As temperatures continue to rise throughout the United States, it's not an equal heating everywhere, researchers say; the southwest and northeast corners are heating up faster than other regions of the country.

An analysis of temperature records shows the U.S. as a whole has warmed up on average by 1.2 degrees, but some regions have surpassed that average, they say.

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

States in the northeast, led by Vermont and Maine, have shown the greatest annual increases in temperatures in the last three decades, with an average rise of 2.5 degrees.

But if just summer temperatures are considered, the southwest is the hot spot: New Mexico summers are on average 3.4 degrees hotter than they were in 1984, while Texas has seen a 2.8-degree increase.

The average summer temperature has risen 1.6 degrees for the 48 contiguous U.S. states.

Every U.S. state bar one -- North Dakota -- has gotten warmer since 1984, the researchers say.

Ten states -- New York, Maine, Vermont, Connecticut, New Jersey, New Mexico, Massachusetts, Delaware, Rhode Island and New Hampshire -- have seen temperature increases of at least two degrees over the last 30 years.

The summer increases in the southwest appear driven mostly by a lack of water, which lets the ground and air warm up more quickly, climate scientist Katharine Hayhoe at Texas Tech University says.

"Heat and drought are a vicious cycle that has been hitting the Southwest hard in recent years," she says.

In contrast, northeast temperatures are being pushed ever higher by warmer waters in the North Atlantic combined with milder winters, says Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado.

The warming figures are the result of analysis of 30 years of temperature records gathered by the National Climatic Data Center in the lower 48 states, including figures from 192 cities and 344 smaller areas.

Cities have seen the greatest variations in recorded temperatures, although their results can be skewed by urban development and heating and the fact that in cities temperatures are recorded by a single weather station, rather than a regional average of several.

Boise, Idaho and Carson City in Nevada have experienced the greatest warming -- both for the year and during summer -- with annual temperature increases averaging at least four degrees in 30 years.