Wednesday, December 23, 2009

The fox and the hedgehog

Isaiah Berlin, IEHO a much overrated philosopher and storyteller of the 20th century talked of foxes who know many things, and hedgehogs who only know one big thing, a very fortunate simile for book review writers.

American Scientist, ΣΞ's house organ reprints Gilbert Plass' seminal 1956 essay on Carbon Dioxide and the Climate with a biographical essay by James Fleming and an appreciation of Plass' place as one of the founders of climatology by Gavin Schmidt. Earlier this year Lightbucket had celebrated Plass'work as a blast from the global warming past, searching out and reprinting interesting contemporaneous evaluations from popular newspapers and magazines such as Time

This spreading envelope of gas around the earth, says Johns Hopkins Physicist Gilbert N. Plass, serves as a great greenhouse. Transparent to the radiant heat from the sun, it blocks the longer wave lengths of heat that bounce back from the earth. At its present rate of increase, says Plass, the CO2 in the atmosphere will raise the earth’s average temperature 1.5° Fahrenheit every 100 years.

As the blanket of CO2 gets thicker, it also prevents the tops of clouds from losing heat as rapidly as before. The smaller temperature difference between cloud base and top cuts down the air currents which must circulate through the cloud before rain or snow can form. Lowered rainfall will make a drier climate. Less cloud cover will be formed, more sunlight will reach the earth, and the average temperature will rise still higher.

Gavin spends time playing fox, listing the things that Plass did not know
He did not know how fast CO2 was accumulating in the atmosphere—Charles Keeling would start his seminal measurements at Mauna Loa only in 1957. Neither did he know how CO2 had varied in the past—the first ice core results only emerged in the 1980s. But he was still able, with his understanding of infrared spectroscopy, to write a paper that qualitatively predicted both these results—although with methods that we can now recognise as being incomplete—and correctly concluded that the impact of CO2 on climate would be clear by the end of the 20th century. There are other things that we know now that he could not possibly have known—the importance of other greenhouse gases (methane in particular, which wasn’t recognised as an important contributor to anthropogenic forcing until 1974, but also chlorofluorocarbons and N2O, which have also increased dramatically because of human influence) and the role of human-emitted particulates and low-level ozone precursors.
concluding, as all jealous foxes do, that Plass was simply lucky
Nonetheless, the coincidences of some of his numbers and the ones we know today are just that, coincidences, and so some part of the high regard in which we hold Plass today may simply be due to luck. Indeed, Lewis Kaplan, the author of a subsequent and more accurate calculation, has been all but forgotten since he incorrectly concluded that CO2 could not play a role in climate change. In 50 years time if someone reviews my work, I would hope to have been as lucky as Gilbert Plass.
Eli dissents. Plass was a hedgehog and he knew the one big thing. Eli knows it too, and has been pointing out for years that the estimates of climate sensitivity have simply not moved much for over a hundred years. This is a reasonable expectation, one big thing overwhelms many small things which since they are many and small are most likely to pull in opposite directions canceling each other out as you discover them and gee, they do. In fact, it would be a miracle if they did not.

Plass could have been writing today
The carbon dioxide theory states that, as the amount of carbon dioxide increases, the atmosphere becomes opaque over a larger frequency interval; the outgoing radiation is trapped more effectively near the Earth’s surface and the temperature rises. The latest calculations show that if the carbon dioxide content of the atmosphere should double, the surface temperature would rise 3.6 degrees Celsius and if the amount should be cut in half, the surface temperature would fall 3.8 degrees.
Ok a bit high on that but look at this answer about water vapor
The fact that water vapor absorbs to some extent in the same spectral interval as carbon dioxide is the basis for the usual objection to the carbon dioxide theory. According to this argument the water vapor absorption is so large that there would be virtually no change in the outgoing radiation if the carbon dioxide concentration should change. However, this conclusion was based on early, very approximate treatments of the very complex problem of the calculation of the infrared flux in the atmosphere. Recent and more accurate calculations that take into account the detailed structure of the spectra of these two gases show that they are relatively independent of one another in their influence on the infrared absorption. There are two main reasons for this result: (1) there is no correlation between the frequencies of the spectral lines for carbon dioxide and water vapor and so the lines do not often overlap because of nearly coincident positions for the spectral lines; (2) the fractional concentration of water vapor falls off very rapidly with height whereas carbon dioxide is nearly uniformly distributed. Because of this last fact, even if the water vapor absorption were larger than that of carbon dioxide in a certain spectral interval at the surface of the Earth, at only a short distance above the ground the carbon dioxide absorption would be considerably larger than that of the water vapor.


Anonymous said...

Does anyone dare to find out what Plass's politics were?

Gavin said...

I didn't say he was just lucky. But I'll put up an RC post soon and we can go over it in more detail.

EliRabett said...

Hi Gavin,

Plass was NOT lucky. As a hedgehog he knew the one important and real thing, that CO2 is the strongest forcing we know and it was growing because of our burning fossil fuels. It is the nature of problems with one major driver that some of the little things that obsess foxes go up and others go down, and in the end they balance leaving the big thing. Ask yourself how much estimates of climate sensitivity vary over the last 100 years, even over the last 50 when many of the things you call Plass out for not knowing were discovered.

Now hedgehogs are not always right, witness Lindzen, who feels it in his bones that climate sensitivity is less than 1K for 2X CO2. He has been turning over every rock to find the majic stone. In the beginning it was a useful exercise as others have closed holes in the models showing why he was wrong, but now he has become a crank and there is no point in even listening to him.

Aha! another post.

Mitchell said...

"Eli knows it too, and has been pointing out for years that the estimates of climate sensitivity have simply not moved much for over a hundred years."

B.P. Levenson's list shows considerable variation.

Even if we do focus on values for the sensitivity similar to the current estimates, are the reasons for those values the same, 100 years ago, 50 years ago, 30 years ago?

EliRabett said...

2-5 C/2x that's about where it has been forever. The Rasool and Schneider estimate only holds if you use the wrong CO2 forcing which they admitted in a footnote.