Permanent shifts in the global water cycle.

Understanding the relationship between atmospheric carbon levels and global temperature dates back to 1895, when Swedish scientist Svante Arrhenius argued that variations in carbon dioxide concentrations could affect Earth's heat budget. How climate warming affects Earth's hydrological cycle—the continuous water movement between Earth and the atmosphere—is a key question for managing water resources and making weather predictions. Although local and regional changes in the water cycle have been observed (1, 2), conclusive proof of a global-scale shift has been elusive. Answering this question requires decades of global mean sea level data and advanced climate and hydrological modeling. On page 1408 of this issue, Seo et al. (3) report how the integration of multiple global geophysical datasets reveals a permanent decline in terrestrial water storage. The study provides robust evidence of an irreversible shift in terrestrial water sources under the present changes in climate. [ABSTRACT FROM AUTHOR]