599. Climate Panel Charts Extreme Weather in a Warming World

By Andrew Revkin, The New York Times, November 18, 2011

Watch live streaming video from ipcc34thsessionenglish at livestream.com

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4:52 p.m. | Updated 
The Intergovernmental Panel on Climate Change, convening in Kampala, Uganda, has produced a valuable summary of science on the influence of human-driven warming on extreme weather and strategies for limiting risks to societies in a changing climate. [12:39 p.m. | Insert | Here's Justin Gillis's news report on the new climate findings.]

Paula Bronstein/Getty ImagesDecommissioned planes on a flooded tarmac at Don Mueang airport in Bangkok earlier this month.

To my eye the summary accurately reflects the body of science aiming to find a signal of greenhouse-gas influence on climate extremes and disaster frequency and severity (the full report is still being finalized).

Some influences are fairly robust, the panel says, particularly a warming of extreme daily maximum (and minimum) temperatures. But the report finds only “medium confidence” 
(a 50/50 chance)
* in a link between human activities and intensification of extreme rainfall on a global scale. (A big issue, of course, is the lack of long-term data outside developed countries.) And the odds go down from there on attributing other recent shifts in weather-related disasters to global warming.

[10:04 a.m. | Insert | The summary contains a sobering message for those eager to point to current patterns of extreme weather as the manifestation of greenhouse-driven warming:

Projected changes in climate extremes under different emissions scenarios generally do not strongly diverge in the coming two to three decades, but these signals are relatively small compared to natural climate variability over this time frame. Even the sign of projected changes in some climate extremes over this time frame is uncertain.]

The core passage on tropical cyclones illustrates the challenge in discerning cause and effect when dealing with rare events:

The uncertainties in the historical tropical cyclone records, the incomplete understanding of the physical mechanisms linking tropical cyclone metrics to climate change, and the degree of tropical cyclone variability provide only low confidence for the attribution of any detectable changes in tropical cyclone activity to anthropogenic influences.

While the summary warns of enormously increasing risks from drought and flooding in decades to come, it is bound to disappoint climate campaigners — and it frustrated at least one, Joe Romm, even before it was released. The section on disaster losses correctly reflects the uncertainty injected in such analysis by confounding factors, including rapidly shifting human populations and the paucity of solid data over long periods.

The report summary notes how wealth and development powerfully shield countries from human losses in disasters while amplifying the financial costs of such events. The section on managing risks is particularly valuable, describing strategies that have a host of benefits no matter which scenario for emissions and climate change plays out. Here’s one important point:

Many measures, when implemented effectively, make sense under a range of future climates (medium evidence, high agreement). These “low regrets” measures include systems that warn people of impending disasters; changes in land use planning; sustainable land management; ecosystem management; improvements in health surveillance, water supplies, and drainage systems; development and enforcement of building codes; and better education and awareness.

The summary for policymakers is posted online and the full report is scheduled to be released in February.

Here’s a presentation that was given today at the Kampala meeting:

IPCC Report on Extreme Weather in Warming World

View more presentations from Andrew Revkin

And here are the prime points in the section projecting impacts on societies from greenhouse heating in coming decades:

—It is likely that the frequency of heavy precipitation will increase in the 21st century over many regions.

—It is virtually certain that increases in the frequency of warm daily temperature extremes and decreases in cold extremes will occur throughout the 21st century on a global scale. It is very likely— 90 percent to 100 percent probability—that heat waves will increase in length, frequency and/or intensity over most land areas.

—It is likely that the average maximum wind speed of tropical cyclones (also known as typhoons or hurricanes) will increase throughout the coming century, although possibly not in every ocean basin. However it is also likely—in other words there is a 66 percent to 100 percent probability — that overall there will be either a decrease or essentially no change in the number of tropical cyclones.

—There is evidence, providing a basis for medium confidence, that droughts will intensify over the coming century in southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa. Confidence is limited because of definitional issues regarding how to classify and measure a drought, a lack of observational data and the inability of models to include all the factors that influence droughts.

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

—Projected precipitation and temperature changes imply changes in floods, although overall there is low confidence at the global scale regarding climate-driven changes in magnitude or frequency of river-related flooding, due to limited evidence and because the causes of regional changes are complex.

There’s much more on Dot Earth on extreme weather in a warming world.

| Postscript |
Please read a short but valuable interview on adaptation strategies with two report authors from the Stockholm Environment Institute, Richard J.T. Kleinand Lisa Schipper (whose father had been featured here a few times).

Sabrina McCormick, a sociologist and filmmaker focused on environment and health and a lead author of the climate report, has written an engaging description of the authors’ work and her feelings about the findings in a guest post on Sheril Kirshenbaum’s Culture of Science blog. There’s more from McCormick on The Daily Climate. I think her pieces would have benefitted from a line expressly clarifying for readers that the posts are her personal interpretation of the panel’s findings and not written in her capacity as an author.

But there’s plenty of wiggle room on that, and every scientist engaged in public outreach has to choose his or her own path.

Joe Romm posted a fresh take on the extremes summary that was slightly less critical of the climate panel. Judith Curry has explored the summary on her Climate Etc. blog. Bryan Walsh of Time Magazine has written a good survey of the findings, including the voices of some authors, including McCormick.

In his article for Nature, Quirin Schiermeier included an important pointabout the delay between issuing the summary and the underlying report — made by Stefan Rahmstorf, a German climate researcher:

“Governments have in the past considerably weakened the language of IPCC summaries for policymakers,” he says. “As long as the full report is not available it is hard to say if, and to what extent, this may have happened again.”

Roger Pielke, Jr., credited the report authors for avoiding injections of spin — with one seeming exception:

There was one interesting change related to the statement on the state of attribution with respect to normalized disaster losses. The draft said:

Long-term trends in normalized economic disaster losses cannot be reliably attributed to natural or anthropogenic climate change, particularly for cyclones and floods (medium evidence, high agreement).

The final version took out the emphasis on cyclones and floods and put in a content free clause — a good example of how the IPCC process can reduce information content:

Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded (medium evidence, high agreement).
It is of course true that a role for climate change has not been excluded in attribution studies — of course, the IPCC also did not exclude a role for solar influences, cosmic rays or for that matter, evil leprechauns. What the draft said with respect to floods and cyclones remains the case, hiding it from view doesn’t make it go away. What silliness.

NOV. 19, 5:58 P.M. Correction

* Michael Oppenheimer, an IPCC author, wrote to note that I incorrectly described the level of confidence in a finding above as 50/50. That was the old panel definition of “medium confidence,” but the group has changed its policies. As Oppenheimer explained: “Confidence is no longer expressed quantitatively (as distinct from likelihood) but is a qualitative judgment reflecting various characteristics of the evidence and the degree of agreement between different types of evidence.”