Are there any lessons to be learnt from the conflict between environmental optimists and pessimists? One potential lesson is that one might want to differentiate between different aspects of the environment. This does not mean that because both optimism and pessimism are extremist views, the 'truth' is likely to lie somewhere in the middle. Even though this would be a tempting conclusion to draw and might indeed be true for certain aspects, there is no more a priori justification for this presumption than for either extremist view. Rather, if one wanted to agree with one side of the debate on some aspects, there is no need to conform with all aspects. For example, even if one shares the environmental pessimists' view on global warming or biodiversity extinction, there is no need to share their view on non-renewable resources as well. The world economy has, so far at least, exhibited a most remarkable capability to overcome natural resource constraints via substitution and technical progress. The frequent falsification of alarms of a running out of essential resources provides a case in point. Global environmental resources, such as the global climate, the ozone layer or biodiversity, on the other hand, lack a well-defined property rights system, functioning markets and therefore prices cannot play the role of a self-correcting feedback loop. Hence these environmental resources are much more vulnerable, and because they are much more important to mankind, one needs to be much more cautious about a threat to these resources, even if the existence of the threat is highly contested.

Friends of the Earth, Oldham

Members of Oldham 'Friends of the Earth' campaigning against the increasing landfill and incineration of household waste. Pictured here, the members are promoting the alternative of 'Reduce, Reuse and Recycle'. For many years direct recycling by producers of surplus and defective materials constituted the main form of recycling. The recycling of materials after their use by consumers, has become the focus of activity in the 1990s. For some time, most solid waste has been deposited in landfills or dumps. However, landfills are filling up and disposal of wastes in them has led to environmental problems.

More generally, the conflict between environmental optimists and pessimists should make one cautious about following the arguments of either side too readily. For the majority of individuals who are not biologists, natural or environmental scientists it is difficult to decide which side of the debate is correct. Scientific laymen and laywomen are dependent on the experts' interpretation and it is often next to impossible to check whether the interpretation is 'correct' or rather, due to the scientifically contested nature of many environmental problems, is consistent with high methodological standards.

Nevertheless, it is important to be cautious and critical towards scientific findings, especially if they conform nicely with one's own conviction. It is always a good idea to expose oneself to the opposite scientific view and to check whether one's conviction upholds the attack from the other side. But does following this advice lead to the danger of getting lost in a plethora of conflicting views without the ability to make an informed decision between them? Maybe, and this is the reason why 'consensus statements' of a great many scientists and the instalment of scientific networks such as the Intergovernmental Panel on Climate Change (IPCC) are so important. But even then one must remain cautious because the majority, even a vast majority, of scientists can still be wrong. The environmental optimists make a good point in stressing that the vast majority of scientists in the 1970s expected global cooling to be the big environmental problem, not global warming.

Ehrlich and Ehrlich themselves admit that they have been wrong on several occasions in predictions made in earlier work. For example, they severely underestimated the potential of the 'green revolution' to increase crop yields and severely overestimated the frequency and severity of famines in the 1970s. In 1990 they said that "global food production per person peaked earlier, in 1984, and has slid downward since then", but according to data from the Food and Agricultural Organisation, world per capita food production has steadily increased between 1980 and 1995 with only small yearly fluctuations. But if there is uncertainty and debate about scientific findings and if the environmental pessimists themselves acknowledge that at times they have been wrong about environmental problems, then there are good reasons to be sceptical towards their current findings and calls for dramatic change as well, even if these are backed by consensus statements of the vast majority of natural scientists.

There is one further aspect in which the Ehrlichs were wrong. Ehrlich and Ehrlich advise "businesspeople with an interest in their children's future{A133}to subscribe to the magazine The Economist. We sometimes disagree with it, but it does an accurate and quite thorough job of covering the environment." Just one year later this very same magazine published an acid critique of environmental pessimism saying that "forecasters of scarcity and doom are not only invariably wrong, they think that being wrong proves them right". The article makes great fun of the 'environmental doomsters', proclaims that there does not exist any real environmental problem and accuses Paul Ehrlich of being 'dangerously close of fascism' because of his alleged belief 'in the need for coerced family planning'. Surely, this is not what the Ehrlichs would subsume under doing a thorough job of covering the environment.