Crazy climate ... does science have a clue what is going on?
Photo: Nick Moir
Melting Arctic sea ice is the focus of research into increasingly erratic weather patterns.
Some people call what has been happening across the
northern hemisphere in the past few years ''weather weirding'' and March
turned out to be a fine example. As a surreal heatwave was peaking
across much of the US 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!''' says Peter Purinton, a maple syrup producer in Vermont. ''Spring is here!''
Now a cold snap in the 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.
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Lurching from one weather extreme to another seems to
have become routine. Parts of the US may be shivering but Scotland is
setting heat records. Across Europe, hundreds of people died during a
severe cold wave in the first half of February but a week later
revellers in Paris were strolling on the Champs-Elysees in 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 scrutiny, may tie at least some of
the erratic weather to global warming. Suspicion is focused on the
drastic decline of Arctic sea ice, 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,''
says Jennifer Francis, a Rutgers University climate researcher. ''The
question is, how can it not be and what are the mechanisms?''
As the planet warms, many scientists say, more energy and water vapour enter the atmosphere and are driving weather systems.
''The reason you have a clothes dryer that heats the air
is that warm air can evaporate water more easily,'' says Thomas C.
Peterson, a researcher with the National Oceanic and Atmospheric
Administration. A report released last week by the Intergovernmental
Panel on Climate Change, the UN body that issues periodic updates on
climate science, confirmed a strong body of evidence links global
warming to an increase in heatwaves, 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,'' it says.
US government scientists recently reported 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 US, many more
record highs are being set at weather stations than record lows, a
bellwether indicator of warming.
So far this year, the US has set 17 daily highs for every
daily low, according to an analysis performed by the New Jersey
research group Climate Central. Last year the country set nearly three
highs for every low. But, while the link between heatwaves and global
warming may be clear, the evidence is much thinner regarding 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 a long-term rise in the most damaging twisters.
And researchers studying specific events such as the
Russian heatwave 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 attempts to link greenhouse gases to weather
extremes. John Christy, a climate scientist at the University of Alabama
in Huntsville, told the US Congress last year ''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 per cent since the early 1980s: 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 releasing it to the atmosphere
in autumn and early winter.
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 meandering fashion. Her research suggests 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 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,'' says Francis, who recently published a paper on her theory. ''If
conditions hang around long enough, the chances increase for an extreme
heatwave, drought or cold spell to occur.'' But the weather can change
rapidly once the kink moves along.
Not all of her colleagues buy that explanation. Martin
Hoerling, a National Oceanic and Atmospheric Administration researcher,
agrees that global warming should be taken seriously but contends some
researchers are in too much of a rush to attribute specific weather
events to human causes. Hoerling says he has 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 says and suspects that future analyses
will find the magnitude of this month's heatwave to have resulted mostly
from natural causes but concedes, ''It's been a stunning March.''
That's certainly what farmers have thought. Purinton
has been tapping maple trees for 46 years. This year he tapped the trees
two weeks earlier than usual, a consequence of the warm winter.
But when the heatwave hit the trees budded early, which
tends to ruin the syrup's taste. That forced him to stop four weeks
earlier and halved his typical production.
''Is it climate change? I really don't know,'' he says.
''This was just one year out of my 46 but I have never seen anything
like it.''
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