Researchers: Sea levels rising 60% faster than previously expected

It's gotten to be a frequent occurrence over the past few years. Dire predictions about the course of climate change and its impacts turn out to be more dire as new data become available. What was expected to happen eventually is happening faster and more extensively than forecasters had thought.

New research published Tuesday has more of this bad news. The study by Stefan Rahmstorf, Grant Foster and Anny Cazenave appears in Environmental Research Letters. They used satellite data from 1993-2011 to measure the rise in sea level, a technique that works better tide gauges:

[T]he rise in CO2 concentration and global temperature has continued to closely match the projections [of the Intergovernmental Panel on Climate Change's models] over the past five years, while sea level continues to rise faster than anticipated. The latter suggests that the 21st Century sea-level projections of the last two IPCC models. reports may be systematically biased low. Further support for this concern is provided by the fact that the ice sheets in Greenland and Antarctica are increasingly losing mass [...] while those IPCC projections assumed that Antarctica will gain enough mass in future to largely compensate mass losses from Greenland

The three scientists said average sea levels are rising at a rate of 3.2mm a year. That contrasts with computer-model estimates of 2mm a year presented by the IPCC just five years ago. That 60 percent higher rate may not sound like much, but sea-level rise is already presenting problems for coastal cities. Princeton University climate professor Michael Oppenheimer says the rise that has already occurred made the impacts associated with Hurricane Sandy worse than they would otherwise have been.

"Generally people are coming around to the opinion that this is going to be far worse than the IPCC projections indicate," said Grant Foster, a US-based mathematician who worked on the paper with German climatologist Stefan Rahmstorf.

The implications are serious'especially for coastal areas of the US. Large portions of America's Atlantic and Pacific coasts are regarded as "hotspots" for sea-level rise, with water levels increasing at twice the rate of most other places on the planet.

In the United States alone, there are tens of millions of people living in those hotspots. Just a one foot rise in sea level would put inhabitants of these areas at risk for having what now are devastating once-a-century storms into once-a-decade occurrences. An interactive map at Climate Central's Surging Seas website explores the incremental impacts of a rise in sea level from one to 10 feet in all the coastal states except Alaska and Hawaii. And here is a map for the whole world.

A Climate Central report in March 2012, Sea level rise, storms & global warming's threat to the U.S. coast, concluded:

Rising seas dramatically increase the odds of damaging floods from storm surges. For more than two-thirds of the locations analyzed (and for 85% of sites outside the Gulf of Mexico), past and future global warming more than doubles the estimated odds of 'century' or worse floods occurring within the next 18 years ' meaning floods so high they would historically be expected just once per century. For more than half the locations analyzed, warming at least triples the odds of century-plus floods over the same period. And for two-thirds of the locations, sea level rise from warming has already more than doubled the odds of such a flood even this year.

These increases are likely to cause an enormous amount of damage. At three quarters of the 55 sites analyzed, century levels are higher than 4 feet above the high tide line. Yet across the country, nearly 5 million people live in 2.6 million homes at less than 4 feet above high tide. In 285 cities and towns, more than half the population lives on land below this line, potential victims of increasingly likely climate-induced coastal flooding. 3.7 million live less than 1 meter above the tide. [...]

The population and homes exposed are just part of the story. Flooding to four feet
would reach higher than a huge amount of dry land, covering some 3 million acres of
roads, bridges, commercial buildings, military bases, agricultural lands, toxic waste dumps, schools, hospitals, and more. Coastal flooding made worse by global warming and rising seas promises to cause many billions of dollars of damage over
the coming decades.

Climate change, of course, knows no national boundaries. Around the world, hundreds of millions of people will be affected, many of them losing their livelihood or being injured or killed. Meanwhile, the costs of repairing storm damage and taking preventive measures will'not might'run into the trlllions of dollars. The longer the wait to take action to reduce the impacts of sea-level rise and other climate-change effects, the worse the consequences, including the economic consequences.

Every time the delegates meeting in Doha, Qater, for the 18th U.N. Climate Change Conference this week and next hear someone say we shouldn't move "too fast" for fear of disrupting the global economy, they might think about the costs of not moving fast enough, human and financial.

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^{DWG has a discussion on the subject here.}