Climate change and California drought in the 21st century.

Climate science has advanced over decades from an initial focus on the development and use of numerical models of Earth’s climate and compilation of rich networks of observational data, to now being in a position to “detect” and “attribute” specific impacts and events to anthropogenic climate change. Recent analyses have thus established the “fingerprint” of anthropogenic climate change in an increasingly diverse array of meteorological and hydrological phenomena around the world, from heat waves to coastal damages during extreme tides and storms, flooding from more intense precipitation events, and severe drought (1). In a new study published in PNAS, Diffenbaugh et al. now add weight to the accumulating evidence that anthropogenic climatic changes are already influencing the frequency, magnitude, and duration of drought in California (2). The authors show that the increasing co-occurrence of dry years with warm years raises the risk of drought despite limited evidence of a trend in precipitation itself, highlighting the critical role of elevated temperatures in altering water availability and increasing overall drought intensity and impact.