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Bridging climate science, citizens, and policy

Climate Sensitivity and 21st Century Warming


I want to write about shoddy opining today.  I will also write about tribalism and cherry-picking; all are disappointing aspects in today’s climate discussion.  In climate circles, a big kerfuffle erupted in the past week that revolves around minutiae and made worse by disinformation.  The Research Group of Norway released a press release that somebody’s research showed a climate sensitivity of ~1.9°C (1.2-2.9°C was the range around this midpoint value) due to CO2-doubling, which is lower than other published values.

Important Point #1: The work remains un-peer reviewed.  It is part of unpublished PhD work and therefore subject to change.

Moving from that context, what happened next?  The Inter-tubes were ablaze with skeptics cheering the results.  Additionally, groups like Investor’s Business Daily jumped on the “global warming is hooey” bandwagon.  Writers like Andy Revkin provided thoughtful analysis.

Important Point #2: Skeptics view some model results as truthful – those that agree with their worldview.

IBD can, of course, opine all it wants about this topic.  What obligation to their readers do they have to disclose their biases, however?  All the other science results are wrong, except this one with which they agree.  What makes the new results so correct when every other result is so absolutely wrong?  Nothing, as I show below.

Important Point #3: These preliminary results still show a sensitivity to greenhouse gas emissions, not to the sun or any other factor.

For additional context, you should ask how these results differ from other results.  What are IBD and other skeptics crowing about?

 photo Climate_Sensitivity_500_zps9f1bcb3a.jpg

Figure 1Distributions and ranges for climate sensitivity from different lines of evidence. The circle indicates the most likely value. The thin colored bars indicate very likely value (more than 90% probability). The thicker colored bars indicate likely values (more than 66% probability). Dashed lines indicate no robust constraint on an upper bound. The IPCC likely range (2 to 4.5°C) is indicated by the vertical light blue bar. [h/t Skeptical Science]

They’re crowing about a median value of 1.9°C in a range of 1.2-2.9°C.  If you look at Figure 1, neither the median nor the range is drastically different from other estimates.  The range is a little smaller in magnitude than what the IPCC reported in 2007.  Is it surprising that if scientists add 10 more years of observation data to climate models, a sensitivity measurement might shift?  The IPCC AR4 dealt with observations through 2000.  This latest preliminary report used observations through 2010.  What happened in the past 10 years that might shift sensitivity results?  Oh, a number of La Niñas, which are global cooling events.  Without La Niñas, the 2000s would have been warmer, which would have affected the sensitivity measurement differently.  No  mention of this breaks into the opinion piece.

Important Point #4: Climate sensitivity and long-term warming are not the same thing.

The only case in which they are the same thing is if we limit our total emissions so that CO2 concentrations are equal to CO2-doubling.  That is, if CO2 concentrations peak at 540ppm sometime in the future, the globe will likely warm no more than 1.9°C.  Note that analysis’s importance.  It brings us to:

Important Point #5: On our current and projected emissions pathway, we will more than double pre-industrial CO2 concentrations.

 photo CO2_Emissions_IPCC_Obs_2011_zpsa00aa5e8.jpg

Figure 2.  Historical emissions (IEA data – black) compared to IPCC AR4 SRES scenario projections (colored lines).

As I’ve discussed before, our historical emissions continue to track at the top of the range considered by the IPCC in the AR4 (between A2 and A1FI).  Scientists are working on the AR5 as we speak, but the framework for the upcoming report changed.  Instead of emissions, planners built Representative Concentration Pathways (RCPs) for the AR5.  A graph that shows these pathways is below.  This graph uses emissions to bridge between the AR4 and AR5.

 photo CO2EmissionsScenarios-hist-and-RCP-2012.png

Figure 3. Representative Concentration Pathways used in the upcoming AR5 through the year 2100, displayed using yearly emissions estimates.

The top line (red; RCP8.5) corresponds to the A1FI/A2 SRES scenarios.  As Figure 3 shows, our historical emissions most closely match the RCP8.5 pathway.  The concentration for this pathway through 2100 is 1370ppm CO2-eq, which results in an anomalous +8.5W/m^2 forcing.  This forcing is likely to result in 4 to 6.1°C warming by 2100.  A couple of critical points: in this scenario, emissions don’t peak in the 21st century; therefore this scenario projects additional warming in the 2100s.  I want to make absolutely clear this point: our business-as-usual concentration pathway blows past CO2-doubling this century, which means the doubling sensitivity is a moot point.  We should investigate CO2-quadrupliung.  Why?  The peak emissions and concentration, which dictates the peak anomalous forcing, which controls the peak warming we face.

The IBD article contains plenty of skeptic-speak: “Predictions of doom have turned out to be nothing more than madness”, “there are too many unknowns, too many variables”, and “nothing ever proposed would have any impact anyway”.

