A change in the climate which has an effect that then causes further climatic change. There can be both negative and positive feedbacks. A negative feedback acts in the opposite direction to the main trend, and a positive feedback works in the same direction as the main trend. So, in terms of global warming, a negative feedback has a cooling effect, while a positive feedback increases warming. An example of a positive feedback that could happen is when warming causes permafrost to melt. This may lead to an increase in methane* being released from Arctic soils. Since methane is a greenhouse gas*, the extra methane may cause further global warming, which may make permafrost melt faster.

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