CAMBRIDGE, MASS. — EDITOR’S NOTE: The writer is addressing the question, Is climate change real?
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.
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 last 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. 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.