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Glom
2004-Oct-02, 11:56 PM
Apparently, the IPCC have omitted to mention the role of water vapour, which is reportedly all natural and accounts for 95% of the Greenhouse effect. What's going on?

PS I hope this isn't getting too political. I meant it is a scientific way.

01101001
2004-Oct-03, 02:45 AM
Apparently, the IPCC have omitted to mention the role of water vapour, which is reportedly all natural and accounts for 95% of the Greenhouse effect. What's going on?

Your comment seems to presume a lot of knowledge on the part of your readers. Have some pity. Could you elucidate? I looked up IPCC (Intergovernmental Panel on Climate Change (www.ipcc.ch/) -- but I can't get there right now), so now I know what that is, but where, in what, did they omit mentioning water vapor? Thanks.

CUStudent
2004-Oct-03, 03:28 AM
I think what he (she?) means is that Water Vapor is a greenhouse gas and contributes more to global warming than just CO2 or CFC's, and yet people talk about pollution as being the cause of global warming. I can see where the argument is going.

Two things to consider, though, as I understand things to be:
1. We can't control how much water vapor is in the atmosphere. It's going to be there absorbing infrared whether we want it to or not. We can control pollution, which is why we make such a big deal of its influence on global warming.

2. In the most simple sense, more water vapor is in the atmosphere when temperatures are warmer. This means that any increase in average global temperature due entirely to CO2 or pollutants will then increase the amount of water vapor in the air, which increases temperatures, etc. It's something akin to a feedback loop.

I sincerely hope this doesn't turn into a flamewar or get locked. Figured I'd take my chances, though.

Glom
2004-Oct-03, 11:10 AM
Here (http://www.john-daly.com/guests/un_ipcc.htm) and here (http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html) are examples of a few sites I've seen that report that the report of the International Panel on Climate Change didn't mention the most important factor affecting the Greenhouse Effect.

swansont
2004-Oct-03, 04:02 PM
2. In the most simple sense, more water vapor is in the atmosphere when temperatures are warmer. This means that any increase in average global temperature due entirely to CO2 or pollutants will then increase the amount of water vapor in the air, which increases temperatures, etc. It's something akin to a feedback loop.


But more cloud cover increases the albedo, which tends to reduce the temperature.

Also, I recall attending a talk some years ago in which the speaker discussed some effects relating to this. Particulates (i.e. pollution) tended to increase cloud cover, because they act as nucleation sites. In the experiment the speaker was discussing, they were able to track ocean-going ships because clouds would form along the track from the emissions. (also, he wasn't offering up pollution as a way to mitigate global warming, though he admitted one could draw that conclusion)

CUStudent
2004-Oct-03, 04:24 PM
But more cloud cover increases the albedo, which tends to reduce the temperature.

I'm no expert on the subject of global warming and have not read the IPCC report. I would like to add, though, that Venus has a rather high albedo and lots of cloud cover, but I wouldn't figure it to be cool down below.

RoboSpy
2004-Oct-04, 12:54 AM
But Venus' clouds are of a radically different chemical composition - mostly CO2 with a bunch of sulfuric acid and whatnot. I'm not going to pretend like I know how the specific composition effects the warming or cooling of the planet, but I want to point out that the high temperatures there may be due to other factors than mere cloud cover alone.

loandbehold
2004-Oct-04, 04:11 PM
Apparently, the IPCC have omitted to mention the role of water vapour, which is reportedly all natural and accounts for 95% of the Greenhouse effect. What's going on?

I'm not sure where you are getting this information from, but there's actually a large part of the 2001 IPCC Working Group I report which discusses water vapour and the role of clouds:

http://www.grida.no/climate/ipcc_tar/wg1/260.htm (Section 7.2)

As for the 95% figure, do you have a reference for that? As far as I know, the contribution of water vapour to the natural greenhouse effect is closer to 60% (source: Kiehl and Trenberth, Bull. Amer. Meteor. Soc. 78, 197 (1997) abstract (http://www.cgd.ucar.edu/cas/abstracts/files/kevin1997_1.html))

Glom
2004-Oct-05, 09:20 AM
That was 2001. Apparently they didn't mention it in the 1995 report.

Tunga compiled a list of skeptical links here (http://personals.galaxyinternet.net/tunga/OSGWD.htm).

This (http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html) one attributed water vapour to 95% of the Greenhouse effect. This (http://www.john-daly.com/guests/un_ipcc.htm) one had a few things to say about the IPCC.

Ooh, here's (http://pubs.acs.org/subscribe/journals/ci/31/special/may01_viewpoint.html) another source for that 95% statistic.

loandbehold
2004-Oct-05, 12:35 PM
That was 2001. Apparently they didn't mention it in the 1995 report.

Well, the 1995 report isn't available online, so unless someone has a copy of SAR lying around you'll either have to order it or see if your library has it.

I would be extremely surprised if they didn't mention it, though. As someone mentioned earlier, one would expect water vapour concentrations to increase with the temperature, leading to further enhancement of the greenhouse effect. So it appears in the models as a source of positive feedback, which will tend to increase the temperature futher (and as far as I know, this has been included in the models for decades). So, if the IPCC did display bias towards AGW, as one of your link alleges, then neglecting water vapour wouldn't make any sense.

Just to mention clouds- they do have an albedo, which tends to cool things, but they also have a greenhouse effect of their own. You then have a competition between the two effects, and whether clouds have a net cooling or heating depends upon the particular conditions (e.g. their altitude). Clouds are also included in the models as a feedback, but there's still a lot of uncertainty about how large this is. With the other feedbacks included you still have a net positive feedback, but the size of it is still uncertain. And actually the cloud feedback is the main reason why there's still a lot of variation in the model outputs when the carbon dioxide is increased.


This (http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html) one attributed water vapour to 95% of the Greenhouse effect.

This link basically references other sites that either no longer work or simply state the 95% figure- they don't actually provide a calculation which justifies this figure.


Ooh, here's (http://pubs.acs.org/subscribe/journals/ci/31/special/may01_viewpoint.html) another source for that 95% statistic.

Seems like a bit of a hand-wave to me. I think really the only way of getting a reliable estimate is to include all of the absorption lines of the various gases (using realistic values of the concentrations, distributions, etc.) and overlay it with the IR emission spectrum of the Earth. Then you can calculate the total absorption of each gas. That's basically what the paper I referenced earlier does (and by the way, you can read it online here (http://www.geo.utexas.edu/courses/388G/KiehlTrenbertth97.pdf) if you're interested).