Last week, I wrote about the Danish statistician Bjorn Lomborg's discovery that information about the state of the environment is being exaggerated, sometimes quite wildly, by scientists and environmental activists. It is perhaps no surprise that many in the scientific community have greeted his book, The Skeptical Environmentalist, with hostility and anger.

This week, I want to outline briefly some of the conclusions Dr. Lomborg reaches, specifically those having to do with the hole in the ozone layer, rising sea levels, increases in extreme weather and the rate at which species are becoming extinct. First, though, I should try to explain why it is important that the risks posed by environmental hazards should not be exaggerated. After all, some people will argue, why shouldn't scientists dramatise their findings?

It is often the only way to get otherwise rather hard-of-hearing and slow-moving governments to do something about environmental problems before it is too late. Governments do move slowly — that's a fact. But it can't be much of an improvement if they are induced to act stupidly as well as slowly.

Decisions about how to spend money, and about how to order projects in terms of priority, cannot be made sensibly on the basis of information that is wrong. That isn't one side of an argument — it is a simple fact. It is not good public policy to spend money on high-cost projects that promise to save few lives, at the expense of projects that would save more lives. But that is exactly what can occur if decision-makers act on bad information, or allow themselves to be persuaded by public opinion that is based on bad information.

For example, figures produced by the Harvard University Center for Risk Analysis, quoted by Dr. Lomborg, demonstrate that the cost in the US, in 1993, of instituting sickle-cell anaemia screening for newborn black children was $240 per life-year saved. The cost of mandatory seat belts for passengers in school buses was $2,800,000 per life-year saved. They are both projects that, if undertaken, would save lives, and are both, therefore, projects that ought to be undertaken.

But there is no question about how a responsible Government should order them in terms of priority. Doing otherwise, Dr.. Lomborg charges, amounts to committing "statistical murder". Similarly, public policy on global environmental problems must be based on reality, not on exaggeration and the effects of media manipulation.

Dr. Lomborg criticises a number of individuals and groups for a tendency to exaggerate, including The Worldwatch Institute, Greenpeace, the World Wide Fund for Nature and, of course, the media who accept what they say without question. Generally speaking, his rather more sober analysis of available figures points the way to conclusions that should concern us, but not terrify us.

To deal with his findings about the ozone layer first, it has been known since 1985 that this thin barrier in the upper atmosphere, that protects people, animals and plants by filtering out the sun's ultraviolet rays, has been adversely affected by chlorofluorocarbons (CFCs). CFCs were widely used, especially in the 1960s, in refrigerators, spray cans and air conditioners, among other things. After the damage had been discovered, an international effort was mounted fairly swiftly to repair it. Six international treaties were signed over the course of 12 years, designed to reduce, then ban consumption of the five main CFC gases.

These protocols were effective — the total production of CFCs in 1996 dropped below that of 1960. United Nations Environment Programme (UNEP) figures published in 1999 demonstrated that ozone-depleting chemicals in the stratosphere would peak by 2000, and recover slowly over the following 50 years.

But the scare that had been put into the popular consciousness, that there would be "frightening" increases in skin cancer as a result of increases in UV levels at the earth's surface, persists. In fact, says Dr. Lomborg, the impact will be less than frightening. He states that: "Assuming no change in behaviour (sun exposure, etc.) and full compliance with the CFC protocols, it is estimated that the current ozone minimum will lead to more cancers in the future, reaching a maximum in 2060 of 27,000 extra annual skin cancers in the US, or an increase in total skin cancer of about three percent. Since the vast majority of extra cancers will be the almost entirely curable skin cancers, the maximum extra deaths in 2060 in the US are estimated at about 350 or about five percent of all skin cancer deaths."

On the subject of rises in sea levels, he has this to say: "First, global warming has often been connected to oceans that will rise several metres and polar ice caps that begin to melt. An article in the UNESCO Courier showed us a picture of a large iceberg detaching, asking us 'Will global warming melt the polar ice caps?'

"There are, however, no grounds for these worries. It is right that the first models predicted extreme sea level increases but these predictions have since been falling constantly. The global water level has risen between ten and 25 centimetres over the last hundred years and...it is envisaged that it will rise by a further 31-49 centimetres over the next hundred. About three-fourths of this rise is due to the fact that the water has got warmer and therefore expanded, and only one fourth comes from changes in glaciers and increased runoff from ice caps."

If the 31-49 centimetres forecast holds true, it will mean a rise of less than 18 inches in 100 years. No doubt that will be difficult and expensive for many countries to deal with, especially Third World countries. But Dr. Lomborg's analysis demonstrates the existence of a problem, not a looming catastrophe, and the rate of rise does allow plenty of time for those affected to consider how to take protective measures to minimise the damage caused.

What about the increased vulnerability to the extreme weather that global warming will surely bring?

According to Dr. Lomborg, there are few signs that there are going to be significant increases in extreme weather...certainly where tropical and extratropical storms are concerned. Dr. Lomborg quotes from a report by Munich Re, the world's largest reinsurer, which claimed that although the incidence of natural catastrophes had increased greatly, these were attributable to societal causes, not natural causes.

The Munich Re report said: "In the last few decades, the international insurance industry has been confronted with a drastic increase in the scope and frequency of great natural disasters. The trend is primarily attributed to the continuing steady growth of the world population and the increasing concentration of people and economic values in urban areas. An additional factor is the global migration of populations and industries into areas such as coastal regions, which are particularly exposed to natural hazards. The natural hazards themselves, on the other hand, have not yet shown a significant trend, in spite of a number of indications."

And finally, where the rate at which species are becoming extinct is concerned, Dr. Lomborg feels that often-quoted estimates have been grossly exaggerated.

The often-quoted estimate, that 40,000 species are dying out every year, was first used in 1979 by a British scientist, Norman Myers. But what Myers actually wrote was this: "Let us suppose that, as a consequence of this manhandling of the natural environments, the final one-quarter of this century witnesses the elimination of one million species, a far from unlikely prospect. This would work out, during the course of 25 years, at an average rate of 40,000 species per year."

That was it — he cited no data at all to back up his assumption. Yet in the face of study after study showing that the figure of 40,000 was absurdly high, environmentalists continue to quote him. Dr. Lomborg's calculation, based on a variety of studies, indicates that the rate of extinction may reach 0.7 percent in 50 years, not the 25 - 75 percent that the Myers figure implies.

Dr. Lomborg's statistical analysis paints a picture very different from the one favoured by many environmentalists. But by removing some of the hysteria and hoopla, he seems to leave a little more room for optimism...and enthusiasm...about getting the environment back into balance and keeping it there.