Ocean warming since when?

New research shows that the world's oceans have started to heat up more than 100 years ago, twice the time previously known.

The results of the study could help scientists better understand Earth's record of rising sea levels, partly because water expands when it heats up. Oceanographer Dean Roemmich of the University of California in San Diego (USA) said: 'Temperature is one of the most fundamental signs of the ocean's physical condition. Just knowing the warming oceans will help answer some of the climate questions'.

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From 1872 to 1876, the HMS Challenger performed 69,000 nautical miles, crossing the Atlantic, Indian Ocean and Pacific Ocean. The scientists measured temperatures at different depths at each stop with a pressure-resistant thermometer.

Roemmich and colleagues compared this temperature profile with data from the modern Argo project, which uses free float to measure the temperature and salinity of the oceans once every 10 days. This comparison shows that the temperature increased by 1.1 degrees F (0.59 degrees C) on the ocean surface over the past 135 years. In the past, ocean warming was caused by melting ice and mass coral bleaching. Roemmich and colleagues said that the average global ocean temperature increased by 0.59 degrees F (0.33 degrees C) at a depth of about 700m. This global temperature change is twice what scientists have observed in the past half century, which suggests that oceans have long warmed up, not just in recent decades. . The findings also help to increase understanding of the green planet's 'energy budget' imbalance. Previous studies have shown that the earth absorbs more heat than heat, and that 90% of the excess heat has been added to the climate system since the 1960s stored in oceans.

If the thermal expansion is thought to be the key driver of sea level rise, Roemmich believes that the results of this study will help scientists better understand the historical record of sea-level rise. , capital has been continuously increasing since the 19th century. The results of this study are published in the Nature Climate Change issue of April 2012.