Highlights
One might think that too much rain in Pakistan would have nothing to do with too little rain in Russia, but two expert analyses by CNN meteorologist Brandon Miller and Weather Underground meteorologist Dr. Jeff Masters find that the two are connected. The Russian heat wave is associated with an intense dome of high atmospheric pressure that has settled in over Eastern Europe. This dome is so immovable that it is blocking the flow of the jet stream, which typically determines where mid-latitude storms drop their rains. A similar “blocking high” was in place over Western Europe during the extremely deadly 2003 European heat wave. The block over Russia forced the jet stream to dive far southward, carrying with it a great deal of moisture that normally would have watered Russia’s substantial wheat crop. Instead, that rain fell in northern Pakistan, combining with the already abundant rainfall normally associated with the Asian Monsoon this time of year. The combination of the two was just too much, so while Russia’s crops withered and burned, Pakistan’s crops drowned.
Returning to the question everyone wants answered: What can we say about the connection between these events and climate change? As usual, there is no definitive answer about these specific events, but direct observations show that extreme weather events have become more frequent in the past half-century, and in the extreme cases that have been studied, the mechanisms are those that one would expect from global warming. At the most basic level, more droughts and heat waves are expected because of hotter, longer-lasting high pressure systems that dry out the land, as witnessed in Russia. On the other hand, more floods are expected because hotter air evaporates more water from the surface and holds more moisture. When the conditions are right, that moisture is released, creating a deluge, as witnessed in Pakistan. The same basic phenomenon was behind the unusually heavy snowstorms that hit the U.S. East Coast this winter.
More specifically, modeling experiments performed by British scientists indicated that the risk of extreme European heat waves like the one in 2003 has at least doubled as a result of human-induced global warming. The same models predicted that continued greenhouse-gas emissions would make similar heat waves commonplace in Europe by the middle of this century. Independent modeling experiments by American climate scientists found that strong blocking highs and associated long, extreme heat waves occurred more frequently in models with elevated greenhouse gas concentrations. (An accessible version of the latter work is available in a report published by the Pew Center in 2007.)
So it is reasonable to conclude that, in aggregate, the documented increase in extreme events is partially a climate response to global warming, and that global warming has increased the risk of extreme events like those in Russia and Pakistan. On the other hand, there is no scientific basis for arguing that these events have nothing to do with global warming.
The source article Climate Risks: Lessons from 2010’s Extreme Weather was published August 23, 2010 by Climate Compass .
