Tony Blair has begun his last full day as British prime minister with a visit from California governor Arnold Schwarzenegger at Downing Street.
Mr Blair, who will resign after prime minister's questions at lunchtime on Wednesday, discussed environmental issues with the former film star.
The two politicians agreed a deal last year to commit California and the UK to developing low-carbon economies.
Mr Schwarzenegger and Mr Blair also visited an eco-friendly school.
At a joint press conference, Mr Schwarzenegger said it was crucial to show leadership is getting other countries to commit to lowering carbon emissions, particularly as the US has 5% of the world's population with 25% of greenhouse gas emissions.
Mr Blair said: "The important thing now is that we have global agreement, we have the possibility of making progress.
"There was no way this thing is going to work unless there is a deal with not just America and the developed world in it, but with China and India in it too."
On a personal note, Mr Schwarzenegger thanked Mr Blair for his "great leadership and great friendship".
On Wednesday, the prime minister - who recently completed 10 years in office - will formally resign, to be replaced by Chancellor Gordon Brown.
Austrian-born Mr Schwarzenegger - a former Mr Universe and the star of films such as The Terminator and Total Recall - has been Californian governor since 2003.
He is expected to be the last foreign official to visit Mr Blair in Downing Street.
Reporters questioned Mr Blair about how effective he thought he could be in a new international position after he leaves office.
But Mr Blair said: "I don't know, because I am not retired yet.
"Maybe one of the benefits when I do step down - and I remember President [Bill] Clinton once saying this to me - is you can then focus on specific issues with a greater intensity than when you are having to deal with the whole gamut of issues as prime minister. We will see."
Mr Blair has refused to say publicly what he plans to do after he resigns, but the quartet of Middle East mediators are meeting in Jerusalem to discuss making him its envoy to the region.
Representatives from the EU, Russia, the UN and the US will attempt to agree exactly what the scope of the job should be, and how in practice it should work, the BBC's Tim Franks in Jerusalem says.
The Bush administration has already signalled its desire for an expanded role for Mr Blair.
The Russians have been cooler, but diplomats say they do not expect Russia to block his appointment.
Mr Blair has said several times that he is committed to advancing peace between Israel and the Palestinians.
Asked what job he would like to see Mr Blair in, Mr Schwarzenegger said he "would feel good" if Mr Blair did become a Mid-East envoy.
"He is without doubt a great, great diplomat and very, very knowledgeable about this."
But he also said "selfishly", he would like to see him as an "envoy for the environment", bringing "all of the countries together to join some kind of treaty".
"Maybe he can take on both of the challenges," Mr Schwarzenegger said.
Mr Blair jokingly told the assembled media at Downing St: "This will be the last press conference I will be giving to you guys.
"That's something I'm really going to miss."
Also on Mr Blair's final full day, the University of Liverpool established a professorship to mark his contribution to peace in Northern Ireland.
The £5m "Blair Chair" has been created and funded by the Irish government.