‘Climate scientists dodge the subject of water vapor’—No, they really don’t 4

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Climate scientists never talk about water vapor -- the strongest greenhouse gas -- because it undermines their CO2 theory.

Answer: Not a single climate model or climate textbook fails to discuss the role water vapor plays in the greenhouse effect. It is the strongest greenhouse gas, contributing 36% to 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered a climate "forcing," because the amount of H2O in the air basically varies as a function of temperature.

If you artificially increase the level of H2O in the air, it rains out immediately (in terms of climate response times). Similarly, due to the abundance of ocean on the earth's surface, if you somehow removed all the water from the air, it would quickly be replaced through evaporation.

This has the interesting consequence that if you could somehow instantly remove all CO2 from the atmosphere, the temperature would begin to drop, causing precipitation to remove H2O from the air, causing even further drops, in a feedback effect that would not end until no liquid water was left, only ice sheets and frozen oceans.

CO2 put into the air by burning fossil fuels, on the other hand, stays in the atmosphere for centuries before natural sinks finish absorbing the excess. This is plenty of time to have substantial and long-lasting effects on the climate system. As the climate warms in response to CO2, humidity rises and increased H2O concentration acts as a significant amplifier of CO2-driven warming, basically doubling or tripling its effect.

An article from RealClimate -- "Water vapor: feedback or forcing?" -- has a good discussion of this subject.

Former musician, turned tree planter, turned software engineer. Same old story…

I have been blogging about climate change since 2006 at A Few Things Ill Considered.

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  1. vaporman Posted 7:17 am
    17 Jun 2007

    water pumped from underground aquifersfor all the talk of "sequestering" CO2 how can we ignore the "de-sequestration" of water from underground aquifers? Here's the bottom line-- the high-end estimate of annual CO2 discharge is 25 billion tons per year. However, the annual rate of groundwater "de-sequestration" i.e. the net amout of water pumped to the surface and not returned underground is 160 billion tons per year. Even though all of this water is now in the atmopheric system, i.e. the lower troposphere, let us just assume that half, or 80 billion tons a year ends up as extra atmospheric water vapor. since water vapor has about ten times the "greenhouse effect" as CO2, this is the CO2 equvalent of 800 Billion tons!! Or about 32 times the impact of CO2 increase!! Water aquifer info is from various sources, including USGS and USAID.

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  2. bobbyfontaine Posted 1:37 am
    25 Jun 2007

    pollution changes water vaporwater vapor does not condense normally into rain when polluted so there is more water vapor in the atmosphere because it has been made toxic and gaseous

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  3. warreno Posted 11:32 pm
    05 Jul 2007

    Low physical concentration limits to water vaporThere is a very strict, and pretty low partial pressure limit to water in the atmosphere, as well as to limits on suspension of ice/water particles in the air. This is true even for slight rises of temperature. Suffice it to say that any amount of water removed from the ground goes into the ocean or possibly into ice.  The main effect is localized freshening of sea water.  The atmosphere really does not count as a storage in the water cycle.

    Water vapor is essentially an system amplifier of heat forcing, where as C02 makes the forcing term larger.

    I'm trying to think of a good mechanical analogy.

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  4. barry schwarz Posted 5:32 pm
    15 Jun 2008

    water vapour discussed at length 2001 2007 IPCC[Transferred in part (and slightly amended) from my post on the subject at illconsidered blogspot]
    Water vapour gets a lot of mention in the IPCC documents (Intergovernmental Panel on Climate Change).
    If you want to corroborate this, you can open the pdf files for each of the IPCC chapters at the links below, type 'vapour' (note the European/Australian spelling) in the search box, and click the appropriate button to search through each document (different versions of pdf have different search buttons).
    IPCC 2001:
    http://www.grida.no/climate/ipcc_tar/wg1/index.htm
    Don't bother with the HTML pages on the left of that web page. They're just summaries of the chapters. Open the pdf files on the right hand side of that page and have a good search.
    IPCC 2007:
    http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
    I chose 3 chapters for 2007, the three I thought most likely would discuss water vapour (2, 3 and 8, from memory).
    I also ran a search on 'carbon dioxide' and 'CO2' and compared the results.
    Again from memory, there was 273 hits for 'water vapour', and 295 for 'CO2' and 'carbon dioxide' from those three chapters, including the studies referenced at the bottom of the page.
    I chose 3 chapters from 2001 and did the same thing. There were tons of hits for water vapour in that one, too. I then checked all the chapters but didn't bother to count, as it was obvious that water vapour was discussed again and again. Some chapters only mention it a little.
    Also, both the 2001 and 2007 reports had sections specifically dedicated to water vapour.
    This says nothing about the focus or quality of the science, of course, but it completely dispels the myth behind this simple statement:
    "Climate scientists dodge the subject of water vapor"

