Date of this Version
In: Climate Science Special Report: A Sustained Assessment Activity of the U.S. Global Change Research Program [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA (2017), pp. 267-300.
1. Average annual temperature over the contiguous United States has increased by 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960 and by 1.8°F (1.0°C) based on a linear regression for the period 1895–2016 (very high confidence). Surface and satellite data are consistent in their depiction of rapid warming since 1979 (high confidence). Paleo-temperature evidence shows that recent decades are the warmest of the past 1,500 years (medium confidence).
2. There have been marked changes in temperature extremes across the contiguous United States. The frequency of cold waves has decreased since the early 1900s, and the frequency of heat waves has increased since the mid-1960s (the Dust Bowl remains the peak period for extreme heat). The number of high temperature records set in the past two decades far exceeds the number of low temperature records. (Very high confidence)
3. Average annual temperature over the contiguous United States is projected to rise (very high confidence). Increases of about 2.5°F (1.4°C) are projected for the next few decades in all emission scenarios, implying recent record-setting years may be “common” in the near future (high confidence). Much larger rises are projected by late century: 2.8°–7.3°F (1.6°–4.1°C) in a lower emissions scenario (RCP4.5) and 5.8°–11.9°F (3.2°–6.6°C) in a higher emissions scenario (RCP8.5) (high confidence).
4. Extreme temperatures in the contiguous United States are projected to increase even more than average temperatures. The temperatures of extremely cold days and extremely warm days are both expected to increase. Cold waves are projected to become less intense while heat waves will become more intense. The number of days below freezing is projected to decline while the number above 90°F will rise. (Very high confidence)