U.S. Heat, February 2017

We found clear and strong links between last month’s record warmth in the United States, and climate change. Temperatures like those seen across the lower 48 this past February are becoming more and more common as cold winter months are getting rarer. The observations show a clear trend and climate models confirm it is caused by greenhouse gases.

Geert Jan van Oldenborgh, senior researcher at the Netherlands Meteorological Institute (KNMI)

• Finds that climate change increased both the intensity and frequency of the kind of record February warmth experienced in most parts of the country
• Finds that climate change tripled the probability of the observed warmth in the US during February 2017 (decreasing the return period from 60 years—in a world without the historical human-induced increases in greenhouse gases—to 18 years)
• Finds that the chances of seeing a February as warm as the one experienced across the lower 48 states in 2017 has increased at least threefold because of human-caused climate change
• Finds that the record-warm February of 1954 was, at the time, a very rare event (probability about 0.5% per year) but similar events should now be expected every few years
• Figure: February temperatures 1895–2016 (NOAA), the 2017 value estimated from analyses. The green line is a 10-year running mean.