Global warming: Salty tropics Nature

56

The oceans are a global reservoir and redistribution agent for several important constituents of the Earth’s climate system, among them heat, fresh water and carbon dioxide. Whereas these constituents are actively exchanged with the atmosphere, salt is a component that is approximately conserved in the ocean.

A comparison of salinity differences across a long transect in the Atlantic Ocean over a 40-year period adds to the growing body of evidence that shifts in the distribution of saline and fresh waters are occurring worldwide as a result of global warming. Salinity has increased in the tropical Atlantic Ocean while water masses at both high-latitude ends of the transect have become fresher.

The results extend a growing body of evidence indicating that shifts in the oceanic distribution of fresh and saline waters are occurring worldwide and possible changes in the hydrologic cycle of the Earth. This is in line with expected changes to the hydrological cycle in a warmer world.

Although it is a fundamental component of the planetary energy budget, the hydrologic cycle remains one of the least-understood elements of the climate system and freshwater budgets one of the largest causes for differences among climate models. Given the great uncertainties in measuring evaporation and precipitation over the oceans, conclusive evidence for changes in the global water cycle will depend on present and future efforts to directly measure salinity changes and freshwater transports by ocean currents.