The Economist USA - 21.09.2019

(Barré) #1
Arcticseaice,annual
minimumextent
Relative
volume
change

Observedtemperaturechangebylatitude,°C
2018,relativeto1951-1980average

TheArcticistheepicentreofglobalwarming

Sources:NSIDC;PIOMAS;NASA;CarbonBrief*Averageforice
thickerthan15cm, 2019 datafromAugust†MinimumatSept16th
‡1st-99thpercentileofvalueswithineachlatitudeband

RUSSIA

CANADA

GREENLAND

UNITED
STATES

ARCTIC
OCEAN

Arctic
Circle
66.5°N

NorthPole

1980

2000

2019†

2019†
4.2m

2000
6.4m

1980
7.9m

Annualminimum
extent, km2 2012 recordlow

90°S

45°S

45°N

0

90°N

02451 3

↑TheArcticis
warmingmuch
fasterthan
everywhereelse

Latitude

Equator

Antarctic

Arctic

Average Range‡

Icethickness*
metres

Annual
minimum
area


Strongerjetstream

Weakerjetstream

Accordingtoone
theory,a bigtemperature
differenceyieldsa strong
jetstreamona relatively
straightpath.Thisformsa
barrierthatkeepscoldair
intheArctic
Smallertemperature
differencesproducea
slower,wavierjetstream
Coldairmovessouth
andwarmairmovesnorth.
Weakerwindsslowthe
movementofweather
systems,causing
heatwavesandcold
snapstolinger

Warmair

Warmair

Coldair

Coldair

1980
2000
2019

2.1
1.6
1.0

TheEconomistSeptember 21st 2019 93

A


round 320bc, a Greek merchant called
Pytheas set off for a long journey north.
He brought back reports of a land called
Thule, six days north of Scotland, “where...
there are no nights during the [summer]
solstice...and also no days during the win-
ter solstice”. It is unclear if Pytheas made it
there himself, or merely heard tales. But for
this and his account of a “congealed sea”, he
is said to have been one of the first Arctic
explorers. Were he to return today, he
would find a very different landscape.
Temperatures in the Arctic are warming
twice as fast as the global average. One
driver is the melting of floating sea ice.
When it vanishes, it exposes deep blue wa-
ters, which absorb more solar energy than

white ice does. In turn, this speeds up melt-
ing: a classic positive-feedback loop. The
ice recedes to an annual minimum extent
every September. The record low was set in
2012; 2007 and 2016 are joint second. This
year is expected to be level with them.
The best-known consequence of Arctic
heating is rising sea levels. Melting sea ice
does not raise the water level, for the same
reason that melting ice cubes do not make a
cup overflow. However, water trapped on
land in Greenland’s ice cap does increase
the sea level when it melts into the ocean.
Greenland has 2.85m cubic kilometres
of ice, enough to lift sea levels seven me-
tres. For now, it is melting slowly. Sea levels
are rising by an average of 3.3mm per year;
owing to an unusually hot summer in 2019,
Greenland will contribute about 1mm.
Another feedback loop involves frozen
soil. Normal garden soil consists of 5% car-
bon; soil in Arctic permafrost regions, rich
in organic matter, contains 20-50%. It is
thought to hold a total of 1.1-1.5trn tonnes of
carbon, more than the atmosphere and ten
times as much as the Amazon.
As the Arctic warms, bacteria in the soil
consume organic matter faster, releasing

more carbon dioxide and methane. These
gases can then speed up the greenhouse ef-
fect—heating the permafrost further and
causing more emissions. This July the Si-
berian tundra warmed and dried enough to
catch fire for weeks, a very unusual event.
The third threat posed by Arctic warm-
ing is less scientifically certain but more
immediate. Higher Arctic temperatures are
thought to affect weather patterns in the
northern mid-latitudes, where weather
systems form as a result of the temperature
gap between the hot tropics and cool pole.
The jet stream pushes them west to east.
Some evidence suggests that as the tem-
perature difference shrinks, the jet stream
weakens and its wavy pattern deepens.
This allows “tongues” of frigid air to reach
south, and warm pockets to approach the
Arctic Circle. It may also cause both storms
and clear skies to stay in place for longer,
leading to extended floods and dry spells.
Climate-change sceptics point to cold
snaps in North America as evidence that
concern about global warming is overheat-
ed. In fact such days, caused by chilly air es-
caping polar latitudes, may be a conse-
quence of Arctic warming. 7

The consequences of a rapidly warming
Arctic will be felt far afield

Ice would suffice


Graphic detailThe altered Arctic

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