 The climate debate is over, said US presidential candidate John McCain |
Delegates agreed that developing countries would also have to meet targets for cutting greenhouse gas emissions, as well as rich countries.
The informal meeting also agreed that a global market should be formed to cap and trade carbon dioxide emissions.
The non-binding declaration is seen as vital in influencing a replacement for the Kyoto Protocol, correspondents say.
The forum's closing statement said man-made climate change was now "beyond doubt".
"Climate change is a global issue and there is an obligation on us all to take action, in line with our capabilities and historic responsibilities," said the statement from the Global Legislators Organisation for a Balanced Environment (Globe).
'Tipping point'
The two-day meeting brought together legislators from countries including the Group of Eight rich nations, plus Brazil, China, India, Mexico and South Africa.
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The BBC's environment analyst Roger Harrabin was at the meeting and says that although the declaration carries no formal weight, it indicates a real change in mood.
The legislators agreed that developing countries had to face targets on greenhouse gas emissions, in the same way rich countries do.
They said they wanted a successor to the Kyoto Protocol - which expires in 2012 - in place by 2009.
US senator Joe Lieberman forecast that the US Congress would enact a law on cutting emissions by the end of next year, possibly this year.
And presidential candidate John McCain, who is co-sponsoring climate legislation with Mr Lieberman, was emphatic on the need for new initiatives.
"I am convinced that we have reached the tipping point and that the Congress of the United States will act, with the agreement of the administration," he told the forum.
But Dr John Holdren, the head of the American Association for the Advancement of Science (AAAS), said President George W Bush needed to appreciate that the US economy would not suffer unnecessarily if emission were capped.
"The economic damage from not addressing climate change is much larger than the economic cost of addressing it," he said.
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Meanwhile, the Canadian parliament moved to force the government to meet its Kyoto Protocol target for reducing emissions.
The ruling Conservative party argues that meeting the target, of reducing emissions by 6% from 1990 levels by the period 2008-2012, is impossible.
The parliamentary vote gives the government 60 days to formulate a plan for getting back on track.
With United Nations climate negotiations in November failing to agree a timetable for mandating new cuts in emissions when the current Kyoto targets expire in 2012, the British-led Globe set up the Washington meeting in the hope of stimulating progress in a less formal setting.
The UN's panel on climate change said earlier this month that higher global temperatures caused by man-made pollution would melt polar ice, worsen floods and droughts and cause more devastating storms.
