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Bridging climate science, citizens, and policy


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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  It is part of unpublished PhD work and therefore subject to change.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.


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CO2 Emissions Continue to Track At Top of IPCC Range

A new Nature Climate Change editorial (subs. req.) has a very useful graph (2 variants) that I have been looking for:

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Note first the y-axis: global CO2-emissions in Petagrams of carbon per year.  This unit is different from the other common unit used: CO2 concentrations.  The emissions eventually lead to the concentrations.  This is only the CO2 emissions, not CO2-equivalent, which might be a better variable but introduces more complexity in analysis.

Let’s go through the lines on the graph before we discuss them.  The “IS92″ lines (a-f; light blue dashed) were the emission scenarios developed for the 1992 Supplementary Report to the IPCC Assessment.  There are 40 SRES scenarios shown (thin green lines) and 6 illustrative scenarios (thick green dashed lines) that the IPCC developed for the 4th Assessment Report (AR4).  These are the scenarios most people discuss: A1B, B2, etc.  For the upcoming AR5, CO2 emissions form the basis of the scenarios.  There are ways to convert from one to the other, which is how all of these different scenarios can be plotted together.  The AR5 scenarios are labeled according to the anomalous forcing value expected in the year 2100 and a “Representative Concentration Pathway”.  Thus, RCP3 represents 3 W/m^2 forcing due to CO2 concentrations.  You can see what has to happen to global emissions to achieve this relatively low forcing value by the end of the century.  Alternatively, there is an RCP4.5, RCP6, and RCP8.5 pathway.  As a side note, my work will likely utilize the RCP8.5 pathway because we will most likely continue to move down this pathway for the foreseeable future.

Historical emissions are the black dots/line.  The estimate for 2012 emissions is the red dot.  It is obvious to see that our historical emissions has tracked near the top of any set of emissions scenarios (IS92-E, IS92-F, A1FI, A2, and A1B) and not the middle or bottom.  That has implications in climate policy because most scientific studies performed to date have focused on the low to moderate scenarios.  The reason is simple: most climate scientists thought there would be no chance of inaction once people saw what was likely to happen using even low or moderate emission scenarios.  In general, scientists were wrong.  The world has continued to increase the amount of CO2 emitted into the atmosphere, with “average annual growth rates of 1.9% per year in the 1980s, 1.0% per year in the 1990s, and 3.1% per year since 2000,” as I’ve covered in 2011 and earlier in 2012.  The post-2000 increase is largely due to China and India.

The lead author of the report posted different form of this graph and included yet another call to action that the world will ignore:

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A quick note: the RCP3 scenario’s absurdity becomes more clear post-2060: emissions have to turn negative to achieve 3 W/m^2 by 2100!  Is anyone aware of technologies that remove emissions from the atmosphere in excess of what we emit to the atmosphere?  Put another way, emissions would have to decrease to near-zero in addition to deployment of removal infrastructure.  I obviously wasn’t involved scenario development, but it strikes me as incredibly myopic to include this pathway in climate scenarios: it exists only as a fantasy, especially when you realize that important feedback processes are still not understood well enough to include them in modeling efforts.

The main point of this graph is valid though: on our current emissions trajectory, global warming of 4–6.1 °C is likely.  Given recent studies showing more sensitivity to temperature changes one order of magnitude less than this that has already started to generate real-world changes, no one can say with certainty what a 4°C rise in global temperature above the pre-industrial average will cause.

Now, I must make a very important point here.  This does not mean the end of civilization or the world.  Our species is remarkably adaptive to a wide range of conditions.  While our species has never lived in a world that warm, we have enormous advantages over our ancestors: technology.  The world might not look like it does today, and we will of course not live in the same way, but I firmly believe that whatever changes we make will allow the great majority of us to continue to live.

That is not to say that we should do nothing at all.  I have made quite clear that the current approach (UNFCCC & IPCC) has proven itself to not work.  I do not know exactly what the correct approach will be, but I think remaining in a failed paradigm is a bad idea moving forward.  We must make new efforts – the more the merrier in the short-term so we can evaluate what does and does not work.  My line of thought has developed to this: I think groups must initiate smaller efforts, and indeed I think in some cases they already have.  Regional cohesive groups generally know better what works for them and why.  A good place to start on a larger scale would be to work to understand why certain actions work in some places better than others and put policies in place to exploit those opportunities.

But 2°C is not achievable by any means that I can see.  Neither is 350ppm CO2 concentration.  Scientists and activists alike should cast aside these hard to understand numbers.  A focus on other goals: energy portfolios, land use, and adaptation plans make more sense (different numbers since we tend to operate that way).


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Good Climate Language Development

I have commented many times in the past few years that the emissions scenarios underlying IPCC climate projections were archaic and focus needed to shift based on historical (observed) emissions away from the emissions set established more than a decade ago.

It is thus refreshing to see in a new short article, written by some of the most well-known names in climate science, the A2 scenario described as “moderate” instead of “extreme” (if it was used in a scientific report in the first place), as was the case even within the last year.  The authors accurately state that to achieve the A2 trajectory, which results in some of the warmest global conditions by the end of the 21st century, we would have to drastically reduce our emissions now.  I have also written many times that this reduction will not happen any time in the near future.  I keep promising some information to back up that claim and I’ll promise it here again.  A different recent report further reinforced the need I feel to share with readers of this blog.  Hopefully I will have time to write it soon.

I highly recommend reading the article I’ve linked to above.  It’s easy to read, short, yet carries a high impact message for those of us experiencing the destructive and sometimes deadly effects of heat waves in recent years (and right now!).


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Climate Change Basics – Energy & Projections

In July, I wrote a post that laid the groundwork for the discussion of climate change basics: Gases, Forcing & Surface Temperature.  This post follows onto that initial post by discussing energy within Earth’s climate system.  As in that post, I will focus on the results in the IPCC’s AR4.  There is a wealth of additional results in the scientific literature since the 2007 Report and I will share some of those in future posts.  In other words, the IPCC information will be used as a baseline.  This post is a little long, but I think it’s worth reading in its entirety.

Energy Content

First, here are two views of the energy content in the climate system.  The first is from the IPCC’s WGI Technical Summary:

Source: IPCC AR4 Figure TS.15.  Energy content changes in different components of the Earth for two periods (1961-2003 (blue) and 1993-2003 (burgundy)).

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