What is certain and uncertain about climate change projections?
While there are uncertainties in climate projections, it is important to realize that the climate projections are based on sound scientific principles, such as the laws of thermodynamics and radiative transfer, with measurements of optical properties of gases. The record of past climate changes that can be inferred, for example, with geochemical methods from ice cores and ocean sediment cores, provides tantalizing hints of large climate changes that occurred over Earth’s history, and it poses challenges to our understanding of climate (for example, there is no complete and commonly accepted explanation for the cycle of ice ages and warm periods). However, climate models are not empirical, based on correlations in such records, but incorporate our best understanding of the physical, chemical, and biological processes being modeled. Hence, evidence that temperature changes precede changes in carbon dioxide concentrations in some climate changes on the timescales of ice ages, for example,
