|Potential climatic changes of the near future have important characteristics that differentiate
them from the largest magnitude and most rapid of climatic changes of the Quaternary.
These potential climatic changes are thus a cause for considerable concern in terms of their
possible impacts upon biodiversity.
Birds, in common with other terrestrial organisms, are expected to exhibit one of two general
responses to climatic change: they may adapt to the changed conditions without shifting
location, or they may show a spatial response, adjusting their geographical distribution in
response to the changing climate. The Quaternary geological record provides examples of
organisms that responded to the climatic fluctuations of that period in each of these ways,
but also indicates that the two are not alternative responses but components of the same
overall predominantly spatial response. Species unable to achieve a sufficient response by
either or both of these mechanisms will be at risk of extinction; the Quaternary record
documents examples of such extinctions.
Relationships between the geographical distributions of birds and present climate have
been modelled for species breeding in both Europe and Africa. The resulting models have
very high goodness-of-fit and provide a basis for assessing the potential impacts of anthropogenic
climatic changes upon avian species richness in the two continents. Simulations
made for a range of general circulation model projections of late 21st century climate lead
to the conclusion that the impacts upon birds are likely to be substantial. The boundaries
of many speciesí potential geographical distributions are likely to be shifted = 1000 km.
There is likely to be a general decline in avian species richness, with the mean extent of speciesí
potential geographical distributions likely to decrease. Species with restricted distributions
and specialized species of particular biomes are likely to suffer the greatest impacts. Migrant
species are likely to suffer especially large impacts as climatic change alters both their breeding
and wintering areas, as well as critical stopover sites, and also potentially increases the distances
they must migrate seasonally.
Without implementation of new conservation measures, these impacts will be severe and
are likely to be exacerbated by land-use change and associated habitat fragmentation. Unless
strenuous efforts are made to address the root causes of anthropogenic climatic change,
much current effort to conserve biodiversity will be in vain.|