Created: 2000-03-05
Last Modified: 2000-03-05
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Global Warming

J. Bradford DeLong


OK. Let's try again...

The earth's cross-section intercepts 1.762 x 10^17 watts of solar radiation: that's 343 watts for each square meter of earth's surface. Of that 343 watts, 34 are reflected back into space by the land and the water, 21 are reflected back into space by the atmosphere, and 44 are reflected back into space by the earth's cloud cover. That leaves 240 watts per square meter of solar radiation hitting the earth's surface and being absorbed. And if the earth's temperature is to be constant the earth must in turn radiate 240 watts per square meter back into space.

If we were to double the atmospheric concentration of CO2, the CO2 would block a very large chunk of the earth's radiation with wavelengths between 14 and 18 micrometers (our current CO2 levels block roughly half of the radiation in this range). This is an important range of wavelengths. It is near the earth's radiation peak: a lot of energy comes out through this band. The physicists tell us that a doubling of CO2 would reduce radiation from the earth back into space from 240 to 236 watts--if the earth's temperature were to remain constant.

But if we have 240 watts coming in and 236 watts going out, the temperature isn't going to remain constant. It will rise, and a global temperature rise of 2.2 Fahrenheit degrees would put us back into thermal equilibrium if nothing else were changing--if cloud cover, the polar icecaps, water vapor, and a bunch of other things we don't understand well don't change.

But other things will change:

--a warmer earth is a wetter earth, with more water vapor in
the atmosphere, and water vapor is also a greenhouse

--a warmer earth has more low clouds, which tend to cool the
earth by reflecting solar radiation before it gets

--a warmer earth has more high clouds, which tend to warm the
earth by reflecting the earth's radiation back down to
the surface.

--a warmer earth has less ice and snow, which means that more
solar radiation would be absorbed.

--a warmer earth produced by human action is likely to have
more dust and sulfur compounds in its atmosphere, which
shade and cool the earth.

What will all this mean? We don't know. Scientists today give estimates of the increase in global temperatures from a doubling of CO2 (and other greenhouse gases) from pre-industrial levels that range from 1.8 degrees Fahrenheit (Lindzen) to 4.5 degrees Fahrenheit (Houghton) or higher.

Since December 23 a lot of people have told me that this is "junk science" because...

...the sea level is not rising, but falling. (Doubtful, but not yet relevant: no one's model would have predicted a noticeable rise in the sea level yet.)

...satellite measurements of atmospheric temperatures show not a warming but a cooling trend since 1979. (False: more recent satellite measurements show a sustained warming trend since 1979.)

...the global warming that occurred over the past century took place before humans had significantly raised CO2 levels. (Sorta true. Something else must have been driving increasing temperatures from 1900 to 1940. Global warming is a candidate explanation only for what we have seen since 1980.)

...people who fear global warming are opposed to nuclear power.

...starting to do something about global warming would expand the power of the government.

...any money raised in carbon taxes will be spent instantly.

...they [presumably scientists who believe in global warming] would like to see a major human die-off.

It seems clear (to me at least) that what most people are objecting to is not the science--the radiative physics, the thermodynamics, and the (crude) attempts to model atmospheres and oceans--but the politics: what they object to is not "junk science" but "junk politics."

It also seems clear (to me at least) that calling global warming "junk science" is extremely counterproductive for three reasons:

First, it's mendacious.

Second, there *is* a lot of junk science out there--a lot of lawsuits based on mendacious stupidity (of the "power lines cause cancer" or the "smoking doesn't cause cancer" level), and at least some juries that find themselves snowed under. This is a problem. Our chances of doing something about this problem will be lower if global warming is labelled "junk science": the argument that we need to stop "junk science" will then be countered by "yeah, well your guys think that global warming is junk science," and my arguments and those of the rest of the good guys will have less force.

Third, there is likely to be an enormous political battle a decade from now as the signal that is higher global temperatures emerges from the noise. The battle will be between those who call for imposing a massive and destructive EPA-led command-and-control regime on industrial civilization, and those who call for more sensible policies--carbon taxes, bounties for carbon sinks, nuclear energy, first world-funded transfer of clean technologies to China and India, better dikes for Bangladesh, living with some global temperature rise, and so forth. My side is going to be a lot weaker if the other side can say: "yeah, a decade ago your guys were saying that global warming was junk science."

