Climate change caused by human activities, such as the burning of fossil fuel, has been raised as one of the most urgent environmental issues of our day. The theory of global warming as a consequence of GHG emissions was raised several times during the 20th century, but it was not until the 1980s that climate change became a political issue. The policy responses to climate change, as established in the United Nations Framework Convention on Climate Change (UNFCCC), are mitigation and adaptation. Mitigation concerns the reduction of GHG emissions and enhancement and protection of sinks and reservoirs, while adaptation concerns various responses to experienced or expected consequences of climate change, such as flood control and adjustment of crops.