According to the UK Green Party website the Green Party will try to achieve the following if they gain power at the 2010 general election:

CC020 The IPCC’s Third Assessment Report, published in early 2001, predicts that with business as usual global mean temperature will rise between 1.4°C and 5.8°C during the 21st century. Work with more advanced models carried out subsequently by the UK Meteorological Office’s Hadley Research Centre suggests that, again with business as usual, rises of up to 8°C can be expected by 2100.

CC021 The most serious direct effects of climate change are an increase in the frequency and severity of extreme weather events, effects of the temperature itself, and rising sea levels. The reinsurance industry has estimated that global damages caused by storms, droughts & floods has roughly doubled each decade since 1950, reaching almost $500 billion in the 90s. Extrapolation of this trend suggests that the annual rate of damages could reach the same magnitude as the annual global GDP by the 2060s.

CC022 Effects on ecosystems, agricultural systems, people and economic systems will be increasingly severe. Many diseases, most notably malaria, are likely to become much more widespread. Rainfall patterns are likely to change drastically, including big seasonal and north/south variations in the UK. Food supplies will become erratic. Low-lying and island states, most notably Bangladesh, will become inundated and lead to at least 10s of millions of eco-refugees.

CC023 Furthermore abrupt changes in climate are quite likely — they show up frequently in the paleological record. Possibilities forecast by different groups of scientists include the shutting down of the Gulf Stream, a complete dieback of the Amazon rainforest, and a rapid increase of perhaps 5°C due to methane emissions from warming continental shelves. Such jumps are potentially much more damaging to ecosystems and to human societies than more gradual change. Several other positive feedback mechanisms are known which could trigger rapid change, without being understood well enough to be accurately included in climate models. These include the effects of clouds, the changes in carbon absorption of plants under stressed conditions, and the link with a cooling stratosphere and ongoing stratospheric ozone depletion.

CC024 Some scientists believe that a ‘runaway’ greenhouse effect is possible, leading to temperature increases of several 10s°C over a timescale of 50-200 years and to large parts or even all of the Earth becoming uninhabitable.

I would be interested to hear both positive and negative views on UK Green Party’s Climate Change Impacts policies in the comments below?