To a significant extent, the issue of climate change revolves around the elevation of the commonplace to the ancient level of ominous omen. In a world where climate change has always been the norm, climate change is now taken as punishment for sinful levels of consumption. In a world where we experience temperature changes of tens of degrees in a single day, we treat changes of a few tenths of a degree in some statistical residue, known as the global mean temperature anomaly (GATA), as portents of disaster.
The Earth has had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a 100,000-year cycle for the past 700,000 years, and there have been previous interglacials that appear to have been warmer than the present despite lower carbon-dioxide levels. More recently, we have had the medieval warm period and the little ice age. During the latter, alpine glaciers advanced to the chagrin of overrun villages. Since the beginning of the 19th century these glaciers have been retreating. Frankly, we don't fully understand either the advance or the retreat, and, indeed, some alpine glaciers are advancing again.
For small changes in GATA, there is no need for any external cause. The Earth is never exactly in equilibrium. The motions of the massive oceans where heat is moved between deep layers and the surface provides variability on time scales from years to centuries. Examples include El Nino, the Pacific Decadal Oscillation, the Atlantic Multi-decadal Oscillation, etc. Recent work suggests that this variability is enough to account for all change in the globally averaged temperature anomaly since the 19th century. To be sure, man's emissions of carbon dioxide must have some impact. The question of importance, however, is how much.
A generally accepted answer is that a doubling of carbon dioxide in the atmosphere (it turns out that one gets the same value for a doubling regardless of what value one starts from) would perturb the energy balance of the Earth about 2 percent and this would produce about 2 degrees Fahrenheit warming in the absence of feedbacks. The observed warming over the past century, even if it were all due to increases in carbon dioxide, would not imply any greater warming.
However, current climate models do predict that a doubling of carbon dioxide might produce more warming: from 3.6 degrees to 9 degrees or more. They do so because within these models the far more important radiative substances, water vapor and clouds, act to greatly amplify whatever an increase in carbon dioxide might do. This is known as positive feedback. Thus, if adding carbon dioxide reduces the ability of the Earth system to cool by emitting thermal radiation to space, the positive feedbacks will further reduce this ability.
ADVERTISEMENT
The IPCC claim that most of the recent warming (since the 1950s) is due to man assumed that current models adequately accounted for natural internal variability. The failure of these models to anticipate the fact that there has been no statistically significant warming for the past 14 years or so contradicts this assumption. This has been acknowledged by major modeling groups in England and Germany.
Given that the evidence (and I have noted only a few of many pieces of evidence) suggests that anthropogenic warming has been greatly exaggerated, so too is the basis for alarm. However, the case for alarm would still be weak even if anthropogenic global warming were significant. Polar bears, Arctic summer sea ice, regional droughts and floods, coral bleaching, hurricanes, alpine glaciers, malaria, etc., all depend not on GATA, but on a huge number of regional variables including temperature, humidity, cloud cover, precipitation, direction and magnitude of wind and the state of the ocean.
The need to courageously resist hysteria is clear. Wasting resources on symbolically fighting ever-
present climate change is no substitute for prudence.
Richard S. Lindzen is the Alfred P. Sloan professor of atmospheric science at the Massachusetts Institute of Technology.
