Geoscience Reference
In-Depth Information
Other evidence for global warming
Other evidence for climate change comes from the high latitudes and from monitoring ex-
treme weather events. The annual mean Arctic sea ice extent has decreased in total between
1979 to 2012 at a rate of 3.5 to 4.1 per cent per decade which means a loss of between 0.45
to 0.51 million km 2 per decade. Whereas the summer sea ice minimum has decreased even
more by between 9.4 to 13.6 per cent per decade which is equivalent to 0.73 to 1.07 million
km 2 per decade. In contrast between 1979 and 2012 the annual mean Antarctic sea ice ex-
tent has increased at a rate between 1.2 to 1.8 per cent per decade, which represents a
growth of between 0.13 to 0.20 million km 2 per decade. There is also evidence from per-
mafrost regions. Permafrost exists in high-latitude and high-altitude areas, where it is so
cold that the ground is frozen solid to a great depth. During the summer months, only the
top metre or so of the permafrost becomes warm enough to melt, and this is called the 'act-
ive layer'. There has been a 3°C warming in Alaska and 2°C warming in northern
European/Russia down to at least a metre over the last 50 years, showing that the active
layer has become deeper. The maximum area covered by seasonal permafrost has de-
creased by 7 per cent in the Northern Hemisphere since 1900, with a decrease in the spring
of up to 15 per cent. This increasingly dynamic cryosphere will amplify the natural hazards
for people, structures, and communication links. Already we have seen this in damage to
buildings, roads, and pipelines, such as the oil pipelines have been damaged in Alaska. In
addition, there is evidence that most if not all non-ice sheet glaciers are in retreat. The
amount of total snowfall and ice cover particularly in the Northern Hemisphere has great
reduced ( Figure 9 ). For example, ice cover records from the Tornio River in Finland, which
have been compiled since 1693, show that the spring thaw of the frozen river now occurs a
month earlier.
There is evidence too that our weather patterns are changing. For example, in recent years
massive storms and subsequent floods have hit China, Italy, England, Korea, Bangladesh,
Venezuela, and Mozambique. In England in 2000, 2007, and 2013/14, floods and storms
classified as 'once-in-200-years events' have occurred within 13 years and frequently with-
in a single year. Moreover, in Britain the winter of 2013/14 was the wettest six months
since records began in the 18th century, while August 2008 was the wettest on record; and
British spring is now coming earlier, with evidence of birds nesting 12±4 days earlier than
35 years previously. Insect species—including bees and termites—that need warm weather
to survive are moving northward, and some have already reached England by crossing the
Channel from France. The frequency of heat waves has increased in Europe, Asia, and
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