Projecting the future climate

Global climate models, which are based on the laws of physics, allow scientists to answer questions about our climate.

Scenarios of future greenhouse gas and aerosol emissions are used to drive the climate models. These scenarios are derived to encompass the uncertainty around future anthropogenic emissions including consideration of unknowns in population and economic growth, technological developments and transfer, and political and social change.

The non-linear and chaotic nature of the climate system creates some natural limits to the predictability of climate, such as decreasing skill in weather predictions beyond a few days.

Future climate cannot simply be extrapolated from past climate, and further may depend sensitively on the evolution of future greenhouse gas concentration. Multi-decadal projections are also affected by the chaotic climate system or natural climate variability.

There is a substantial international climate science and modelling community . Around the world, many groups have created global climate models and all of them vary to a lesser or greater degree from each other. This is mainly due to the justifiably different ways some physical processes are mathematically represented in these models.

Global modelling groups perform simulations using the same emissions scenarios and make their results available for further analysis and evaluation. Model evaluation determines how well climate models represent historical climate and forms an integral part of the confidence building exercise for climate change projections.

Confidence in a climate projection is a measure of how plausible the projected range of change is for a given emission scenario. Confidence comes from multiple lines of evidence including physical theory, past climate changes and climate model simulations.