A study has shown that world sea levels are rising at a rate of 2mm (0.08 inches) a year; double the speed at which levels rose for 5,000 years before the start of the industrial age.

The switch occurred after the mid-19th century, when factories and increased use of coal and later oil started pouring greenhouse gases into the atmosphere.

Kenneth Miller, a professor at Rutgers University in New Jersey, and colleagues produced a new sea level record spanning 100 million years.

They took five 500m-deep (1,640ft) core samples from sediments along New Jersey’s coastline. A study was then made of the sediment type, the fossils it contained and variations in the atomic forms, or isotopes, of elements.

These measurements were correlated with others from around the world, enabling sea levels to be calculated.

Some of the findings, published in the journal Science, were surprising. They showed that during the Late Cretaceous period, at the end of the dinosaurs’ reign, sea level frequently fluctuated by tens of metres.

Only changes in the size of the ice caps could produce these fluctuations, showing that the Earth was not ice-free at this time in its history, as most experts had thought.

The team found that over the period, sea levels had been steadily rising at about 1mm a year until the Industrial Revolution. Since then, the rise had doubled.

Professor Miller said: “The main thing that’s changed since the 19th century and the beginning of modern observation has been the widespread increase in fossil fuel use and more greenhouse gases. Our record therefore provides a new and reliable baseline to use in addressing global warming.”

A second paper in Science states that the levels of global warming gases such as methane and carbon dioxide have steadily risen.

Ed Brook, a professor at Oregon State University in Corvallis, and colleagues analysed ancient bubbles in Antarctic ice cores.

The results add another 210,000 years to knowledge of the make-up of the atmosphere, and confirm that levels of greenhouse gases have risen dramatically since the Industrial Revolution.

The results, he said, made it clear that the conditions of the past 150 years were unusual.

“The levels of primary greenhouse gases such as methane, carbon dioxide and nitrous oxide are up dramatically since the Industrial Revolution, at a speed and magnitude that the Earth has not seen in hundreds of thousands of years,” he said.

“There is now no question this is due to human influence.”

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