WASHINGTON (AP) -
The United States is warming fastest at two of its corners, in the Northeast
and the Southwest, an analysis of federal temperature records shows.
- led by Maine and Vermont - have gotten the hottest in the last 30 years in
annual temperature, gaining 2.5 degrees on average. But Southwestern states
have heated up the most in the hottest months: The average New Mexico summer
is 3.4 degrees warmer now than in 1984; in Texas, the dog days are 2.8
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.”
For example, while
people in the East and Midwest were complaining about a cold winter this
year, Redmond’s Nevada and neighboring California were having some of their
warmest winter months ever.
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. Climate scientists
suggested 1984 as a starting date 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 NCDC using
the least squares regression method, which is a standard statistical tool.
All but one of the
lower 48 states have warmed since 1984. 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.
Since 1984, 92
percent of the more than 500 cities and smaller regions within states have
warmed and nearly two-thirds of them have warmed by at least a degree. The
regions that have warmed the most have been New York’s St. Lawrence Valley,
northeastern Vermont, northern Maine, the northeastern plains of New Mexico
and western Vermont, all of which have warmed by more than 2.5 degrees.
Cities - where data
is a tad more suspect because they are based on a single weather station and
readings can be affected by urban heating and development - see the greatest
variation. Carson City, Nevada, and Boise, Idaho, are the cities that have
seen the most warming - both year-round and in summer - since 1984. Both
cities’ average annual temperatures have jumped more than 4 degrees in just
30 years, while Dickinson, North Dakota, has dropped the most, a bit more
than 2 degrees.
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 said.
And in the
Northeast, the temperatures are pushed up by milder winters and warm water
in the North Atlantic, said Kevin Trenberth, climate analysis chief at the
National Center for Atmospheric Research. And less snow on the ground over
the winter often means warmer temperatures, said Alan Betts, a climate
scientist at Atmospheric Research in Pittsford, Vermont.
The Southeast and
Northwest were among the places that warmed the least. In the Southeast and
Mid-Atlantic, industrial sulfur particle pollutants from coal burning may be
reflecting sunlight, thus countering heating caused by coal’s carbon dioxide
emissions, said Pennsylvania State University professor Michael Mann.
The data came from
National Climatic Data Center: