Recent and Likely Future Changes in the Hydrological Cycle
How much rain and snow fall and where? How much of this precipitation evaporates? How much water is covered with ice? How much water is frozen in glaciers and permafrost? These linked questions—all aspects of climate—affect the "global energy balance," or the ratio of energy emitted by Earth and energy received from the sun. In the past half-century, trends have emerged in each area that are consistent with a warming climate due to the accumulation of greenhouse gases in the lower atmosphere. Using the assumption that greenhouse gas emissions will continue to rise, James McCarthy, the Alexander Agassiz Professor of Biological Oceanography at Harvard University, extrapolates future-climate scenarios from these recent trends.