Humans cause global warming, US admits

But it has again refused to shift its position on the Kyoto Protocol, an international treaty designed to mitigate global warming which the Bush administration rejected last year.

In a 268-page report submitted to the United Nations, the US Environmental Protection Agency (EPA) endorsed what many scientists have long argued - that human activities such as oil refining, power generation and car emissions are significant causes of global warming.

The White House had previously said there was not enough scientific evidence to blame industrial emissions for global warming.

The submission of the EPA report came on the same day that all 15 European Union nations ratified the Kyoto pact.

At odds with industry

"Greenhouse gases are accumulating in the Earth's atmosphere as a result of human activities, causing global mean surface air temperatures and subsurface ocean temperatures to rise," the report concluded.

"The changes observed over the last several decades are likely mostly due to human activities."

That position is at odds with the president's supporters in the motor, oil and electricity industries - who maintain that more research is needed to be certain of the link between global warming and the by-products of manufacturing.

The United States is the world's largest emitter of so-called greenhouse gases.

Last year, the Bush administration triggered international outrage when it walked away from the Kyoto treaty.

President Bush said the treaty's goal of reduction in emissions would be too costly to the American economy.

Despite the admission of a link between human activities and global warming, the US Government has still refused to ratify the treaty, instead emphasising a voluntary approach to greenhouse gas emissions.

Such an approach is "expected to achieve emission reductions comparable to the average reductions prescribed by the Kyoto agreement, but without the threats to economic growth that rigid national emission limits would bring," the report said.

Areas 'wiped out'

The EPA report also acknowledged that global warming was set to continue - forecasting that total US greenhouse gas emissions will increase by 43% from 2000 and 2020.

The report recommended various adaptation strategies, such as "changing planting dates and varieties to significantly offset economic losses and increase relative yields".

It also concluded that global warming would probably wipe out certain fragile areas altogether.

"A few ecosystems, such as alpine meadows in the Rocky Mountains and some barrier islands, are likely to disappear entirely," the report said.

Environmental groups claim the new report is a major U-turn by the Bush administration.

"[The report] undercuts everything the president has said about global warming since he took office," said Philip Clapp, president of the National Environmental Trust.

Climate change is on the agenda of a global summit on sustainable development taking place in Johannesburg in August.

The US is expected to face heavy criticism at the meeting, especially from the EU, for not doing more to fight global warming.