World sea levels will keep rising for more than 1,000 years even if governments manage to slow a projected surge in global temperatures this century, a draft United Nations climate report says.
The study, by a panel of 2,500 scientists who advise the UN, also says that dust from volcanic eruptions and air pollution seems to have slowed warming in recent decades by reflecting sunlight back into space, scientific sources said.
The Intergovernmental Panel on Climate Change (IPCC) will publish its report, the most complete overview of climate change science, in Paris on February 2nd after a final review.
It will guide policy makers combating global warming.
The draft projects more droughts, rains, shrinking Arctic ice and glaciers to 2100 and cautions that the effects of a build-up of greenhouse gases in the atmosphere will last far longer.
"Twenty-first century anthropogenic [human] carbon dioxide emissions will contribute to warming and sea level rise for more than a millennium, due to the timescales required for removal of this gas," the sources quoted the report as saying.
The report has good news by quoting six models with central projections of sea level rises this century of between 28 and 43 cm (11 and 16.9 inches) - compared to a far wider band of 9 to 88 cm (3.5 to 34.6 inches) in a 2001 report, they said.
Sea levels rose by 17 cm (6.7 inches) in the 20th century. Rising seas would threaten low-lying Pacific islands, coasts from Bangladesh to Florida and cities from Shanghai to Buenos Aires.
The report says there is a 90 per cent likelihood that human activities, led by burning fossil fuels, are to blame for warming since 1950. The previous report in 2001 said the link at least 66 per cent.
Lingering uncertainties include whether higher temperatures will bring more clouds which bounce heat back into space.
IPCC chairman Rajendra Pachauri said: "I hope this report will shock people, governments into taking more serious action as you really can't get a more authentic and a more credible piece of scientific work."
The draft projects temperatures will rise by 2 to 4.5 Celsius (3.6 to 8.1 Fahrenheit) above pre-industrial levels with a "best estimate" of a 3C (5.4 F) rise, assuming carbon dioxide levels are stabilised at about 45 per cent above current levels.
The European Union says any temperature rise above 2C will cause "dangerous" changes.