全球变暖使海平面迅速上升

The rate of sea level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years--and has shown a consistent link between changes in global mean surface temperature and sea level. The findings are published this week in the journal Proceedings¹ of the National Academy of Sciences (PNAS).

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The research, funded by the National Science Foundation (NSF), was conducted by Andrew Kemp, Yale University; Benjamin Horton, University of Pennsylvania; Jeffrey Donnelly, Woods Hole Oceanographic Institution; Michael Mann, Pennsylvania State University; Martin Vermeer, Aalto University School of Engineering, Finland; and Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany.

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"Having a detailed² picture of rates of sea level change over the past two millennia³（千年） provides an important context for understanding current and potential future changes," says Paul Cutler, program director in NSF's Division of Earth Sciences. #

"It's especially valuable for anticipating the evolution of coastal⁴ systems," he says, "in which more than half the world's population now lives."

Adds Kemp, "Scenarios⁵ of future rise are dependent on understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections⁶."

Kemp and colleagues developed the first continuous sea-level reconstruction⁷ for the past 2,000 years, and compared variations（变更，变种） in global temperature to changes in sea level over that time period.

The team found that sea level was relatively⁸ stable from 200 BC to 1,000 AD.

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Then in the 11th century, sea level rose by about half a millimeter each year for 400 years, linked with a warm climate period known as the Medieval Climate Anomaly. #

Then there was a second period of stable sea level during a cooler period called the Little Ice Age. It persisted until the late 19th century.

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Since the late 19th century, sea level has risen by more than 2 millimeters per year on average, the steepest rate for more than 2,100 years. #

"Sea-level rise is a potentially disastrous⁹ outcome of climate change," says Horton, "as rising temperatures melt land-based ice, and warm ocean waters." #

To reconstruct sea level, the scientists used microfossils（微化石） called foraminifera（有孔虫类） preserved in sediment¹⁰ cores extracted from coastal salt marshes¹¹ in North Carolina. The age of the cores was estimated using radiocarbon dating and other techniques.#p#分页标题#e#

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To test the validity of their approach, the team compared its reconstructions¹² with tide-gauge measurements from North Carolina for the past 80 years, and global tide-gauge records for the past 300 years. #

A second reconstruction from Massachusetts confirmed their findings.

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The records were corrected for contributions to sea-level rise made by vertical¹³ land movements.

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The reconstructed changes in sea level over the past millennium¹⁴ are consistent with past global temperatures, the researchers say, and can be determined¹⁵ using a model relating the rate of sea level rise to global temperature.

"Data from the past helped calibrate¹⁶ our model, and will improve sea level rise projections under scenarios of future temperature increases," says Rahmstorf.

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