The Role of Water Vapor in Climate Change

Craig James Blog ^ | March 31,2007 | Craig James

[DouglasKC]

The Role of Water Vapor in Climate Change

Posted By Craig James @ March 31st, 2007 under All Blog Posts, Craig James.

 

You have probably heard the comment that if it wasn’t for the greenhouse effect, the Earth’s average temperature would be around zero degrees Fahrenheit instead of the 57 degrees we currently enjoy. Obviously, the greenhouse effect is a good thing. But of course, the current questions is: can we get too much of a good thing?

There are five main greenhouse gases (gases that trap the Earth’s long wave radiation and produce a warmer climate). These naturally occurring plus human generated greenhouse gases include water vapor (H2O), Carbon Dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3), plus a few other minor ones. What I have found is that the generally accepted numbers for the contribution of water vapor to the greenhouse effect is 60- 70%. It varies somewhat depending upon cloud cover but everyone agrees water vapor plays the major role in the greenhouse effect. You can find a technical discussion of the subject in this article in the Bulletin of the American Meteorological Society. If you don’t want to wade through all the technical jargon, the main thing I want to point out from the conclusion of this paper is “in discussing increases in greenhouse gases and their impact on climate change, the dominant contribution of water vapor to the current greenhouse effect is often overlooked.”

That is an amazing statement. There is just a brief mention in the latest IPCC Summary that water vapor in the atmosphere has increased due to greater evaporation because of warmer temperatures, but a more significant discussion of the role of water vapor can be found in the IPCC report released in 2001. If the atmospheric water vapor concentration increases as a result of a global warming, then it is expected that it will enhance the greenhouse effect further. This is called a positive feedback. Here is what the IPCC report says about water vapor feedback:

Water vapour feedback continues to be the most consistently important feedback accounting for the large warming predicted by general circulation models in response to a doubling of CO₂. Water vapour feedback acting alone approximately doubles the warming from what it would be for fixed water vapour (Cess et al., 1990; Hall and Manabe, 1999; Schneider et al., 1999; Held and Soden, 2000). Furthermore, water vapour feedback acts to amplify other feedbacks in models, such as cloud feedback and ice albedo feedback. If cloud feedback is strongly positive, the water vapour feedback can lead to 3.5 times as much warming as would be the case if water vapour concentration were held fixed (Hall and Manabe, 1999).

The climate models had better be getting the water vapor feedback correct or the projected warming may be too high by a factor of 2 to 3.5. This doesn’t sound like something that should be “overlooked”. While it is certainly true more evaporation will take place in a warmer world, there are many meteorologists who believe “the average amount of water vapor that resides in our atmosphere is not controlled by evaporation. Instead, it is controlled by precipitation (rain and snow) systems.” This quote comes from Dr. Roy Spencer, principal research scientist at the University of Alabama in Huntsville in an article at this site.

Here is what a study by NASA has to say on the subject:

The study cites satellite observations showing the rate that warm rain depletes clouds of water is substantially higher than computer models predicted. This research may help increase the accuracy of models that forecast rainfall and climate. The rate water mass in a cloud rains out is the precipitation efficiency. According to the study, when it comes to light warm rains, as sea surface temperature increases, the precipitation efficiency substantially increases.

Here is Dr. Spencer’s concluding comment on the subject:

I believe that it is the inadequate handling of precipitation systems — specifically, how they adjust atmospheric moisture contents during changes in temperature — that is the reason for climate model predictions of excessive warming from increasing greenhouse gas emissions.

It appears very possible, therefore, that the increased amount of water vapor in the atmosphere gets “precipitated out” by an increase in rainfall efficiency of precipitation systems, thereby lowering the amount of water vapor feedback the models are currently projecting, which results in LESS warming than the models are predicting. Here is another of the many reasons why I feel we shouldn’t formulate public policy and enact carbon taxes based on the still inadequate computer models.

