Kyoto Protocol - Background

Background

Main article: Global warming See also: global climate model#Projections of future climate change and Scientific opinion on climate change

The view that human activities are likely responsible for most of the observed increase in global mean temperature ("global warming") since the mid-20th century is an accurate reflection of current scientific thinking. Human-induced warming of the climate is expected to continue throughout the 21st century and beyond.

The Intergovernmental Panel on Climate Change (IPCC, 2007) have produced a range of projections of what the future increase in global mean temperature might be. The IPCC's projections are "baseline" projections, meaning that they assume no future efforts are made to reduce greenhouse gas emissions. The IPCC projections cover the time period from the beginning of the 21st century to the end of the 21st century. The "likely" range (as assessed to have a greater than 66% probability of being correct, based on the IPCC's expert judgement) is a projected increased in global mean temperature over the 21st century of between 1.1 and 6.4 °C.

The range in temperature projections partly reflects different projections of future greenhouse gas emissions. Different projections contain different assumptions of future social and economic development (e.g., economic growth, population level, energy policies), which in turn affects projections of future greenhouse gas (GHG) emissions. The range also reflects uncertainty in the response of the climate system to past and future GHG emissions (measured by the climate sensitivity).