The US insisted it was committed to protecting the environment, finally giving an official response to questions raised by a British report that warned global warming could devastate the world economy.
By ignoring the problem, the Stern Report released on Monday said, rising sea levels, heavier floods and more intense droughts could displace 200 million people by the middle of the century.
The US is by far the biggest emitter of gases blamed for global warming, yet President George Bush has kept his country out of the Kyoto international treaty to reduce greenhouse gases, saying the pact would harm the US economy.
Responding to questions about the report, White House spokesman Tony Snow told reporters that Mr Bush “has, in fact, contrary to stereotype, been actively engaged in trying to fight climate change and will continue to do so”.
Australia and the United States are the only industrialised countries that have refused to ratify the 1997 Kyoto agreement, which sets targets for 35 countries to reduce carbon emissions that are widely blamed for global warming.
Critics say the battle against global warming can only succeed with the cooperation of the United States and have questioned US policies on climate change.
James Connaughton, the White House environment council chief, said: “The notion that the nations of the world are sitting still is just patently absurd.
“Hundreds of billions of dollars of investment are going into this very important issue, and trillions more will go into it in the coming decades. So our effort is harnessing that as wisely as we can."
Paula Dobriansky, the under secretary of state for global affairs, said the United States has invested more than $20bn over the last five years in research and technology development on the issue.
“Our approach comprises taking actions now. We put significant money into actions now,” she said.
Ms Dobriansky and Mr Connaughton made their comments at an event for the Asia-Pacific Partnership, which joins the United States with Australia, China, India, Japan and South Korea – producers of half the world’s greenhouse gases - in efforts to attract private money for cleaner energy technologies.
The US officials said the six countries have endorsed 98 collaborative projects meant to find new technologies to reduce emissions of carbon dioxide and other gases believed to be warming Earth’s atmosphere.
In the UK, a new Climate Change Bill will include moves to help the UK reduce its emissions from 1990 levels by 60%, by 2050, according to Environment Secretary David Miliband.