evidence: A summary of radiative forcings of climate in 2019 resulting from the increases in the principal long-lived and short-lived GHGs from human activities since 1750 is shown in Figure Q17-1. Positive forcings lead to warming and negative forcings lead to cooling of Earth’s surface. Climate forcings also lead to other changes, for example reductions in glacier and sea-ice extent, variations in precipitation patterns, and more extreme weather events. International climate assessments conclude that much of the observed surface warming and changes in other climate parameters over the last several decades are due to increases in the atmospheric abundances of CO2 and other GHGs, which result from a variety of human activities.