Global warming unlikely to change weather much

With reference to the rainfall record set in Dubuque and surrounding areas on July 28, Charles R. Crawley of Cedar Rapids writes that extreme weather “will become far more common … And the reason for this is climate change.”(Aug. 6 letter, “Climate change drives recent rough weather.”)

It is very unlikely that global warming will cause increased extreme weather. If the world warms due to increasing greenhouse gas emissions, temperatures at high latitudes are forecast to rise the most, reducing the difference between arctic and tropical temperatures. Since this differential drives weather, we should see weaker midlatitude cyclones in a warmer world and so less extremes in weather, not more.

It is also a mistake to blame human activities for current weather extremes. For example, the 2010 Russian heat wave has been thoroughly studied, and scientists conclude that it was almost certainly a natural event. In their scientific paper in “Geophysical Research Letters,” Dole at al (2011) concluded that “the Russian heat wave was due to internal atmospheric dynamical processes” and “it is unlikely that the warming attributable to increasing greenhouse gas concentrations contributed significantly to the magnitude of the heat wave.”

We will probably find the same when this summer's weather events are analyzed.

Over the past 100 years, there has been only a one-quarter-inch rise in rain on average on the heaviest day of the year across the United States. While records are set in specific regions all the time, of course, overall, the average change is likely to continue to be small.

Tom Harris

Executive Director,

International

Climate Science

Coalition

Ottawa, Ontario

Canada