27 April 2015

Was Your Record High Temperature A Result of Climate Change? Probably.

Posted by Dan Satterfield

This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole. [ENLARGE] (©UCAR, graphic by Mike Shibao.)

This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole. [ENLARGE] (©UCAR, graphic by Mike Shibao.) From research by Gerald Meehl at UCAR.

A paper in Nature Climate Change today is getting international press and for good reason, It contains a rather astounding statistic. Here is a quote from the beginning of the paper with my highlights in red: 

Climate change includes not only changes in mean climate but also in weather extremes. For a few prominent heatwaves and heavy precipitation events a human contribution to their occurrence has been demonstrated12345. Here we apply a similar framework but estimate what fraction of all globally occurring heavy precipitation and hot extremes is attributable to warming. We show that at the present-day warming of 0.85 °C about 18% of the moderate daily precipitation extremes over land are attributable to the observed temperature increase since pre-industrial times, which in turn primarily results from human influence6. For 2 °C of warming the fraction of precipitation extremes attributable to human influence rises to about 40%. Likewise, today about 75% of the moderate daily hot extremes over land are attributable to warming. It is the most rare and extreme events for which the largest fraction is anthropogenic, and that contribution increases nonlinearly with further warming. 

This means that about 75% of daily temperature records are the result of the warming we have already experienced, and the paper says this number will rise rapidly as we get warmer. This research dove-tails with the graphic above based on research by Gerald Meehl at UCAR in 2009.You can read the Nature Climate Change paper here: