Geography Reference
In-Depth Information
have to put this into the context of the fact that we are living an
interglacial which is usually a settled period without sudden tem-
perature changes. The Intergovernmental Panel on Climate
Change (IPCC) stated in their report in 2007 (see further reading)
that: 'warming of the climate system is unequivocal, as is now
evident from observations of increases in global average air and
ocean temperatures, widespread melting of snow and ice and rising
global average sea level'.
The temperature increase is widespread over the globe but more
exaggerated at higher northern latitudes. For the Arctic the tem-
peratures over the last 100 years have increased at twice the rate of
the global average. The oceans have warmed down to depths of at
least 3,000 metres. Numerous other long-term changes in climate
have been observed. For example, there have been increases in
rainfall in northern Europe, northern and central Asia and eastern
North and South America between 1900 and 2005. Rainfall has
declined in the Sahel, the Mediterranean, southern Africa and parts
of southern Asia. The IPCC noted in their 2007 report that it is
very likely that cold days, cold nights and frosts have become less
frequent over most land areas, while hot days and hot nights have
become more frequent. It is also likely that both heatwaves and
heavy precipitation events have become more frequent over most
land areas.
Some have argued that these changes are naturally driven. For
instance, solar cycles including sunspots, which are dark marks on
the solar surface and occur in 11-year cycles, affect the energy we
receive. However, the Sun's energy release between 1990 and
2010 was lower than normal and therefore goes against any
observed rise in near-surface ocean temperatures. Volcanic erup-
tions eject greenhouse gases into the atmosphere but these have not
become more frequent over the last 100 years and so cannot be the
cause of the trend in global warming.
It is absolutely certain that humans have emitted large quantities
of carbon dioxide by burning fossil fuels and vegetation. Similarly,
the increases in methane concentrations (which are currently rising
at faster rates than carbon dioxide) can be attributed to energy pro-
duction, food production from rice fields or ruminant livestock,
landfills, waste treatment and vegetation burning. Recent estimates
suggest that one-third of nitrous oxide emissions are caused by
