To a significant extent the issue of climate change revolves around the elevation of the commonplace to an ominous omen. In a world where climate change has been the norm, it’s 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 globally averaged temperature anomaly or GATA, as portents of disaster.
Climate in Perspective
Earth has had ice ages and warmer periods. Ice ages have occurred in a 100,000-year cycle for the past 700,000 years, and there have been previous interglacial periods 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.
For small changes in the GATA, there is no need to look for any external cause. The earth never is exactly in equilibrium. The motions of the massive oceans, where heat is moved between deep layers and the surface, provide variability.
Examples include El Niño, the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation, etc. Recent work suggests that this variability is enough to account for all change in the GATA since the 19th century.
To be sure, man’s emissions of carbon dioxide must have some impact. The important question, however, is how much.
Feedback Assumptions Are Key
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 Earth’s energy balance 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 because of increases in carbon dioxide, would not imply any greater warming than that.
Climate models, by contrast, predict a doubling of carbon dioxide would produce more warming: 3.6 degrees to 9 degrees Fahrenheit 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 Earth’s ability to cool itself by emitting thermal radiation to space, the positive feedbacks will further reduce this ability.
Models May Be Way Off
It is acknowledged such processes are poorly handled in current models, and there is substantial evidence the feedbacks may be negative rather than positive. For example: 2.5 billion years ago the sun’s brightness was 20-30 percent less than it is today, 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 a modest negative feedback from clouds is entirely adequate to explain it. With the positive feedback in current models, the resolution would be essentially impossible.
Models Haven’t Matched Reality
Interestingly, according to the United Nations’ Intergovernmental Panel on Climate Change, the greenhouse forcing from manmade gases is already about 86 percent of what one would expect 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. Instead, they have arbitrarily removed the difference and attributed this to essentially unknown aerosols.
The IPCC’s claim that most of the warming since the 1950s is because of man assumed current models adequately accounted for natural internal variability. The failure of these models to anticipate that there has been no statistically significant warming for the past 14 years or so contradicts this assumption.
However, the modelers chose not to stress this. Instead, they suggest the models can be further corrected and warming would resume by 2009, 2013, or even 2030.
Exaggerated Concerns
Global warming enthusiasts have responded to the recent absence of warming by arguing the 2000s was the warmest decade on record. We are still speaking of tenths of a degree, and the temperature records have come into question. But since we are, according to these records, in a relatively warm period, it is not surprising the past decade was the warmest on record.
Given that the evidence suggests the anthropogenic component of warming has been greatly exaggerated, so is the basis for alarm. But this basis would 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 regional variables such as temperature, humidity, cloud cover, precipitation, direction and magnitude of wind, and the state of the ocean.
This is not to say disasters will not occur as they always have. However, fighting global warming with symbolic gestures certainly will not change this. On the other hand, history tells us greater wealth and development can profoundly increase our resilience.
Richard S. Lindzen ([email protected]) is the Alfred P. Sloan professor of atmospheric science at the Massachusetts Institute of Technology. This article initially appeared in the Modesto Bee and is reprinted with permission.
