The decreasing sea water temperature in the tropical Pacific has temporarily played the role of "cold water" in holding down the rise of the Earth's temperature by around 0.3 degrees Celsius since the Industrial Revolution in the latter half of the 18th century, according to a study conducted by experts including University of Tokyo associate professor Yu Kosaka.
The research finding was released in the British science journal Nature Geoscience. According to the Intergovernmental Panel on Climate Change (IPCC), the global temperature rose 0.85 degrees Celsius over the period from 1880 to 2012, but it did not rise steadily, and instead it repeated a rise and hiatus in a staircase pattern over time. The phenomenon in which the temperature stops rising is called a "hiatus," but the cause of such a phenomenon was not known.
The research team focused its attention on sea water temperatures in the tropical Pacific. The team confirmed that a drop in the sea water temperature that continued for 10 to 40 years had occurred multiple times, roughly coinciding with the corresponding drop in the pace of the increase in the global temperature.
The researchers assume that without such "cold water effects," carbon dioxide should have pushed up the global temperature by 1.2 degrees Celsius over the period from the Industrial Revolution to 2012. The temperature had stopped rising since the 2000s and it is believed to be in a transitional period now.
Kosaka said, "The cyclical changes in sea water temperature are believed to occur due to the strength and weakness of easterly winds over the Pacific. A hiatus could occur in the future again, but as long as CO2 keeps increasing, global warming will continue."