When you hear about climate change it's
most often about melting glaciers and sea ice, increasing frequency
of heatwaves and powerful storms. Maybe, just maybe, you'll hear
about the acidification of the oceans too. What you don't hear about
is the saltiness of the seas. But that's changing too, according to a
new piece of research just published in Geophysical Research Letters
(see the abstract and figures).
The saltiness, or salinity, of the
oceans is controlled by how much water is entering the oceans from
rivers and rain versus how much is evaporating; what my kids
recognize as “The Water Cycle.” The more sunshine and heat there
is, the more water can evaporate, leaving the salts behind in higher
concentrations in some places. Over time, those changes spread out as
water moves, changing the salinity profiles of the oceans.
Oceanographers from Scripps Institution of Oceanography and Lawrence
Livermore National Laboratory fingerprinted salinity changes from
1955 to 2004 from 60 degrees south latitude to 60 degrees north
latitude and down to the depth of 700 meters in the Atlantic, Pacific
and Indian oceans. They found salinity changes that matched what they
expected from such natural changes as El Niño or volcanic eruptions
(the latter can lower evaporation by shading and cooling the
atmosphere).
Next
the ocean data was compared to 11,000 years of ocean data generated
by simulations from 20 of the latest global climate models. When they
did that they found that the changes seen in the oceans matched those
that would be expected from human forcing of the climate. When they
combined temperature changes with the salinity, the human imprint is
even clearer, they reported.
“These results add to the evidence
that human forcing of the climate is already taking place, and
already changing the climate in ways that will have a profound impact
on people throughout the world in coming decades,” the oceanographers
conclude.
That the oceans are often left out of
climate change talk is surprising considering the fact that oceans
cover more than 70 percent of the planet and so should logically be
expected to show the effects of our excessive releases of carbon
dioxide over the last 150 years or so.
Image: A NASA animation shows the global
movement of Earth's ocean surface currents from June 2005 to December
2007. The animation was created using data from NASA satellites, direct
ocean measurements and a numerical model developed by NASA JPL and the
Massachusetts Institute of Technology. Image credit: NASA/SVS
