Water vapor, the factor that matters in global warming?

The sea stores a million times more energy than the atmosphere and has a temperature memory of up to thousands of years. Water is better at holding energy than air, hence why we use water bottles, the sea is the earths water bottle and the sun heats it. This is called the "hot water bottle effect".

The Pacific Decadal Oscilation (PDO) is responsible for most of the warming of the last 50 years as a positive PDO results in increased El Nino effects, and a negative PDO results in more La Nina effects. Some claim this is caused by human influence (with little justification), the truth is the causes are little understood but correlate reasonably well with solar actvity though this may not be the primary driver. It is however apparent that the seas PDO is a major climate driver.

It has been warming at a constant rate of around 0.5c/100 years for the last 300 years (Akasofu, 2008) since the Maunder Minimum ended (a period of low solar activity) and solar activity increased, which may account for the warming of the sea since the little iceage and any increase in water vapour and co2.

Co2 is released as the sea warms (the sea accounts for around 70% of co2 5n the atmosphere) and as around 97% of co2 in the atmosphere is natural, as would be most of the claimed rise in co2, the seas temperature could be considered a strong climate driver.

Assuming co2 increases results in significent warming as is claimed by some, after hundreds of years it could warm the sea causing enhanced warming or a runaway greenhouse effect. This has however never happened naturally in the past from the available data, and ice core data used by GS Callender, stomatal data and chemical gas analysis from around 1850 shows that co2 was similar or higher than today. Of course during the Cambrian Era co2 was around 20 times higher than today (around 7600ppm) and the earth was only 7 degrees warmer (IPCC, 2007), so we know increasing co2 doesnt trigger horendous positive feedbacks or runaway warming, but instead may cause <1c of warming with a doubling of co2 ontop of natural variation (as many studies have concluded independantly by revisiting the IPCC's calculations).

Of course we know that the sun can warm water below the surface more effectively as energy is absorved by particles in the water (hence why it gets darker with depth and why clearer water in rivers takes longer to warm), whereas increasing air temp only warms the surface of the sea where evaporation occurs (a negative feedback), and of course solar activity over the last 70 years has been the highest of the last 11,400 years (Usoskin, et al. 2005, Hathaway,et al. 2004, IAU, et al. 2004, Solanki, et al. 2005) though it has now dramatically dropped.

With the recent drop in solar activity the sea has now switched into a negative PDO (confirmed by NASA) and NOAA JPL have reported that sea temperatures have been falling since 2003, with this the global mean temperature has also cooled rapidly and solar actvity has dropped. Temperatures have fallen for 7 years and the jan 2007 - jan 2008 fall was the sharpest drop in temps since 1880 (GISS, Hadley, NCDC, RSS, UAH, all 2008)

So to sum up I think the sea is a key driver of climate due to its massive energy store and slow response to climatic shifts which helps stabilise the earths climate. Solar activity may be a key factor of warming or cooling of the ocean as well as other effects, but many of the factors envolving PDO are little understood and further research is required to better understand the earths natural cycles before we can attempt to assess our effects on the system.

I'm not sure exactly what your question is, but it's not completely clear what happens with water vapor as the global mean temperature goes up. One expects the vapor pressure to increase because of the Clausius-Clapeyron relation. The typical assumption is that tropical tropospheric relative humidity will remain constant at something like 80%. However, that is just an assumption and it may behave differently than that. Certainly the vapor pressure of water will not go down. This will be a key to how fast warming occurs.

Since water vapor is the most important greenhouse gas, if the amount of clouds remain the same, more water vapor in the atmosphere means more warming. Clouds can act either way--high clouds have a net positive effect on warming, while stratocumulus and stratus tend to cool the planet, since they are highly reflective.

EDIT: There's a lot of strange answers out there by people that should know better. Water vapor certainly matters to global warming scenarios because of its strong dependence on temperature--the saturation vapor pressure approximately doubles for every 10 C increase in temperature.

I'll say this again: clouds can have a net positive or negative effect on surface heating, depending on what type of clouds we're talking about. That's probably one of the biggest weaknesses of global climate models--the way clouds are parameterized in them, and especially stratus/stratocumulus, since they have a net negative effect.

Finally, what's up with the whole mantle convection answer Heretic? That's an interesting subject too (although not relevant here), and I might add that in 1980 I showed that upper and lower mantle convection was not decoupled in the Sea of Okhotsk subduction zone...but that's another story.

When all the fossil fuel that we have been burning was instead being formed much faster than it was being consumed, we can expect that carbon dioxide levels could only be increasing as a result of global warming rather than the other way around. When our oceans warm up they reduce the rate of sequestration of CO2... they may even gas off somewhat. When plants on land get too warm, they discontinue absorbing CO2 for the rest of the day. Warmer soils also emit more CO2, so as global warming progresses we will see increased CO2 in the air, and incidentally in glacier core samples. Now we have had up and down gradual global warming since mid way through the last ice age. We know that CO2 does increase the rate of global warming just as global warming increases CO2. Increased CO2 does further increase the rate of GW. But we can not assert that elimination of all CO2 emissions will stop or reverse global warming. Global warming itself will go on increasing the greenhouse effect both because of CO2 and water vapour.

