During the 20th century, the global climate has warmed by about 0.6C, or about 0.06C per decade. Computer models which simulate the effects on climate of increasing atmospheric greenhouse gas concentrations project that global average surface temperatures will rise by a further 3C by the end of the 21st century, or 0.3C per decade. It is currently believed that most ecosystems can withstand at most a 0.1C global temperature change per decade, before experiencing severe ecological stresses, leading in some cases to species extinction.
A warming of even 2C over the next 100 years would shift current climate zones in temperate regions of the world about 300 km towards higher latitudes, and vertically by 300 m. The composition and geographical distribution of unmanaged ecosystems will change as individual species respond to new conditions. At the same time, habitats will be degraded and fragmented by the combination of climate change, deforestation, desertification and other environmental pressures.
The most vulnerable ecosystems to global warming include forests, deserts and semi-deserts, low-lying islands, polar regions, mountain systems, wetlands, peatbogs, coastal marshes and coral reefs. Changes in other climatic elements in addition to temperature, such as rainfall, sunshine, cloud cover, and the frequency and intensity of extreme weather events, will influence these vulnerable ecosystems.
Ecosystems have evolved to cope with natural climate changes, and in some cases, the influences of mankind. It is doubtful, however, given todays globalised and ever-increasingly energy- and resource-consuming society that ecosystems will be able to respond to unprecedented climatic pressures as they have managed to in the past.