Antarctica: a global change perspective - Antarctica: Global Science from a Frozen Continent - page 302

planet driven by both the formation of sea ice and the interaction of the ocean
with ice shelves. The Southern Ocean also has a large protein resource (krill) that
will be exploited much further and faster as pressures increase on global food
supplies, with consequent effects on the marine food web.

Current climate change in Antarctica

Both the northern and southern hemispheres have warmed signi cantly over

the last century by about 0.6 and 0.8 C, respectively, with 2009 being the warmest
year ever in the south. The difference between the hemispheres is mainly the result
of the different distribution of land and sea, the latter having greater thermal
capacity and thus warming more slowly. Globally 15 out of the 16 warmest years
have occurred since 1995. There is considerable year-to-year variability, a signi cant

element of which can be attributed to the effects of El Niño and La Niña. El Niño is a
pattern of climate with approximately a 5-year periodicity whereby the eastern
tropical Paci c Ocean temperature warms, and then cools (La Niña). This

oscillation causes signi oods

and droughts in many regions. In Antarctica, the major impacts are on sea ice
distribution, which in turn impacts the breeding success of animals and birds as
discussed later.
The warming is not uniform in either hemisphere with the Arctic and the
Antarctic Peninsula showing rises well above average. The winter temperatures on
the Antarctic Peninsula show a temperature rise of over 4 C in the last 50 years, a
larger increase than in other seasons. Recent studies have demonstrated that these
changes are outside the normal ranges of natural variability of the climate, and are
consistent with the effects of human in

cant weather variations and extreme events, such as

uences, partly owing to carbon dioxide
increases and partly due the effects of the ozone hole. The rest of Antarctica shows
some small variations but no statistically signi cant temperature trends. The caveat

to this is that data sets are very short compared with those in other parts of the
world and there are too little data to detect signi cant trends.

finding is that the mid-troposphere (~5 km altitude)
over Antarctica has been warming at a rate faster than anywhere else. The cause of
the warming has not been determined. One suggestion is that it results from an
increased occurrence of polar stratospheric clouds (~40 km altitude). These clouds
form when the temperature falls below about

One very surprising recent

78 C and their impact is to change
the radiation balance through the atmosphere, trapping more incoming radiation in
the lower atmosphere. Over Antarctica, the stratosphere is cooling, as the result of
the combination of increased greenhouse gases and the ozone hole, making the
formation of polar stratospheric clouds more likely.