NASA's James Hansen has stepped ahead of most Texas climatologists by declaring in a draft paper that global warming is unequivocally to blame for Texas' record-breaking temperatures that contributed to our worst one-year drought on record last year. Most Texas-based climatologists — including state climatologist John Nielsen-Gammon — have so far only been willing to suggest that global warming played a part in the heat wave or that is was not likely the principle cause.
However, Hansen's paper (produced along with two colleagues from NASA's Goddard Institute for Space Studies and New York's Sigma Space Partners, and now being circulated for comment from the scientific community) says the extreme heat waves that swept Texas and Oklahoma last year were caused by global warming, “because their likelihood was negligible prior to the recent rapid global warming.”
Drawing on more than 50 years of Goddard air and land temperature data, the group concluded that the earth's climate has been “loaded” by climate change propelling extreme temperature that would not have occurred if left solely to the earth's natural climate variability.
Writes Elizabeth Grossman at Inside Climate News:
Hansen has posted a draft of the new study, Perceptions of Climate Change: The New Climate Dice, on his website and is circulating it to colleagues for comment, a practice he has followed with other research. Meanwhile, NASA's Goddard Institute has posted to the institution's website the scientists' analysis of 2011 temperature data—an analysis that Hansen and his colleagues also used in the new paper.
Hansen, who directs the Goddard Institute, has become a target for climate change skeptics who say his activism undermines his science. But his scientific standing is so solid that his research continues to be published in respected scientific journals, including Environmental Science & Technology, Atmospheric Chemistry & Physics and the Review of Geophysics.
"Our paper deals with the frequency of hot seasons, mainly hot summers, because that is the most important season," Hansen said. "The times and places with hot summers tend to be where the weather is dominated ... by high pressure, so there is high correspondence between the [extremely hot outliers or extreme] heat waves and drought conditions." They also point out that summer, "when most biological productivity occurs, is the most important season for humanity and thus the season when climate change may have its biggest impact."
In the paper's concluding discussion section, they write:
The most important change of the climate dice is the appearance of a new category of extremely hot summer anomalies, with mean temperature at least three standard deviations greater than climatology. These extreme temperatures were practically absent in the period of climatology, covering only a few tenths of one percent of the land area, but they have occurred over about 10% of land area in recent years. The increased frequency of these extreme anomalies, by more than an order of magnitude, implies that we can say with a high degree of confidence that events such as the extreme summer heat in the Moscow region in 2010 and Texas in 2011 were a consequence of global warming. ...
It is not uncommon for meteorologists to reject global warming as a cause of these extreme events, offering instead a meteorological explanation. For example, it is said that the Moscow heat wave was caused by an atmospheric "blocking" situation, or the Texas heat wave was caused by La Nina ocean temperature patterns. Certainly the locations of the extreme anomalies in any given case are related to specific weather patterns. However, blocking patterns and La Ninas have always been common, yet the large areas of extreme warming have come into existence only with large global warming. Today's extreme anomalies occur because of simultaneous contributions of specific weather patterns and global warming.