Daffodils in London by March 1? |
By Justin Gillis and Joanna M. Foster, The New York Times, March 29, 2012
Some people call
what has been happening the last few years “weather weirding,” and March is
turning out to be a fine example.
As a surreal heat
wave was peaking across much of the nation last week,
pools and beaches drew crowds, some farmers planted their crops six weeks
early, and trees burst into bloom. “The trees said: ‘Aha! Let’s get
going!’ ” said Peter Purinton, a maple syrup producer in Vermont.
“ ‘Spring is here!’ ”
Now, of course, a
cold snap in Northern states has brought some of the lowest temperatures of the
season, with damage to tree crops alone likely to be in the millions of
dollars.
Lurching from one
weather extreme to another seems to have become routine across the Northern
Hemisphere. Parts of the United States may be shivering now, but Scotland is
setting heat records. Across Europe, people died by the hundreds during a
severe cold wave in the first half of February, but a week later revelers in
Paris were strolling down the Champs-Élysées in their shirt-sleeves.
Does science have a
clue what is going on?
The short answer
appears to be: not quite.
The longer answer
is that researchers are developing theories that, should they withstand
critical scrutiny, may tie at least some of the erratic weather to global warming. Specifically, suspicion is
focused these days on the drastic decline of sea ice
in the Arctic, which is believed to be a direct consequence of the human
release of greenhouse gases.
“The question
really is not whether the loss of the sea ice can be affecting the atmospheric
circulation on a large scale,” said Jennifer A. Francis, a Rutgers University
climate researcher. “The question is, how can it not be, and what are the
mechanisms?”
Some aspects of the
climate situation are clear from earlier research.
As the planet
warms, many scientists say, more energy and water vapor are entering the atmosphere and driving weather
systems. “The reason you have a clothes dryer that heats the air is that warm
air can evaporate water more easily,” said Thomas C. Peterson, a researcher
with the National Oceanic and Atmospheric Administration.
A report released on Wednesday by the
Intergovernmental Panel on Climate Change, the United Nations body that issues
periodic updates on climate science, confirmed that a strong body of evidence
links global warming to an increase in heat waves, a rise in episodes of heavy
rainfall and other precipitation, and more frequent coastal flooding.
“A changing climate
leads to changes in the frequency, intensity, spatial extent, duration and
timing of extreme weather and climate events, and can result in unprecedented
extreme weather and climate events,” the report found.
Some of the
documented imbalances in the climate have certainly become remarkable.
United States
government scientists recently reported, for instance, that February was the
324th consecutive month in which global temperatures exceeded their long-term
average for a given month; the last month with below-average temperatures was
February 1985. In the United States, many more record highs are being set at weather stations than record
lows, a bellwether indicator of a warming climate.
So far this year,
the United States has set 17 new daily highs for every new daily low, according
to an analysis performed for The New York Times by Climate
Central, a research group in New Jersey. Last year, despite a chilly
winter, the country set nearly three new highs for every low, the analysis
found.
But, while the link
between heat waves and global warming may be clear, the evidence is much
thinner regarding some types of weather extremes.
Scientists studying
tornadoes are plagued by poor statistics that
could be hiding significant trends, but so far, they are not seeing any
long-term increase in the most damaging twisters. And researchers studying specific
events, like the Russian heat wave of 2010, have often come to conflicting
conclusions about whether to blame climate change.
Scientists who
dispute the importance of global warming have long ridiculed any attempt to
link greenhouse gases to weather extremes. John R. Christy, a climate scientist
at the University of Alabama in Huntsville, told Congress last year that “the weather is
very dynamic, especially at local scales, so that extreme events of one type or
another will occur somewhere on the planet every year.”
Yet mainstream
scientists are determined to figure out which climate extremes are being
influenced by human activity, and their attention is increasingly drawn to the
Arctic sea ice.
Because greenhouse
gases are causing the Arctic to warm more rapidly than the rest of the planet,
the sea ice cap has shrunk about 40 percent since the early 1980s. That means
an area of the Arctic Ocean the size of Europe has become dark, open water in
the summer instead of reflective ice, absorbing extra heat and then releasing
it to the atmosphere in the fall and early winter.
Dr. Francis, of
Rutgers, has presented evidence that this is affecting the jet
stream, the huge river of air that circles the Northern Hemisphere in a loopy,
meandering fashion. Her research suggests that the declining temperature
contrast between the Arctic and the middle latitudes is causing kinks in the
jet stream to move from west to east more slowly than before, and that those
kinks have everything to do with the weather in a particular spot.
“This means that whatever weather you
have today — be it wet, hot, dry or snowy — is more likely to last longer than
it used to,” said Dr. Francis, who published a major paper on her theory a few weeks ago.
“If conditions hang
around long enough, the chances increase for an extreme heat wave, drought or
cold spell to occur,” she said, but the weather can change rapidly once the
kink in the jet stream moves along.
Not all of her
colleagues buy that explanation.
Martin P. Hoerling,
a NOAA researcher who analyzes climate events, agrees with other scientists
that global warming is a problem to be taken seriously. But he contends that
some researchers are in too much of a rush to attribute specific weather events
to human causes. Dr. Hoerling said he had run computer analyses that failed to
confirm a widespread effect outside the Arctic from declining sea ice. “What’s
happening in the Arctic is mostly staying in the Arctic,” he said.
Dr. Hoerling
suspects that future analyses will find the magnitude of this month’s heat wave
to have resulted mostly from natural causes, but he conceded, “It’s been a
stunning March.”
That was certainly
what farmers thought. Mr. Purinton, the syrup producer in Huntington, Vt., has
been tapping maple trees for 46 years, since he was a boy.
This year he tapped
the trees two weeks earlier than normal, a consequence of the warm winter. But
when the heat wave hit, the trees budded early, and this tends to ruin the
taste of maple syrup. That forced him to stop four weeks earlier than normal and
cut his production in half compared with a typical year.
“Is it climate
change? I really don’t know,” he said. “This was just one year out of my 46,
but I have never seen anything like it.”
No comments:
Post a Comment