Leading article: Two cheers for Gordon

Almost immediately after the G20, therefore, the bear market began. Mr Brown's numbers did not add up and were savagely denounced as "spin". Well, a sober reflection on the deal, such as Hamish McRae's on page 13 today, suggests that, while there was little new agreed last week, much of its importance lay in the mere fact of agreement. The symbolism should not be underestimated. An economic system of paper money – or, today, digital money – depends on confidence. Last week's deal helped to prevent its collapse.

Nor should we deprecate the power of apparently empty words. That the leaders of countries accounting for four-fifths of the world's economy put their names to a declaration against protectionism will help to hold the line against countries seeking advantage by doing down their neighbours.

So far, by Thursday, so good. Then it was on to Strasbourg for the Nato summit. If an economic crisis concentrates minds, and warm words are sufficient to hold together the different policy responses of nation-states, then the military challenges to our security are more difficult. That does not mean that Barack Obama – or Mr Brown – have gone from heroes on Thursday to zeroes on Saturday. Assuming, as we do, that the US and the UK are bearing their fair share of the military burden in Afghanistan, persuading the rest of the world to assume its responsibilities has been as inconclusive as the struggle against the Taliban for the past eight years. Yesterday's deal temporarily to supply up to 4,000 non-US/UK troops was welcome, but hardly enough.

Nor was the mere fact of a Nato summit in Strasbourg likely to affect the complex diplomatic effort to restrain North Korea's nuclear missile ambitions. Equally, yesterday's meeting had no prospect of resolving the alliance's troubled relations with Russia: applications from Georgia and the Ukraine to join Nato remain on the shelf.

This Nato summit was never going to achieve great things. We are reduced, therefore, to praising it for holding firm by appointing Anders Fogh Rasmussen as secretary general against the objections of illiberal opinion in Turkey. (The Turkish government initially resisted the Dane's appointment because he had defended the right to publish the Mohammed cartoons.)

Whereas the 50th anniversary of Nato coincided with one of its most important challenges, the Kosovo conflict, which prompted a fundamental and welcome recasting of its role, the 60th passes without any comparable significance.

Now the caravan of summitry moves on. Next stop, the combined G8 and other "major economies" meeting in La Maddalena, Sardinia, in July. (This is a "G17": Argentina, Turkey and Saudi Arabia are not invited.) This meeting is intended to pave the way for a global deal on climate change at Copenhagen in December. Now this really is important, because the one tough decision that was postponed last week was, as many of the protesters' banners declared, action to deal with the "climate crunch".

That was the real missed opportunity of the Brown-Obama mutual admiration society. All the difficult choices were shuffled off to a separate strand of talks currently being held in Bonn. These talks, as Geoffrey Lean, our Environment Editor, reports on page 12 today, are going badly. Now, too much depends on a ministerial-level meeting in Washington at the end of this month to prepare for La Maddalena. Precious time has been lost, as has the chance decisively to link action to ward off a global slump with that to save the environment – the so-called Green New Deal that this paper has championed.

Considered assessment of last week's jaw-jawing, therefore, should be pitched between the hyperbole of Friday morning's headlines and the determined negativity of the critics of international summits in general and Mr Brown in particular. As we said last week, the Prime Minister deserves praise for what was agreed at the G20, even if it was rather less than he claimed. But he and other world leaders deserve criticism for what was barely discussed: namely, the difficult choices that all governments and all citizens, especially of the rich countries of the world, have to face if the worst effects of climate change are to be averted.