There is no doubt that water vapor is the primary mover of the greenhouse effect no scientist has said otherwise, despite denier attempts to bend the facts. Without the GH effect the Earth would be around 20 to 30c cooler than the current average temp, so the 0.6c we have added to world temp is less than 2% over a century another 2-3c would be at most ~8-10% total effect over a total of 250 years i.e. the end of this century, but as just 6c is the sort of temp rise capable of melting the Antarctic and Greenland these small temp rises are a worry and the reason scientists are trying to sound a warning.

This is more of a precis of science fact rather than opinion, but water vapor also plays a critical role in global warming through the effect of deep convection and through the formation of clouds in the troposphere (stratospheric clouds of ice crystals are also important in the energy budget, but those ice crystals are not formed from water vapor from the ocean surface). Tropospheric clouds affect the albedo of the planet and also provide a positive surface radiative forcing. Whether the net effect of clouds is warming or cooling is the matter of some debate, although the IPCC WG1 AR4 concludes they have a net warming affect, although rather smaller than the forcing from the radiatively important trace species.

Deep convection is probably the largest radiative effect of water vapor. When warm humid air rises, the water vapor condenses, releasing large amounts of latent heat, warming the air, and driving it above the troposphere. The warm air can then radiate to space without the intervening layers of greenhouse gases (once you get to the tropopause, approximately 75% of the atmosphere is below you, deep convection easily makes it up to the tropopause). This process drives the meridional flow in the tropics, and is responsible for the trade winds. Although crude calculations might suggest that deep convection is *more* important than radiative transfer (this idea is the basis of Lindzen's Iris Hypothesis), the fact is that there is a finite amount of moisture available to drive tropical convection, and the global average flux of water vapor from the ocean to the atmosphere (expressed by convention as a heat flux using the latent heat of vaporization of water) is around 100 W/m^2. Typically, the longwave surface upwelling radiative flux is over double that at 350 W/m^2. Efforts to demonstrate that deep convection has increased enough to offset the increase in radiative forcing from CO2 have been inconclusive.

(As an aside, if deep convection has increased, a consequence would be in increase in the tropical mid-troposphere temperature. However, as many of the skeptics here point out ad nauseum, the MSU temperature sounders show no consistent upward trend in the mid-troposphere temperature. They use this lack of increase to justify that CO2 is not warming the planet. However, many of these same skeptics trot out deep convection as the reason there is no need to worry about increasing CO2. It makes me wonder if they really understand the dynamics. But I digress.)

There's no true consensus on parameter layering, or whole mantle convection. Models are often expressed as a closed lid conception. Something that just doesn't happen on earth. First and foremost lower viscosity is expressed as a vanishing lower level boundary being determine by a fourth order Runge-Kutta integration scheme. . Parameter layering can be seen as a contrast where heat and cooling is subjective on each dependent layer. Only end number temperature constraints can be used, because the effective activation of earths energy can not be determine. Urey ratios give a proximate ratio for end numbers and constants can be emphasized as to thickness and proportion in Rayleigh calculations. So in one means your are right about constants being used. That is the average number should fall in between parametrized and whole mantle modeling. So if the bottom layer exceeds 4000K it's to hot, and if the top layer is less then 1500K it's considered to cool.

Water vapor is an easy one - it's a feedback, not a forcing. Carbon dioxide is both. So water vapor can amplify global warming, but cannot initiate it. Carbon dioxide can do both.

The argument that water vapor is more important than CO2 or that CO2 doesn't matter because water vapor plays a bigger role in the greenhouse effect ignores this very basic principle. As with most denier arguments, it misses some very simple physics which believe it or not, climate scientists have taken into account.

Might it be that the believers have a religious desire to blame an innocuous side effect gas for causing the natural warming that has occurred over the last 150 years in order to keep from blaming their god for it like the skeptics do. It is mostly that a group of young science students bought into a hypothesis that Co2 was a major greenhouse effect contributor based on a misunderstanding of just how things work. Of course Hansen and Mann playing with the numbers to make our current optimum look unusually hot instead of slightly cool and below normal does not help either.

http://www.aip.org/history/climate/co2.htm

Because this fits in with their mistaken belief that all the resources mankind will ever have are already being used they jumped on it and reworked data streams to fit this hypotheses they then used to promote the human caused global warming, Climate change hoax. Here are two links that explain the science and then point out the errors that allow those with a narrow focus to believe the AGW hypotheses

http://www.bruderheim-rea.ca/warming9.htm

http://www.weatherquestions.com/Roy-Spencer-on-glo...

http://www.jamesphogan.com/bb/bulletin.php?id=1142