1991-2012 average temperature compared with 1901-1960 average
The
effects of human-induced climate change are being felt in every corner
of the United States, scientists reported Tuesday, with water growing
scarcer in dry regions, torrential rains increasing in wet regions, heat
waves becoming more common and more severe, wildfires growing worse,
and forests dying under assault from heat-loving insects.
Such
sweeping changes have been caused by an average warming of less than 2
degrees Fahrenheit over most land areas of the country in the past
century, the scientists found. If greenhouse gases like carbon dioxide
and methane continue to escalate at a rapid pace, they said, the warming
could conceivably exceed 10 degrees by the end of this century.
“Climate
change, once considered an issue for a distant future, has moved firmly
into the present,” the scientists declared in a major new report
assessing the situation in the United States.
“Summers
are longer and hotter, and extended periods of unusual heat last longer
than any living American has ever experienced,” the report continued.
“Winters are generally shorter and warmer. Rain comes in heavier
downpours. People are seeing changes in the length and severity of
seasonal allergies, the plant varieties that thrive in their gardens,
and the kinds of birds they see in any particular month in their
neighborhoods.”
Photo
Residents of Pensacola, Fla.,
were ferried to safety last month. Severe weather killed at least 38
people in eight states in mid-April.Credit
Bruce Graner/Pensacola News Journal, via Associated Press
The
report is the latest in a series of dire warnings about how the effects
of global warming that had been long foreseen by climate scientists are
already affecting the planet. Its region-by-region documentation of
changes occurring in the United States, and of future risks, makes clear
that few places will be unscathed — and some, like northerly areas, are
feeling the effects at a swifter pace than had been expected.
Alaska
in particular is hard hit. Glaciers and frozen ground in that state are
melting, storms are eating away at fragile coastlines no longer
protected by winter sea ice, and entire communities are having to flee
inland — a precursor of the large-scale changes the report foresees for
the rest of the United States.
The study, known as the National Climate Assessment, was prepared by a large scientific panel overseen by the government and received final approval at a meeting Tuesday.
The
White House, which released the report, wants to maximize its impact to
drum up a sense of urgency among Americans about climate change — and
thus to build political support for a contentious new climate change
regulation that President Obama plans to issue in June.
But
instead of giving a Rose Garden speech, President Obama spent Tuesday
giving interviews to local and national weather broadcasters on climate
change and extreme weather. The goal was to help Americans connect the
vast planetary problem of global warming caused by carbon emissions from
cars and coal plants to the changing conditions in their own backyards.
It was a strategic decision that senior White House staff members had
been planning for months.
Speaking
to Al Roker of NBC News, in an interview scheduled to be shown
Wednesday morning on the “Today” show, Mr. Obama said “This is not some
distant problem of the future. This is a problem that is affecting
Americans right now. Whether it means increased flooding, greater
vulnerability to drought, more severe wildfires — all these things are
having an impact on Americans as we speak.”
Play Video|0:48
White House on Climate Change Report
White House on Climate Change Report
In a video released by the White House,
President Obama’s science adviser, John P. Holdren, discussed a new
study on climate change.
In
the Northeast, the report found a big increase in torrential rains and
risks from a rising sea that could lead to a repeat of the kind of
flooding seen in Hurricane Sandy. In the Southwest, the water shortages
seen to date are likely just a foretaste of the changes to come, the
report found. In that region, the report warned, “severe and sustained
drought will stress water sources, already overutilized in many areas,
forcing increasing competition among farmers, energy producers, urban
dwellers and plant and animal life for the region’s most precious
resource.”
The
report did find some benefits from climate change in the short run,
particularly for the Midwest, such as a longer growing season for crops
and a longer shipping season on the Great Lakes. But it warned that
these were likely to be countered in the long run by escalating damages,
particularly to agriculture.
“Yes,
climate change is already here,” said Richard B. Alley, a climate
scientist at Pennsylvania State University who was not involved in
writing the report. “But the costs so far are still on the low side
compared to what will be coming under business as usual by late in this
century.”
