Letters to the Editor

Climate Change, Obesity and the Need for Modesty

The doctor has the patient’s medical history, including weight and heart data (blood pressure and electrocardiogram), showing an undesirable trend. If the doctor is careful, the heart data have to be somewhat discounted because they are taken only in office visits, with unknown distortion from daily life.

The physicist has the earth’s CO₂ and climate history, with similar or worse need for caution.  The one thing the doctor knows for sure is that the patient’s current weight is higher than in past years. The one thing the physicist knows for certain is that atmospheric CO₂ is higher now than in the last 100 years. The doctor thinks, but cannot prove, that the heart is showing worrisome symptoms, which will improve with loss of weight. The physicist thinks, but cannot prove, that global temperatures have risen and that the trend will be reduced by lowering CO₂ emissions.

Why does the doctor tell the patient to lose weight? There are excellent statistical correlations between obesity and life-shortening diseases. But the patient knows the difference between statistical correlations and prediction of a particular case. There is no proof that the patient’s particular case of obesity will adversely affect the patient’s life span, or, even if it does, there is no proof that the quality of life remaining will be adversely affected. Similar objections apply if we tell the world’s population to reduce CO₂ emissions. 

The doctor’s confidence in statistical correlations is much improved by theory. Current medical science offers plausible scientific reasons why obesity harms health. Current physical science offers plausible reasons why anthropogenic CO₂ increases global temperature.

There are imperfections in this analogy. They tend to favor the doctor and disfavor the physicist.  For a start, the patient is paying the doctor for advice. This can motivate belief. The doctor’s heart data, although imperfect, are harder to disqualify than data on mean global temperature. In the end, the doctor’s job is important, and no one expects the doctor to be fully scientific. The doctor has a responsibility to speak forcefully even if strict scientific standards are impossible to meet. What about the physicist? The analogy suggests two things. (1) It is important to acknowledge that physical science cannot provide perfect guidelines, and that scientists will seek a consensus about likely truth and still disagree with each other about the details. Just as people should ask their doctor (rather than their pastor, mayor, or astrologer) for advice about health, so they should ask physical scientists for advice about the earth’s climate. They should not expect greater certainty from physical science than from medical science. (2) When speaking forcefully, it should be done with at least as much modesty as we expect from our doctor, because we have at least as much reason for modesty.
 
Philip B. Allen
Stony Brook, NY

APS Could Use Division of Global Climate

Since 1966, APS has become a federation of Divisions. There is no Division that has scientific jurisdiction over global climate, and therefore APS Council has no jurisdiction either. APS should have a clearly stated policy with respect to the scope of its statements on issues of public policy. Such a statement should acknowledge that physics is a scientific discipline with limited scope, and not a source of special knowledge on every topic of public concern. If it aspires to enjoy public respect, it must recognize the importance of restraint on matters beyond its ken. At this time, global climate is a case in point.

However, if and when the Council decides to create a Division on Global Climate, it would then, in due course, have a body of expertise on which to base responsible policy statements.

Lawrence Cranberg
Austin, TX