Mr Barroso said talks with the US president had led to progress on climate change Mr Bush saying both sides recognised the severity of the problem.
He told journalists: "We agree there's a threat, there's a very serious and global threat. We agree that there is a need to reduce emissions. We agree that we should work together."
But Mr Bush stopped short of endorsing calls for mandatory caps on carbon emissions.
Dr Merkel, for her part, said the summit had laid the foundations for the G8 summit in June, of which Germany is the head of this year, but she told journalists that in terms of concrete policy "the glass being half full instead of half empty".
She said the G8 must work with 'outreach' countries such as China, South Africa, Brazil and India.
"If we were not doing that, we would not be able to combat this problem that is truly a global one," she said.
She added leaders agreed for 'a proper agenda' for UN talks on the environment in December in Bali.
On this issue, Mr Bush said: "I think that each country needs to recognise that we must reduce our greenhouse gases and deal, obviously, with their own internal politics to come up with an effective strategy that hopefully, when added together, that it leads to a real reduction."
He added: "We will also need to work on this in view of the upcoming G8 summit where we will make it clear, as European Union, as United States of America, that we don't want to isolate ourselves or shut ourselves off against the rest of the world, but where we want to enlist the support of others, invite them to join us."
The 27-nation EU agreed in March to reduce greenhouse gas emissions by at least 20 per cent by 2020.
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