Scenarios

The future development of emissions considerably determines the concentrations of CO₂ and other greenhouse gases that are found in the future atmosphere. Since future emissions depend largely upon the actions of mankind - which we do not currently know - future developments can only be incorporated on the basis of plausible futures. Depending on the future course of emissions, greenhouse gas concentrations will rise in the future. Increasing concentrations of CO₂ and other greenhouse gases change the radiation budget of the earth. As a result the global mean temperature will rise:

The gray curve in this figure shows the response of the climate model to the observed course of greenhouse gas concentrations; the colored curves show the "answers" of the climate system to the various emission scenarios.

The direct comparison of the more "pessimistic" scenario A2 and the "optimistic" scenario B1 shows to which extent the climate system will react to further emissions within the next 100 years.

According to the calculations, the mean warming at the end of this century will be between 2.5 and 4.1 degrees Celsius relative to the average of the years 1961-1990 - depending on the amount of greenhouse gases emitted into the atmosphere until then.