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Monday, August 30, 2010

Attribution of Climate-Related Events -- scientists meet to discuss calculating probabilities for extreme climate events occurring now

Time to blame climate change for extreme weather?

Scientists are working on linking extreme weather events happening today to climate change now. Scientists have been careful in the past to state the distinction between weather and climate change. As NASA states, some "scientists define climate as the average weather for a particular region and time period, usually taken over 30 years."   Some scientists and government officials have recently moved the ball forward, saying that the Pakistan floods and Russian fires might be linked to climate change.  Last week, atmospheric scientists met to discuss Attribution of Climate-Related Events or the use of simulations to calculate probabilities for extreme climate events now. 
Climate Event Attribution "seeks to explain the complex causes behind a given weather event, be it an especially cold winter, an intense heat wave or a devastating flood, with the particular aim of detecting a possible departure from "normal" conditions, and the role – if any – that human activities played."  The ability of scientists to "attribute specific extreme weather events to manmade or natural causes" would be a "major step forward" to answer questions about human-caused climatic changes and their causal relationship to current extreme events, such as the floods, fires, iceberg calving and droughts. Presently, scientists can't say that the recent extreme weather events are "proof" of climate change.
Frustration arises because these extreme events are "exactly the stuff" that "scientists have been warning would be a likely consequence of climate change." Yet, news reports then say:  "While these events are consistent with climate change, no single event can be directly linked to or regarded as proof of climate change." What scientists can say at this point are that extreme events are related to climate change because the "odds of them happening are much greater with climate change."
The purpose of this meeting last week on climate attribution was to "discuss what information is needed to determine the extent to which human-induced climate change can be blamed for extreme weather events -- possibly even straight after they have happened." Kevin Trenberth of the US National Center for Atmospheric Research, a federally funded research and development center, says that we "should assume global warming plays a role in every climate event, then ask whether that role is a significant one."
There is precedent for assigning blame:  "In 2004, Allen and his colleagues showed to a high level of confidence that human greenhouse gas emissions had at least doubled the risk of the European heatwave of 2003 occurring." The tool to obtain the information is computer "simulations of the climate as it is and as it would have been without human influences, then compare the number of times a given event occurs in each scenario."  Thus, scientists can estimate probabilities, but "rarely can it be asserted with 100% confidence that there is a causal relationship between variables."
Trenberth thinks that similar analyses can be done within weeks of an event, such as with the Pakistani floods and Russian fires.
For instance, we know that high sea-surface temperatures and large amounts of moist air over the Indian Ocean helped bring about the Pakistani floods and the heatwave in Russia. It should be possible to determine how great a role human climate change played in these events, Trenberth says.
Assigning numbers to the consequences or impacts of climate change might be used in a variety of ways.   First, the public might then realize that climate change impacts are happening now, and be more supportive of comprehensive climate change legislation. Second, lawsuits based on climate change and pollution are already being filed in the courts. Third, an analysis of specific events and their causes will help governments and people try to be prepared for the climate change impacts with adaptation and mitigation. And, a United Nations fund to assist developing countries with adapting to climate change might be able to use the numbers to help determine which regions are suffering the most from climate change impacts.
For more information on climate event attribution, please see links provided here.

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