UN and EU officials have welcomed the US declaration that greenhouse gases are threatening to human health.

联合国和欧盟官员对于美国关于温室气体威胁人类健康的宣言表示欢迎。

An EU spokesman said the announcement showed "a degree of resolve" on the part of President Barack Obama to address climate change.

The US move came as delegates代表 from 192 countries got down to work at the UN climate summit in Copenhagen哥本哈根.

Danish PM Lars Loekke Rasmussen has said the summit is an "opportunity the world cannot afford to miss".

The US declaration could mean the Environmental Protection Agency (EPA) can order cuts in emissions¹ without the approval of Congress.

Rajendra Pachauri, chairman of the UN scientific network on climate change, said the Obama administration was "showing what it can do, even while legislation is pending²".

"It also sends a powerful signal to Congress. It shows a degree of resolve on the part of the president," he told the Associated Press news agency.

The environment minister for Sweden - which currently holds the EU presidency³ - said the outcome of the summit depended mostly "on what will be delivered by the United States and China".

Andreas Carlgren said he would be "astonished惊讶的" if US President Barack Obama did not offer further concessions优惠 when he arrives at the summit next week.

The BBC's Mark Mardell in Washington said the US announcement had been expected for some time, but still sends an important signal to leaders attending the summit that Mr Obama is intent on passing legislation to curb抑制，束缚 emissions.