By Roger Harrabin
BBC environment analyst
Leading US politicians are meeting legislators from the EU, China, Japan and India to seek a breakthrough in the international climate deadlock.
Emissions targets have proved a sticking point
The meeting, organised by British-run parliamentarians' group Globe, is strongly supported by the UK Prime Minister Tony Blair.
On Thursday, it will publish recommendations for a new world deal on climate change at the G8 summit.
G8 leaders will be meeting in Germany this summer.
The gathering in the US senate has attracted two presidential candidates - John McCain and the Senate Foreign Relations committee chair Joe Biden.
In addition, four other Senate committee chairs will attend; Joe Lieberman (homeland security); Jeff Bingaman (energy), Olympia Snow (finance) and Barbara Boxer (environment).
US climate-watchers say it is an indication that since the mid-term elections the US is shifting towards re-joining the international fold on climate.
It is highly likely, they believe, that even if President Bush continues to refuse mandatory emissions cuts the next president will want to return to the fray.
But this is a complex equation.
Many Republicans still demand that the competitor economies of China and India accept emissions cuts to prevent industry being re-located without any benefit to the global atmosphere.
Presidential hopeful John McCain is among the delegates
This question will need somehow to be addressed, but China and, particularly, India are outraged that the US refuses to take the lead in emissions cuts when it has much higher pollution per person and has signed the 1992 UN Framework Convention on Climate Change, which obliges rich nations to reduce emissions first.
It is perhaps unsurprising that the only Indian delegate to the meeting has dropped out.
Mr Blair hopes the Globe (Global Legislators Organisation for a Balanced Environment) forum will clear the way for a historic agreement between the G8 and five biggest developing nations on a stabilisation goal for greenhouse gases - a limit beyond which the world should not pass.
He also wants to see a global price for carbon and a big increase in the funds available for developing countries to expand their economies more cleanly.
If a stabilisation goal is agreed it could prove a surprising legacy for Mr Blair - depending on the CO2 level agreed.
But without a matching deal on mandatory cuts for the US it could amount to little more than a resolution in a student flat that someone needs to do the washing up.
In the diplomatic game we are still lagging behind 1992 when the Framework Convention clearly delineated responsibilities, or 1997 when the US promised to cut emissions as part of the Kyoto Protocol.
Signs of hope may lie in the steely scientific consensus on the human origins of climate change and in the increasing recognition by big business that something must be done - a message that major corporations are transmitting clearly to the White House.
But the major stumbling block remains the President's Office itself.
While Congress moves steadily greenwards, America's policy remains dictated by a knot of advisers in the White House Council on Environmental Quality with close links to the oil industry. It is not yet clear whether they will attend this week's meeting.