Scientists warn UN "drastically under-estimated" climate change costs

The global cost of adapting to global warming will be many times greater than the official estimates currently being considered by international negotiators preparing to take part in the UN's Copenhagen talks.

That was the stark warning issued yesterday as part of a major new report on the cost of adapting to climate change published by the Grantham Institute for Climate Change at Imperial College London and the International Institute for Environment and Development.

Currently, the UN's climate secretariat, the UNFCCC, estimates that the costs of adapting to climate change will total between $40bn (£24.4bn) to $170bn a year up to 2030, dependent on the pace of global warming.

However, report lead author Professor Martin Parry, former co-chair of the Intergovernmental Panel on Climate Change (IPCC), said that this estimate had been developed "in a matter of weeks" by the UNFCCC and excluded a huge range of potential adaptation costs.

For example, the costs associated with the adaptation or protection of the energy, tourism, manufacturing, retail and mining sectors, as well as the economic costs arising from damage to ecosystems were all left out.

"Just looking in-depth at the sectors the UNFCCC did study, we estimate adaptation costs to be two to three times higher, and when you include the sectors the UNFCCC left out the true cost is probably much greater," he warned.

The new report also argues that where the UN has analysed adaptation costs it "substantially underestimates" the scale of spending required.

For example, the UNFCCC's estimate that adapting to changes in water distribution will cost $11bn a year fails to include any costs arising from adapting to increased flood risk, nor the cost of transferring water to drought-afflicted areas.

Similarly, the official estimate that the increased incidence of climate-change related diseases will cost $5bn excluded developed nations and only assessed malaria, diarrhoea and malnutrition.

"The costs of adapting to live with a changing climate are very uncertain," said Professor Sir Brian Hoskins, director of the Grantham Institute. "However, this new study suggests that previous attempts to figure out the costs have drastically under-estimated how expensive this could be."

The report was released as the countdown to the UN's crucial climate change meeting in Copenhagen today entered its last 100 days.

Camilla Toulmin, director of the International Institute for Environment and Development, said that there was an urgent need for the UN to update its estimates on adaptation costs. "Finance is the key that will unlock the negotiations in Copenhagen but if governments are working with the wrong numbers, we could end up with a false deal that fails to cover the costs of adaptation to climate change," she said.

A spokesman for the UNFCCC defended the original estimates, telling the BBC that they represented the "best estimates" available in 2007 when the original study was undertaken, and that the UN had to "err on the side of caution".

However, a consensus is growing that both the UN's cost estimates and the official IPCC report on climate change on which the Copenhagen process has been based are now out of date and that the threat presented by climate change is even more grave than first thought.

Earlier this year, a meeting of 2,000 climate scientists in Copenhagen concluded that the latest scientific evidence suggests temperatures are currently rising in line with the IPCC's worst-case scenarios.