Introduction - Climate Change Impacts on Freshwater Ecosystems - page 2

Changes in temperature, sea level and
northern hemisphere snow cover

(a)

14.5

0.5

0.0 14.0

-0.5 13.5

(b)

50

0

-50

-100

-150

(c)

4

40

0

36

-4

32

1850 1900 1950 2000

Year

Figure 1.1 Summary of climate and sea-level change to date. (a) Global average
temperature. (b) Global average sea level. (c) Northern hemisphere snow cover. (From
Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to
the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
(eds S. Solomon, M. Manning, Z. Chen, et al .). Cambridge University Press, Cambridge
and New York.)

Climate is a master variable, and all activity on this planet eventually depends
upon it. It determines the overall structure of natural biomes, be they deserts,
grasslands or deciduous or evergreen forests. It has driven the evolution of life
histories, the dynamics of food webs and the development of homeostases. It
fixes the circulation of the oceans, the availability of nutrients to the plankton
community, the onset of rain and ripening for crops and the reflectance of
radiation from the Poles. It manifests itself in the day-to-day weather, a
preoccupation of everyone, not just the British. It is the greatest determinant of
leisure travel, and, in its extremes, a source of extreme misery to match its delights
of balmy summer days, exciting ski runs and the fresh spring rain. A major change
in climate is a very considerable issue.