6.7. Observed Climate Variations

Sections 6.4 to 6.6 discussed the increases in concentration of atmospheric greenhouse gases and aerosols due to anthropogenic pollution since the Industrial Revolution, and the accompanying global changes in radiative forcing. There is now considerable model-based evidence that indicates a causal relationship between the net positive global-mean radiative forcing and the observed global temperature increase during the twentieth century. Before reviewing this evidence (section 6.8), temperature, and other contemporary climatic changes which have occurred, will be considered by examining the modern instrumental records.