Warming is Twice as Fast in Arctic than Elsewhere

Reducing black carbon (also known
as soot) and ozone in the lower part of the atmosphere, especially in the
Arctic countries of America, Canada, Russia and Scandinavia, could cut warming
in the Arctic by two-thirds over the next three decades. The UN report
suggests, if these and other mitigation measures were adopted everywhere they
could halve the wider rate of warming by 2050.

Arctic sea ice is melting far
faster than climate models predict. Why?

The Economist (24 September
2011):

ON SEPTEMBER 9th, at the height
of its summertime shrinkage, ice covered 4.33m square km, or 1.67m square
miles, of the Arctic Ocean, according to America’s National Snow and Ice Data
Centre (NSIDC). That is not a record low—not quite. But the actual record,
4.17m square km in 2007, was the product of an unusual combination of sunny
days, cloudless skies and warm currents flowing up from mid-latitudes. This
year has seen no such opposite of a perfect storm, yet the summer sea-ice
minimum is a mere 4% bigger than that record. Add in the fact that the
thickness of the ice, which is much harder to measure, is estimated to have
fallen by half since 1979, when satellite records began, and there is probably
less ice floating on the Arctic Ocean now than at any time since a particularly
warm period 8,000 years ago, soon after the last ice age.

That Arctic sea ice is
disappearing has been known for decades. The underlying cause is believed by
all but a handful of climatologists to be global warming brought about by
greenhouse-gas emissions. Yet the rate the ice is vanishing confounds these
climatologists’ models. These predict that if the level of carbon dioxide,
methane and so on in the atmosphere continues to rise, then the Arctic Ocean
will be free of floating summer ice by the end of the century. At current rates
of shrinkage, by contrast, this looks likely to happen some time between 2020
and 2050.

The reason is that Arctic air is
warming twice as fast as the atmosphere as a whole. Some of the causes of this
are understood, but some are not. The darkness of land and water compared with
the reflectiveness of snow and ice means that when the latter melt to reveal
the former, the area exposed absorbs more heat from the sun and reflects less
of it back into space. The result is a feedback loop that accelerates local
warming. Such feedback, though, does not completely explain what is happening.
Hence the search for other things that might assist the ice’s rapid
disappearance.

Forcing the issue

One is physical change in the ice
itself. Formerly a solid mass that melted and refroze at its edges, it is now
thinner, more fractured, and so more liable to melt. But that is (literally and
figuratively) a marginal effect. Filling the gap between model and reality may
need something besides this.

The latest candidates are
“short-term climate forcings”. These are pollutants, particularly ozone and
soot, that do not hang around in the atmosphere as carbon dioxide does, but
have to be renewed continually if they are to have a lasting effect. If they
are so renewed, though, their impact may be as big as CO2’s.

At the moment, most eyes are on
soot (or “black carbon”, as jargon-loving researchers refer to it). In the
Arctic, soot is a double whammy. First, when released into the air as a result
of incomplete combustion (from sources as varied as badly serviced diesel
engines and forest fires), soot particles absorb sunlight, and so warm up the
atmosphere. Then, when snow or rain wash them onto an ice floe, they darken its
surface and thus cause it to melt faster.

Reducing soot (and also ozone, an
industrial pollutant that acts as a greenhouse gas) would not stop the summer
sea ice disappearing, but it might delay the process by a decade or two.
According to a recent report by the United Nations Environment Programme,
reducing black carbon and ozone in the lower part of the atmosphere, especially
in the Arctic countries of America, Canada, Russia and Scandinavia, could cut
warming in the Arctic by two-thirds over the next three decades. Indeed, the
report suggests, if such measures—preventing crop burning and forest fires,
cleaning up diesel engines and wood stoves, and so on—were adopted everywhere
they could halve the wider rate of warming by 2050.

Without corresponding measures to
cut CO2 emissions, this would be but a temporary fix. Nonetheless, it is an
attractive idea because it would have other benefits (soot is bad for people’s
lungs) and would not require the wholesale rejigging of energy production which
reducing CO2 emissions implies. Not everyone agrees it would work, though.
Gunnar Myhre of the Centre for International Climate and Environmental Research
in Oslo, for example, notes that the amount of black carbon in the Arctic is
small and has been falling in recent decades. He does not believe it is the
missing factor in the models. Carbon dioxide, in his view, is the main culprit.
Black carbon deposited on the Arctic snow and ice, he says, will have only a
minimal effect on its reflectivity.

The rapid melting of the Arctic
sea ice, then, illuminates the difficulty of modelling the climate—but not in a
way that brings much comfort to those who hope that fears about the future
climate might prove exaggerated. When reality is changing faster than theory
suggests it should, a certain amount of nervousness is a reasonable response.

It’s an ill wind…

The direct consequences of
changes in the Arctic are mixed. They should not bring much rise in the sea
level, since floating ice obeys Archimedes’s principle and displaces its own
mass of water. A darker—and so more heat-absorbent—Arctic, though, will surely
accelerate global warming and may thus encourage melting of the land-bound
Greenland ice sheet. That certainly would raise sea levels (though not as
quickly as News Corporation’s cartographers suggest in the latest edition of
the best-selling “Times Atlas”, which claims that 15% of the Greenland sheet
has melted in the past 12 years; the true figure is more like 0.05%). Wildlife
will also suffer. Polar bears, which hunt for seals along the ice’s edge, and
walruses, which fish there, will both be hard-hit.

Watch our animation of the
receding Arctic ice-shelf and the shipping routes it could unlock

The effects on the wider climate
are tricky to assess. Some meteorologists suspect unseasonal snow storms off
the east coast of America in 2010 were partly caused by Arctic warming shifting
wind patterns. One feedback loop that does seems certain, though, is that the
melting Arctic will enable the extraction of more fossil fuel, with all that
that implies for greenhouse-gas emissions.

The Arctic is reckoned to hold
around 15% of the world’s undiscovered oil reserves and 30% of those of natural
gas. Hence a growing polar enthusiasm among energy companies—as witnessed last
month in an Arctic tie-up between Exxon Mobil, of America, and Rosneft,
Russia’s state-controlled oil giant. Recent plankton blooms suggest a warmer
Arctic will provide a boost to fisheries there, too. And the vanishing ice has
begun to allow a trickle of shipping across the Arctic’s generally frozen
north-west and north-east passages, thus linking the Atlantic and Pacific
oceans. In August a Russian supertanker, the Vladimir Tokohonov, aided by two
nuclear icebreakers, became the first such vessel to cross the north-east route
(or, as Russians refer to it, the northern sea route), hugging the Siberian
coast.

So far, despite some posturing by
Canada and Russia, there are few territorial disputes in the region and the
Arctic Council, the club of Arctic nations, has functioned reasonably well.
Whether the interests of these countries coincide with those of the wider
world, though, is moot. A warming Arctic will bring local benefits to some. The
rest of the world may pay the cost.

Source: www.economist.com