Scientists from NASA's Goddard Institute for Space Studies, led by Dr. James Hansen have shown that hotter summers are becoming the new normal across the northern hemisphere.
The NASA GISS visualization below uses a bell curve to show the increasing frequency of extreme summer temperatures in the Northern hemisphere going back to 1951 and compared to the 1951 to 1980 base period.
The mean temperature for the base period is centered at the top of the green curve, while hotter than normal temperatures (red) are plotted to the right and colder than normal (blue) to the left. By 1981, the curve begins to shift noticeably to the right, showing how hotter summers are the new normal. The curve also widens, due to more frequent hot events. (from NASA/GISS)
Video courtesy of YouTube . Visualization courtesy of NASA/Goddard Space Flight Center GISS and Scientific Visualization Studio.
According to the NASA story, Hansen and colleagues turned to statistics in order to distinguish the trend from natural variability. 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.
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. (from NASA GISS)
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