Four Futures : Standing at the Crossroads of Global Warming

IPCC Projections of the effects of a 1C to 5C increase in global temperature

1: Mild impact 1C to 2C rise on pre-industrial levels

This scenario is already 30% complete as there has been a temperature rise of 0.7C since 1900 and the inertia in the climate system from greenhouse gases already emitted means a 1C or 2C rise is virtually certain. A 1C rise would remove small glaciers in the Andes and 2C would make dry regions much drier. Mediterranean countries, parts of southern Africa and South America would experience 20% to 30% less water availability. Up to 10 million more people would be affected by coastal flooding and 40 million to 60 million more people will be exposed to malaria in Africa.

2: Significant impact 3C rise on pre-industrial levels

In southern Europe, serious droughts occur once a decade. Between 1 billion and 4 billion people will suffer water shortages. Agricultural yields will be higher in mid-latitude countries such as Britain and the US, but there will be sharp drops in the tropics, putting 150-550 million people at risk of hunger. Between 1 million and 170 million more people will be affected by coastal flooding. One study suggests that between 20% and 50% of species will face extinction. On current trends, temperatures are predicted to rise 2C-3C by mid-century, which would result in 150-200 million climate refugees.

3: Strong impact 4C rise on pre-industrial levels

Dry regions such as the Mediterranean and southern Africa will suffer a 30% to 50% drop in water availability. Agricultural yields will fall by 15% to 35% in Africa and up to 80 million more people will be exposed to malaria. Between 7 million and 300 million more people will be exposed to coastal flooding. Half of the Arctic tundra will be lost. The west Antarctic ice sheet may collapse, leading to significant sea level rise.

4: Catastrophic impact 5C rise or above

This is equivalent to the temperature rise since the last ice age. Most Himalayan glaciers will disappear, depriving 25% of China's population and hundreds of millions of Indians of water - melt water provides 70% of the water in the Ganges, for example. Sea level rise threatens cities such as London, New York and Tokyo. Rising ocean acidity will disrupt ecosystems and fish stocks. Feedback effects such as carbon dioxide release from soils and methane from permafrost kick in.

Key IPCC* Dates for 2007

1. The Report of Working Group 1 will be finalised in early February 2007.
2. The Working Group 2 Report will be completed in early April 2007
3. The Working Group 3 Report in early May 2007
4. The Synthesis Report by mid-November 2007.

*IPCC - The Intergovernmental Panel on Climate Change