Bono and Bill Gates of Microsoft argue for a better deal for the poor of the world in 2005.

There are moments in history when civilisation redefines itself. Times when momentum builds to bring down a status quo that people are no longer willing to accept. The abolition of slavery was one. So were the fall of the Berlin Wall and the end of apartheid.

When it comes to the wanton loss of lives to extreme poverty and disease, 2005 might be such a moment. Right now it seems unthinkable: the year has begun on an incomprehensibly tragic note in Asia. Yet momentum has been building to make this the year when the world finally gets serious about changing the future for its poorest people. The coming 12 months are a test for us all - especially the leaders of G8 nations, whose vision and resolve have never been more on the line.

History's judgment will be harsh if we fail, precisely because we are the first generation with the power to succeed. New tools and ideas are creating opportunities that were, very recently, unthinkable. Conventional wisdom used to be that foreign aid could not buy measurable results. That attitude - with its ally, indifference - is eroding in the face of dramatic progress, particularly in health.

Diseases that have wiped out generations of poor people are now, themselves, on the brink of extinction. Fifteen years ago, polio afflicted 350,000; today, that number is 800, and could soon be zero. In the past five years, increased immunisation has saved the lives of half a million children, a number that could triple over the next decade.

Another old, unjust idea is fading: the notion that poor countries, shackled by old Cold War debts to the richest countries, have to pay us back, no matter the cost in human suffering. Now that wealthy nations are writing off some of that debt, the poorest countries have been able to boost their spending on other urgent priorities such as health and education. Uganda, for example, has used its savings to double the number of children in primary school.

More than ever, the world knows what works. Five years ago, world leaders vowed to make it work even better, in more places, for more people. A set of Millennium Development Goals pledged to the world's poor that, in this new century, basic human needs would finally be met. Food, clean water, health services and education would be the birthright of every child.

Heads of state are talking seriously not just about fighting disease and deprivation, but about ending them. After a decade of declining aid flows, some wealthy countries are stepping up to their pledges to do more, including Britain. In 2005, Britain's role in the chair of the G8 group of nations and as president of the EU means that Tony Blair and Gordon Brown are ideally placed to broker a much better deal from other countries.

The temptation to trim or cut back is a strong force in nations facing budget pressures. This has to be weighed against the costs of inaction. In Africa today, 10 million Aids orphans need care because their parents could not get access to anti-retroviral drugs. There may be 20 million more by 2010. Surely it's cheaper, smarter and easier to prevent fires like these from starting than to stop them once they're raging.

Only one of us is known for crunching numbers. But we both believe that investments in human potential pay off many times over. They have the power to end extreme poverty. But only if we learn to think big again.

The Marshall Plan, which rebuilt Europe after the Second World War and became a bulwark against Soviet expansion, cost the United States two per cent of its GDP over four years. Today, in tense, nervous times, an investment of less could not only transform more people's lives, but also transform the way those people see us.

Our momentum, then, is real but fragile. This year brings a unique convergence of global summits, progress reports, and negotiations on debt, trade and effective aid. The acronyms - G8, UN MDGs, WTO, IMF - cause eyes to glaze, but they amount to the best chance yet for the world to learn from its successes and to keep moving forward.

For a start, we hope that the leaders of every developed nation will resolve to take four crucial steps in 2005. The wealthy world has already committed itself to some of these ideas. Promises made must be promises kept.

First: double the amount of effective foreign assistance - possibly through the International Finance Facility, a UK proposal to frontload aid and get it flowing immediately.

A British- and French-backed initiative using the same principles is ready to roll now and could save five million lives by increasing child immunisation.

Second: finish the job on poor countries' debts. They need more than relief - they need full debt cancellation.

Third: change unfair trade rules, creating a pathway for poor countries to reach self-reliance.

Fourth: provide funding for the Global HIV Vaccine Enterprise, a more aggressive and coordinated approach to developing an HIV vaccine.

In these and other ways, our governments can make history - and we must demand that they do so. That is why, three days into the year, "2005" movements have already taken root, bringing unlikely allies - CEOs and NGOs, pop stars and priests, mothers' unions and student unions - together in a global campaign for justice.

The story of 2005 will have its leaders and laggards, and in a year's time it will be clear to all of us who was which. In the meantime, it is up to us how we want our generation to be remembered. For the internet? Or the war on terror? Or for finally deciding that where a child happens to live will no longer determine whether that child gets to go on living?

Lines of latitude and longitude are stronger than any Iron Curtain and divide us more than apartheid. The world has the resources and the technology to change all this. The question to be answered in 2005 is whether we can summon the will.'

Bill Gates is chairman of Microsoft and co-founder of the Bill & Melinda Gates Foundation.

More on DATA (Debt, Aids, Trade, Africa), co-founded by Bono, here - http://www.data.org/