Sir

To understand why many physical scientists regard economists with scepticism, one need look no further than the Concepts essay on discounting (“An eye on the future” Nature 419, 673–674; 2002) by L. H. Goulder and R. N. Stavins. After describing an example in which a $4-billion investment now would prevent us from causing $800 billion of environmental damage 100 years hence, they ask: “If future generations do not actually compensate the present one, is it still appropriate to enact the policy?”

Who but an economist could imagine that future generations would owe us an impossible debt for not damaging their environment? Isn't it we who owe future generations a sound environment? Discounting provides a well-defined measure relating present and future sums. The problem is that this measure is not particularly useful for problems involving intergenerational transfer.