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Don Wuebbles, expert in climate and climate change
On Aug. 8, the National Oceanic and Atmospheric Administration said that July 2012 was the hottest month in the U.S. since record keeping began in 1895. U. of I. atmospheric sciences professor Don Wuebbles, an expert on climate and climate change, talked with News Bureau physical sciences editor Liz Ahlberg about the exceptionally hot and dry conditions across the United States and how 2012 fits into historical weather trends.
What does it mean when we say it was the “hottest month on record”?
Averaging thermometer measurements across the contiguous United States is historically considered to be adequately representative since 1895. The highest average temperature across the U.S. over the last 117 years was this July. The previous record was in 1936. As one reporter put it, we have now left the Dust Bowl in the dust. In addition, the first seven months of 2012 are the warmest since the record keeping started in 1895. Not only that, it has also been the driest year across the contiguous United States. For the Midwest, this has clearly been one of our worst droughts on record and it still goes on. The U.S. Department of Agriculture has now designated more than half of all U.S. counties as disaster zones because of the drought conditions in the Midwest and elsewhere.
Are these high temperatures part of an upward trend, or merely an anomaly?
The United States has generally seen an increasing trend in temperature over the last 50 years, in line with the increasing temperature trend worldwide. These temperature trends are part of an overall change in climate that is not only affecting temperature but also precipitation patterns.
That doesn’t mean all areas warm the same. This year, Washington state has been cooler and wetter than average, but the rest of the country has been significantly warmer and drier. In general, looking over recent decades, parts of the Southeast, plus Iowa, South Dakota and Nebraska, have not had as much warming as the rest of the country. In the case of Iowa and its neighbors, current analyses indicate this is a result of increased soil moisture with the higher amount of rainfall they had been seeing before 2012.
In general, the U.S. is seeing that when it does rain, there are more large precipitation events. In the Midwest, the heaviest 1 percent of rainfalls historically have increased by 46 percent over the last 50 years. In recent decades, some parts of the country have seen an overall likelihood of an increase in floods and also more likelihood for droughts. An extremely large drought occurred in Texas and Oklahoma in 2011, and now in 2012, we have an extremely large drought throughout much of the U.S. In a general sense, both in the U.S. and worldwide, the wet are getting wetter and the dry drier, but this year has been a major exception in the U.S.
What can recent weather patterns tell us about the direction of global climate shift, if anything?
Scientific evidence clearly indicates that not only is our climate changing in the U.S. and worldwide, but that the human activities are playing a major role in bringing about the observed changes in our global climate system, particularly in the last five decades. These changes in climate are not only bringing warmer temperatures, but also increasing concerns about severe weather. Every scientific assessment, nationally and worldwide, has come to the same conclusions about the importance of climate change to this and future generations.
The only real debate is what to do about it. It is clear that adaptation to the changes that are already occurring will be necessary, as well as reducing emissions and atmospheric concentrations of carbon dioxide and other gases and particles that are largely responsible for the changes in climate – and increasing because of human activities. These gases and particles are affecting the energy budget of our planet, resulting in the ever increasing concerns about warming but also the increasing concerns about extreme events like heat waves, floods and droughts.
How has the heat contributed to the drought conditions being experienced by much of the U.S.?
These hot and dry weather patterns, with the strong stationary high pressure conditions we’ve seen this year, can occur naturally just like they did in the 1930s. A simplistic analysis would say this has been a natural event. However, scientific studies now indicate that the changing climate has greatly increased the likelihood of such events occurring. Every weather event that happens now takes place in the context of the changes that have occurred in the background climate system.
Attribution studies have been done on the very extensive 2003 European heat wave, the 2010 Russian heat wave, and the 2011 Texas-Oklahoma heat wave and drought that all indicate the changes occurring in climate have greatly increased the likelihood for such events. These events suggest that the likelihood of record-breaking temperature extremes has increased and will likely continue to increase as the global climate warms. The analyses have not been done yet on the current heat wave and drought in the U.S., but I wouldn’t be surprised if upcoming scientific studies come to similar conclusions.
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