The view beyond the Lincoln Tunnel Helix. (Photo Credit: joiseyshowaa / Flickr)

The view beyond the Lincoln Tunnel Helix. (Photo Credit: joiseyshowaa / Flickr)

Former NASA climate scientist James Hansen has some bad news for the planet: Oceans could rise at least 10 feet in just 50 years.

This is an extreme contrast to official estimates of climate-induced sea level rise, which most experts agree will become more pronounced in the coming decades but disagree in the level of its severity. The variables involved make estimates tricky; warming waters, melting glaciers, melting ice sheets, land subsidence, erosion and overdevelopment all have a part to play, leaving the degree to which seas will rise subject to the available data.

For instance, the UN’s preeminent climate change organization, the Intergovernmental Panel on Climate Change (IPCC), estimated in its Fifth Assessment Report a maximum rise of nearly three feet by 2100. However, a study published last year in Environmental Research Letters included in its dataset the current unprecedented melt rate across the Greenland and Antarctic ice sheets. With this data included, researchers calculated that sea levels could rise by more than six feet by the end of the century.

While no one is anticipating a Waterworld situation (it would take several thousand years for all of the Earth’s ice to melt), most climate scientists agree that man-made greenhouse gas emissions are trapping heat in the Earth’s atmosphere and warming the planet. Recently, NASA confirmed that most of this heat is being absorbed by the ocean, and that’s what’s accelerating sea level rise.

Thus far, the sea has risen an average 20 centimeters (almost a foot) since the beginning of the 20th century. According to the new study from James Hansen and 16 other scientists, the Earth is on track to heat up an average of 2°C by the end of this century, accelerating glacial melt in Greenland and Antarctica by tenfold. This is generating a feedback loop of cool water entering the ocean and forcing warmer, saltier water up and underneath ice sheets, speeding up their melt rate and the volume of cool water entering the ocean. This could result in ocean levels rising by at least 10 feet in just 50 years, though when the loop will really kick in is unknown. Researchers say that it is “likely” to occur before 2100.

Melting ice caps. (Photo Credit: Gerald Simmons)

Melting ice caps. (Photo Credit: Gerald Simmons)

One study estimates that sea level-related damages could cost the U.S. as much as $1.1 trillion, and Hansen says it could cost the planet substantially more than that.

“We conclude that continued high emissions will make multi-meter sea level rise practically unavoidable and likely to occur this century,” said Hansen. “Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.”

There is an important caveat to Hansen’s prediction, however. The study itself has yet to be peer-reviewed. Hansen and his colleagues, all scientists in good standing and experts in their fields, chose to publish their study ahead of the upcoming climate summit in Paris, in which policymakers from around the world may decide on international carbon emission reform.

The study can currently be read in Atmospheric Chemistry and Physics, an open-access discussion journal, and will be reviewed in real time.

Hansen spent 46 years working for NASA at the Goddard Institute for Space Studies in Manhattan before choosing to leave the agency in pursuit of more direct climate action. Hansen has become a fervent activist and one of the leading voices for climate action in the U.S. According to the New York Times, he has been arrested or cited in connection to climate protests a half dozen times.

Hansen left NASA in part to change the system from without. “As a government employee, you can’t testify against the government,” he said in an interview.

For Hansen, the issue of anthropogenic climate change is one of utmost importance. “If we burn even a substantial fraction of the fossil fuels, we guarantee there’s going to be unstoppable changes,” he said. “We’re going to leave a situation for young people and future generations that they may have no way to deal with.”

Unfortunately, whether in 50 years or 100, the Earth’s future coastlines (and many of its largest cities) are already endangered. Last year, a State of the Climate report found that even if nations manage to cap global warming at 2°C, oceans are already locked in to centuries of irreversible sea level rise.

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