"You have opened a window on our future. Looking through that window, we see a future in which global warming will reshape our planet and our society," House of Representatives speaker Nancy Pelosi said in a hearing with four scientists who contributed to the report, which was released in Paris last week.

"We also see a future in which harsh consequences could be blunted by our prompt action," the Democrat leader said.

Scientists from the UN's Intergovernmental Panel on Climate Change on February 2 delivered their starkest warning yet about global warming, saying fossil fuel-related pollution would raise temperatures this century, worsen floods, droughts and hurricanes and melt polar sea ice.

Pelosi told the hearing Thursday that "scientific evidence suggests that to prevent the most severe effects of global warming, we will need to cut global greenhouse gas emissions roughly in half from today's levels by 2050."

"The Bush administration continues to oppose mandatory limits on greenhouse gases, restating this position immediately upon the release of the IPCC report," charged Pelosi, who in January asked for the creation of a special committee on US energy independence and climate change.

On Thursday Pelosi underscored that she has asked all House of Representatives committees with jurisdiction over energy and the environment to submit draft legislation on these issues by July.

Pelosi additionally called on the United States to press Beijing to get a Chinese commitment to cooperate on clean and renewable energy sources.

"The US and China are the two largest contributors of carbon dioxide emissions in the world, and it's estimated that China will surpass the US in just three years."

Currently the United States is responsible for 25 percent of global carbon dioxide emissions.

Pelosi's latest offensive on climate change came on the heels of some harsh criticism by Democrats who accused the Bush administration of muzzling government-employed climatologists.

On Wednesday Senator John Kerry blasted a top government environment official over the administration's record reporting climate change data.

"You're not doing your job, the administration is not doing its job, it's a disgrace. You're turning your back on future generations, you're just inviting this catastrophe," he said in a Senate hearing.

If the Bush administration has been less than activist on the issue, the focus on climate change has been growing in intensity among US scientists, business people and some individual states.

California, the most populous and most economically influential US state, recently decided to impose a carbon dioxide emissions reduction.

Though under increasing pressure, President George W. Bush has continued to favor an approach based on voluntary measures. He believes that imposing reductions could have disastrous economic consequences.

White House spokesman Tony Snow on Wednesday said the United States -- despite Bush's refusal to sign the Kyoto protocol -- was doing more than Europe on reducing carbon dioxide emissions. Since 2001 a record 40 billion dollars has been put toward research and development for new technologies to fight climate change, he said.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.