James Hansen predicts higher sea level rises

World famous climate scientist James Hansen, known as the “father of global warming” for being the first to see the threat of catastrophic climate change in 1988, has issued a new warning. Sea level changes are likely to be much higher, less stable and happen much sooner than previous predictions.

The warnings are contained in a new study published in the European Geophysical Union’s open-access journal Atmospheric Chemistry and Physics.

The study, written by Hansen, NASA’s former lead climate scientist, and 16 co-authors — many of whom are considered the top in their fields — concludes that glaciers in Greenland and Antarctica will melt ten-times faster than previous consensus estimates, resulting in a sea level rise of at least three metres in as little as 50 years. A sea level rise of three metres would inundate most Australian coastal cities and other cities around the world, from New York to Shanghai.

The prospect that every coastal city on the planet may be uninhabitable in a few decades requires, in the study’s authors’ view, “emergency cooperation among nations”.

“We conclude that continued high emissions will make multi-metre sea level rise practically unavoidable and likely to occur this century. 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 civilisation.”

Hansen and his colleagues analysed how an influx of cold freshwater from the planet's melting ice sheets will disrupt the ocean's circulation — a factor they say has not been fully explored in the scientific literature to date.

In addition to running climate models, they compared modern warming to similar temperature increases from about 120,000 years ago, when sea level was 5 to 9 metres higher than it is today due to the release of glacial water. They concluded the influx of freshwater from melting ice sheets in modern times would essentially shut down the ocean's circulation, causing cool water to stay in the Earth's polar regions and equatorial water to warm up even faster.

The study found this temperature gradient would generate more intense storms around the tropics and accelerate melting at the poles by so much that the melt could double in just a decade.

“The cooling mechanism is cut off, so it’s melting ice shelves,” Hansen explained in an interview with Grist. “It’s a really dangerous situation where you get melting that causes more melting.”

Hansen also said that in the past, temperature increases of 1°C have resulted in higher sea levels than we have projected to accompany that temperature rise in the future.

The study rejects the presumption that only global warming in excess of 2°C represents a threat to life on the planet. So far, we have already warmed about 0.8°C, and even if we stopped emitting all greenhouse gases tomorrow, there are still several decades of warming to come from our recent emissions.

Meanwhile, as global emissions keep rising, some scientists say that even 2°C is an unrealistic goal because the global community simply is not reducing emissions enough to get there.

Yet Hansen’s study suggests that 2°C is too unambitious, and that the point at which warming becomes exponential instead of linear is more like 1.5°C. Other scientists have reached similar conclusions recently, such as those behind a United Nations report released in May that looked at the effect of sea level rise on Pacific island nations.

At a press conference to publicise the study, Hansen framed his findings as a plea to world leaders to pursue a new 1.5°C target: “I wanted to publish now, so the information is available well before the Paris meetings,” he said, referring to the next round of climate talks due in December. He said he will spend the next few months educating delegates on the study.

"Politicians need to understand that the issue is more urgent than previously realised," Hansen said. If warming reaches 2°C, "we will hand young people a climate system in which it is impossible to avoid large sea level rise."

The study should serve as a sobering wake-up call to all those, like Prime Minister Tony Abbott, who still dispute the threat posed by our ongoing burning of fossil fuels.

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