People who call global warming "junk science" are trying to steal the bad connotations that have been (deservedly) attached to junk science and attach them to global warming. This is a bad thing to do because global warming *ain't* "junk science." And this is a bad thing to do because the blowback might be extremely destructive.


Brad DeLong


He disputes that the warming trend is caused by CO2. But as far as I
know no one disputes that the CO2 in the atmosphere a century ago
warmed the earth a lot...

Brad DeLong


I dispute it. Prove it, with logic and facts that do not include assumptions.

My Comment:

The flux of radiant energy from the sun onto a surface of one square meter normal to the sun at the mean distance of the earth from the sun is some 1370 watts. But each square meter of the Earth receives on average a quarter of this amount of radiation: remember that the surface of the Earth has four times the area of an earth-sized disk facing the sun. So that the average flux of radiant energy onto a square meter of the Earth is some 343 watts.

The atmosphere scatters about 6% of this radiation back into space before it even hits the Earth's surface. Because the earth is not a black body, an additional 10% of this radiation gets reflected back from the surface. Thus the average square meter of the Earth absorbs 288 watts.

To balance this incoming energy, the Earth must radiate at a rate of 288 watts per square meter. A body at a temperature of -6 degrees Celsius would radiate this amount of energy. Yet the average temperature of the Earth's surface is not -6 degrees Celsius, but about 15 degrees Celsius. A body at a temperature of 15 degrees Celsius radiates at a rate of not 288 watts per square meter but 390 watts per square meter. Something is absorbing the extra 102 watts per square meter of thermal radiation, and so keeping the Earth in thermal equilibrium at an average surface temperature that is comfortable 15 degrees Celsius, rather than a chilly -6 degrees.

What is this something? Our greenhouse gases:

--H20 (water vapor) (1% of the atmosphere)
--C02 (carbon dioxide) (.036%)
--CH4 (methane) (.00018%)
--N20 (nitrous oxide) (.00003%)
--O3 (ozone) (.0005%)

Water vapor is good at absorbing radiation with a wavelength of less than .0078 millimeters or of more than .018 millimeters or so. Methane and nitrous oxide are good at absorbing radiation with a wavelength between .0078 and .0083 millimeters or so. Ozone is very good at absorbing radiation with a wavelength between .0093 and .01 millimeters. And carbon dioxide is good at absorbing radiation with a wavelength of between .014 and .018 millimeters.

Take away all our greenhouse gases, and the earth looks a lot more like Mars...


Brad DeLong


I feel like I'm feeding the Troll

First observed by measurement 1956 by Dobson the guy who name is
on the measurement units. I suppose he's not reliable.

My Comment: ain't working.

But reports that:

There is an oft quoted statement that the Antarctic ozone hole was discovered in 1956 and therefore it can't be caused by CFCs. This remark originates from a paper by Professor G M B Dobson, the scientist who designed the ozone spectrophotometer which has been the standard for ozone measurements since the 1930s. The big advantage in standardising on one make of instrument is that we can be certain that changes in ozone amount that are measured, are changes in the atmosphere rather than changes due to observational technique. The following is taken from Dobson's paper in Applied Optics, March 1968, Vol 7, No3.

'One of the more interesting results on atmospheric ozone which came out of the IGY (International Geophysical Year) was the discovery of the peculiar annual variation of ozone at Halley Bay (76 south, 26 west). The annual variation of ozone at Spitzbergen was fairly well known at that time, so, assuming a six months difference, we knew what to expect. However, when the monthly telegrams from Halley Bay began to arrive and were plotted alongside the Spitzbergen curve, the values for September and October 1956 were about 150 units lower than was expected. We naturally thought that Evans has made some large mistake or that, in spite of checking just before leaving England, the instrument had developed some fault. In November the ozone values suddenly jumped up to those expected from the Spitzbergen results. It was not until a year later, when the same type of annual variation was repeated, that we realized that the early results were indeed correct and that Halley Bay showed a most interesting difference from other parts of the world. It was clear that the winter vortex over the South Pole was maintained late into the spring and that this kept the ozone values low. When it suddenly broke up in November both the ozone values and the stratosphere temperatures suddenly rose.'

