How will climate change affect biodiversity?
 K Kaufmann
Birds' migratory movements are already being affected by climate change
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Climate change is already impacting on biodiversity. By the end of the century, climate change and its impacts may be the dominant direct driver of biodiversity loss. Severe effects, including bird extinctions, are predicted. Without urgent action, it is estimated that by the middle of this century almost one-third of land-based species could be committed to extinction as a result of climate change.
Biodiversity is already being lost and degraded at an escalating rate. Climate change adds yet another pressure.
Over the past 50 years, humans have changed ecosystems more rapidly and extensively than during any comparable period of time in human history, largely to meet rapidly growing demands for food, fresh water, timber, fibre and fuel. The result has been a substantial and largely irreversible loss in biodiversity. Threatened species are becoming more threatened and many common ones are in decline. Current extinction rates are exceptionally high. The Red List Index shows that birds have become more threatened since 1988, with more species slipping closer to extinction. In total 1,211 bird species (12% of total) are globally threatened. Of these 189 are Critically Endangered – facing imminent extinction. Effects include increased extreme weather (floods and droughts), the retreat of mountain glaciers, the thawing of permafrost, later freezing and earlier break-up of ice on rivers and lakes, lengthening of mid- to high-latitude growing seasons, poleward and altitudinal shifts of plant and animal ranges (resulting in declines in some plant and animal populations, and the potential extinction of species where no such shift in range is possible) and phenological changes, such as the earlier emergence of leaves and insects, earlier return of migrant species, and earlier egg-laying by birds. These changes, particularly the shifts in range and abundance, will have profound impacts on species, sites and habitats. Climate change may also impact species indirectly, impacting in combination with major threats such as alien invasive species and the spread of disease.