I object in the strongest terms to your heading "Science defends itself against The Skeptical Environmentalist." You have no intellectual warrant whatsoever to divide the world into two camps"science," including the Lomborg critics you publish, plus their allies, Paul Ehrlich et al., and, apparently, "nonscience," including Lomborg, Matt Ridley, Lewis Wolpert and his many other allies. If you wanted to say "Environmentalism (or The Green Movement) defends itself against The Skeptical Environmentalist," that would be acceptable. But there is no question that Lomborg and his allies are within science.

Editor, Philosophy and Literature
University of Canterbury
Christchurch, New Zealand

The generally accurate essay by John Bongaarts, "Population: Ignoring Its Impact," may perpetuate one common misperception. Bongaarts says that in North America growth is near zero. In fact, the U.S. population is currently growing by about 3.2 million people a year. About 40 percent of this is from natural increase; the rest is from immigration. The Census Bureau projects that the U.S. population will grow from the current 286 million to 400 million by 2050. Even without immigration, the population would continue to grow considerablyby 16 percent within that period, according to one estimate. This trend makes a very substantial contribution to the worlds environmental problems. Readers ought not to be left with the impression that the U.S. is exempt either as a cause or recipient of these population-related problems.

Ann Arbor, Mich.

If this is an example of how "science defends itself," then woe betide science. Science rests above all on rigorous use of evidence and logic. Unfortunately, some scientists have apparently come to believe that the political cause of environmentalism is so important that they need not worry about the normal rules of evidence and logic. This was the essence of Lomborgs critique, and Thomas Lovejoys "Biodiversity: Dismissing Scientific Process" only confirms the indictment. Most remarkable is the defense Lovejoy offers for Norman Myers's completely unsubtantiated 1979 assertion that 40,000 species are being lost every year to extinction. Myers, Lovejoy says, "deserves credit for being the first to say that the number was large and for doing so at a time when it was difficult to make more accurate calculations." But shoddy methodology is shoddy methodology, whether it gives the result one is after or not.

In fact, the "more accurate calculations" that Lovejoy and others have advanced in the years since are hardly any more scientific than Myerss original guess. They are based on the naive and simplistic assumption that numbers of species are solely and mechanistically determined by habitat areaan assumption that the definitive review article in the literature has shown to be without merit. (The authors, E. F. Connor and E. D. McCoy, concluded that even as a descriptive tool, the species-area relation is merely "a correlation without a functional relationship.")

Lovejoy admits that hundreds of thousands of species that should already be extinct according to his and Myerss calculations are not extinct but explains this away by insisting that they will be extinct. But this is pure circular logic, in which one unsubstantiated assertion is invoked to prop up another.

The question of species loss and the other issues addressed by Lomborg are complex ones. It is disappointing that in replying to Lomborg, your authors and editor chose to engage in selective use of evidence, unsubstantiated assertions, lapses of logic, and ad hominem attacks disparaging Lomborgs presumption in questioning the "experts." These are the tactics of demagogues and rabble-rousers, not scientists.

Leesburg, Va.

Stephen Schneiders "Global Warming: Neglecting the Complexities" entirely missed the point of Lomborgs views on global warming and the Kyoto Protocol. A low-end (1.5 degree Celsius) 21st-century warming is the logical projection of the most inclusive collection of climate models and data that can currently be assembled.

As is shown graphically in the latest report by the United Nations Intergovernmental Panel on Climate Change (IPCC), the ensemble of climate models predicts a warming that, once started, will continue at a virtually constant rate for the next century. Although there are a few outliers, the clear consensus of these models is linear; they differ, however, in the rates of their projected warming.

It is also the consensus of the IPCC, first stated in 1996 and repeated in 2001, that "the balance of evidence suggests a discernible human influence on global climate." In other words, alterations of the atmosphere resulting from human emissions are producing a detectable signal in global and regional temperatures.

By using the combination of these two realities, Lomborg is forced to conclude that warming will be relatively modest. That is all a scientist can do: reconcile disparate models with observed data. Indeed, the warming of surface temperatures in the past three decades is highly linear, as predicted by the climate models. The differences in model slope, though, have obviously been adjudicated by nature, and they point to a warming of 1.5 degree C in the next 100 years. (A relatively small solar component to recent warming reduces this estimate to 1.4 degree C, assuming solar constancy in the next century.) Any argument against this logic must conclude that the very functional form of the consensus of climate models is wrong, which would be very unpopular among climate scientists.

Schneider is also more angry than correct when he dubs Lomborgs claims about the inconsequentiality of the Kyoto Protocol a straw-man argument, because Kyoto represents only a beginning for climate policy in the next 100 years. It is a fact not disputed by atmospheric scientists that assuming midrange sensitivity of climate to greenhouse forcing, the net warming saved by the original Kyoto Protocol is 0.07 degree C in 50 years and 0.14 degree C in 100 years (thanks to the aforementioned model linearity). That result was published in the refereed literature shortly after the 1997 Kyoto Conference, and it stands today.

The problem with Schneiders argument is that the Kyoto Protocol itself was so diluted in an effort to achieve Japanese compliance that the same model now estimates a savings in warming of 0.02 degree C by 2050. There is no known network of ground-based sensors that could ever discriminate this from climate noise. Yet the cost is considerable, as was recently demonstrated by William D. Nordhaus in Science. Consequently, the nation that would assume, according to Nordhaus, by far the largest costthe U.S.now considers Kyoto dead, and on December 30, 2001, the Japanese refused even the small mandatory emissions restrictions that were imposed on them. This is not a first step at all. It is no step, even if adopted. Lomborg himself is too optimistic about climate policy, and Schneider is simply unrealistic.

Professor of Environmental Sciences, University of Virginia
Senior Fellow in Environmental Studies, Cato Institute
Virginia State Climatologist

In the 1970s there was a lot of excitement over two books: one theorized that our planet had been visited by friendly aliens who had helped our ancestors with all kinds of "impossible" achievements, including the building of the pyramids; another proposed paranormal explanations for the Bermuda Triangle, complete with "irrefutable" evidence. I cant remember the titles of these books or the authors names, but I do remember watching one of them being interviewed on television. Although the interviewer was definitely hostile, the author remained confident and self-assured. After 15 minutes or so of well-informed questioning, however, the interviewer had effectively boxed his guest into a corner. At which point the still smiling, recently successful author finally stated, "If Id said it that way, I probably wouldn't have sold many books."

As far as Lomborg and his book go, I don't think we need look any further than the above statement. Also, growing up and going to school in Cambridge, England, I am extremely disappointed that Lomborg's book was published by Cambridge University Press. I just hope they realize how they have tarnished their reputation by publishing such a work. I think a more suitable vehicle would have been the checkout stand at the local supermarket, which thrives on misinformation and distorted facts.

Flemington, N.J.