This table shows the difference between what Dobson expected from Spitzbergen, the normal values observed at Halley between 1956 and 1975 and the values presently observed. Mean October ozone values have fallen by around 3% per year since 1976, while the amount of chlorine has risen by 3% per year.

Spitz Feb Mar Apr May Jun Jul Aug Sep Oct
1956 440 470 450 400 350 320 300 280 280

Halley Aug Sep Oct Nov Dec Jan Feb Mar Apr
1956 300 300 300 330 350 320 300 280 280
1996 172 155 149 181 260 278 265 245 242

The Antarctic ozone hole is the depletion in the spring over and above that caused by the different atmospheric circulations in the two hemispheres. Signs can be seen in data from 1976 when you know what to look for, but suspicion didn't really arise until the end of the decade and the paper announcing the discovery of ozone loss in the Antarctic was not published until 1985. When American satellite data was reanalysed it became apparent that it was a phenomena that covered the whole of the Antarctic and it was given the name ozone hole. The latest data also show ozone depletion during the summer and autumn months, in addition to the spring- time 'hole'.


Climate is _WAY_ more complex than you are
bothering to pay any attention to. So until
the eco-nuts are willing discuss the fact
that their "statistics" are hogwash and their
"facts" are theories, and theories as full of
holes as Swiss Cheese, I'm going to keep
pounding them.

However, if you were confused by this
response, I'll keep it simple: You are
spouting political bullshit and not science.

My Comment:

Ah, once again the manners of a pig...

It's hard to be polite in response. But I will try.

First, we are making progress in this thread: we have agreement that CO2 is being pumped into the atmosphere by human activity, that more CO2 makes a warmer world, and that climate is complex.

Please note that this is pretty far away from where you were a couple of days ago: now you're saying that we don't know how much human-induced global warming is happening; then you were saying that we had no good reason to think that human-induced global warming was happening.

But there is one important point that you have missed: uncertainty about the effects is not an argument for doing nothing. Uncertainty is an argument for buying insurance against the bad things that might happen.

The bad things that might happen from global warming over the next century are pretty clear: the potential for a lot of dead Bengalis as storm surges come up the Bay of Bengal, and the loss of some species as their habitats shift north too fast.

Figuring out what kind of insurance we should buy is hard. Please think about it. I think that we should shift some of our tax burden away from income and sales taxes and towards greenhouse gas-emissions taxes; I think that we need to fund a lot of research into oceanic and atmospheric physics; I think that we should fund a bunch of research into greenhouse gas-free sources of energy; I think that we should fund a bunch of research into carbon sinks.

Most important, however, we need people who are willing to update their beliefs in response to data: to take a fresh look at the information we have and evaluate it. So far in this thread I have said that:

...measurements of troposphere temperatures that used to show a
(slight) downward trend over time now show a (slight)
upward trend.

...dumping CO2 into the atmosphere will in all probability warm
the earth.

...noisy data is still data--albeit noisy.

...we shouldn't casually act to change the earth's climate without
thinking about what we are doing.

...there are big uncertainties.


Your response has been that I am "spouting political bullshit and not science." There are people who are spouting ideology--who are not looking at the data or using any more brainpower than a snail does. But I am not among them. I am trying very hard to mark my beliefs to market.

Please do the same.


Brad DeLong


I snipped the thing about the Ganges bull herder because my answer is I
don't care about Ganges bull herders...

My Comment:

Adam Smith would say--did say--that human society is held together by sympathy: an inborn propensity to think yourself into someone else's shoes, and imagine what they feel. I don't think he would have thought it possible for anyone sane not to care...

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Professor of Economics J. Bradford DeLong, 601 Evans Hall, #3880
University of California at Berkeley
Berkeley, CA 94720-3880
(510) 643-4027 phone (510) 642-6615 fax

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