They do have a point with their first quoted statement.  I avoid catastrophic language because doom has not befallen the vast majority of people on this planet.  Conditions are changing, to be sure, but not drastically.  There are too many unknowns.  Most of the unknowns scientists worked on the last 10 years ended up with the opposite result that IBD assumes: scientists underestimated feedbacks and results.  Events unfolded much more quickly than previously projected.  That will continue in the near future due mainly to our lack of knowledge.  The third point is a classic: we cannot act because others will not act in concert with us.  This flies in the face of a capitalist society’s foundation.  Does IBD really believe that US innovation will not increase our competitiveness or reduce inefficiencies?  Indeed, Tim Worstall’s Forbes piece posited a significant conclusion: climate change becomes cheaper to solve if the sensitivity is lower than previously estimated.  IBD should be cheering for such a result.

Finally, when was the last time you saw the IBD latch onto one financial model and completely discard others?  Where was IBD in 2007 when the financial crisis was about to start and a handful of skeptics warned that the mortgage boom was based on flawed models?  Were they writing opinion pieces like this one?  I don’t think so.  Climate change requires serious policy consideration.  This opinion piece does nothing to materially advance that goal.


5 thoughts on “Climate Sensitivity and 21st Century Warming

  1. Hi there! Excellent synopsis as usual.

    I must admit to being completely baffled by skeptics on WUWT and elsewhere behaving as if this Norwegian PhD analysis – or even James Annan’s commentary – was a victory for their side of this argument. As Dana Nuccitelli pointed out on SkS, both leave the likes of Roy Spencer and Richard Lindzen completely isolated (and almost certainly wrongly) claiming CS is less than 1 Celsius.

    However, as if to confirm that both my posts on the CS subject this week (see here) were justified, I should like to re-iterate what I see as the key points to take away from all that you have written here:

    “Important Point #4: Climate sensitivity and long-term warming are not the same thing.

    The only case in which they are the same thing is if we limit our total emissions so that CO2 concentrations are equal to CO2-doubling. That is, if CO2 concentrations peak at 540ppm sometime in the future, the globe will likely warm no more than 1.9°C. Note that analysis’s importance. It brings us to:

    Important Point #5: On our current and projected emissions pathway, we will more than double pre-industrial CO2 concentrations.”

    If what we are witnessing now are the consequences of merely an 0.8 Celsius temperature rise since pre-Industrial times, I really find it hard to understand why anyone is still arguing about whether or not a rise of 2.5 Celsius (more than 3 times 0.8) might be OK.

    Anyone who is not alarmed by this is clearly assuming that the climate will settle down once we bring CO2 emissions under control. However, anyone who thinks that is remotely possible is I think deluding themselves: The way in which the Arctic sea ice has melted faster than predicted even 7 years ago strongly suggests we have now started something that cannot be stopped (in any timescale relevant to humans). Ice caps like that on Greenland and Western Antarctica may take decades to melt but they will take a thousand times longer to re-form.

    • Martin-
      Wordpress is being funky today. Your comment appears with a blockquote, but it doesn’t show up correctly on the blog. I’ve added quotation marks to offset your comments from mine. I won’t let anyone charge you with not citing material. 😉

      Your point following my Point #5 are dead-on. This whole situation has me somewhat baffled as well. Somehow 1.9C warming is no problem because it’s not 2.9C warming. That result absolutely refutes every work that claimed something other than 1.9C warming … including Lindzen’s and Spencer’s. Of course, their argument could unfold as follows: they don’t think 0.8C warming is a problem, so an additional 1.9C won’t be either. It’s only non-skeptics who think that 0.8C warming is having deleterious effects on eco- and human-systems.

      Hopefully I built on what Nuccitelli and others wrote on this topic. I think a good deal of it is good. I liked the Revkin brainstorming session, even though I think some details were brushed aside. I couldn’t join the discussion as early as I wanted, but was instantly puzzled when the news first broke of the press release and early commentary. It wasn’t until I was working on this post that I found out the release dealt with still unaccepted PhD work. Hey, we should all issue press releases on research we haven’t completed! I guess that also works to reinforce the skeptics’ disdain for peer-reviewed science. I’m sure if the final reviewed work shows something different than what the press release contained, the skeptics will issue their own updates.

      • Thanks for tidying that up. I was really impressed by the fact that Revkin felt it was necessary to rebut my criticism of his “optimism”. Judging by the responses to his comments, the majority of his (self-selecting) readers are not fooled by this optimism.

        Once I found out (from Dana/SkS) the reality of the situation in Norway I did not dig any further. However, I decided to finish my research and am soon going to publish it as a book! Some academics do not approve of publishing academic research in non-peer-reviewed journals but I am trying to reach a non-academic audience… Only time will tell if I fail to reach either but, at least I cam up with a snappy title for my book: “The Denial of Science…”

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