Summers are heating up faster in the Southwest than anywhere else in the country, an analysis of federal temperature records shows.

The average Arizona summer is now 2.4 degrees warmer than in 1984, giving it the fourth fastest summertime increase among the lower 48 states. Tucson’s summertime average rose 1.7 degrees in that period.

A typical New Mexico summer is 3.4 degrees warmer now than in 1984; in Texas, the dog days are 2.8 degrees hotter.

But Northeastern states — led by Maine and Vermont — have gotten the hottest in the last 30 years in annual temperature, gaining 2.5 degrees on average.

Arizona’s annual average temperature has risen 1.5 degrees in that period — the 18th fastest increase among the lower 48 states. Tucson’s average annual temperature rose 1.1 degrees in the past 30 years.

To determine what parts of the country have warmed the most, The Associated Press analyzed National Climatic Data Center temperature trends in the lower 48 states, 192 cities and 344 smaller regions within the states.

The contiguous United States’ annual average temperature has warmed by 1.2 degrees since 1984, with summers getting 1.6 degrees hotter. But that doesn’t really tell you how hot it’s gotten for most Americans. While man-made greenhouse gases warm the world as a whole, weather is supremely local. Some areas have gotten hotter than others because of atmospheric factors and randomness, climate scientists say.

“In the United States, it isn’t warming equally,” said Kelly Redmond, climatologist at the Western Regional Climate Center in Reno, Nevada. “Be careful about extrapolating from your own backyard to the globe.”

Climate scientists suggested 1984 as a starting date for the analysis because 30 years is a commonly used time period and 1984, which had an average temperature, is not a cherry-picked year to skew a trend either way. The trend was calculated by the climate data center by using the least squares regression method, which is a standard statistical tool.

Southwest warming, especially in the summer, seems to be driven by dryness, because when there is little water the air and ground warm up faster, said Katharine Hayhoe, a climate scientist at Texas Tech University in Lubbock.

“Heat and drought are a vicious cycle that has been hitting the Southwest hard in recent years,” Hayhoe noted.

Arizona’s rank in the AP analysis contrasted with how the state ranked when the temperatures were looked at over a longer period, contrasting 2000-2010 with the entire 20th century.

Arizona’s statewide average temperature was about two degrees higher in 2000-2010 than it was during the 20th century.

That was the highest increase in those periods of any of the lower 48 states, according to data that the Arizona Daily Star obtained from the Western Regional Climate Center.

Redmond said he doesn’t believe either data set is more valid than the other.

“It always depends on what you’re trying to get at,” he said. “Maybe it’s like a horse race. It’s which horse is ahead right now, on the back stretch or quarter turn, versus the overall flow of the race.”

All but one of the lower 48 states have warmed since 1984, the AP analysis found. North Dakota is the lone outlier, and cooled slightly.

Ten states — Maine, Vermont, New Jersey, Massachusetts, New Hampshire, Rhode Island, Delaware, New Mexico, Connecticut and New York — have gotten at least 2 degrees warmer in the past 30 years.

Arizona Daily Star reporter Tony Davis contributed to this story. Contact him at