Public Perception of Climate Change and the New Climate Dice

by James Hansen^a, Makiko Sato^a, Reto Ruedy^b

Should the public be able to recognize that climate is changing, despite the notorious variability of weather and climate from day to day and year to year?

We investigate how the probability of unusually warm seasons has changed in recent decades, with emphasis on summer, when changes are likely to have the greatest practical effects. We show that the odds of an unusually warm season have increased greatly over the past three decades, but also the shape of the frequency distribution has changed so as to enhance the likelihood of extreme events.

A new category of hot summertime outliers, more than three standard deviations (3σ) warmer than climatology, has emerged, with the occurrence of these outliers having increased 1-2 orders of magnitude in the past three decades. Thus we can state with a high degree of confidence that extreme summers, such as those in Texas and Oklahoma in 2011 and Moscow in 2010, are a consequence of global warming, because global warming has dramatically increased their likelihood of occurrence.  Continued...

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