Global Dimming

David Tiley has an has an interesting summary of a BBC program on Global Dimming. It seems that, over the past 40 years, while the amount of sunlight reaching the top of the atmosphere has not changed, the amount of sunlight reaching the surface has declined. Despite this, the earth has warmed over the same time span. The BBC program raises the alarming prospect that burning fossil fuels is making aerosols that produce the dimming and global cooling that is partially masking the warming produced by increased greenhouse gasses. That suggests that the greenhouse gasses are much more potent than previously estimated and the program suggests that catastrophic warming of 10°C this century may occur.

Now the Tech Central Station crew like to use the pejorative term "alarmist" to describe the mainstream scientists that believe that anthropogenic warming is occurring, but the BBC program really is alarmist. Climate Scientist Gavin Schmidt hoses down the speculation:

The suggested 'doubling' of the rate of warming in the future compared to even the most extreme scenario developed by IPCC is thus highly exaggerated. Supposed consequences such as the drying up of the Amazon Basin, melting of Greenland, and a North African climate regime coming to the UK, are simply extrapolations built upon these exaggerations.

Now let me show you the bizarre world where the anti-Kyoto bloggers live. According to Spear Shaker the BBC program shows that

the Kyoto Protocol, fully implemented, would lead to a dramatic increase in the Earth's temperature.

and John Ray thinks this is the death knell for global warming:

Is this the ultimate kick in the pants for the global warming fanatics---that what they advocate will PRODUCE the problem, not solve it?

To be fair, they had an assist from this atrocious Reuters story by Matt Falloon, where Falloon managed to completely misunderstand what the scientists were saying. He wrote:

The researchers say cutting down on the burning of coal and oil, one of the main goals of international environmental agreements, will drastically heat rather than cool climate.

No, the researchers did not say that. What they said was:

Take away fossil fuel by-products like sulfur dioxide without tackling greenhouse gas emissions, and the extra heat will speed warming, irreversibly melting ice sheets and rendering rain forests unsustainable within decades, Dr Cox said.

If you stop burning fossil fuels you reduce sulfur dioxide and greenhouse gas emissions. Apparently Falloon is unaware that burning fossil fuels releases greenhouse gasses. Cox is referring to technology like sulfur dioxide scrubbers that remove the sulfur dioxide from burning coal but do not remove the carbon dioxide. Cox is absolutely not saying that reducing the burning of fossil fuels will cause global warming. I imagine we'll soon see a Tech Central Station article about how Kyoto will cause global warming.

Falloon disgraces himself further with this statement:

Scientists differ as to whether global warming is caused by man-made emissions of carbon dioxide and other "greenhouse" gases, by natural climate cycles or if it exists at all.

Yes, and scientists differ over whether evolution explains the origin of species. Chris Mooney has the goods on how this sort of "balance" misinforms readers. At least you can rate Falloon's story at Yahoo. I gave it a "1".

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I imagine we'll soon see a Tech Central Station article about how Kyoto will cause global warming.

That should peovide an interesting conuundrum for the people at the Warming Earth Society who claim that lgobal warming is a good thing. Presumably, if they buy Falloon's argument, they'll now start supporting Kyoto.

By Ian Gould (not verified) on 19 Jan 2005 #permalink

Other Greenhouse gases? Water Vapour is the dominant greenhouse component. Period.

By Louis Hissink (not verified) on 19 Jan 2005 #permalink

Yes. Louis water vapor is the dominant greenhouse gas. however, water vapor makes up a considerably larger proportion of the atmosphere (on average) than does CO2. It's therefore considerably less prone to human interference than Co2 or other trace components such as methane.
I haven't looked at the relevant science for quite some time but if I recall correctly it's also the case that existing water vapor concentrations trap virtually all the heat reradiated by the Earth at the frequencies which are absorbed by water vapor. So further increases in water vapor have minimal additional impact.

By Ian Gould (not verified) on 19 Jan 2005 #permalink

Actually Louis the sun is the number one component.

I remember an old song where a man rates this woman he sees in a bar and gives her a 9 because he doesn't give out 10's. She then begins a detailed rating of him and ended by saying that she will give him a 1 because she doesn't give out zeros.

The Yahoo news rating reminds me of that. I gave it a 1 because Yahoo doesn't let me give it a 0!

Yelling, you're thinking of "Numbers", written by the late, great Shel Silverstein and sung by Bobby Bare. I must tip my John Deere hat to you for working the most underrated country song of all time into a discussion about global warming. Now back to the mudslinging ...

Rob, the sun is not a greenhouse gas component because it is not a gas (although it is composed of gas), and it is not part of our atmosphere.

Whoa Tim, don't open up the Evolution as origin of species can of worms, you've got enough on your plate.

Ben, Louis didn't say "gas".

By Ken Miles (not verified) on 19 Jan 2005 #permalink

FWIW, increasing atmospheric water vapor content is an important issue. HOWEVER, there are things called oceans. If you increase the sea surface temperature by any means, you will increase water vapor in the atmosphere, which will increase the temperature further. Basically the Clausius Clapyron equation with teeth.

That being the case, the rise directly associated with doubling the atmospheric CO2 mixing ratio accounts for a change of about 0.7 C (approximate, very approximate) and you get an amplification of about 2 C additional from the increase in water vapor concentration caused by heating the sea surface. All numbers subject to rounding windage.

So now Louis asks, well what if we increased water vapor content without increasing the temperature, and the answer is that it would rain (snow where I am now) out in a few days before any global effect would occur. The response of the earth system to rising humidity in the absence of other forcings is too fast. Water vapor content is a feedback not a forcing.