Additional comment added on April 5: Please check out this weblog from Roger Pielke Sr. for more on the subject of water vapor. Roger is currently a Senior Research Scientist in CIRES and a Senior Research Associate at the University of Colorado-Boulder in the Department of Atmospheric and Oceanic Sciences (ATOC) at the University of Colorado in Boulder (November 2005 -present). He is also an Emeritus Professor of Atmospheric Science at Colorado State University.

[Tenacious 1]

[Try to pass water vapor instead of the other stuff.]

I have on occassion done this. When it does happen, the vapor is not pure water, however. It is polluted.

[JustDoItAlways]

Global warming theory depends on this feedback from increased water vapour. In essence, the physics says that increased CO2 will provide a slight increase in temperatures. A slightly warmer atmosphere can then hold more water vapour and hence you get even more warming.

Without the increased water vapour feedback, increased CO2 would only increase temperatures by about 1.0C for every doubling of CO2 or about 1.0C of warming by the year 2,100. That is nothing really to worry about at all. Natural variability of the climate is even greater than this.

So, global warming is a dud (theory alone) without the water vapour feedback.

What does the evidence show?

- Water vapour has increased slightly in the last 50 years (nowhere near the level global warming theory predicts); and,
- the historical climate evidence shows that water vapour is probably a stablizing factor in the climate (rather than a runaway positive feedback) It gets warmer, more water vapour goes into the atmosphere, we get more rain and more clouds reducing the temperature and stabilizing the climate. The planet has been here for 4.5 Billion years and it seems the climate has usually been around today’s temperature give or take about 6.0C. All those oceans and all that water keeps Earth at a nice temp.

[Wonder Warthog]

"Global warmers hate to discuss clouds and snow because these act as giant natural mirrors bouncing sun heat back out to space. They especially don’t want to talk about man-made clouds and snow and the role of wind blown sand, dirt, and pollution which increase their formation. GWers are afraid to even research and model clouds because then the Luddite party would be over."

Got it in one. As I understand it, clouds in the troposphere increase heat retention more than they increase albedo, but clouds in the stratosphere work oppositely (they increase albedo more than heat reflection).

Sooooooo...the answer to global warming is to increase the sulfur content of jet fuel.

[CPT Clay]

Never here this from MSM

[curiosity]

I am also a devout Catholic.

I call you a GW denier because you are denying basic scientific facts and bringing up red herrings that are irrelevent to the question.

Like this business of Water Vapor. For the last time, yes, water vapor accounts for the bulk of the greenhouse effect. No one denies this. Even the most alarmist of the GW fanatics admits this.

But just because water vaper is the largest greenhouse-causing material doesn't mean it's the only one. The very same article at the top of this thread to says it only accounts for about 70% of the greenhouse effect, and that fluctuates, since the concentration of water vapor also fluctuates.

That leaves 30% of the greenhouse effect to other gasses, the bulk of which are CO2 and methane, which don't flucutate much. 30% is a significant amount, and it's enough to make a difference.

So please, stop repeating this silly and fallacious argument that CO2 doesn't matter because water vapor is a more important greenhouse-causing material. Just becasue CO2 is not the most important doesn't mean it's not important.

[DouglasKC]

water vapor bump...

[<1/1,000,000th%]

Time for dihydrogen monoxide credits?

[DouglasKC]

That leaves 30% of the greenhouse effect to other gasses, the bulk of which are CO2 and methane, which don't flucutate much. 30% is a significant amount, and it's enough to make a difference.
So please, stop repeating this silly and fallacious argument that CO2 doesn't matter because water vapor is a more important greenhouse-causing material. Just becasue CO2 is not the most important doesn't mean it's not important.

Here's the problem: This kind of information is almost never focused on in the news media or in most of the global warming information that is out there. The greenhouse effect when it's reported or taught in the context of global warming is skewed and misrepresented toward being anything other than an increase in water vapor.

For example, here is an "educational" website from the NOAA, apparently for children, that discusses the greenhouse effect. A quick glance throughout will show that they don't even mention water vapor as the major constituent of global warming.