“We’re in danger of handing young people a situation that’s out of their control,” said James E. Hansen, the retired NASA climate scientist who led the new research. The findings were released Tuesday morning by a European science journal, Atmospheric Chemistry and Physics.

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The nations of the world agreed to try to limit the warming to 3.6 degrees Fahrenheit, or 2 degrees Celsius, above the preindustrial level, though they have yet to agree on any program remotely ambitious enough to achieve that goal. The Earth has already warmed by about half that amount, with the consequence that virtually all land ice on the planet has started to melt and that the oceans are rising at an accelerating pace.

The paper by Dr. Hansen and 18 co-authors dwells on the last time the Earth warmed naturally, about 120,000 years ago, when the temperature reached a level estimated to have been only slightly higher than today. Much of the polar ice disintegrated then, and scientists have established that the sea level rose 20 to 30 feet.

Climate scientists agree that humanity is about to cause an equal or greater rise in sea level, but they have tended to assume that such a large increase would take centuries. The new paper argues that it could happen far more rapidly, with the worst case being several feet of sea-level rise over the next 50 years, followed by increases so precipitous that they would force humanity to beat a hasty retreat from today’s coastlines.

Scientists Warn of Perilous Climate Shift Within Decades, Not Centuries
http://www.nytimes.com/2016/03/23/science/global-warming-sea-level-carbon-dioxide-emissions.html