Scientists forecast more rainfall overall, but say the risk of drought in inland areas during hot summers will increase. More flooding is expected from storms and rising sea levels. There are, however, likely to be very strong regional variations in these patterns. Poorer countries, which are least equipped to deal with rapid change, could suffer the most.
Plant and animal extinctions are predicted as habitats change faster than species can adapt, and the World Health Organization (WHO) has warned that the health of millions could be threatened by increases in malaria, water-borne disease and malnutrition.
As an increased amount of CO2 is released into the atmosphere, there is increased uptake of CO2 by the oceans, and this leads to them becoming more acidic. This ongoing process of acidification could pose major problems for the world's coral reefs, as the changes in chemistry prevent corals from forming a calcified skeleton, which is essential for their survival.
Computer models are used to study the dynamics of the Earth's climate and make projections about future temperature change. But these climate models differ on "climate sensitivity" - the amount of warming or cooling that occurs as a particular factor, such as CO2. goes up or down.
Models also differ in the way that they express "climate feedbacks".
Global warming will cause some changes that look likely to create further heating, such as the release of large quantities of the greenhouse gas methane as permafrost (permanently frozen soil found mainly in the Arctic) melts. This is known as a positive climate feedback.
But negative feedbacks exist that could offset warming. Various "reservoirs" on Earth absorb CO2 as part of the carbon cycle - the process through which carbon is exchanged between, for example, the oceans and the land.
The question is: how will these balance out?
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