To the editor:

With regard to the letter March 20 titled “Global warming isn’t man-made,” the recent Second International Conference on Climate Change, discussed by James Rust of Georgia Tech, was put on by the Heartland Institute, a Chicago-based libertarian/conservative think tank. The Heartland Institute called the conference “the largest-ever gathering of global warming skeptics” and billed it under the subheading “Global warming: Was it ever really a crisis?”

While skepticism is an important part of the scientific process, one cannot help but wonder whether the conference seriously debated the merits of climate change theory or was merely a meeting of the converted preaching to the converted.

The “findings” of the conference, as reported by Rust, are the same, old, tired skepticisms that have been around for years and are easily debunked:

• The argument that today’s warming is just a recovery from the Little Ice Age relies on the assumption that there is a particular climatic baseline to which Earth inexorably returns, so a period of globally lower temperatures will be followed by a rise in temperatures. There is no scientific basis for this assumption. Another problem is that the temperature has risen to levels higher than the assumed baseline. Secondly, this argument does not explain why a 35 percent increase in carbon dioxide would not affect global temperature.

• It is true that carbon dioxide produced by human activity is much less than that from natural sources. But for roughly 10,000 years, until the industrial revolution, every gigaton of carbon going into the atmosphere was balanced by one coming out. What humans have done is alter one side of this cycle. We put approximately 6 gigatons of carbon into the air but, unlike nature, are not taking any out. Nature is compensating in part for our emissions because only about half the carbon dioxide we emit stays in the air. Nevertheless, since we began burning fossil fuels in earnest more than 150 years ago, the atmospheric concentration has risen by more than 35 percent. Humans have clearly upset the balance and significantly altered an important part of the climate system.

• It’s inaccurate to say the computer climate models are inaccurate. Many modeled predictions of global temperature have been validated. Every year of increasing global mean temperature is one more year of “success” for the climate models. The acceleration of the rise is also playing out as predicted, though decades will need to pass before such confirmation is inarguable. Putting global surface temperatures aside, there are many other significant predictions made and confirmed, too numerous to list here. Only long-term predictions need time to prove or disprove them, but we don’t have that time at our disposal. Whether we take the many successes of climate models as strong validation for their long-term predictions is a legitimate policy question, but to deny the near-term accuracy of the models is not.

• The argument that increased atmospheric carbon dioxide has beneficial effects on plant growth and food supply sounds almost desperate. While some flora might flourish under increased carbon dioxide conditions, others likely won’t. Geologic history demonstrates that dramatic climate changes — up, down or sideways — are a shock to the biosphere and usually cause mass extinctions. All in all, that is not likely to be a good thing.

• Finally, to say that an attempt to control global temperatures by restricting the production of carbon dioxide is a greater threat to human well-being than climate change itself in no way implies that global warming is or is not occurring. One cannot come to a rational decision about the reality of a danger by considering how hard it might be to avoid. The corollary is to say that combating global terrorism is too difficult, so there must not be such a thing as global terrorism. Even if mitigating global warming would be harmful, given that famine, droughts, disease, loss of coastal cities and a mass extinction event are possible consequences of doing nothing, we could be faced with a choice of the lesser of two evils. I challenge anyone to conclusively demonstrate that such catastrophes await us if we try to reduce fossil fuel use.

Steven W. Hart