President George W. Bush made a breakthrough in last week's State of the Union address by pledging $15bn (£9bn) of US support over the next five years to the fight against Aids in Africa and the Caribbean.

Over 20 years, the global pandemic of Aids has ravaged Africa and spread to all corners of the world. The US commitment to increase its spending by $10bn is the first time that an appropriate level of financial resources has been put into the battle by either the US or Europe. Disappointment, however, comes in the fine print.

The US, as is its wont these days, has decided to go it alone. The new programme is designed to be run by US agencies rather than going through the Global Fund to Fight Aids, Tuberculosis, and Malaria, the international initiative that is best placed by far to achieve the global goals of curbing the three pandemic diseases. Of the new US funding, only $1bn over five years is to go through the Global Fund. It is now up to European nations to ensure success in the scaled-up campaign against the killer diseases. They could do so by matching the US financial commitment, and pulling the US back into the fold within the Global Fund.

As a recent convert to the war on Aids, the US administration has latched on to a simplistic vision of what to do, based on the example of a single country - Uganda. It knows little of the measures in place in different parts of the world and has not recognised that each country needs to shape the best local response. It is here that the Global Fund plays an important role.

The fund is organised as a consortium of donors and recipient countries, civil society and business. It is set up to encourage rigorous and sensible plans that meet local needs. Specifically, the fund invites the leading stakeholders within each recipient country - governments, academia, non-governmental organisations, civil society - to prepare a unified national plan. If this is approved by the fund, it is supported by a single pool of unified financing. To ensure results, the fund insists on a technical review by an expert panel as well as an extensive system of monitoring, evaluation and audits once a programme starts.

The fund builds on an important recent insight of the European donor agencies, that support is most effective when the donors pool their resources to support a single coherent strategy - known as a "sector-wide approach". Otherwise, each country has to grapple with 20 or more separate aid agencies, each with its own quirks, politics, reporting requirements and tied aid. The US plan would undermine a sector-wide approach by pushing Aids control back to a scramble of individual donor projects.

In just one year of operation, the fund has energised the fight against Aids, tuberculosis and malaria all over the world. It has generated hundreds of proposals and has approved support for creative programmes in more than 80 low-income countries. Of the 14 countries targeted by the new US effort, 13 are already receiving Global Fund support, a point overlooked in the US initiative. Only last Friday, the fund approved another $866m for the next two years in programmes across 60 countries.

The US effort is a bold part, but only a part, of the total financing needs. Its limits are implicit in the fact that it is directed only at Aids (not malaria and TB), and only at 14 countries. The Global Fund has said it will require new donor support of about $7bn this year and next - or roughly $3.5bn a year - in order to meet the needs of the high-quality proposals that it is considering.

A reasonable financing framework is clear. Europe should match the US initiative with its own $3bn a year, while Japan and other donors should contribute at least $1bn a year in addition. That would make a total of at least $7bn a year during 2003 and 2004. Half of that should be devoted to the Global Fund, and the other half should be spent on programmes (such as manpower training and expanded information technology) that would indirectly bolster, rather than undermine, the Global Fund.

Silence from Europe at this moment would be deadly for the Global Fund. If the US is the only country to put up large new sums for the war against Aids, then it will be a US programme. On the other hand, with a bold European response to Mr Bush's daring initiative, the transatlantic alliance - under great strain over Iraq - would prove to the world that it continues its historic commitments to freedom and human betterment. Impoverished and dying people around the world await a clarion call from the US and Europe together.

The writer is director of the Earth Institute at Columbia University and chairman of the World Health Organisation Commission on Macroeconomics and Health Copyright Financial Times Limited 2003. All Rights Reserved.