The rise in sea levels seen over the past century is unmatched by any period in the past 6,000 years, according to a long-lasting analysis of historical sea level trends.
The reconstruction（再现）of 35,000 years of sea level fluctuations（变动）finds that there is no evidence that levels changed by more than 20cm in a relatively steady period that lasted between 6,000 years ago and about 150 years ago.
This makes the past century extremely unusual in the historical record, with about a 20cm rise in global sea levels since the start of the 20th century. Scientists have noted rising temperatures, which have caused polar ice to melt and thermal expansion of the sea, as a primary cause of the sea level increase.
The 35,000-year span of the study was chosen as this consists of an interglacial period. Researchers could pick submerged sediments（沉淀物）that may include tree roots, suggesting a previously lower sea level.
Ice started melting about 16,000 years ago, with this melting ending about 8,000 years ago. A slowdown in sea level changes didn’t occur until 6,000 years ago, however.
“It’s like if you leave a big block of ice on the table, it doesn’t melt immediately, there’s always a delay in the system,” said Kurt Lambeck, who led the research. “We know from the last interglacial period that when temperatures were several degrees warmer than today there was a lot more water in the oceans, with levels around 4 to 5m higher than today. The question is how fast that change occurs when you increase temperatures.”
Lambeck said the sea level increase of the past 100 years is “beyond dispute”, backed up by separate data from salt flats and also changes to the sea floor caused by the extra weight of water.
“All the studies show that you can’t just switch off this process. Sea levels will continue to rise for some centuries to come even if we keep carbon emissions at present day levels,” he said.
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