Whoever it was that said '24 hours is a long time in politics' certainly wasn't kidding. While I'm still feeling worn out by the political frenzy that surrounded last week's G20 summit, even by Saturday the world had moved on.

The story at the weekend was Obama's speech in Prague. And given it's the new president's first official tour of Europe, he's certainly been making the most of it.

In between the invitations for dinner and beers, he managed to deliver a historic speech to an audience of 20,000 (though by his crowd-pulling standards, I imagine it was all in a day's work) where he outlined his vision of a nuclear weapons free world. And from the language he used, and with the intensity with which he spoke, it was clear that he meant what he was saying. A notable moment indeed.

But what much of the world's media missed is that Obama's speech - and the corresponding EU-US meetings - were about more than the need for nuclear disarmament. It was also about the relationship between European nations and the States, and - importantly - climate change. And when there's climate change on the agenda at big, important meetings, then Oxfam's never too far away.

Oxfam activists took the opportunity to dust off the infamous 'big heads' (see the photo above) to restate the point that the clock is ticking down to December's climate change talks.

After the vague political mumblings about "[building] an inclusive, green, and sustainable recovery" that came out of the G20, we had our fingers crossed that the new president was saving the real, gusty climate change policy for the weekend.

No such luck.

The outcome of the EU-US meetings was more talk. Particularly of the 'ambitious' role the EU has taken with regard to tackling climate change (we'd beg to differ), and the need for the EU and US to work together on achieving an 'ambitious outcome' (there's that word again).

Sure, it's language that's a million miles on from the noises the Bush Administration had been making.

Given we've now only eight months until the world must agree how to replace the Kyoto Protocol, there's a pressing need for real commitments to action.

What's all-the-more worrying is that it was the second major meeting in less than seven days where some of the world's most influential heads of state had managed to demote climate change to little more than a footnote.

The EU and US have an unprecedented opportunity to take a truly leading role in the global efforts to fight climate change. And to do so, as international political heavyweights, they will have to work together. But that means not just talk, but action.

That's real action which puts figures for providing adaptation financing (and that means providing poor countries with the cash they need to adapt to the effects of climate change) on the table. Real action that commits to emissions reductions that have a chance of limiting global warming to 2°C. And real action that puts the lives of the world's poorest people - those suffering worst from the impacts of climate change - at the heart of the global deal.

Mr Obama did go so far as to say that "the United States is now ready to lead [on tackling climate change.]" But, in such an important year, we need to see Obama and Co talking with the same language with which he talked about nuclear weapons. And we need to see it now.

Richard Casson, Oxfam campaigner