A new study finds that the upper layer of the world's oceans has warmed since 1993, which researchers say is a strong signal that the planet's climate is changing.
"We are seeing the global ocean store more heat than it gives off," John Lyman, an oceanographer with the National Oceanic and Atmospheric Administration's Joint Institute for Marine and Atmospheric Research and lead author of the study, said in a news release. The study's findings are being published in the journal Nature today (May 20).
The international team of scientists looked at multiple estimates of the heat content of the oceans' upper layer and drew on data from more than 3,200 Argo floating monitors deployed around the globe and from other devices dropped earlier from ships to take the water's temperature. Though there are some uncertainties about the data - the ship-deployed bathythermographs are not as accurate as the Argo floats - the researchers concluded that on average the heat content of the oceans' upper 2,000 feet has been increasing the past 16 years.
"The ocean is the biggest reservoir for heat in the climate system," according to Josh Willis, an oceanographer at NASA's Jet Propulsion Laboratory who contributed to the study. "So as the planet warms, we're finding that 80 to 90 percent of the increased heat ends up in the ocean."
Warming oceans cause sea level to rise, because water expands and takes up more space as its temperature increases. Estimates are that this thermal expansion accounts for one-third to one-half of the rise in sea level.
As the oceans warm, so do bays and inland waters. The mean temperature in the Patuxent River has risen 3 degrees Fahrenheit since the 1930s, according to University of Maryland scientists. Sea level in the Chesapeake Bay has risen about one foot in the past century.
For more on the finding that oceans are warming, read this piece in Time by Michael Lemonick.
(NOAA photo)