What will the impacts be?
The basic impact of climate change is an increase in global average temperatures. However this statement masks the considerable variation of possible impacts. A very few places will actually get cooler but some places will get far warmer than others. Some will get drier while others get wetter. Ice sheets will melt but snowfall may increase. While there are many apparent contradictions some consensus on major impacts is emerging.
Sea Level Rises
As the ice on land melts sea levels will almost inevitably rise. We have already seen a rise of almost 20cm since 1900. The melting may provide water short communities with a short lived bounty of water until the melt water finally dries up completely, of particular concern are the people living below the massive melting ice fields of the Himalayas. Predicted sea level rises of 15-95cm would create millions of climate refugees and result in considerable economic impacts for countries with coast lines.
Flooding and Storms
While it is unclear as to whether there will be more or less rainfall over all, it seems likely that rainfall will become increasingly intense. As the world warms the areas in which you would expect to find storm downpours is expected to increase resulting in more frequent flooding. An extension of this effect is the role of warming in the frequency and intensity of cyclones, typhoons and hurricanes. These fierce cyclonic storms are a product of warm sea surface temperatures within the tropics. As global temperatures rise so should sea surface temperatures possibly leading to an increase in the numbers of storms and also their intensity.
Conservation
Ecological impacts are likely to be exaggerated by habitat fragmentation. A few thousand years ago animals and plant distributions would be able to change to accommodate climate change by moving, either immediately or gradually over generations. However as wildlife is increasingly isolated in protected areas it is no longer able to move as the regions outside the protected areas are filled with agriculture or human habitation. As a result many scientists are predicting a significant increase in the rate of extinction.
Agriculture
Similarly changes in rainfall and temperature will change agricultural practice all over the world. Hotter temperatures will push much agriculture into higher altitudes and further North and South away from the equator. This may have significant impacts on countries in which agriculture is already marginal.
Economics
The Stern Review emphatically endorses the economic case for early action. The longer we leave it the more expensive the problem will become to fix and at some point it may simply become unfixable.