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'There is no evidence' -- Yes, there is 59
'Mauna Loa is a volcano' -- CO2 rise is measured on top of a volcano! 8
'Warming is due to the Urban Heat Island effect' -- No, it isn't 25
'One hundred years is not enough'--Yes it is 18
'The scientists aren't even sure' -- No scientist ever is 33
'One record year is not global warming'--Luckily, there are plenty more years to consider 19
'Glaciers have always grown and receded'--A few glaciers melting does not mean global warming 14
'The temperature record is unreliable'--But temperature trends are clear and widely corroborated 8
'It's cold today in Wagga Wagga'--Weather and climate are different 2
'The satellites show cooling'--No, they don't 15
'What about mid-century cooling?'--No one said CO2 is the only climate influence 11
'Antarctic ice is growing'--Well, probably not, but even if it were, we are not off the hook 8
'Global warming stopped in 1998'--Only if you flagrantly cherry pick 170
'But the glaciers are not melting'--Except ... they are! 3
'Antarctic sea ice is increasing'--Yes, but ... 14
'Sea level in the Arctic is falling'--Sea level is a surprisingly complicated thing 11
'Climate sensitivity is not very high'--Thermal inertia of the oceans means the jury is still out 2
'Some sites show cooling'--But you can't draw global conclusions from individual sites 0
'Global warming is a hoax'--I wish James Inhofe were just a hoax ... 12
'There is no consensus'--If this is not consensus, what would consensus look like? 109
'Position statements hide debate'--True enough, but that is not the whole picture 5
'Consensus is collusion'--Is climate science maturing, or should we reach for our tinfoil hats? 8
'Peiser refuted Oreskes'--In a poor piece of work that has been retracted by its author 4
'Models don't account for clouds'--Clouds are complex and uncertain, but unlikely to stop warming 6
'Climate models are unproven'--Actually, GCM's have many confirmed successes under their belts 13
'Aerosols should mean more warming in the south'--More North. Hemisphere warming is well-understood 1
'We can't even predict the weather next week'--But weather is not climate 11
'Chaotic systems are not predictable'--Sure, but who says climate is chaotic? 13
Understanding what is happening right under our noses does not require paleoclimate perfection 1
'They predicted global cooling in the 70s'--But that didn't even remotely resemble today's consensus 29
'Hansen has been wrong before'--Maybe, but not about the climate! 13
'It was warmer during the Holocene Climatic Optimum'--This period was not global and not like today 4
'The Medieval Warm Period was just as warm as today'--Repeating this point does not make it true 216
'Greenland used to be green'--Don't judge a book by its cover, much less a land by its name 23
Yes, the last ice age started thawing over 20,000 years ago, but that stopped a long time ago 5
'The hockey stick is broken'--Well, no ... but who's playing hockey anyway? 6
'Vineland was full of grapes'--Or was it an early advertising campaign? 4
'Global warming is part of a natural cycle'--This idea is one short step above appealing to magic 39
'Mars and Pluto are warming too'--No they aren't -- and what if they were? 24
'Volcanoes emit more CO2 than humans'--Not even close ... 31
'The null hypothesis says warming is natural'--An inappropriate test, and one that would fail anyway 4
'Climate is always changing'--That doesn't mean it isn't different today 5
'Natural emissions dwarf human emissions'--But emissions are only one side of the equation 5
'The CO2 rise is natural'--No skeptical argument has been more definitively disproven 12
'We are just recovering from the LIA'--Why should we expect this to happen? 4
'Climate scientists dodge the subject of water vapor'--No, they really don't 4
Water vapor is indeed a powerful greenhouse gas, but there is plenty of room for CO2 to play a role 29
There is no proof in science, but there are mountains of evidence 78
'CO2 doesn't lead, it lags'--Turns out CO2 rise is both a cause and an effect of warming 43
'Geological history does not support CO2's importance'--Just not true 0
'Historically, CO2 never caused temperature change'--Not so 19
'It's the sun, stupid'--Very bright, yes, but not getting brighter 18
The problem is not how high the temperature may go, but how fast it is changing 14
'Kyoto is a big effort for almost nothing'--Kyoto is only in its first phase 16
China and India have joined Kyoto, they just have different obligations, as is morally appropriate 3
'Climate change mitigation would lead to disaster'--Not really, but this may be lesser of two evils 6
Only if you ignore fossil fuel emissions 10
In 2008, did temperatures drop as much as they rose over the whole 20th century? 71
Is the IPCC so wrong their theories contradict a basic laws of physics? 23
Is the American Physical Society a crack in the climate change consensus? 3
Summer ice in the Arctic has recovered--Was the Arctic ice retreat a climate anomaly? 7
'Global warming comes from within'--Is heat at the Earth's core the real cause of global warming? 10
Was there another breathless announcement of another phony record, and another quiet retraction? 1
Hansen wants the skeptics thrown in jail--Did James Hansen really want to try the climate skeptics? 6
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