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Politics : The Environmentalist Thread -- Ignore unavailable to you. Want to Upgrade?

To: Thomas A Watson who wrote (20381)	2/15/2008 4:49:38 PM
From: maceng2	Read Replies (1) \| Respond to of 36921

# 21 It's water vapor 1.7% skepticalscience.com Click on #21 and you get the argument presented ======================================================== Water vapor is the most powerful greenhouse gas The skeptic argument...Water vapour is the most important greenhouse gas. If you get a fall evening and the sky is clear, heat will escape, the temperature will drop and you get frost. If there's cloud cover, the heat is trapped by water vapour as a greenhouse gas and the temperature stays warm. If you go to In Salah in southern Algeria, they recorded at noon 52°C. By midnight, it's -3.6°C. That’s a 56°C drop in temperature in 12 hours. It's caused because there is very little water vapour in the atmosphere and is a demonstration of water vapour as the most important greenhouse gas (source: Interview with Tim Ball). What the science says... Water vapour is indeed the most dominant greenhouse gas. The radiative forcing for water is around 75 W/m2 while carbon dioxide contributes 32 W/m2 (Kiehl 1997). Water vapour is also the dominant positive feedback in our climate system and a major reason why temperature is so sensitive to changes in CO2. Unlike external forcings such as CO2 which can be added to the atmosphere, the level of water vapour in the atmosphere is a function of temperature. Water vapour is brought into the atmosphere via evaporation - the rate depends on the ocean and air temperature and is governed by the Clausius-Clapeyron relation. If extra water is added to the atmosphere, it condenses and falls as rain or snow within a week or two. Similarly, if somehow moisture was sucked out of the atmosphere, evaporation would restore water vapour levels to 'normal levels' in short time. Water Vapour as a positive feedback As water vapour is directly related to temperature, it's also a positive feedback - in fact, the largest positive feedback in the climate system (Soden 2005). As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation. How does water vapour fit in with CO2 emissions? When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air more to a higher (more or less) stabilized level. So CO2 warming has an amplified effect, beyond a purely CO2 effect. How much does water vapour amplify CO2 warming? Without any feedbacks, a doubling of CO2 would warm the globe around 1°C. Taken on its own, water vapour feedback roughly doubles the amount of CO2 warming. When other feedbacks are included (eg - loss of albedo due to melting ice), the total warming from a doubling of CO2 is around 3°C (Held 2000). Empirical observations of water vapour feedback and climate sensitivity The amplifying effect of water vapor has been observed in empirical studies such as Soden 2001 which observed the global cooling after the eruption of Mount Pinatubo. The cooling led to atmospheric drying which amplified the temperature drop. A climate sensitivity of around 3°C is also confirmed by numerous empirical studies examining how climate has responded to various forcings in the past. Satellites have observed an increase in atmospheric water vapour by about 0.41 kg/m² per decade since 1988. A detection and attribution study (Santer 2007), otherwise known as "fingerprinting", was employed to identify the cause of the rising water vapour levels. Fingerprinting involves rigorous statistical tests of the different possible explanations for a change in some property of the climate system. Results from 22 different climate models (virtually all of the world's major climate models) were pooled and found the recent increase in moisture content over the bulk of the world's oceans is not due to solar forcing or gradual recovery from the 1991 eruption of Mount Pinatubo. The primary driver of 'atmospheric moistening' was found to be the increase in CO2 caused by the burning of fossil fuels. Basic theory, observations and climate models all show the increase in water vapor is around 6 to 7.5% per degree Celsius warming of the lower atmosphere. The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way. When skeptics cite water vapour as the most dominant greenhouse gas, they are actually invoking the positive feedback that makes our climate so sensitive to CO2 as well as another line of evidence for anthropogenic global warming.

