.carbonbrief.org/guest-post-what-will-be-in-the-next-ipcc-climate-change-assessment

Extract: "At a meeting in Montreal last week, the member countries of the United Nations reached an important decision about the next few years of the IPCC – the scientific body that assesses climate change. All countries agreed on the outlines for the three main components of the next major report, due in 2021-22, which is the vital groundwork that will now guide the contributions of climate change researchers from all over the world.

A final important aspect of our new outline is that it is designed to complement and build on the three special reports that are already underway.

The idea of special reports is that they are smaller than the main assessment reports and focus on a specific topic of interest. The first one is on global warming of 1.5C (the first draft of which is currently out for expert review). The second special report is on the oceans and cryosphere in a changing climate and the third is on climate change and land. AR6 will revisit the findings of these special reports and update them on the basis of new lines of evidence. New results from climate model simulations performed under the sixth phase of the Climate Model Intercomparison Project (CMIP6) will be available by the time of AR6, for example."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Archimid

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Re: Conservative Scientists & its Consequences
« Reply #1909 on: September 15, 2017, 06:00:18 PM »
Parkinson's law:  "work expands so as to fill the time available for its completion"

The IPCC is too slow to keep up with climate change. They need to set shorter deadlines but at the same time iterate more than before.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

rboyd

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Re: Conservative Scientists & its Consequences
« Reply #1910 on: September 15, 2017, 08:10:42 PM »
That they are even discussing 1.5 degrees shows how out of touch they are from the reality of climate change. By 2022 we may already be pretty damn close to 1.5 degrees. Perhaps an early breach of that will allow for a reconnection with reality? I wont hold my breath ....

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1911 on: September 15, 2017, 10:20:47 PM »
That they are even discussing 1.5 degrees shows how out of touch they are from the reality of climate change. By 2022 we may already be pretty damn close to 1.5 degrees. Perhaps an early breach of that will allow for a reconnection with reality? I wont hold my breath ....


In the linked article, Beck & Mahony (2017) question the role of science/politics w.r.t. the IPCC in monitoring/regulating the Paris Agreement.  For example the scientists are being asked to vouchsafe that countries will actually implement BECCS (bio-energy with carbon capture and storage) to suck CO2 from the sky so that the 1.5C target is still possible.

Beck, S. & Mahony, M. (2017), "The IPCC and the politics of anticipation", Nat. Clim. Change 7, 311–313

http://www.nature.com/nclimate/journal/v7/n5/full/nclimate3264.html

See also:
http://www.nature.com/nclimate/journal/v7/n9/full/nclimate3379.html
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1912 on: September 15, 2017, 10:28:58 PM »
The following is an example of how scientists are being asked by the US DOE management to include subroutines in their climate model (here ACME) that allow human control of the biosphere to suck CO2 out of the atmosphere after 2050 (see second image).  I doubt that humans will implement sufficient BECCS by 2050 to start sucking CO2 out of the air.

Peter E. Thornton et al, Biospheric feedback effects in a synchronously coupled model of human and Earth systems, Nature Climate Change (2017). DOI: 10.1038/nclimate3310

http://www.nature.com/nclimate/journal/v7/n7/full/nclimate3310.html?foxtrotcallback=true

Abstract: "Fossil fuel combustion and land-use change are the two largest contributors to industrial-era increases in atmospheric CO 2 concentration. Projections of these are thus fundamental inputs for coupled Earth system models (ESMs) used to estimate the physical and biological consequences of future climate system forcing. While historical data sets are available to inform past and current climate analyses, assessments of future climate change have relied on projections of energy and land use from energy–economic models, constrained by assumptions about future policy, land-use patterns and socio-economic development trajectories. Here we show that the climatic impacts on land ecosystems drive significant feedbacks in energy, agriculture, land use and carbon cycle projections for the twenty-first century. We find that exposure of human-appropriated land ecosystem productivity to biospheric change results in reductions of land area used for crops; increases in managed forest area and carbon stocks; decreases in global crop prices; and reduction in fossil fuel emissions for a low–mid-range forcing scenario. The feedbacks between climate-induced biospheric change and human system forcings to the climate system—demonstrated here—are handled inconsistently, or excluded altogether, in the one-way asynchronous coupling of energy–economic models to ESMs used to date."

See also the associated linked article entitled:  Titan simulations show importance of close two-way coupling between human and Earth systems"

https://phys.org/news/2017-07-titan-simulations-importance-two-way-coupling.html

Extract: "Through the Advanced Scientific Computing Research Leadership Computing Challenge program, Thornton's team was awarded 85 million compute hours to improve the Accelerated Climate Modeling for Energy (ACME) effort, a project sponsored by the Earth System Modeling program within DOE's Office of Biological and Environmental Research. Currently, ACME collaborators are focused on developing an advanced climate model capable of simulating 80 years of historic and future climate variability and change in 3 weeks or less of computing effort.

Now in its third year, the project has achieved several milestones—notably the development of ACME version 1 and the successful inclusion of human factors in one of its component models, the iESM.

"What's unique about ACME is that it's pushing the system to a higher resolution than has been attempted before," Thornton said. "It's also pushing toward a more comprehensive simulation capability by including human dimensions and other advances, yielding the most detailed Earth system models to date.

The development of iESM started before the ACME initiative when a multilaboratory team aimed to add new human dimensions—such as how people affect the planet to produce and consume energy—to Earth system models. The model—now a part of the ACME human dimensions component—is being merged with ACME in preparation for ACME version 2.

