If I'm still around in the year 2050 the fact will count as a tribute to medical science, but a severe blow to the bookies. Many of you would probably say the same. The leaders of the G8, chatting about food prices and world hunger over some doubtless exquisite Hokkaido sushi, are also certainly old enough to be acquainted with the idea of mortality.

It works like this: nothing that happens to be going on in mid-century will make the slightest difference to them. No careers will be at stake; no public clamour will touch them; no reputations, other than of the posthumous variety, will be at risk of stain.

What better date to set, then, for victory celebrations in the battle to cut carbon emissions? Fifty per cent by 2050: it has a nice rhetorical symmetry. It also counts as a small gift to the summit's Japanese hosts, who have pinned their hopes on global "progress" in tackling climate change. Clearly, and luckily for them, the government of Yasuo Fukuda has no deep knowledge of the 33-year history of (variously) G5, G7, G8 or G8 "plus".

Anyone who knows even a little better is liable to think: "Here we go again." That 50% cut is, after all, merely the minimum reduction most scientists in the field want now, today - or, better still, a lost decade ago. The fact that a self-selecting group of world leaders will not commit itself to targets, or even vague aspirations, involving years less distant than 2050 is also revealing. One non-revelation: at this rate, it simply won't happen. And they know it.

Signing up to 2050 involves neither effort nor cost. George Bush, biggest obstacle of them all, will be gone by the year's end, far less the planet's end. He has convinced himself, in any case, that by the time the century is half-done, gee-whiz technologies will have painted the skies blue and caused every car to run on soda pop.

His G8 partners are equally myopic, self-seeking or hemmed in by domestic concerns. Isn't Green Gordon Brown facing yet another rebellion from back-bench Labour MPs, this time questioning his real commitment to the environment? Elsewhere, a game of liars' poker is going on between the industrialising and the industrialised. But this much I do believe: a form of words postponing reality until 2050 was actually the best the G8 was ever likely to offer.

Which brings us to a now traditional summer season question: what is this august and mighty grouping for? The answers are very hard to come by. When the G8 circus came to Gleneagles in 2005 I wrote a good deal of sceptical stuff in these pages about pious rhetoric and reality. Sometimes it's really no fun being right.

It was cheering, back then, to see so many people determined to "make poverty history". It was depressing, meanwhile, to hear Bob Geldof talk as though he knew nothing about the miserable history of these summits, from the first "fireside gathering" at Rambouillet in 1975 onwards. Sir Bob is available for optimistic interview again this week, I see. Best of luck.

But what actually happened with that Gleneagles pledge, solemn as you like, to increase overseas aid, 50% of it for Africa, by $50bn - how neat can numbers be? - by 2010? There are 17 months to go and rich countries are feeling a touch strapped. There are also rich countries, though Britain has been better than most, who clearly had no intention of honouring their solemn pledges.

A low-cost programme to provide mosquito nets has had a remarkable impact on the incidence of malaria in parts of Africa. Reforms to aid and trade - essentially no more complicated - have been harder to come by. You might wish to add that the developing world made certain hollow promises of its own in 2005 concerning democracy, conflict and corruption. But the onus rested, in the nature of such things, on the rich and powerful. The record is pitiful.

This is not, as some would have you believe, because the club of the prosperous lacks power. There is a difference between the absence of capability and the absence of will. NGOs and transnational corporations alike do not despatch hosts of lobbyists to these summits because they believe the G8 is impotent. Some hope to see it flex its muscles; others intend to prevent the very possibility. But the idea that the group "can do nothing" is a myth. All is choice.

So 2050 is chosen. So the choice is made to regard the ramping of food and oil prices as a mere "concern" for the leaders of the world's biggest economies. To say otherwise among the G8 leaders would be like swearing in church. Better the invisible hand than the blasphemous admission that a speculative bubble has put hundreds of millions, perhaps billions, of people are real risk.

The leaders know perfectly well that speculative trades in commodities futures have shot up recently, and have matched price spikes so neatly as to render coincidence impossible. Some responsibility can, of course, be ascribed to Far Eastern demand, biofuels, Australian droughts or the imminence of peak oil. But what the G8 will not, cannot, explain to domestic audiences is a failure in their holy writ.

That's the simplistic one about supply-demand-price. The home audience knows all about prices. It can understand new sources of demand. So is there an actual shortage, anywhere, of oil or of food? Is there even a true increase in physical demand for the black stuff, whose price is having such an effect on food producers? No, emphatically. Third World food riots and British fuel protests are solely to do with price.

Yet there is nothing, apparently, that the G8 can do. Nothing, that is, save to make matters worse. The carbon emissions target offers a clear, parallel argument. What is the postponement of a real concerted effort, after all, if not a signal to interested players in the market?

Let's call them, for three examples, oil giants, car makers and developing nations. Each could have faced some very difficult choices if the Eight had chosen to take the planet's future seriously. In each case - and in many others - the pressure to think hard and develop strategies has been relieved. Have not the leaders of the global economy put everything, no pun intended, on the back burner? I think I'll start a hedge fund.

There is a contradiction, of course, in complaining about the failures and broken promises of the G8. Speaking personally, I'm fairly sure I have never voted for some sort of all-powerful world government with George Bush and Silvio Berlusconi at the top table. You cannot usefully talk of the group's stance on Zimbabwe, for example, without wondering about democratic legitimacy.

But these, severally, are our democratic leaders, more or less. They make speeches, they make fine promises, and they abdicate their responsibilities without a backward glance. It may be naive to expect more. But when capitalism's club offers mere platitudes in the face of capitalism's most profound crisis in seven decades, it is remarkable that we can be offered so much less.

I only hope that whoever is the last to leave in 2050 will still have a light to turn off.