Alarmism vs Scepticism

Acknowledgements to the Climate Sceptic web site for the following entry

We Are Finally Seeing Healthy Perspectives on CO2 in the Media

April 11, 2011, 12:19 am

The media loves lurid debates. Which in the climate debate has meant that to the extent skeptics even get mentioned or quoted in media articles, it is often in silly, non-scientific sound bites. Which is why I liked this editorial in the Financial Post, which is a good presentation of the typical science-based skeptic position – certainly it is close to the one I outlined in this video. An excerpt:

Let’s be perfectly clear. Carbon dioxide is a greenhouse gas, and other things being equal, the more carbon dioxide in the air, the warmer the planet. Every bit of carbon dioxide that we emit warms the planet. But the issue is not whether carbon dioxide warms the planet, but how much.

Most scientists, on both sides, also agree on how much a given increase in the level of carbon dioxide raises the planet’s temperature, if just the extra carbon dioxide is considered. These calculations come from laboratory experiments; the basic physics have been well known for a century.

The disagreement comes about what happens next.

The planet reacts to that extra carbon dioxide, which changes everything. Most critically, the extra warmth causes more water to evaporate from the oceans. But does the water hang around and increase the height of moist air in the atmosphere, or does it simply create more clouds and rain? Back in 1980, when the carbon dioxide theory started, no one knew. The alarmists guessed that it would increase the height of moist air around the planet, which would warm the planet even further, because the moist air is also a greenhouse gas.

This is the core idea of every official climate model: For each bit of warming due to carbon dioxide, they claim it ends up causing three bits of warming due to the extra moist air. The climate models amplify the carbon dioxide warming by a factor of three — so two-thirds of their projected warming is due to extra moist air (and other factors); only one-third is due to extra carbon dioxide.

That’s the core of the issue. All the disagreements and misunderstandings spring from this. The alarmist case is based on this guess about moisture in the atmosphere, and there is simply no evidence for the amplification that is at the core of their alarmism.

That is just amazingly close to what I wrote in a Forbes column a few months back:

It is important to begin by emphasizing that few skeptics doubt or deny that carbon dioxide (CO2) is a greenhouse gas or that it and other greenhouse gasses (water vapor being the most important) help to warm the surface of the Earth. Further, few skeptics deny that man is probably contributing to higher CO2 levels through his burning of fossil fuels, though remember we are talking about a maximum total change in atmospheric CO2 concentration due to man of about 0.01% over the last 100 years.

What skeptics deny is the catastrophe, the notion that man’s incremental contributions to CO2 levels will create catastrophic warming and wildly adverse climate changes. To understand the skeptic’s position requires understanding something about the alarmists’ case that is seldom discussed in the press: the theory of catastrophic man-made global warming is actually comprised of two separate, linked theories, of which only the first is frequently discussed in the media.

The first theory is that a doubling of atmospheric CO2 levels (approximately what we might see under the more extreme emission assumptions for the next century) will lead to about a degree Celsius of warming. Though some quibble over the number – it might be a half degree, it might be a degree and a half – most skeptics, alarmists and even the UN’s IPCC are roughly in agreement on this fact.

But one degree due to all the CO2 emissions we might see over the next century is hardly a catastrophe. The catastrophe, then, comes from the second theory, that the climate is dominated by positive feedbacks (basically acceleration factors) that multiply the warming from CO2 many fold. Thus one degree of warming from the greenhouse gas effect of CO2 might be multiplied to five or eight or even more degrees.

This second theory is the source of most of the predicted warming – not greenhouse gas theory per se but the notion that the Earth’s climate (unlike nearly every other natural system) is dominated by positive feedbacks. This is the main proposition that skeptics doubt, and it is by far the weakest part of the alarmist case. One can argue whether the one degree of warming from CO2 is “settled science” (I think that is a crazy term to apply to any science this young), but the three, five, eight degrees from feedback are not at all settled. In fact, they are not even very well supported.