Geoscience Reference
In-Depth Information
ing gaps of eight, two, zero, eight, three, and, again, zero years, respectively. Recon-
struction of past climate using coral reefs in the western Pacific shows sea-surface
temperature variations dating back 150 years, well beyond our historical records. The
sea-surface temperature shows the shifts in ocean current, which accompany shifts in
the ENSO and reveal that there have been two major changes in the frequency and
intensity of El Niño events. First was a shift at the beginning of the 20th century from
a 10-15-year cycle to a 3-5-year cycle. The second was a sharp threshold in 1976
when a marked shift to more intense and even more frequent El Niño events oc-
curred. Some climate modelling results suggest that there could be a future
'heightened' state of El Niño which would permanently shift weather patterns. For
example, it seems that the drought region in the USA could be shifting eastward.
However, predicting an El Niño event six months from now is hard enough, without
trying to assess whether or not ENSO is going to become more extreme over the next
100 years. Most computer models of ENSO in the future are inconclusive; some have
found an increase and others have found no change. This is, therefore, one part of the
climate system which we do not know how global warming will affect. Not only does
ENSO have a direct impact on global climate, but it also affects the numbers, intens-
ity, and pathways of hurricanes and cyclones, and the strength and timing of the Asi-
an monsoon. Hence, when discussing the potential impacts of climate change, one of
the largest unknowns is the variation of ENSO and its knock-on effects on the rest of
the global climate system.
On a more theoretical note, a recent study by Chris Thomas and colleagues (published in
Nature in 2004) investigated the possible increase in the likely extinction rate over the
next 50 years in key regions such as Mexico, Amazonia, and Australia. The theoretical
models suggest that by 2050 the climatic changes predicted by the IPCC would commit
18 per cent (warming of 0.8-1.7°C), 24 per cent (1.8-2.0°C), and 35 per cent (above
2.0°C) of the species studied to extinction in these regions. That means one-quarter of all
species in these regions may be committed to extinct by the middle of this century. This
study has been criticized as there are many assumptions in their models which may or
may not be true; for example, they assume we know the full climatic range in which each
species can persist and the precise relationship between shrinking habitat and extinction
rates. So these results should be seen only as the likely direction of extinction rates, not
necessarily the exact magnitude. However, these predictions do represent a huge future
threat to regional and global biodiversity and illustrate the sensitivity of biological sys-
tems to the amount and rate of warming that will occur in the future.
Search WWH ::




Custom Search