This chapter consists of a brief overview of the climate change problem, the international response to it, and key elements of the climate change regime. The basic information provided aims to give readers the tools that are needed to understand and work with the more detailed chapters that follow.

The climate change problem

Causes and projections

Climate change is linked to the presence of greenhouse gases (GHGs) in the atmosphere. The natural greenhouse effect, however, which is essential to life on earth, is now being disrupted by human activity due to rising emissions of GHGs from the consumption of fossil fuels – coal, oil and gas – along with intensive agriculture. Forest clearance and other land-use changes are also releasing carbon stored in trees and other vegetation, while reducing the amount of CO2 that is naturally absorbed by such carbon sinks. The man-made chemicals hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and other fluorocarbon gases are additional contributors to the growing cocktail of GHGs. The concentration of CO2 in the atmosphere, for example, has risen by over a third since pre-industrial levels in 1750. All other things being equal, the greater concentration of GHGs in the atmosphere generates an enhanced greenhouse effect, trapping more heat and raising temperatures at the earth's surface.

The atmospheric concentration of GHGs, however, is only one factor among many that govern the climate system. The climate itself is subject to natural variability, and is also influenced by both natural and anthropogenic (human-induced) factors.