The Impacts and Costs of Climate Change
new areas after a change in mean temperature. This is only the case for rapidly adapting
ecosystems such as deserts and grasslands but is not true of forest ecosystems.
The study also reports that the adaptive capacity of forests rapidly declines at increasing global mean
temperature increases. In ecosystems, many species, such as trees, have long lifetimes and limited
dispersal capacities. For example, the maximum dispersal rate of common tree species is less than
100km per century.
At a rate of warming of 0.10C per decade (i.e. 1C GMTI in 2100), 50% of all impacted ecosystems
are able to adapt within a century but only 36% of all impacted forests. Even when no
additional increase in temperature is assumed, this percentage of ecosystems able to adapt increases
only slowly when simulations continue beyond 2100. The adapted areas encompass immediate shifts
along current ecosystem boundaries and ecosystems that can easily adapt, such as grasslands. Further
spread of adapted ecosystems continues at an extremely slow pace (up to 100km per century).
Even small climate changes will have substantial consequences on temperature-limited ecosystems,
such as tundra and it is suggested that the large-scale impacts will occur. All other ecosystems
will, however, also be influenced but there are large regional differences depending on the original
species, ecosystem and landscape, their sensitivity and exposure to regional changes in temperature
and precipitation patterns. Not all impacts are negative. For example, tundra that is replaced by forests
could potentially store more carbon and provide additional ecosystem services (e.g. wood). However,
the decline of stressed species and ecosystems is generally a fast process (years to decades), often
triggered by disturbances, while adaptation through migration and regrowth is a slow process (decades
to centuries to millennia).
Forest ecosystems require the longest response times and have a low adaptive capacity, while most
other ecosystems respond more rapidly. Large changes are projected in the boreal and temperate
forests but they will probably not be realised during this century. There will be severe time lags in
the response, which will lead to a sub-optimal functioning of these ecosystems and increase their
sensitivity to pests and other disturbances, which are sources of additional stress. This highlights the
vulnerability of ecosystems with increasing temperatures. The key conclusion from Leemans and
Eickhout's paper is that even with a small global mean temperature increase, ecosystem impacts will
be pronounced.
More recent research into ecosystem impacts indicates that impacts and vulnerability of ecosystems
are likely to be underestimated. Leemans presented findings at the International Symposium on the
Stabilisation of Greenhouse Gases, February 2005, concluding that ecosystems respond faster to
changes in extreme weather than to average climate change. This helps to explain the more rapid
appearance of ecological responses around the world, as a result of an increase in extreme weather
events. In order to minimise ecosystem destruction, Leemans proposed that efforts be made to limit
global warming to maximally 1.5oC above pre-industrial levels and limit the rate of change to less than
0.050C per decade (Leemans 2005).
Water resources, water supply and water quality
There are likely to be significant changes in future European precipitation (rainfall), both in terms of
average precipitation, seasonal variations, and the levels of heavy events. The projections for Europe
show increases in precipitation, but there will be seasonal variations, and strong regional differences
between northern and southern countries. Northern Europe is likely to see increases in rainfall, and
increases in annual river discharges. Southern Europe is likely to see decreases in rainfall and river
discharges, which may lead to further stress on water resources (EEA 2004). This may have important

impacts on agriculture as moisture availability is already often limited in summer.
Water resources are sensitive to climatic variations in almost all regions of the world. In central Asia,
melting glaciers and shorter winter seasons alter river flows. In mid-latitude regions increased
temperatures lead to higher demand for water, particularly for irrigation. Decreased rainfall and more

AEA Technology Environment, August 2005

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