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Joined: 05 Nov 2003
Posts: 387
Location: Auckland, New Zealand
Posted: Thu Apr 19, 2007 7:28 pm Post Subject: Water Vapor Rules the Greenhouse System
Although we don’t hear much about it in the Global Warming debate, it is an undeniable fact that water vapour is a Greenhouse gas and overwhelmingly the number one contributor to the Greenhouse effect. Not a bad thing - without it we would freeze to death, but when the natural system goes out of balance, we're in trouble. So is water vapour rather than carbon dioxide the real Global Warming culprit? Some scientists think so…
Quote:
Scientists are increasingly recognizing the importance of water vapor in the climate system. Some, like Wallace Broecker, a geochemist at Columbia's Lamont-Doherty Earth Observatory, suggest that it is such an important factor that much of the global warming in the last 10,000 years may be due to the increasing water vapor concentrations in Earth's atmosphere.
His research indicates that air reaching glaciers during the last Ice Age hadless than half the water vapor content of today. Such increases in atmospheric moisture during our current interglacial period would have played a far greater "role in global warming than carbon dioxide or other minor gases.
" I can only see one element of the climate system capable of generating these fast, global changes, that is, changes in the tropical atmosphere leading to changes in the inventory of the earth's most powerful greenhouse gas-- water vapor. "
From a lecture presented at R. A. Daly Lecture at the American Geophysical Union's spring meeting in Baltimore, Md., May 1996.
By comparison to water vapour, carbon dioxide and nitrous oxide are relatively minor contributors.
One set of figures:
I wonder though, how much of the atmospheric water vapour is Anthropogenic (man made). Scientific opinion seems to vary but normal human activity is usually portrayed as contributing very little, I've seen figures as low as 0.001%. I tend to doubt numbers like this and suspect that they may be very different if contributions of atmospheric water vapour from aviation was accurately factored in – and also included the extent of Cirrus Aviaticus in the atmosphere.
The IPCC Report "Aviation and the Global Atmosphere" had this to say on the matter:
Quote:
4.4. Water Vapor
Most subsonic aircraft water vapor emissions are released in the troposphere where they are rapidly removed by precipitation within 1 to 2 weeks. A smaller fraction of water vapor emissions is released in the lower stratosphere where it can build up to larger concentrations. Because water vapor is a greenhouse gas, these increases tend to warm the Earth's surface, though for subsonic aircraft this effect is smaller than those of other aircraft emissions such as carbon dioxide and NOx.
4.5. Contrails
In 1992, aircraft line-shaped contrails are estimated to cover about 0.1% of the Earth's surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth's surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 in the reference scenario (Fa1), at a rate which is faster than the rate of growth in aviation fuel consumption.
This faster growth in contrail cover is expected because air traffic will increase mainly in the upper troposphere where contrails form preferentially, and may also occur as a result of improvements in aircraft fuel efficiency. Contrails are triggered from the water vapor emitted by aircraft and their optical properties depend on the particles emitted or formed in the aircraft plume and on the ambient atmospheric conditions. The radiative effect of contrails depends on their optical properties and global cover, both of which are uncertain. Contrails have been observed as line-shaped clouds by satellites over heavy air traffic areas and covered on average about 0.5% of the area over Central Europe in 1996 and 1997.
4.6. Cirrus Clouds
Extensive cirrus clouds have been observed to develop after the formation of persistent contrails. Increases in cirrus cloud cover (beyond those identified as line-shaped contrails) are found to be positively correlated with aircraft emissions in a limited number of studies. About 30% of the Earth is covered with cirrus cloud. On average an increase in cirrus cloud cover tends to warm the surface of the Earth. An estimate for aircraft-induced cirrus cover for the late 1990s ranges from 0 to 0.2% of the surface of the Earth. For the Fa1 scenario, this may possibly increase by a factor of 4 (0 to 0.8%) by 2050; however, the mechanisms associated with increases in cirrus cover are not well understood and need further investigation.
4.7. Sulfate and Soot Aerosols
The aerosol mass concentrations in 1992 resulting from aircraft are small relative to those caused by surface sources. Although aerosol accumulation will grow with aviation fuel use, aerosol mass concentrations from aircraft in 2050 are projected to remain small compared to surface sources. Increases in soot tend to warm while increases in sulfate tend to cool the Earth's surface. The direct radiative forcing of sulfate and soot aerosols from aircraft is small compared to those of other aircraft emissions. Because aerosols influence the formation of clouds, the accumulation of aerosols from aircraft may play a role in enhanced cloud formation and change the radiative properties of clouds.
Are they understating the matter? One group, Astronomers, would probably accuse them of that; they undoubtedly consider the aviation industry a very real threat to the practise of their science.
I know we've posted a link to this BBC article before, but it's worth reading as it's content is rather startling:
Quote:
“ground-based astronomy could be impossible in 40 years because of pollution from aircraft exhaust trails and climate change”.
I was listening to National Radio a couple of weeks ago, they were talking to a group of Pararparaumu astronomers. One related a story about a visiting American astronomer who was using their telescope. Noticing that he was showing signs of impatience, they asked if he was having problems.
"I'm waiting for this cloud to get out of the way!"
"Mate", they laughed, "That’s the Milky Way"
I don't really know if that has anything to do with anything above, but I thought it was funny...
Joined: 15 May 2007
Posts: 977
Location: north-east victoria
Posted: Wed Nov 21, 2007 4:07 pm Post Subject:
i met a guy who had scientific training , who has made a video , on the theme that the micron-thick layer of oil slick on the ocean surface , might be responsible for inhibiting the evaporative process significantly
sounds as good as , or better than some "science" being bandied about?
worth speculating how it might tie in with the above ?
if anyone can find some good educational material on how rain works, can they please post the link? (where is Hector when you need him?)
