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Con: Earth is never in equilibrium
By Richard S. Lindzen
Thursday, April 8, 2010
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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.
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 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 F to 9 degrees F 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.
It is again acknowledged that such processes are poorly handled in current models, and there is substantial evidence that the feedbacks may actually be negative rather than positive. Citing but one example, 2.5 billion years ago the sun’s brightness was 20 percent to 30 percent less than it is today (compared to the 2 percent change in energy balance associated with a doubling of carbon-dioxide levels) yet the oceans were unfrozen and the temperatures appear to have been similar to today’s.
This was referred to by Carl Sagan as the Early Faint Sun Paradox. For 30 years, there has been an unsuccessful search for a greenhouse gas resolution of the paradox, but it turns out that a modest negative feedback from clouds is entirely adequate. With the positive feedback in current models, the resolution would be essentially impossible.
Interestingly, according to the U.N.’s Intergovernmental Panel on Climate Change, the greenhouse forcing from manmade gases is already about 86 percent of what one expects from a doubling of carbon dioxide (with about half coming from methane, nitrous oxide, freons, and ozone). Thus, these models should show much more warming than has been observed. The reason they don’t is that they have arbitrarily removed the difference and attributed this to essentially unknown aerosols.
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.
However, the modelers chose not to stress this. Rather they suggested that the models could be further corrected, and that warming would resume by 2009, 2013, or even 2030.
Global warming enthusiasts have responded to the absence of warming in recent years by arguing that the past decade has been the warmest on record. We are still speaking of tenths of a degree, and the records themselves have come into question. Since we are, according to these records, in a relatively warm period, it is not surprising that the past decade was the warmest on record. This in no way contradicts the absence of increasing temperatures for over a decade.
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