This is really the point. Fossil CO2 is forever (OK, at least half a millenia to a millenia to return CO2 mixing ratios to the status quo ante, and about 10-100K years to put it back into rocks). Water vapor is one or two days.

Ken, Louis said

Other Greenhouse gases?
Water Vapour is the dominant greenhouse component.

which seems clearly to imply *gas* to me.

ben, Louis was thinking "gas" when he wrote component, but he wrote "component", so Rob was correct in his comment. More importantly, the point of his remark was to imply that the other gasses were unimportant and aren't going to make a difference. This implication is untrue, as Eli explained.

ER is correct. The assertion that "WV is the dominant GHG therefore we don't need to worry about CO2" is an old skeptic trick. However, they often overplay their hand and assert that WV is 95% of the greenhouse effect. Its hard to get good numbers, but about 60-70% for WV is the value I've seen (see http://en.wikipedia.org/wiki/Greenhouse_effect for some more details). As ER points out, WV has such a short lifetime (about a week), its not really a driver, so I don't think anyone is interested in quantifying the effect too closely.

Water vapour is a gas? It does become a gas at greater than 373 Kelvin. Below that temperature it is. But Tim, how on earth could you know what I was thinking when I posted that.Global Dimming is related to aerosols which are essentially "particulate matter". Sulphur dioxide is a gas, and therefore not an aerosol.there is a limitation to the amount of energy that either water vapour or CO2 can absorb, and simple arithmetic suggests that if the current atmosphere is absorbing most of the energy from space, (sun etc), then increases in these heat trappers will not increase temperatures, merely redistribute the energy amonsgt more deserving gases, based on egalitarian principles for the distribution of energy to gases.

By Louis Hissink (not verified) on 20 Jan 2005 #permalink

Whoops, below 373 Kelvin it is a liquid. Apologies.

By Louis Hissink (not verified) on 20 Jan 2005 #permalink

Oh Louis, why do you do this to yourself?

Water vapour is a gas? It does become a gas at greater than 373 Kelvin
Clothes on a washing line do not reach a temperature of 373 Kelvin (for people unfamiliar with the Kelvin scale, this is 132 degrees McKitrick). Nevertheless, after you've left them up there in a stiff breeze for a few hours, the water content has gone. Only a small amount of it has dripped out as a liquid, it has not been converted into energy - what has happened is that the water has evaporated.
Louis' confusion over the significance of boiling points would have the implication that there can be no evaporation on high mountaintops; on top of Everest, water boils at 80C (=353K or 112M).

dsquared, I think you have misundertood Louis. In his world, water still evaporates at temperatures under 100C, its just that the when it evaporates it does not become a gas but, errm, a vapour. Which I guess is like a gas only different in that it is really a liquid. I think.

Hey Louis, does water vapour (the liquid kind below 100C) obey Boyle's Law?Oh, and while sulphur dioxide is a gas, it turns into sulphates which are aerosols.

Are you ever going to get around to addressing Lott's substantiative points in his posts on Volokh.com? You seem to be obsessing on the issue of alleged panel bias, to the exclusion of all else.

By Brett Bellmore (not verified) on 20 Jan 2005 #permalink

Eeeps, came in this morning and took a look but managed to double post. Apologies. OTOH, the additions were interesting to read. Tim, please delete the double post

A lot of it was the normal confusion between natural and scientific language. There is a way of referring to what we are talking about clearly, "gas phase water (GPW)", but, because the stuff is so ubiquetous, we have zillions of ways of naming it, depending on circumstance. Generally speaking, water vapor refers to GPW at temperatures below the local boiling point. Steam refers to GPW at the local boiling point, and superheated stea refers to GPW above the local boiling point. Then you have high steam, wet steam, dry steam and more. http://www.hyperdictionary.com/dictionary/steam
This is one of those places where context is everything.

However, there are two serious issues raised. All substances have some vapor pressure (a proportion of the material that exists in the gas phase) at all temperatures above absolute zero. For things like chunks of iron, it may be 1 atom per cubic parsec, but it does exist. For substances such as water it is substantial at temperatures characteristic of where we live, as substantial as the humitidy....

One of the most interesting things about aerosols is how they grow and change their properties when you add water vapor. So yes, aerosol effects are coupled to the humidity. To show how complicated this can be there is an interesting paper by the Molina group about how atmospheric oxidation of soot allows the particles to pick up water vapor and become cloud condensation nuclei. This may be the mechanism which simultaneously sets both upper and lower limits for the atmospheric lifetime of soot.

>simple arithmetic suggests that if the current atmosphere is absorbing most of the energy from space, (sun etc), then increases in these heat trappers will not increase temperatures, merely redistribute the energy amonsgt more deserving gases, based on egalitarian principles for the distribution of energy to gases.....

Louis, you really have no idea do you??? Prehaps you might post for us your simple arithmetic? If your maths is correct, you will be in line for the Nobel prize in physics.

Why don't you just admit that your denial of enhanced greenhouse effect is faith based... full stop, rather than hiding behind pseudo scientific terms that only the climate illiterate would fall for.

BTW, if you really want to understand a little more about the greenhouse affect, and how it is a verified observational fact, have a read of Harries et al. Nature, 410, 355-357 "Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the earth in 1970 and 1997." Simple arithmetic and conservation of energy (you do believe in that don't you?) imply that this energy goes somewhere - ie warming... you are right that there is a limit to how much energy CO2 can absorb, but we are not there!

conservation of energy (you do believe in that don't you?)

I wouldn't count of that. Louis doesn't believe in plate tectonics or the Neosynthetic theory. So it's entirely possible that he doesn't go for the conservation of energy stuff.

The neosynthetic theory is BTW, a very alternative way of saying Darwin's theory of evolution.

By Ken Miles (not verified) on 20 Jan 2005 #permalink