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Sea versus senators

North Carolina sea-level rise accelerates while state legislators put the brakes on research.

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The tide will not be held back by law-makers.

Could nature be mocking North Carolina's law-makers? Less than two weeks after the state's senate passed a bill banning state agencies from reporting that sea-level rise is accelerating, research has shown that the coast between North Carolina and Massachusetts is experiencing the fastest sea-level rise in the world.

Asbury Sallenger, an oceanographer at the US Geological Survey in St Petersburg, Florida, and his colleagues analysed tide-gauge records from around North America. On 24 June, they reported in Nature Climate Change that since 1980, sea-level rise between Cape Hatteras, North Carolina, and Boston, Massachusetts, has accelerated to between 2 and 3.7 millimetres per year. That is three to four times the global average, and it means the coast could see 20–29 centimetres of sea-level rise on top of the metre predicted for the world as a whole by 2100 (A. H. Sallenger Jr et al. Nature Clim. Change; 2012).

“Many people mistakenly think that the rate of sea-level rise is the same everywhere as glaciers and ice caps melt,” says Marcia McNutt, director of the US Geological Survey. But variations in currents and land movements can cause large regional differences. The hotspot is consistent with the slowing measured in Atlantic Ocean circulation, which may be tied to changes in water temperature, salinity and density.

North Carolina's senators, however, have tried to stop state-funded researchers from releasing similar reports. The law approved by the senate on 12 June banned scientists in state agencies from using exponential extrapolation to predict sea-level rise, requiring instead that they stick to linear projections based on historical data.

Following international opprobrium, the state's House of Representatives rejected the bill on 19 June. However, a compromise between the house and the senate forbids state agencies from basing any laws or plans on exponential extrapolations for the next three to four years, while the state conducts a new sea-level study.

According to local media, the bill was the handiwork of industry lobbyists and coastal municipalities who feared that investors and property developers would be scared off by predictions of high sea-level rises. The lobbyists invoked a paper published in the Journal of Coastal Research last year by James Houston, retired director of the US Army Corps of Engineers' research centre in Vicksburg, Mississippi, and Robert Dean, emeritus professor of coastal engineering at the University of Florida in Gainesville. They reported that global sea-level rise has slowed since 1930 (J. R. Houston and R. G. Dean J. Coastal Res. 27, 409417; 2011) — a contention that climate sceptics around the world have seized on.

Speaking to Nature, Dean accused the oceanographic community of ideological bias. “In the United States, there is an overemphasis on unrealistically high sea-level rise,” he says. “The reason is budgets. I am retired, so I have the freedom to report what I find without any bias or need to chase funding.” But Sallenger says that Houston and Dean's choice of data sets masks acceleration in the sea-level-rise hotspot.

North Carolina is not the only hotspot for efforts to legislate away the reality of sea-level rise. In 2011, the Texas Commission on Environmental Quality removed all references to rising sea levels from a scientific study of Galveston Bay on the Gulf of Mexico. And this month, the Virginia General Assembly passed a bill commissioning a study on rising sea levels — but only after references to sea-level rise and climate change had been removed.

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