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View Diary: Global Warming Discussions On The Airplane (124 comments)

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  •  CO2, aerosols (and the ozone layer too) (none)
    I read somewhere that the greenhouse gases are actually helping to block the sun's rays to keep us from burning to a crisp.

    I can't deal with all your questions this morning (fuzzy head :-), but I'll tackle the first one. It sounds like you were being confused with references to several different things, as often happens with anthropogenic climate change issues.  

    Apart from water, there are no greenhouse gases, as far as I know, that double as screens of sunlight, but many processes that emit carbon dioxide (the most notorious and significant greenhouse gas, though one of the least powerful, ton for ton) also produce aerosols that linger for various periods in the atmosphere.  It is estimated that the Sulphates belched out by the dirty industrial activity in the twentieth century helped to mask some of the warming, and as we clean up our act, that masking will go away and the temperature will rise even more sharply.

    Some points to note:

    • the masking effect wasn't powerful enough to lead to cooler temps, only less warm ones than would otherwise occur
    • It wouldn't be a good thing to keep pumping sulphates out, as it's the cause of acid rain, which is an environmental pest all it's own.
    • nature also provides this effect all by itself without our help, when volcanoes go off. However, she does so at random, and also just because it happens naturally desn't mean we need to stick our own contribution in as well.
    So, to summarise, stopping was a good thing, but it looks like the underlying warming trend (caused, remember, by CO2, not sulphate) will be even harder to ignore now.

    Water itself is a greenhouse gas, and a light-blocking aerosol (also known as clouds :-). We don't have to worry about making it ourselves, but we do need to consider the positive or negative feedbacks it contributes to the climate. Did temperatures go up over North America on 9/11? I hadn't heard that, but it's possible, if the condensation trails (caused by the water produced by jet engines) also screened sunlight, but I wouldn't treat this as a significant or long term effect (the fact that it came and went in a day tells you it's a much more ephemeral phenomenon than the centuries-long CO2 forcing trend).

    I mentioned other, more powerful greenhouse gases; Methane is one. the good news is that it's not persistent, so if you can stop producing it via industry and agriculture, it will disappear from the atmosphere quickly. The bad news is that biological and geological processes can produce it in vast quantities, and we can release it into the atmosphere by... warming the planet. Hello, positive feedback cycle! The nightmare scenario here is if our climate forcing activities set off a chain reaction that causes a really fast warming. There is some evidence that extra methane is already about to enter the atmosphere in a big way from the melting permafrost of Siberia.

    Haloalkanes are the chemicals you've heard about that go in refrigerators, spray cans, and dry cleaning. They're actually very powerful greenhouse gases, but we never produced them in enough quantities for that to be a big issue. The real problem with haloalkanes is that they go up into the stratosphere and destroy the ozone layer that blocks the UV light that causes skin cancer. Apart from being bad in itself, the disappearance of the ozone layer also causes the stratosphere to cool and the lower atmosphere to warm, because UV energy that would be trapped in the stratosphere makes it down to the ground. Fortunately this is a problem we as a species are tackling fairly well at the moment, although of course right wingers are bitching about not being able to make cheap spray cans anymore.

    I think that's it. I'll try to sum it up with a check list.

    Carbon dioxide
    Effect: global warming
    industry, transportation (no warming feedback)
    volcanoes  (no warming feedback)

    Effect: global cooling, acid rain
    industry (no warming feedback)
    volcanoes (no warming feedback)

    Effect: global warming
    farming, industry (no warming feedback)
    volcanoes  (no warming feedback)
    natural biosphere (+ve warming feedback)
    ground and ocean reservoirs  (strong +ve warming feedback)

    Effect: global warming and/or cooling
    the whole planet (+ve and -ve warming feedback)

    Effect: global warming, ozone depletion, stratosphere cooling
    industry (no warming feedback)

    Finem respice et principiis obsta—Consider the end, and thwart the beginning

    by Del C on Sat Dec 31, 2005 at 03:16:42 AM PST

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