tag:blogger.com,1999:blog-9093436161326155359.post4941643449139379859..comments2024-03-28T06:43:02.954+00:00Comments on Variable Variability: Is it time to freak out about the climate sensitivity estimates from energy budget models?Victor Venemahttp://www.blogger.com/profile/02842816166712285801noreply@blogger.comBlogger25125tag:blogger.com,1999:blog-9093436161326155359.post-24982538229935890252016-08-23T00:11:11.714+01:002016-08-23T00:11:11.714+01:00When ECS2x is discussed, it amazes me that Schmitt...When ECS2x is discussed, it amazes me that Schmittner, Urban, Shakun, Mahowald, Clark, Bartlein, Mix, and Rosell-Melé seldom comes up. See https://667-per-cm.net/2016/08/21/ecs2x-land-sea-and-all-that/ and the figure reproduced therein. That's from:<br /><br /><b><i>Science</i> 09 Dec 2011:<br />Vol. 334, Issue 6061, pp. 1385-1388<br />DOI: 10.1126/science.1203513</b><br /><br />and it was a full Bayesian treatment. There's a kind of follow-up investigation at http://dx.doi.org/10.1002/2014GL059484Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-1275161171448454352016-07-12T18:25:30.496+01:002016-07-12T18:25:30.496+01:00I argue above that the climate sensitivity is stil...I argue above that the climate sensitivity is still 3°C like it has been for decades. How should that staying the same make a difference for projections of the future?Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-10697179002506939422016-07-12T18:22:13.358+01:002016-07-12T18:22:13.358+01:00Hi Victor,
So does any of this impact the finding ...Hi Victor,<br />So does any of this impact the finding that adhering to the Paris Agreement results in temp. rise of 2.3-3.5C by 2100?Michaelnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-70493689823634496352016-07-10T20:05:48.320+01:002016-07-10T20:05:48.320+01:00From my perspective the Republican PR machine'...From my perspective the Republican PR machine's obsession with the "Climate Sensitivity number" is nothing but another smooth cynical distraction. It's not like people have any benchmark to help us understand precisely what this or that number actually means in terms of its ultimate impact.<br /><br />What we do know is the observed transition over the past half century when compared with the previous centuries. Aren't those changes scary enough to know that we have invited profound disruption into our lives and should do everything in our power to slow it down?citizenschallengehttps://www.blogger.com/profile/04559990934735912814noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-42968751821087099582016-07-08T18:30:57.184+01:002016-07-08T18:30:57.184+01:00If nothing unexpected is published, I would expect...If nothing unexpected is published, I would expect that the lower bound will go up. My feeling is that 1.5°C is too low for our current understanding. <br /><br />I would not dare to give numbers for the probable range out of the blue. That would require gathering all the evidence we currently have, similar to the previous review of Knutti and Hegerl (2008). That is work.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-32316177255370627942016-07-08T18:19:12.938+01:002016-07-08T18:19:12.938+01:00So what would be a good probable range for ECS? 2....So what would be a good probable range for ECS? 2.5-4.5?Michaelnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-85523631741823620772016-07-08T13:56:37.106+01:002016-07-08T13:56:37.106+01:00andthentheresphysics, thanks. I should also have a...andthentheresphysics, thanks. I should also have added to my answer to Michael that the temperature in 2100 depends on what humanity does, while the climate sensitivity is physics and does not depend on human action.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-33574877559689064292016-07-08T13:54:20.658+01:002016-07-08T13:54:20.658+01:00Eli, 4.2°C still sounds a bit high to me. But I wo...Eli, 4.2°C still sounds a bit high to me. But I would not be surprised if the next IPCC report would give 3.5°C as best estimate of the ECS, if the current results for the energy balance models still holds, we still have many studies showing faster than expected changes in several other climate systems and the models with the higher sensitivities are still the ones with the most realistic cloud properties.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-42853465281574040462016-07-08T12:57:33.066+01:002016-07-08T12:57:33.066+01:00Somewhat amusing that Hansen et al 1988 used an EC...Somewhat amusing that Hansen et al 1988 used an ECS of 4.2 C and has been taking stick for it ever since. <br /><br />Time to revise all those blog posts, although as Hansen pointed out, for the difference between 3 and 4.2 to show up you have to go out more than 20 years.EliRabetthttps://www.blogger.com/profile/07957002964638398767noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-59973364786126975782016-07-08T12:38:37.659+01:002016-07-08T12:38:37.659+01:00To respond more to Michael, Victor's post is m...To respond more to Michael, Victor's post is mainly about the equilibrium climate response, which is how much we will eventually warm (due to fast feedbacks only) if we double atmospheric CO2. As others have pointed out, this does ignore slow feedbacks, which will also become relevant on multi-century scales, and the system sensitivity (ESS) may well be above 4C. <br /><br />However, for the next century (till 2100, say) what is probably relevant is the transient climate response, which is between 1C and 2.5C and is the amount we will have warmed at the instant when we have doubled atmospheric CO2. <br /><br />However, an issue with this is that it doesn't really tell us how to relate this to our emissions. There is another metric called the Transient Response to Cumulative Emissions (TCRE) which is between 0.8C and 2.5C per 1000 GtC. We've emitted about 600GtC and warmed by about 1C, so a reasonable best estimate would be about 1.7C per 1000 GtC. Therefore, how much we will probably warm by 2100 depends on how much we emit by 2100. If we emit another 400GtC, we will probably reach 1.7C. If we emit another 1400 GtC, we will warm by more than 3C (relative to pre-industry). <br /><br />We're currently emitting 10GtC/yr, so to keep below 2C (50% chance) would require emitting no more than about 500GtC, and to keep below 1.5C would require emitting no more than about another 250GtC. In other words, having a reasonble chance (50%) of keeping below 2C would require no more than 50 years of current emissions, and less if emissions continue to rise. Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-11018427980699852362016-07-08T03:21:24.071+01:002016-07-08T03:21:24.071+01:00Climate Sensitivity Estimated From Earth's Cli...<a href="http://www.columbia.edu/~jeh1/mailings/2012/20120508_ClimateSensitivity.pdf" rel="nofollow">Climate Sensitivity Estimated From Earth's Climate History</a>, James E. Hansen and Makiko Sato: <br /><i>"Our best estimate for the fast-feedback climate sensitivity from<br />Holocene initial conditions is 3 ± 0.5°C for 4 W/m2 CO2 forcing (68% probability)."</i><br /><br />and <br /><br /><i>"The Earth system sensitivity relevant to humanity now is the sensitivity of the present climate state to a positive (warming) forcing. That sensitivity is not as great as for a negative forcing, but it is much larger than the 3°C fast-feedback climate sensitivity."</i><br /><br />It seems we eventually catch up to Hansen. Perhaps we should consider freaking out :)Kevin O'Neillhttps://www.blogger.com/profile/15751040367339659805noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-64268552412862803152016-07-08T02:16:58.720+01:002016-07-08T02:16:58.720+01:00Under a business as usual scenario the values are ...Under a business as usual scenario the values are similar, which may lead some people to confuse them, but these two number are by definition fundamentally different. Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-55014431341372149712016-07-08T02:11:52.531+01:002016-07-08T02:11:52.531+01:00Thanks, Victor. I know ECS is the warming associat...Thanks, Victor. I know ECS is the warming associated with a doubling of CO2. Is that roughly the warming that would take place in the latter half of the century?Michaelnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-55961152566904040512016-07-08T00:43:00.115+01:002016-07-08T00:43:00.115+01:00Michael, Kyle just wrote on twitter: "3C is s...Michael, Kyle just wrote on twitter: "3C is still consistent with new studies, but 4-5C is too. Other evidence needed to rule out high ECS values."<br /><br />https://twitter.com/karmour_uw/status/751196706822189056Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-62789883023819747062016-07-08T00:39:44.623+01:002016-07-08T00:39:44.623+01:00Thanks for the reply. Do you think 3C ECS is reaso...Thanks for the reply. Do you think 3C ECS is reasonable as well?Michaelnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-91463052247788749282016-07-08T00:19:12.956+01:002016-07-08T00:19:12.956+01:00Steve, good point about other feedbacks. The ECS v...Steve, good point about other feedbacks. The ECS values discussed here exclude carbon cycle feedbacks, ice sheet feedbacks, and feedback nonlinearities that might arise if warming becomes large enough.Anonymoushttps://www.blogger.com/profile/10784334318828085549noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-63668137848961622912016-07-08T00:14:53.587+01:002016-07-08T00:14:53.587+01:00An ECS around 4 C seems reasonable to me; it's...An ECS around 4 C seems reasonable to me; it's very likely above 2 C, but we have little information about the upper bound at the moment. It will be interesting to see if consensus emerges as these new results are examined more closely and combined with other lines of evidence.Anonymoushttps://www.blogger.com/profile/10784334318828085549noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-83479038717607665752016-07-07T23:38:44.503+01:002016-07-07T23:38:44.503+01:00Nice post, but:
