Twenty-four summers ago, NASA scientist James Hansen first warned the world about what he called the dangers of global warming. In front of a Senate panel, he said he was "99% certain" that a recent warming trend was not a natural variation but caused by a buildup of carbon dioxide and other gases in the atmosphere from burning fossil fuels.
Now, a study released this weekend by Hansen, the dean of climate scientists, concludes that the recent heat waves and extreme summers likely were caused by climate change.
"We can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small," Hansen and his NASA co-authors write in the Proceedings of the National Academy of Sciences.
In 2011, Texas and Oklahoma had their hottest summer on record, according to the National Climatic Data Center. The summer of 2010 in much of Russia was the hottest in 130 years of records.