Global warming isn't uniform. The continental U.S. has warmed by about 1.3°F over the past 100 years, but the temperature increase hasn’t been the same everywhere: some places have warmed more than others, some less, and some not much at all. Natural variability explains some of the differences, and air pollution with fine aerosols screening incoming solar radiation could also be a factor.
Our state-by-state analysis of warming over the past 100 years shows where it warmed the most and where it warmed the least. We found that no matter how much or how little a given state warmed over that 100-year period, the pace of warming in all regions accelerated dramatically starting in the 1970s, coinciding with the time when the effect of greenhouse gases began to overwhelm the other natural and human influences on climate at the global and continental scales. [Text continues after map.]
We looked at average daily temperatures for the continental 48 states from 1912 to the present, and also from 1970 to the present and found:
- Over the past 100 years, the top 10 states warmed 60 times faster than the bottom 10 (0.26°F per decade vs. 0.004°F per decade), when looking at average mean temperatures. During this timeframe, 45 states showed warming trends, although 21 were not statistically significant. Three states experienced a slight cooling trend.
- Since 1970, warming began accelerating everywhere. The speed of warming across the lower 48 more than tripled, from 0.127°F per decade over the 100-year period, to 0.435°F per decade since 1970, while the gap between the fast and slowly warming states narrowed significantly; the 10 fastest warming states heated up just twice as fast, not 60 times as fast as the 10 slowest warming states (0.60°F vs. 0.30°F per decade). Over the past 42 years 17 states warmed more than half a degree F per decade.
- The states that have warmed the most — whether you look at the past 100 years or just the past 40 — include northern-tier states from Minnesota to Maine and the Southwest, particularly Arizona and New Mexico. Places that have warmed the least include Southeast states, like Florida, Alabama, Georgia and South Carolina, along with parts of the central Midwest, like Iowa and Nebraska.