G8 or G20 – will it really make much difference to the world?

Is there any point to the continued existence of G8? As this week's summit looks increasingly irrelevant, should we care if the power shifts away to the G20?

President Lula of Brazil has declared that G8 "doesn't have any reason to exist". Next year's hosts, Canada, are being urged by their own commentariat to turn their G8 into a G20. Meanwhile this year's hosts, Italy, are trying to bring more countries into the G8 tent, to reduce the glaring gap between the two. In doing so, they are basically accepting the logic that it's the wrong group of countries to have in the room to address the problems of the world.

Despite the attractions of inclusivity, I have fears that the transfer of power from G8 to G20 might prove more style than substance. G20 leaders need to show they are more willing than G8 have been to take actions that matter for the world's poorest.

The G8's scope seems to be narrowing, with substantive issues increasingly kept for the G20. The big question for the L'Aquila summit is who is keeping the promises they made at Gleneagles in 2005 (not Italy, despite Berlusconi being the only leader in this year's crop who was actually there).

And in the meantime, the shiny new G20 is waiting in the wings. The second meeting of G20 leaders in September to discuss the global financial crisis will be presided over by the world's favourite man, Barack Obama, and will quite likely be able to bask in the glory of success, if the tentative signs of recovery continue to be felt.

At the very least the current situation seems a little inefficient. Two summit dinners. Two rounds of official entertainment laid on for the long-suffering group of G8 spouses. Two huge logistical nightmares for the organising country. And all to pursue what is essentially one agenda of trying to unravel the mess of global governance and the outrage of global poverty by squaring the circle of what poor countries want and what rich countries are prepared to give up.

So why bother? Just read the last rites, declare the show over for the G8, and let the G20 take its rightful place as the photo opportunity of choice for world leaders.

Of course, there would be more competition for the prized spot on Obama's righthand side in the group photocall. But think of the kudos, in these austerity-obsessed times, that G8 leaders could get by cutting out a whole swathe of expensive and increasingly pointless diplomacy – no more stories about what they had for dinner or how much the whole thing cost. Instead, a mature and sensible decision to give up their privileged and exclusive position for the good of global democracy.

That's not quite the end of the matter. The G20 might be, numerically speaking, two and a half times as democratic as the G8, and many hopes for a better world are resting on that fact. But it's still not exactly a bastion of democracy. The majority of the world's countries are still out of the club. And having got in, many of the newly anointed global leaders don't seem willing to widen the net further. Exclusivity can look pretty good from the inside.

From the point of view of the countries outside the room, the difference between the G8 and the G20 might seem a little academic. What they need is a group that will keep its promises. Whether on aid or on climate change or on tax havens, what the poorest countries need is for the richest countries – however they organise themselves – to make the right choices and then stick to them.

If the bigger size of the G20 means better decisions, because more different points of view are represented and, most crucially, because leaders are more likely to force one another to keep their promises, that's when the shift from eight to 20 will start to make an actual difference to the world.

Basically, it's about rich countries being persuaded to give up a bit more money and power for the greater good. Can China and Brazil, for example, force the US to cough up more than the paltry $1bn it recently announced to help the poorest countries cope with the impact of climate change? Would South Africa be any more successful than the UK in making Italy keep its promises on foreign aid? Will the combined weight of India, China, Brazil and South Africa be enough to force the US to give up its position as the world's banker by backing a new reserve currency?

Unless the answer to any of these questions is yes, the supposed big shift in global power embodied in the new-look G20 will be more hype than hope.

Clarie Melamed, head of policy at ActionAid.