The Impact of a Global Temperature Rise of 4 [degrees]C (7 [degrees]F)

Article excerpt

Climate change--the evidence

This map, produced by the Met Office in collaboration with the Walker Institute, Tyndall Centre and Quest, is part of the Science Museum's new exhibition "Prove It! All the Evidence You Need to Believe in Climate Change". For further information, go to sciencemuseum.org.uk/proveit

A guide to the impact of varying global temperature rises can be found on page 30 of this supplement.

The Amazon forest

With high levels of climate change, large areas of the Amazon forest could be lost through either drought stress on vegetation or the uncontrolled spread of fire. This depends largely on whether rainfall will decrease in Amazonia. While some climate models suggest rainfall may increase, some of the more realistic models project severe drying in the Amazon, increasing the risk of major droughts.

Agriculture

Climate change directly affects crop productivity and food production. Changes in the regional differences in climate patterns may widen production and consumption gaps between the developed and developing world. Current assessments are mainly limited to alterations in mean climate, but extreme weather or glacial retreat would potentially accelerate declines in productivity further.

Agricultural yields are expected to decrease for all major cereal crops in all major regions of production, once the global average temperature increases beyond 3 [degrees]C. For some crops the yield could decrease by over 20% at low latitudes, where the Impact will be greatest. This could result in tens to hundreds of millions of additional people (roughly a 10-20% increase), at risk from hunger. Most of this increase is expected in Sub Saharan Africa, and in some parts of south Asia and Central America, particularly for child mainutrition. For the population at 2050 the increase in the number of malnourished children could be as high as 24 million.

Water availability

A rise in global average temperature of 4 [degrees]C (7 [degrees]F) would have a substantial effect on river flows and the availability of water.

For the population rise at 2080, without climate change, just over 3 billion people, out of a global population of 7.5 billion, could be living in areas with limited per capita water availability (less than 1000 [m.sup.1]/person/year).

By reducing river run-off, climate change could mean that significantly less water was available to approximately 1 billion of these people (range 0.4 to 2 billion), substantially increasing the pressure of managing water supplies. In addition, as glaciers retreat, communities relying on glacier melt-water will also come under further threat.

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Sea-level rise is an inevitable consequence of increasing global temperatures. Low-lying coastal areas will become more vulnerable to flooding and land loss. As these areas often have dense populations, important infrastructure and high value agricultural and bio-diverse land, significant impacts are expected. At the beginning of the 21st Century, an estimated 600 million people live no more than 10 meters above present sea level.

South and East Asia have the highest populations living in low-lying deltas, but small islands are also venerable from sea-level rise and storm surges. Flooding from sea-water would cause loss of land, crops and freshwater suppliers, posing a risk to stability and security. For some, forced migration will be inevitable.

Carbon cycle

The 20th Century rise in [CO.sub.2] concentration was only 40-50% of the actual rate of emissions, because the rest was absorbed by the world's ecosystems and oceans. This process may be damaged by climate change, so that the impact of emissions on atmospheric concentrations could be greater in the future. At 4 [degrees]C (7 [degrees]F) Increase in global average temperature, the proportion of [CO.sub.2] emissions remaining in the atmosphere could rise to as much as 70%. …