Extreme Summer Heat Due to Global Warming, says NASA Study

A new statistical analysis by NASA published in the Journal Proceedings of the National Academy of Sciences has found that Earth's land areas have seen increasing summer heat waves over the last 30 years, and this is definitely because of global warming.

According to the study that is being led by prominent climate scientists James Hansen of NASA's Goddard Institute for Space Studies (GISS) in New York, the intense weather events such as the heat waves that have broiled the High Plains and Midwest this summer, smashing thousands of temperature records, are a direct consequence of global warming,

"This summer people are seeing extreme heat and agricultural impacts," Hansen says. "We're asserting that this is causally connected to global warming, and in this paper we present the scientific evidence for that."

In order to support the statement, Hansen and his colleagues analyzed the mean temperatures since 1951 and noticed how massive changes have occurred in the recent decades. They detailed how 'extremely hot' summers are becoming far more routine.  Since 2006, about 10 percent of land area across the Northern Hemisphere has experienced extreme hot temperatures each summer.

To distinguish the trend from natural variability, Hansen and colleagues turned to statistics. In this study, the GISS team including Makiko Sato and Reto Ruedy did not focus on the causes of temperature change. Instead the researchers analyzed surface temperature data to establish the growing frequency of extreme heat events in the past 30 years, a period in which the temperature data show an overall warming trend.

Data on global temperature anomalies collected by NASA climatologist indicate how much warming or cooling regions of the world have experienced when compared with the 1951 to 1980 base period. The study was done using a bell curve tool that is frequently used by the statisticians and society. They noticed mean temperature is centered at the top of the bell curve. Decreasing in frequency to the left of center are "cold," "very cold" and "extremely cold" events. Decreasing in frequency to the right of center are "hot," "very hot" and "extremely hot" events.

Plotting bell curves for the 1980s, 1990s, and 2000s, the team noticed the entire curve shifted to the right, meaning that more hot events are the new normal. Widening of the curve also led to the designation of the new category of outlier events labeled "extremely hot," which were almost nonexistent in the base period.

Hansen says this summer is shaping up to fall into the new extreme category. "Such anomalies were infrequent in the climate prior to the warming of the past 30 years, so statistics let us say with a high degree of confidence that we would not have had such an extreme anomaly this summer in the absence of global warming," he says.

According to the study other regions around the world also have felt the heat of global warming. Global maps of temperature anomalies show that heat waves in Texas, Oklahoma and Mexico in 2011 and in the Middle East, Western Asia and Eastern Europe in 2010 fall into the new "extremely hot" category.