The report was supervised and approved by a large committee
representing a cross section of American society, including
representatives of two oil companies. It is the third national report in
14 years, and by far the most urgent in tone, leaving little doubt that
the scientists consider climate change an incipient crisis. It is also
the most slickly produced, with an elaborate package of interactive
graphics on the Internet.
One
of the report’s most striking findings concerned the rising frequency
of torrential rains. Scientists have expected this effect for decades
because more water is evaporating from a warming ocean surface, and the
warmer atmosphere is able to hold the excess vapor, which then falls as
rain or snow. But even the leading experts have been surprised by the
scope of the change.
The
report found that the eastern half of the country is receiving more
precipitation in general. And over the past half-century, the proportion
of precipitation that is falling in very heavy rain events has jumped
by 71 percent in the Northeast, by 37 percent in the Midwest and by 27
percent in the South, the report found.
“It’s
a big change,” said Radley M. Horton, a climate scientist at Columbia
University in New York who helped write the report. He added that
scientists do not fully understand the regional variations.
In recent years, sudden intense rains have caused extensive damage.
For instance, large parts of Nashville were devastated by floods in 2010 after nearly 20 inches of rain fell in two days. Last year, parts of Colorado flooded after getting as much rain in a week as normally falls in a year. Just last week, widespread devastation occurred in the Florida Panhandle from rains that may have exceeded two feet in 24 hours.
The
new report emphasized that people should not expect global warming to
happen at a steady pace, nor at the same rate throughout the country.
Bitterly cold winters will continue to occur, the report said, even as
they become somewhat less likely. Warming, too, will vary. While most of
the country has warmed sharply over the past century, the Southeast has
barely warmed at all, and a section of southern Alabama has even cooled
slightly.
The report cited the likely role of climate change in causing an outbreak
of mountain pine beetles that has devastated millions of acres of pine
forest across the American West and the Canadian province of British
Columbia; warmer winters and longer summers have let more of the beetles
survive and reproduce at an exponential rate. And the report warned of
severe, long-lasting heat waves. For instance, it cited research saying
the type of record-breaking heat that scorched Texas and Oklahoma in
2011 had become substantially more likely because of the human release
of greenhouse gases.
On rising sea levels, the new report went beyond warnings issued
in September by the United Nations Intergovernmental Panel on Climate
Change, which said that by the end of the century, sea levels could rise
by as much as three feet globally if emissions continue at a rapid
pace. The American scientists said the rise could be anywhere from one
to four feet, and added that six feet could not be ruled out. Along much
of the East Coast, the situation will be worse than the global average
because the land there is sinking, the scientists said.
Historically,
the United States was responsible for more emissions than any other
country. Lately, China has become the largest emitter over all, though
its emissions per person are still far below those of the United States.
The
report pointed out that while the country as a whole still had no
comprehensive climate legislation, many states and cities had begun to
take steps to limit emissions and to adapt to climatic changes that can
no longer be avoided. But the report found that these efforts were
inadequate.
“There
is mounting evidence that harm to the nation will increase
substantially in the future unless global emissions of heat-trapping
gases are greatly reduced,” the report warned.
Correction: May 6, 2014
An earlier version of a picture caption with this article
misidentified a town where overflow from the South Platte River in
Colorado submerged cars. It is Greeley, Colo., not Greenley.
Wash.Hibbing, Minn.+3.1 degreesMaineN.D.Mont.Ore.Vt.N.H.IdahoMass.Minn.S.D.N.Y.Wis.Wyo.R.I.Mich.Conn.Pa.IowaNeb.N.J.Nev.OhioDel.UtahIll.Md.Colo.Ind.W.Va.Grand Junction, Colo.+3.2Va.Calif.Mo.Kan.Ky.N.C.Tenn.Ariz.Okla.N.M.Ark.S.C.Ga.Ala.Miss.Okmulgee, Okla.–0.6La.TexasTroy, Ala.–0.6Fla.CoolerWarmerSource: NationalClimatic Data Center–0.50+0.5+1+2 degrees
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