Common Wealth, by Jeffrey Sachs

How to save a planet

In the early pages of his new book on "economics for a crowded planet", Jeffrey Sachs makes the point that the challenges he is addressing don't conform to the neat theories and divisions of academic research. What's more, they vary in important detail from place to place. Tackling the linked scourges of global poverty and environmental disaster will depend on pragmatic, inter-disciplinary solutions to specific problems. This "new approach to development practice" is now the consensus among serious economists in development economics, which for many decades was an ideologically-riven battleground of competing theories.

It is a paradox of this book, though, that most of it is devoted to the highest level of generalities. Professor Sachs aims to set out the principles by which humanity as a whole can end poverty and hunger, and save the planet. His prescription combines international agreement on climate-change measures, policies to reduce fertility rates in the poorest countries and hasten population stability, new technologies to improve the productivity of agriculture and the use of water and, for good measure, a new approach to foreign policy, especially by the post-Bush US. The reader is torn between admiration for the ambition, and optimism of this programme and open-mouthed amazement about its naivety.

Perhaps, to Sachs, it doesn't seem naive at all. After all, with help from rock stars and NGO campaigns, he has affected the policy debate in leading industrial countries. The policies may be inadequate still, but world poverty and climate change are taken seriously. I find his passion and commitment to global problem-solving genuinely impressive. Also welcome, amid all the doom-mongering on these subjects, is his insistence on the potential of technological progress to help reduce hunger and safeguard the environment. One example among several is the scope for improved irrigation techniques (a simple method using perforated rubber hoses at ground level) to increase the yield of crops. Another is reduced ploughing to preserve moisture in soil, letting worms aerate it. Sachs advocates genetic techniques to develop less thirsty crops, and the use of the price mechanism to ensure farmers value water appropriately – both much more controversial among campaigners.

When it develops this kind of pragmatic detail, and you sense the hinterland of researchers in many disciplines at the Columbia University Earth Institute (where Sachs is director), the book is at its most impressive. Much less persuasive are the grandiose, big-picture passages. Their message – "all we need to do is X" – in fact undermines the convincing detail. Sachs has been criticised by other development economists (most publicly, Bill Easterly) for over-simplifying problems and solutions.

As he has immersed himself in detail, it's no wonder he feels aggrieved by the attacks. Yet there is a Sachs paradox: he does advocate big gestures, to create the momentum to change policies, at the same time as recognising their incompleteness as practical guidelines. One example of the paradox is the programme of Millennium Villages, so far built in ten African countries under the auspices of the UN, the Earth Institute and the NGO Millennium Promise. The five-year programme aims to spend $120 per villager to deliver effective agriculture, malaria control, health facilities, water access and schooling. Sachs presents this as an effective approach to ending poverty and triggering growth, if only donor governments will put in enough money.

As it happens, my nephew Sam Rich works as a development consultant in East Africa and visited, in its early days, one of the Millennium Villages in Kenya. He wrote a slightly sceptical scholarly article, arguing that more money was having a helpful impact but was not enough to solve the governance problems which affect so many African countries. After the publication of this article, Sachs got in touch to persuade Sam that his interpretation was wrong, and the project would succeed. Who could fail to warm to that passion and sense of purpose? But, equally, the passion alone won't solve the problems.

Those are precisely the mixed feelings provoked by Common Wealth. Sachs stands in the great tradition of campaigning intellectuals and has been an effective advocate of urgent policy action. At the same time, he is a fine economist demonstrating all that profession's admirable attention to complex detail and evidence. This book falls between the two stools, with sections which will satisfy alternately one audience then the other, but not both simultaneously. Still, this is an honourable shortcoming given that both arguments need to be won: we need both the political momentum and technical detail. More important is the book's ultimately optimistic message: that together we can tackle the daunting global economic and environmental problems facing us.

Diane Coyle's latest book is 'The Soulful Science' (Princeton)