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| One of the dry pools at the Quivira National Wildlife Refuge in Hudson, Kansas |
By Justin Gillis, The New York Times, January 8, 2013
The numbers
are in: 2012, the year of a surreal March heat wave, a severe drought in the
Corn Belt and a huge storm that caused broad devastation in the Middle Atlantic
States, turns out to have been the hottest year ever recorded in the contiguous
United States.
How hot was it? The temperature differences between years are usually
measured in fractions of a degree, but last year’s 55.3 degree average
demolished the previous record, set in 1998, by a full degree Fahrenheit.
If that does not sound sufficiently impressive, consider that 34,008
daily high records were set at weather stations across the country, compared
with only 6,664 record lows, according to a count maintained by the Weather Channel meteorologist
Guy Walton, using federal temperature records.
That ratio, which was roughly in balance as recently as the 1970s, has
been out of whack for decades as the country has warmed, but never by as much
as it was last year.
“The heat was remarkable,” said Jake Crouch, a scientist with the National Climatic
Data Center in Asheville, N.C., which released the official climate
compilation on Tuesday. “It was prolonged. That we beat the record by one
degree is quite a big deal.”
Scientists said that natural variability almost certainly played a
role in last year’s extreme heat and drought. But many of them expressed doubt
that such a striking new record would have been set without the backdrop of global warming caused by the human release of
greenhouse gases. And they warned that 2012 was probably a foretaste of things
to come, as continuing warming makes heat extremes more likely.
Even so, the last year’s record for the United States is not expected
to translate into a global temperature record when figures are released in the
coming weeks. The year featured a La
Niña weather pattern, which tends to cool the global climate over
all, and scientists expect it to be the world’s eighth- or ninth-warmest year
on record.
Assuming that prediction holds up, it will mean that the 10 warmest
years on record all fell within the past 15 years, a measure of how much the
planet has warmed. Nobody who is under 28 has lived through a month of global
temperatures that fell below the 20th-century average, because the last such
month was February 1985.
Last year’s weather in the United States began with an unusually warm
winter, with relatively little snow across much of the country, followed by a
March that was so hot that trees burst into bloom and swimming pools opened
early. The soil dried out in the March heat, helping to set the stage for a
drought that peaked during the warmest July on record.
The drought engulfed 61 percent of the nation, killed corn and soybean
crops and sent prices spiraling. It was comparable to a severe drought in the
1950s, Mr. Crouch said, but not quite as severe as the legendary Dust Bowl
drought of the 1930s, which was exacerbated by poor farming practices that
allowed topsoil to blow away.
Extensive records covering the lower 48 states go back to 1895; Alaska
and Hawaii have shorter records and are generally not included in long-term
climate comparisons for that reason.
Mr. Crouch pointed out that until last year, the coldest year in the
historical record for the lower 48 states, 1917, was separated from the warmest
year, 1998, by only 4.2 degrees Fahrenheit. That is why the 2012 record, and
its one degree increase over 1998, strikes climatologists as so unusual.
“We’re taking quite a large step above what the period of record has
shown for the contiguous United States,” Mr. Crouch said.
In addition to being the nation’s warmest year, 2012 turned out to be
the second-worst on a measure called the Climate
Extremes Index, surpassed only by 1998.
Experts are still counting, but so far 11 disasters in 2012 have
exceeded a threshold of $1 billion in damages, including several tornado
outbreaks; Hurricane Isaac, which hit the Gulf Coast in August, and, late in
the year, Hurricane Sandy, which caused damage likely to
exceed $60 billion in nearly half the states, primarily in the mid-Atlantic
region.
Among those big disasters was one bearing a label many people had
never heard before: the derecho, a line of severe, fast-moving
thunderstorms that struck central and eastern parts of the country starting on
June 29, killing more than 20 people, toppling trees and knocking out power for
millions of households.
For people who escaped both the derecho and Hurricane Sandy relatively
unscathed, the year may be remembered most for the sheer breadth and oppressiveness
of the summer heat wave. By the calculations of the climatic data center, a
third of the nation’s population experienced 10 or more days of summer
temperatures exceeding 100 degrees Fahrenheit.
Among the cities that set temperature records in 2012 were Nashville;
Athens, Ga.; and Cairo, Ill., all of which hit 109 degrees on June 29;
Greenville, S.C., which hit 107 degrees on July 1; and Lamar, Colo., which hit
112 degrees on June 27.
With
the end of the growing season, coverage of the drought has waned, but the
drought itself has not. Mr. Crouch pointed out that at the beginning of
January, 61 percent of the country was still in moderate to severe drought
conditions. “I foresee that it’s going to be a big story moving forward in
2013,” he said.
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