The effects of climate change are being felt almost a kilometre down in the biggest ocean on Earth.
A new record of water temperatures shows how the Pacific has warmed and cooled since the last ice age. It shows that the ocean has warmed 15 times faster in the last 60 years than at any time in the previous 10,000.
The fact that the heat of global warming is penetrating deep into the oceans is yet more evidence that we are dramatically warming the planet, says Yair Rosenthal of Rutgers University in New Brunswick, New Jersey, who led the study.
Time capsules
To take the temperature of the ancient Pacific, Rosenthal's team turned to the preserved remains of single-celled organisms called foraminifera.
Each "foram" builds a hard shell around itself, and the amount of magnesium in the shell varies depending on the temperature of the surrounding water. By measuring the amount of the mineral in the shells, it is possible to work out the temperature of the water in which the forams lived.
Rosenthal examined preserved forams found in sediments from the seas around Indonesia. These seas receive water from the north and south Pacific, so their temperature should reflect the average across the entire Pacific. He focused on three species, which lived at different depths, giving him a measure of temperature changes between 500 and 900 metres deep.
Heat spike
Rosenthal found that after a period of warming following the end of the last ice age, the Pacific steadily cooled by 2.1 °C over the next 9000 years. Temperatures then shot up at an unprecedented rate: increasing by 0.25 °C in 200 years. The timing of the uptick reflects the onset of the industrial revolution.
Similar temperature trends are known to have happened over land – encapsulated in the famous hockey stick graph.
It takes more energy to heat water by 1°C than it does to heat the same mass of air, so the oceans act as a gigantic heat sink that shields us from the effects of global warming.
"If we didn't have the ocean, we would be much warmer", says Rosenthal.
Journal reference: Science, DOI: 10.1126/science.1240837
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
Have your say
Only subscribers may leave comments on this article. Please log in.
Only personal subscribers may leave comments on this article
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support.