ACME version 1 will be publicly released in late-2017 for analysis and use by other researchers. Results from the model will also contribute to the Coupled Model Intercomparison Project, which provides foundational material for climate change assessment reports."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1913 on: September 17, 2017, 08:45:24 PM »
As a follow-on to my last post, and in an attempt to be clearer, when I state that consensus climate scientists err on the side of least drama, ESLD, I mean that consensus climate science as expressed in AR5 is biased.  More specifically, I mean that applications of the scientific method (as opposed to IPCC processes) should deal with uncertainty by examining a range of values from the lower to the upper bounds for all climate change issues in an unbiased manner.

For those who believe that the IPCC process is unbiased I offer the following counter arguments:
1. Regarding anthropogenic radiative forcing, since FAR (first assessment report) actual emissions have followed BAU pathways near the upper bounds of the SRES (Special Report on Emissions Scenarios) and RCP (Representative Concentration Pathways) families of scenarios.  If these scenarios were constructed in a nonbiased manner we would have followed a median scenario.  Furthermore, scientists decreased the ranges of uncertainties of emissions in SRES scenarios when they constructed RCP, yielding to pressure from policies maker to accept that emission regulations would limit the range of uncertainties; however, this has not consistently been the case (e.g. the Trump Administration & methane leaks from both fracking and agriculture).  Now for AR6 some scientists are trying to resist political pressure to include hypothetical negative emissions technology into the lower bounds of future emission scenarios.

2. Given that radiative forcing rates currently many times higher than during the PETM, IPCC should be reporting measures of dynamical climate sensitivity rather than reporting their 'canonical' range for equilibrium climate sensitivity, ECS, and also rather than using transient climate response, TCR, to calculate our carbon budget.  Also, I note the fact that the 'canonical' range for ECS has largely not changed for decades hints that the IPCC process in thwarting the scientific method from narrowing down this range of uncertainty.  Furthermore, IPCC inappropriately mixes together several different definitions of ECS [e.g. see Proistosescu and Huybers (2017)], which is just bad science.

3.  The paleo record contains numerous cases of abrupt climate change within periods of several decades, say due to hosing events, which are excluded from AR5 projections.  In unbiased analysis cases would be presented both with and without such short-term forcings (such as the abrupt collapse of the WAIS within the next several decades).

4.  Not only does the IPCC process ignore short-term dynamical forcing, but it also ignores numerous 'slow-response' feedback mechanisms (such as carbon emissions from permafrost degradation this century).  An unbiased process would examine cases both with and without such 'slow response' feedback mechanism.

These are just a few examples of how the IPCC process caveats their projections in a manner that introduces bias due to ESLD.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Conservative Scientists & its Consequences
« Reply #1914 on: September 19, 2017, 06:21:18 PM »
The linked reference indicates that Arctic permafrost regions may change from a carbon sink to a carbon source sooner than conventional scientists are assuming:

Parazoo, N. C., Koven, C. D., Lawrence, D. M., Romanovsky, V., and Miller, C. E.: Detecting the permafrost carbon feedback: Talik formation and increased cold-season respiration as precursors to sink-to-source transitions, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-189, in review, 2017.

https://www.the-cryosphere-discuss.net/tc-2017-189/

Abstract. Thaw and release of permafrost carbon (C) due to climate change is likely to offset increased vegetation C uptake in Northern High Latitude (NHL) terrestrial ecosystems. Models project that this permafrost C feedback may act as a slow leak, in which case detection and attribution of the feedback may be difficult. The formation of talik, a sub-surface layer of perennially thawed soil, can accelerate permafrost degradation and soil respiration, ultimately shifting the C balance of permafrost affected ecosystems from long-term C sinks to long-term C sources. It is imperative to understand and characterize mechanistic links between talik, permafrost thaw, and respiration of deep soil C to detect and quantify the permafrost C feedback. Here, we use the Community Land Model (CLM) version 4.5, a permafrost and biogeochemistry model, in comparison to long term deep borehole data along North American and Siberian transects, to investigate thaw driven C sources in NHL (> 55° N) from 2000–2300. Widespread talik at depth IS projected across most of the NHL permafrost region (14 million km2) by 2300, correlated to increased cold season warming, earlier spring thaw, and growing active layers. Talik formation peaks in the 2050s in warm permafrost regions in the sub-Arctic. Comparison to borehole data suggests talik formation may even occur sooner. Accelerated decomposition of deep soil C following talik onset shifts the surface balance of photosynthetic uptake and litter respiration into long-term C sources across 3.2 million km2 of permafrost. Talik driven sources occur predominantly in warm permafrost, but sink-to-source transition dates are delayed by decades to centuries due to high ecosystem productivity. In contrast, most of the cold permafrost region in the northern Arctic (3 million km2) shifts to a net source by the end of the 21st century in the absence of talik due to the high decomposition rates of shallow, young C in organic rich soils coupled with low productivity. Our results provide important clues signaling imminent talik onset and C source transition including: (1) late cold season (Jan–Feb) soil warming at depth (~ 2 m), (2) increasing cold season emissions (Nov–Apr), (3) enhanced respiration of deep, old C in warm permafrost and young, shallow C in organic rich cold permafrost soils. Our results suggest a mosaic of processes that govern carbon source-to-sink transitions at high latitudes, and emphasize the urgency of monitoring soil thermal profiles, organic C age and content, cold season CO2 emissions, and atmospheric 14CO2 as key indicators of the permafrost C feedback.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson