Sea level rise doubles in 150 years

Increase blamed on fossil fuel use since 19th century·Cut in greenhouse gases futile, researchers say

November 25, 2005
Ian Sample, science correspondent
The Guardian

Global warming is doubling the rate of sea level rise around the world, but attempts to stop it by cutting back on greenhouse gas emissions are likely to be futile, leading researchers will warn today.

The oceans will rise nearly half a metre by the end of the century, forcing coastlines back by hundreds of metres, the researchers claim. Scientists believe the acceleration is caused mainly by the surge in greenhouse gas emissions produced by the development of industry and introduction of fossil fuel burning.

Today's warning comes from US researchers at Rutgers University in New Jersey who analysed cores drilled from different sites along the eastern seaboard. By drilling down 500 metres through layers of different sediments and using chemical dating techniques, the scientists were able to work out where beaches and dry land were over the past 100m years.

The analysis showed that during the past 5,000 years, sea levels rose at a rate of around 1mm each year, caused largely by the residual melting of icesheets from the previous ice age. But in the past 150 years, data from tide gauges and satellites show sea levels are rising at 2mm a year.

"The main thing that has happened since the 19th century and the beginning of the modern observation has been the widespread increase in fossil fuel use and more greenhouse gases," said Professor Kenneth Miller, who led the study. "We can say the increase we're seeing is much higher than we've seen in the immediate past and it is due to humans."

The rising tide is expected to make oceans 40cm higher by 2100. "This is going to cause more beach erosion. Beaches are going to move back and houses will be destroyed," he said. Rising sea levels will also add to the destructive power of storm surges triggered by hurricanes such as Katrina which battered New Orleans and surrounding areas this year.

The research, published in the US journal Science, comes a week before the countries that embraced the Kyoto protocol meet for the first time in Montreal to discuss future agreements for cutting carbon dioxide and other greenhouse gas emissions further. While Britain has adopted the protocol, the government has suggested that voluntary targets rather than the mandatory cuts demanded by Kyoto could be a more practical way to trim greenhouse gas emissions.

According to Prof Miller, there is little chance of slowing the rising tide caused by global warming. "There's not much one can do about sea level rise. It's clear that even if we strictly obeyed the Kyoto accord, it's still going to continue to warm. Personally, I don't think we're going to affect CO2 emissions enough to make a difference, no matter what we do. The Bush administration should stop asking whether temperatures are globally rising and admit the scientific fact that they are, but then turn the question around politically and say: 'We can't really do anything about this on any kind of cost basis at all'," he said.

In two further studies, also published in Science, a team of German researchers put figures on the extent to which the climate is warming compared with any time during the past 650,000 years. They report that levels of the most ubiquitous greenhouse gas, carbon dioxide, are rising 200 times faster than could be caused by any natural process. Carbon dioxide levels are now 380 parts per million, some 27% higher and methane levels 130% higher than at any time over the period they analysed.

The researchers measured levels of greenhouse gases locked into a core of ice drilled from Antarctica. At more than 3km long, the ice core holds pockets of air that were in the earth's atmosphere from nearly 1m years ago until the present day.

The cores are the best record left on the planet of the earth's environmental history. By analysing the gases locked up in 10cm chunks of ice, the researchers can reconstruct the gases that made up the atmosphere at any time from present day until before the four previous ice ages.

"If you really want to make a case for global warming, you just have to look at the past 1,000 years, because the current increase in carbon dioxide stands out dramatically," said lead author Dr Thomas Stocker at the Physics Institute of the University of Bern, Switzerland.

Ed Brook, a climate scientist at Oregon State University said the rise in greenhouse gases ... was a stark indication of the influence industry was having on the environment. "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. There is now no question this is due to human influence."