This chapter assesses and quantifies projections of future climate change using global climate models. It covers the period from 1990 to 2100, focusing on scenarios for changes in greenhouse gas concentrations and sulphate aerosol loadings. The results are based on simulations from various types of model experiments, including forced climate change experiments and ensemble methods to account for natural variability. Key findings include: - Global mean surface air temperature (SAT) is projected to increase by +1.3°C to +1.7°C by 2050 under the IS92a scenario, with a range from +0.8°C to +2.1°C under the SRES A2 and B2 scenarios. - By 2100, the global mean SAT change is projected to be +3.0°C under the SRES A2 scenario and +2.2°C under the B2 scenario. - The transient climate response (TCR) is estimated to be +1.1°C to +3.1°C, with an average of 1.8°C. - The effective climate sensitivity (ECS) is defined as the change in global mean temperature when the climate system reaches a new equilibrium after a doubling of CO₂ concentration, and it is inversely proportional to the strength of feedback processes. - The "commitment" to future warming occurs even if the forcing stops increasing, with the additional warming commitment being the further increase in temperature before the system reaches a new equilibrium. - Multi-model ensembles are used to better characterize projected climate change, reducing the impact of natural variability and providing a more robust estimate of the forced climate change signal. - Uncertainty in projections arises from uncertainties in forcing scenarios, model responses, and missing or misrepresented physical processes in models. The chapter also discusses the limitations and caveats of the ensemble approach and the importance of using a range of models to improve the reliability of projections.This chapter assesses and quantifies projections of future climate change using global climate models. It covers the period from 1990 to 2100, focusing on scenarios for changes in greenhouse gas concentrations and sulphate aerosol loadings. The results are based on simulations from various types of model experiments, including forced climate change experiments and ensemble methods to account for natural variability. Key findings include: - Global mean surface air temperature (SAT) is projected to increase by +1.3°C to +1.7°C by 2050 under the IS92a scenario, with a range from +0.8°C to +2.1°C under the SRES A2 and B2 scenarios. - By 2100, the global mean SAT change is projected to be +3.0°C under the SRES A2 scenario and +2.2°C under the B2 scenario. - The transient climate response (TCR) is estimated to be +1.1°C to +3.1°C, with an average of 1.8°C. - The effective climate sensitivity (ECS) is defined as the change in global mean temperature when the climate system reaches a new equilibrium after a doubling of CO₂ concentration, and it is inversely proportional to the strength of feedback processes. - The "commitment" to future warming occurs even if the forcing stops increasing, with the additional warming commitment being the further increase in temperature before the system reaches a new equilibrium. - Multi-model ensembles are used to better characterize projected climate change, reducing the impact of natural variability and providing a more robust estimate of the forced climate change signal. - Uncertainty in projections arises from uncertainties in forcing scenarios, model responses, and missing or misrepresented physical processes in models. The chapter also discusses the limitations and caveats of the ensemble approach and the importance of using a range of models to improve the reliability of projections.