Sea level rise due to warming higher than estimated

MIAMI • The amount of sea level rise caused by the oceans warming and expanding has been underestimated and is likely about twice as much as previously calculated, German researchers say.

The findings, published in the Proceedings of the National Academy of Sciences, a peer-reviewed US journal, suggest that increasingly severe storm surges can be expected as a result.

Sea levels can rise due to two factors - melting ice and the thermal expansion of water as it warms. Until now, researchers believed that the oceans rose between 0.7mm and 1mm a year due to thermal expansion. But a fresh look at the latest satellite data from 2002 to 2014 shows the seas are expanding at about 1.4mm a year, said the study.

"To date, we have underestimated how much the heat-related expansion of the water mass in the oceans contributes to a global rise in sea level," said co-author Jurgen Kusche, a professor at the University of Bonn.

The overall sea level rise rate is about 2.74mm a year, combining both thermal expansion and melting ice.

Sea level rise was also found to vary substantially from place to place, with the rate around the Philippines "five times the global rate". But sea levels on the US West Coast are largely stable because of negligible ocean warming in that area, said the findings.

Last year was the hottest since records began in the 19th century in a trend that almost all scientists blame on greenhouse gases from the burning of fossil fuels - stoking heatwaves, droughts, downpours and rising sea levels.

The record-breaking string of hot years since 2000 is almost certainly a sign of man-made global warming, with an extremely small chance that it was caused by random natural swings, another study has said.

"Recent observed runs of record temperatures are extremely unlikely to have occurred in the absence of human-caused global warming," a US-led team of experts wrote in the journal Scientific Reports.

It estimated the chance of the record run - with up to 13 of the 15 warmest years all from 2000 to 2014 - occurring with no human influence at between one in 770 and one in 10,000.

Lead author Michael Mann, a meteorology professor at Pennsylvania State University, said in an e-mail: "Climate change is real, human-caused and no longer subtle - we're seeing it play out before our eyes."

On Monday, the United Nations' World Meteorological Organisation (WMO) confirmed US and British data showing that 2015 was by far the hottest year on record and noted that a powerful El Nino event warming the surface of the Pacific Ocean had stoked extra heat.

"The power of El Nino will fade in the coming months but the impacts of human-induced climate change will be with us for many decades," WMO secretary-general Petteri Taalas said.


A version of this article appeared in the print edition of The Straits Times on January 27, 2016, with the headline 'Sea level rise due to warming higher than estimated'. Print Edition | Subscribe