Blockbuster IPCC Chart Hints at Dust-Bowlification, But Report Is Mostly Silent on Warming’s Gravest Threat to Humanity

Blockbuster IPCC Chart Hints at Dust-Bowlification, But Report Is Mostly Silent on Warming’s Gravest Threat to Humanity

A USA Today (not IPCC) chart emphasizes the risk of drought in heavily populated areas.

The IPCC Special Report “Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX)” is now online.  I had seen the previous draft and the changes to it, so I knew that it was a big missed opportunity, as I explained here.

Even so, since the media hasn’t been spending much time connecting the dots between extreme weather and climate change, the report has garnered some headlines:

There is definitely some good material in the report (I’ll do a separate post on that).  We should all appreciate the hard work that a great many scientists put into this report.  I’ve been highly supportive of IPCC scientists over the years, pushing back against the attacks by the deniers and confusionists — even as I have been critical of the IPCC process that tends to water down even the most obvious conclusions.

For instance, the report states:

It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur in the 21st century on the global scale. It is very likely that the length, frequency and/or intensity of warm spells, or heat waves, will increase over most land areas.

Virtually certain means “99-100% probability” while very likely means “90-100% probability.”  Is there really as much as a 10% chance that the length, frequency and/or intensity of warm spells, or heat waves, will NOT increase over most land areas over the next 90 years?

Then we have this line:

It is very likely that mean sea level rise will contribute to upward trends in extreme coastal high water levels in the future.

C’mon guys and gals.  You couldn’t put a “virtually certain” on that?  Note that the sentence is already hedged with “will contribute” and “upward trends” and even the vague “in the future.”  Precisely how could mean sea level rise — even sticking with the lowball estimate from the 2007 report — have as much as a 10% chance of NOT contributing toward an upwards trend in extreme coastal high level waters sometime in the future.

So you can see the effect of the IPCC process that waters down even the most innocuous conclusions.  And by the way, since this is a 2011 report, it ought to base such statements on the recent literature of sea level rise, which is considerably higher than the 2007 estimate (see the discussion in “Scientists withdraw low-ball estimate of sea level rise“).

My biggest problem with the report remains the short shrift it gives to the vast literature on drought that I reviewed in my recent Nature article.  As I wrote, “Feeding some 9 billion people by mid-century in the face of a rapidly worsening climate may well be the greatest challenge the human race has ever faced.”

You can see from the chart above that USA Today (and Jeff Masters, who helped put it together) figured out that drought may be the biggest extreme weather danger in that it affects 5 heavily populated areas.

Reuters, in its story, states what should be obvious:

Droughts, perhaps the biggest worry for a world with a surging population to feed, were also expected to worsen.

The 29-page report itself has quite little on droughts, and the word “agriculture” appears only once in the main text, but it does have this blockbuster chart:

Figure SPM.5: Projected annual changes in dryness….  Changes in soil moisture (soil moisture anomalies, SMA). Increased dryness is indicated with yellow to red colors; decreased dryness with green to blue. Projected changes are expressed in units of standard deviation of the interannual variability in the three 20-year periods 1980-1999, 2046-2065 and 2081-2100. The figures show changes for two time horizons, 2046-2065 and 2081-2100, as compared to late-20th-century values (1980–1999), based on GCM [Global Climate Models] simulations under emissions scenario SRES A2 relative to corresponding simulations for the late-20th-century. Results are based on 17 (CDD) and 15 (SMA) GCMs contributing to the CMIP3. Colored shading is applied for areas where at least 66% (12 out of 17 for CDD, 10 out of 15 for SMA) of the models agree in the sign of the change; stippling is added for regions where at least 90% (16 out of 17 for CDD, 14 out of 15 for SMA) of all models agree in the sign of the change….

We can’t tell exactly how serious this is since they aren’t using a standard metric, like, say, the Palmer Drought Severity Index, and since the full report won’t be out until February!

But those large red patches around the global look pretty worrisome since they are where a great many people live and where a considerable amount of arable land is.  Indeed, the United States breadbasket looks to be headed for some very serious soil moisture drying in the second half the of the century if we stay anywhere near our current emissions path.

The IPCC has but one paragraph on this (plus the chart and a table):

There is medium confidence that droughts will intensify in the 21st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration. This applies to regions including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa. Elsewhere there is overall low confidence because of inconsistent projections of drought changes (dependent both on model and dryness index). Definitional issues, lack of observational data, and the inability of models to include all the factors that influence droughts preclude stronger confidence than medium in drought projections. See Figure SPM.5. [3.5.1, Table 3.3, Box 3.3]

The Table simply focuses on “Droughts in the context of food security in West Africa,” which is certainly important subject but only one of many, many areas around the world threatened by every-worsening droughts.

You would never know from this summary report that there is in fact a large literature just on the drying projected for the U.S. Southwest (which I reviewed here).  Heck, 3 years ago, the Bush Administration (!) released a US Geological Survey report that found:

The serious hydrological changes and impacts known to have occurred in both historic and prehistoric times over North America reflect large-scale changes in the climate system that can develop in a matter of years and, in the case of the more severe past megadroughts, persist for decades. Such hydrological changes fit the definition of abrupt change because they occur faster than the time scales needed for human and natural systems to adapt, leading to substantial disruptions in those systems. In the Southwest, for example, the models project a permanent drying by the mid-21st century that reaches the level of aridity seen in historical droughts, and a quarter of the projections may reach this level of aridity much earlier.

And there have been another half a dozen major studies covering the SW since then.

So yes the report was a missed opportunity to review this literature and highlight the  very real threat to food security.  The most comprehensive published literature review to date remains the must-read study from the National Center for Atmospheric Research, “Drought under global warming: a review,” which I discussed here.


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