Looking Forward


Figure 2: Projected Frequency of Extreme Heat: 1-in-20 Year Events. Source: U.S. Global Change Research Program

Confidence has risen in computer model projections of future changes in hot extremes because recent observations are consistent with the results of past model predictions.1

Models predict that the same summertime temperatures that ranked among the top 5% in 1950–1979 will occur at least 70% of the time by 2035–2064 in the U.S. if global emissions of greenhouse gases grow at a moderate rate (as modeled under the IPCC SRES A2 scenario). Such a growth rate would require a decline from the current high rate of growth.2

The South, Southwest, and Northeast may be especially prone to large increases in unusually hot summers.3 Parts of the South that currently have about 60 days per year with temperatures over 90 degrees are projected to experience 150 or more days a year above 90 degrees by the end of this century.4

By the end of this century, a once-every-20 year heat wave is projected to occur every other year.5

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(Full List of References)


  1. Meehl et al. op. cit.
  2. Duffy, P.B., and C. Tebaldi. (2012)
  3. Duffy et al. op. cit.

  4. Karl, T.R.,et al. (2008)
  5. Ibid.