The inevitable rise of the oceans

Glaciers in North-East Greenland, in an image released by NASA on December 15, 2014 Glaciers in North-East Greenland, in an image released by NASA December 15, 2014

A rise of oceans of at least one meter due to global warming is inevitable in the coming 100 to 200 years and could hit hard cities located on the seashore like Tokyo or Singapore, warned NASA Wednesday.

The ice sheets of Greenland and Antarctica are melting faster than ever before, but some uncertainty remains, especially on the exact timing of the rising waters. Indeed, scientists do not know how fast will melt the main ice caps of the poles.

"Given what is known today about the expansion of the oceans with warming, and the melting of glaciers and ice caps that add water to the oceans, it is almost certain that we will have a sea level rise of at least one meter, and probably more, "said Steve Nerem of the University of Colorado, who heads the NASA team charged with monitoring rising sea levels.

"However, we do not know if this will happen in the next century or over a longer period," he added.

Miami flooded by the tides

"Rising sea levels are having a huge impact," said Michael Freilich, director of the Earth Sciences Division at NASA headquarters in Washington.

"More than 150 million people, mostly in Asia, live in areas less than one meter from the current sea level, and in the United States the rising waters will also change the course of our shores, especially in States like Florida, "he noted, recalling that already today the high tides cause flooding in some streets of Miami, which was not the case in the past.

"Some Pacific islands could be completely eliminated and big cities like Dhaka, Bangladesh, Singapore or Tokyo will be greatly affected," warned Freilich.

The latest serious predictions, dating back to 2013 by an intergovernmental panel of the United Nations on climate change, evoked a rise of oceans from 30 to 90 cm by the end of the century. But according to Nerem, the latest data measured by NASA satellites point to the high range of these forecasts.

Scientists are particularly watching the ice in Greenland, which has lost an average of 303 billion tonnes per year in the last decade. Antarctica, for its part, has melted by 118 billion tons a year.

Since 1992 and the first precise measurements by satellites, the oceans have risen by about 7.6 centimeters, with peaks to 23 cm in some places due to natural variations.

"Fast melting period"

"One thing we've learned is that the ice caps are melting faster than previously thought," said Josh Willis, NASA oceanographer. "In the next 20 years we will probably see an increase in the water level faster than the average, so we have to prepare for it."

For Eric Rignot, a glaciologist at the University of California, as the planet warms up, the ice melts automatically faster: "We are not talking about a futuristic scenario.I personally, the data collected in recent years worry me a lot".

"We have seen by studying the climatic changes since the birth of the Earth that rising water up to three meters in a century or two is possible if the ice melts quickly", said Tom Wagner, another scientist of the Nasa specialist in ice studies.

"We are seeing evidence that ice sheets are waking up," but we need to understand them better before saying that we are entering a new period of rapid melting, "he concluded.

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