Study warns UN sea rise estimates are too conservative

The risk presented by rising sea levels is likely to be far worse than official UN projections, according to a major new study from the US Geological Survey on the threats presented by "abrupt" climate change.

The report claims that while predictions on sea level changes arising from climate change are predictions are "highly uncertain due to shortcomings in existing climate models" the latest evidence suggests rises will "substantially exceed" UN estimates and could reach one and a half metres by the end of the century.

Such a rise would prove disastrous for vast areas of low lying land and coastal cities resulting in hundreds of millions of people be affected by flooding.

The UN's Intergovernmental Panel on Climate Change's most recent 2007 study predicted that sea levels would rise by between 28cm and 42cm by 2100.

However, the new US report, commissioned by the US Climate Change Science Program, claims that the latest observable evidence shows that glaciers in Greenland and the West Antarctic are sliding into the ocean significantly faster than was predicted by the models cited by the UN report. It claims that the potential for the melting of glaciers to accelerate further means that rapid increases in sea levels of over 150cm by the end of the century could result.

US Geological Survey director Mark Myers said that the study effectively " summarises the scientific community's growing understanding regarding the potential for abrupt climate changes".

The study also warned that the south western US could already be beginning an abrupt period of increased drought and that a feed back loop that accelerates the loss of Arctic sea ice meant "rapid and sustained September arctic sea ice loss is likely in the 21st century" – a scenario that has already led to increased geopolitical tensions between countries bordering the Arctic.

The only comfort the report appeared to offer was the conclusion that an " abrupt" release of methane from natural deposits such as Siberian permafrost was unlikely and that while the northward flow of warm water in the upper layers of the Atlantic Ocean will slow by around 25 to 30 per cent it is "very unlikely that this circulation will collapse", as envisaged in the disaster movie The Day After Tomorrow.

The report will come as a stark warning to political and business leaders. Rising sea levels represent one of the most potentially damaging effects of climate change and could result in hundreds of millions of climate change refugees and multi-trillion dollar property losses.

A study last year from Organisation for Economic Co-Operation and Development (OECD) warned that a combination of climate change, population growth and urban sprawl meant that up to 150m people in the world's largest coastal cities will be at risk of severe flooding by 2070. It also calculated that the financial impact of coastal floods would also increase more than 10-fold, with $35tr worth of property and infrastructure exposed to increased coastal flood risk by 2070, compared to just $3tr now.

Malcolm Tarling of the Association of British Insurers said that the insurance industry would be assessing the latest study and likely including some of its findings into their risk calculations.

"The industry is constantly monitoring the latest science as it is a changing picture," he said. "Insurers certainly use studies like this and ally that to their claims data – and that also shows that the cost of flooding and weather related claims are increasing."