To: Thomas A Watson who wrote (20381)	2/15/2008 4:55:40 PM
From: maceng2	Read Replies (1) \| Respond to of 36921

# 8 CO2 lags temperature 3.8% skepticalscience.com CO2 lags temperature The skeptic argument...Joe Barton to Al Gore: "You display a timeline of temperature compared to CO2 levels over a 600,000 year period. You indicate this is conclusive proof of the link of increased CO2 emissions and global warming. A closer examination reveals something entirely different. I have an article from Science magazine that explains a rise in CO2 concentrations actually lagged temperature by 200 to 1000 years. CO2 levels went up after the temperature rose. Temperature appears to drive CO2, not vice versa. You’re not just off a little. You’re totally wrong." (Source: Office of Congressman Joe Barton) What the science says... Does temperature rise cause CO2 rise or the other way around? A common misconception is that you can only have one or the other. In actuality, the answer is both. Milankovitch cycles - how increased temperature causes CO2 rise Looking over past climate change, scientists have observed a cycle of ice ages separated by brief warm periods called interglacials. This pattern is due to Milankovitch cycles - gradual, regular changes in the earth's orbit and axis. While there are several different cycles, the dominant climate signal is the 100,000 year eccentricity cycle as the Earth's orbit changes from a more circular to a more elliptical orbit (Petit 1999, Shackleton 2000). The eccentricity cycle causes changes in insolation (incoming sunlight). When springtime insolation increases in the southern hemisphere, this coincides with rising temperatures in the south, retreating Antarctic sea ice and melting glaciers in the southern hemisphere (Shemesh 2002). As temperature rises, CO2 also rises but lags the warming by 800 to 1000 years (Monnin 2001, Caillon 2003, Stott 2007). How does warming cause a rise in atmospheric CO2? As the oceans warm, the solubility of CO2 in water falls (Martin 2005). This causes the oceans to give up more CO2, emitting it into the atmosphere. The exact mechanism of how the deep ocean gives up its CO2 is not fully understood but believed to be related to vertical ocean mixing (Toggweiler 1999). The greenhouse effect - how increased CO2 causes temperature rise When there's more CO2 in the atmosphere, the earth absorbs more heat. Shortwave radiation from the sun passes straight through our atmosphere and is absorbed by the earth. The earth reemits it as longwave (infrared) radiation which is partially absorbed by atmospheric CO2. This is the greenhouse effect. CO2 lets energy in, doesn't let as much get out. CO2 warming explains how the relatively weak forcing from Milankovitch cycles can bring the planet out of an ice age. It begins with the high southern latitudes (eg - Antarctica) warming and releasing CO2 from the oceans. The CO2 mixes through the atmosphere, amplifying and spreading the warming to northern latitudes (Cuffey 2001). This is why warming in the southern hemisphere precedes warming in the northern hemisphere (Caillon 2003). This is confirmed by marine cores that show tropical temperatures lag southern warming by ~1000 years (Stott 2007). Climate sensitivity - how CO2 amplifies temperature increase Climate sensitivity is defined as how much global temperature increase if we doubled CO2. Studies of past CO2 and temperature records have helped quantify exactly how sensitive our climate is to changes in CO2. Temperature and various forcings (including CO2) over the past few centuries shows a climate sensitivity between 1.5 to 6.2°C (Hegerl 2006). One study combines the results from various paleontological studies to narrow climate sensitivity to around 2.5 to 3.5°C (Annan 2006). Basically, multiple studies covering many different periods of earth's history confirm that when CO2 is doubled, global temperatures go up around 3°C. So what does the CO2 lag tell us? The behaviour of CO2 in the past is well understood by climatologists and confirms the amplifying effect of CO2 in the atmosphere. Also, sharp temperature rises in the past indicate how sensitive climate is to change. Our past history shows how our climate is prone to "tipping points" where warming can lead to positive feedbacks sparking a runaway warming effect. Share this article: Digg Newsvine Reddit Del.icio.us Furl Technorati Related ArgumentsClimate sensitivity is low Further readingThat CO2 lags and amplifies temperature was actually predicted in 1990 in a paper The ice-core record: climate sensitivity and future greenhouse warming by Claude Lorius (co-authored by James Hansen): "Changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing" The paper also notes that orbital changes are one initial cause for ice ages. This was published over a decade before ice core records were accurate enough to confirm a CO2 lag (thanks to John Mashey for the tip). see also (linked on site) environmentaldefenseblogs.org