Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 283

on snow to act as a reservoir to regulate river flow and water supply throughout the
year (Barnett et al., 2005a). If in a warmer world there is a smaller volume of snow
melt then either other water reservoirs will need to be constructed (or have increased
aquifer abstraction) to meet human and ecological need or we must accept the impact.
This may be a theoretical and an expensive choice (especially when considering the
currently free service that snow provides). It may be that action is taken to help meet
human needs, but wildlife outside of semi-natural systems is not likely to see similar
investment and will probably be the hardest hit.
In terms of human numbers, perhaps the most critical region in which vanishing
snow, ice and glaciers will negatively affect water supply will be China and parts of
India, or the Himalaya Hindu Kush region. This area not only supports some 2 billion
people but also currently represents the largest volume of ice outside of polar and
peri-polar regions. Nearly 70% of the Ganges' summer flow and 50-60% of other of
the regions' major rivers comes from melt water (Barnett et al., 2005a).
Once again, as with virtually all areas of the climate-biology relationship, there
are complications in the detail. It is undeniable that with global warming we are
moving away from a world with many local areas of seasonably variable snow cover
(similarly affecting many water catchments) to a world with far fewer areas of snow
cover. However, this reduction in cover does act to reduce carbon loss from soils
around the margins of snowfields. Such mountains areas of thin snow cover tend also
to be ecotones, which are special biological communities in border areas between
two habitat types. Because, with climate change, biological communities migrate
and change, ecotones are particularly sensitive. As has been mentioned previously
(Chapters 3, 4 and 5) carbon in soils can either accumulate or be released, in no small
part depending on climate and climate change. Areas of thin snow cover are less
insulated from the cold and this in turn affects the rate of carbon release from the soil
(Monson et al., 2006). Such detail informs climate computer models.
Of course, all the changes noted in this section relate to change observed to date.
Further change is anticipated with further warming. The scientific consensus (from
the IPCC) is clear: warming will continue through the rest of this century and beyond.
The only questions that remain are how much warming and at what rate. This in turn
depends on the future emissions of greenhouse gases. Nonetheless, future species
migration and other climate-related biological impacts will continue beyond those
already seen.
For example, in the UK biological surveys between 1940 and 1989 have shown
that a species of butterfly, the speckled wood ( Pararge aegeria ), occupies much of
the UK south of the central Midlands. However, given Business-as-Usual (B-a-U)
climate forecasts to the end of the century, the species is expected to be found virtually
throughout the UK up to the Shetland Isles, with only the Scottish highlands and the
highest North Pennine peaks being excepted. So, in the UK warming is extending the
northern limits of P. a e g e r i a . Meanwhile, at the other end of a species' thermal range
the opposite can happen. For example, in North America, where Edith's checkerspot
( Euphydryas editha ) has a range that extends in places from Mexico to Canada, there
is a real risk that with warming its southern limits will move north, and in the south
its lower altitudinal limits will rise (Hill and Fox, 2003).