In his third Reith Lecture, The Great Convergence, Jeffrey Sachs addresses the prospects for international cooperation. Faced with multiple global environmental and developmental challenges, Sachs focuses on the place of the USA in fostering global agreement.

Confronting man-made global problems, Sachs offers us 'practical answers'. However, of the four necessary steps to meet these challenges – sound science, public awareness, technological solutions and global agreement – it is the last which poses the biggest hurdle. Obstacles to cooperation are several but it is on the vulnerability of humans to 'the allure of war' that Sachs concentrates.

The background to discussions of these issues is, for Sachs, a world which is ever poised between cooperation and conflict. Human beings are psychologically torn between cooperative and conflictual impulses. It is fear which for Sachs tips the balance one way or another.

Two futures are thus presented, one in which "fear begets fear, conflict begets conflict" and another in which "trust begets trust, cooperation begets cooperation".

In emphasising the mutual benefits of international cooperation, Sachs is firmly within a long liberal tradition. Yet, as he acknowledges, surely the difficulty is not so much in seeing what might be achieved by global agreement, but in breaking the cycle of fear, mistrust and conflict which stands in its way.

What is it that can put the world on a virtuous path to cooperation?

Here we come to one of Sachs' main political targets of the lecture. In response to the terrorist attacks of 2001, he argues, the USA's actions created an 'us versus them' conflict with military action at its core. An utter neglect by the USA of environmental and developmental challenges has been the result.

A sceptic might point out that in order to achieve cooperation, the USA needs partners with whom to cooperate. Sachs' answer is, following President Kennedy, to look inwards, to assess what changes in the USA's behaviour would elicit changed behaviour from others.

But what are the changes that would produce such a response? Sachs offers a rather mixed bag: tolerance towards different ethnicities, managed immigration, efforts to reduce population growth abroad and withdrawal of troops from Iraq.

This illustrates some of the strengths and weaknesses of the lecture. In rolling together so many different problems Sachs speaks to the real interconnectedness of the world. But doesn’t this also create a danger of assuming all problems are somehow the same? Can and should the USA's response to terrorism be the same as its response to the rise of China? Are population control and terrorism similar kinds of problem? Is the war in Iraq really so fundamental that it is the major block to agreement on all other issues?

What are the prospects for the kinds of change in US politics that Sachs hopes for? Is the USA so important that "inward change" will, by itself, change others, or are other forces at work in the world? Can human beings tip the balance from conflict to cooperation, from fear to trust?

What do you think? Share your responses in the Reith Lectures forum.