I realize I'm a broken record...Nice post, but:<br /><br />I realize I'm a broken record on this point, but the stable global temperature implied by ECS isn't something that can ever exist in the real world, primarily because ECS omits carbon feedbacks. Even speaking in terms of ESS (earth system sensitivity) is somewhat misleading since, unlike in past climates, we won't be in anything resembling an equilibrium climate state until we're on the other side of the peak. At this point we'll be lucky if that peak temperature is less than +5C, even if we manage to limit the CO2 concentration directly resulting from our emissiobs to a doubling (doubtful). Steve Bloomhttps://www.blogger.com/profile/12943109973917998380noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-82015353336546353862016-07-07T21:32:27.048+01:002016-07-07T21:32:27.048+01:00Hi Kyle,
What would your personal guess of ECS...Hi Kyle,<br /> What would your personal guess of ECS be?<br /> Michaelnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-35564371990587589862016-07-07T18:50:17.685+01:002016-07-07T18:50:17.685+01:00The short answer is that I'm not sure. My susp...The short answer is that I'm not sure. My suspicion is that some portion of the Marvel et al result may actually be due to feedback time-dependence, even though they (and I) have framed it in terms of forcing efficacy. This would mean that their forcing efficacy revision may not be totally independent of the time-dependent feedback revision, so that they can't be simply combined as I've done here. So, for now, you can take the 'Marvel et al' curve above as a conservative estimate if you'd like (giving ECS = 3.9 C with a 2.1-10.7 C 95% range, by my estimate, when combined with the Richardson et al result). But note also that I've not included uncertainty in my 'time dependence' correction here (I've used the model average of 25%, while the range across models is about 0 to 100% based on work I'm about to submit); so, that too is a conservative estimate.<br /><br />We definitely need additional studies to examine forcing efficacy, feedback time-dependence, and their possible relation, and with more models to get a sense of the robustness of the results. I'm working on this, and it sounds like Gavin and collaborators are too.<br />Anonymoushttps://www.blogger.com/profile/10784334318828085549noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-87907018461544336022016-07-07T18:03:10.058+01:002016-07-07T18:03:10.058+01:00Kyle, agree. That is what I hinted at with my tong...Kyle, agree. That is what I hinted at with my tongue in cheek remark: "Someone promoting a climate sensitivity of 12.8°C deserves a place in statistical Purgatory."<br /><br />That upper limit estimate is just that we do not have enough information to restrain the energy balance models, not a real upper bound, which will have to come from other considerations.<br /><br />If there were an interaction between the forcing efficiency and the time-dependence, is there any reason to expect that to reduce the ECS bias or increase it or does it need a separate study to even guess the sign of the effect?Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-43322266210306247572016-07-07T17:48:49.383+01:002016-07-07T17:48:49.383+01:00Nice post, Victor. Another interpretation of how t...Nice post, Victor. Another interpretation of how the new energy-budget constraints fit into the broader picture is that the upper bound on climate sensitivity must come from something else. That is, both models and energy-budget constraints allow sensitivity > 4.5 C, so we must rely on those other lines of evidence (e.g., paleoclimate, emergent constraints, etc) to rule out this high tail.Anonymoushttps://www.blogger.com/profile/10784334318828085549noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-71771294791484304202016-07-07T16:24:01.352+01:002016-07-07T16:24:01.352+01:00JCH, thanks.
MarkR, space is even more limited in...JCH, thanks.<br /><br />MarkR, space is even more limited in blog posts. :) I already tend to write too long posts by mentioning all those "important" details. I thought the change in ice cover was the smaller effect and skipped it. If it is about half, maybe I should add it.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-36331772127664476992016-07-07T16:08:06.736+01:002016-07-07T16:08:06.736+01:00Hi Victor,
Nice post.
The 9% difference between ...Hi Victor,<br /><br />Nice post.<br /><br />The 9% difference between air and SST reported warming includes an effect from changing sea ice. Air only warms <5% more than the water below (exact number depends on the model), but the switch from measuring air temperatures over ice to measuring water temperatures when ice retreats boosts the effect to about 9%. It turns out this is mainlym related to how the anomalies are calculated.<br /><br />Limited space in the paper means we couldn't dwell on this too much, but a more detailed explanation is in Cowtan et al. 2016 which we cite.MarkRnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-37742872111737888782016-07-07T15:04:28.251+01:002016-07-07T15:04:28.251+01:00Excellent read.
"The promotion of the cherry...Excellent read.<br /><br />"The promotion of the cherry picked climate sensitivity of 2°C, or lower, was disingenuous. "<br /><br />Agreed.JCHnoreply@blogger.com