Measuring ocean salinity from space

Amber Jenkins at NASA/Jet Propulsion Laboratory: We know that average sea levels have risen over the past century, and that global warming is to blame. But what is climate change doing to the saltiness, or salinity, of our oceans? This is an important question because big shifts in salinity could be a warning that more severe droughts and floods are on their way, or even that global warming is speeding up.

Now, new research coming out of the United Kingdom (U.K.) suggests that the amount of salt in seawater is varying in direct response to man-made climate change. Working with colleagues to sift through data collected over the past 50 years, Peter Stott, head of climate monitoring and attribution at the Met Office in Exeter, England, studied whether or not human-induced climate change could be responsible for rises in salinity that have been recorded in the subtropical regions of the Atlantic Ocean, areas at latitudes immediately north and south of Earth’s tropics.

By comparing the data to climate models that correct for naturally occurring salinity variations in the ocean, Stott has found that man-made global warming -- over and above any possible natural sources of global warming, such as carbon dioxide given off by volcanoes or increases in the heat output of the sun -- may be responsible for making parts of the North Atlantic Ocean more salty.

…Stott’s analysis suggests that global warming is changing precipitation patterns over our planet. Higher temperatures increase evaporation in subtropical zones; the moisture is then carried by the atmosphere towards higher latitudes (towards the poles), and by trade winds across Central America to the Pacific, where it provides more precipitation. This process concentrates the salt in the water left behind in the North Atlantic, causing salinity to increase.

These are just the sort of effects that Gary Lagerloef and Amit Sen hope to uncover over the next few years. Lagerloef and Sen are, respectively, principal investigator and project manager of Aquarius, part of a brand new satellite mission due to be launched into orbit in May 2010. …By covering the entire globe once every seven days, Aquarius will fill in the blanks and provide an unprecedented global picture of salinity….

Artist’s illustration of the Aquarius/SAC-D spacecraft, scheduled for launch in May 2010. It will be the first NASA instrument to measure sea salinity from space. Image from the NASA/JPL website