OSLO (Reuters) – World sea levels will keep rising for more than 1,000 years even if governments manage to slow a projected surge in temperatures this century blamed on greenhouse gases, a draft U.N. climate report says.
The study, by a panel of 2,500 scientists who advise the United Nations, also says that dust from volcanic eruptions and air pollution seems to have braked 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 2 after a final review. It will guide policy makers combating global warming.
The draft projects more droughts, rains, shrinking Arctic ice and glaciers and rising sea levels 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.
Still, 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 it is “very likely” — or more than a 90 percent chance — that human activities, led by burning fossil fuels, are to blame for warming since 1950.
The previous report in 2001 said the link was “likely”, or at least 66 percent. Lingering uncertainties include whether higher temperatures will bring more clouds — their white tops bounce heat back into space.
In New Delhi, IPCC chairman Rajendra Pachauri said he hoped the report would shock governments into action.
“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,” he told Reuters.
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 percent above current levels.
That is a narrower range than the 1.4-5.8C (2.5-10.4F) projected in the previous IPCC report in 2001, which did not say which end of the band was most likely. The European Union says any temperature rise above 2C will cause “dangerous” changes.
Stabilising carbon dioxide levels would lead to a further temperature rise of about 0.5C (0.8F), mostly between 2100-2200, and push up sea levels by a further 30 to 80 cm (11 to 31 inches) by 2300 with decreasing rates in later centuries, it said.
It notes that sea levels were probably 4 to 6 metres (13 to 19-1/2 feet) higher when temperatures were 3C higher than the present in a period between Ice Ages 125,000 years ago.
The Gulf Stream, bringing warm waters to the North Atlantic, was likely to slow but not enough to offset an overall warming. And there was scant chance of an abrupt shutdown of the ocean current system by 2100.