Here is some interesting news; according to data from NOAA’s Earth System Laboratory, atmospheric water vapor is on the decline globally.
You’ve probably heard many times how water vapor is actually the most important “greenhouse gas” for keeping our planet warm, with an effectiveness far greater than that of CO2.
It is generally accepted that the rank of important greenhouse gases is:
- water vapor and clouds which causes up to 70% of the greenhouse effect on Earth.
- carbon dioxide, which causes 9–26%
- methane, which causes 4–9%
- ozone, which causes 3–7%
Note the range of uncertainties, on water vapor some say the percentage goes up to 90% with reduced numbers on the other three.
It is absolutely true that water vapor is the gas most responsible for the “greenhouse effect” of our atmosphere. Greenhouse gases let short-wave solar radiation through the atmosphere, but impede the escape of long-wave radiation from the Earth’s surface. This process keeps the planet at a livable temperature: Without a suitably balanced mixture of water vapor, CO2, methane, and other gases in the atmosphere, Earth’s average surface temperature would be somewhere between -9 and -34 degrees Fahrenheit, rather than the balmy average 59 degrees it is today.
This graph then from NOAA’s Earth System Research Laboratory, showing specific humidity of the atmosphere up to the 300 millibar pressure level (about 8 miles altitude) is interesting for it’s trend:
Click for original source of the graph
[UPDATE2: After reading comments from our always sharp readers, and collaborating with three other meteorologists on the graph, I’m of the opinion now that this graph from ESRL, while labeled as “up to 300mb only” is misleading due to that label. The first impression I had would be from the surface to 300mb i.e. the “up” portion of the label, but on the second thought I believed the label was intended to be numerical meaning “zero to 300mb” or from the top of the atmosphere down as opposed from the surface up as we normally think of it. The values looked like anomaly values, but are inthe range of absolutes for that elevation also.
Thanks to some work by commenter Ken Gregory, looking at other ways this and similar graphs can be generated from the site, it has be come clear that this is a level, not a range from a level. The label ESRL placed “up to 300mB was intended to list the availability of all data levels. Thus there is no 200mb data.
This demonstrates the importance of labeling a graph, as without any supplementary description, it can be viewed differently than the authors intend. A better label would be “at 300mb” which would be unambiguous. ESRL should correct this to prevent others from falling into this trap.]
For some background into atmospheric absorption efficiency of the electromagnetic spectrum, this graph is valuable:
Note the CO2 peak at 15 microns is the only significant one, as the 2.7 and 4.3 micron CO2 peaks have little energy to absorb in that portion of the spectrum. But the H2O (water vapor) has many peaks from .8 to 8 microns, two that are fairly broad, and H2O begins absorbing almost continuously from 10 microns on up, making it overwhelmingly the major “greenhouse gas”.
Here is another graph looking at it in a different way:
Click for a larger image
Note that water vapor plays quite a role in keeping the planet cool by absorbing some percentage of incoming radiant energy.
The yellow line is what we’d get without an atmosphere, and the blue line what we get with it. Sunlit temperatures on the earth’s surface are substantially less than those on the moon (up to 123°C) because our atmosphere intercepts some incoming solar short-wave radiation as well as some outgoing long-wave infrared.
So when we see atmospheric water vapor dropping as shown in the NOAA ESRL graph above, you know it has to have an effect on our overall planetary energy budget, the question that will be argued is; “how much”?
h/t: Thanks to atmospheric physicist Jim Peden, and also to Barry Hearn, and Alan Siddons for some of the graphs and background to this post.
UPDATE: See part2 of this post here
[…] A Window on Water Vapor and Planetary Temperature […]
The lead post says the CO2’s contribution to the greenhouse effect:
“carbon dioxide, which causes 9–26%”, then says “Note the range of uncertainties”.
This range is not due to uncertainty, but due to different methods of calculating the effect. The contributions of each greenhouse gas component (water vapor & clouds, CO2, O3 etc.) are not additive due to over-lapping absorbing spectra, and nature does not allocate the effect to the various components. If one removes some CO2, water vapor will capture most of the long wave-length radiation (LWR) that the CO2 would have captured.
If all CO2 is removed from the atmosphere (all other components unchanged) the greenhouse effect would be reduced by 9%. If all components are removed except CO2, CO2 would still cause 26% of the effect. The sum of each component for the two methods do not sum to 100%. If the methods are normalized and averaged, CO2 accounts for about 16% and water vapor & clouds for 75% of the greenhouse effect. These numbers are from the GISS climate model. Further details are at http://members.shaw.ca/sch25/FOS/CO2_Versus_Water.html
However, adding CO2 to the atmosphere does not add to the greenhouse effect because the strength of the effect is controlled by the overall energy balances which is unchanged. So adding CO2 just rains out extra water vapor to maintain a constant greenhouse effect.
Mark Andrew (16:32:31) says:
This is wrong as it does not account for the over-lapping absorbing spectra. Other greenhouse gases will capture some LWR not captured by the loss of water vapor.
Ken Gregory 19:46
“These numbers are from the GISS climate model.”
With CO2 –>H2O feedback on , or off? The plots show that it should be off.
Although it is an interesting observation, it has very limited implications. NOAA itself warns about how small data we have about water vapor (http://lwf.ncdc.noaa.gov/oa/climate/gases.html) where they say “Also, while we have good atmospheric measurements of other key greenhouse gases such as carbon dioxide and methane, we have poor measurements of global water vapor, so it is not certain by how much atmospheric concentrations have risen in recent decades or centuries, though satellite measurements, combined with balloon data and some in-situ ground measurements indicate generally positive trends in global water vapor.”
There are so many uncertainties associated with measuring water vapor. Satellites probably could do a better job now for profiling concentrations with respect to altitude using perpendicular and diagonal measurements, but earlier satellites did not have that capability. If we go way back to 1950s and before, they were using only ground based measurements, which cannot account for the variability in water vapor (both with respect to time and location). There is also a disconnect when ground based measurements were supplemented with satellite measurements when satellites data became available. Even now, satellite measurement of water vapor is only 30 to 40 % accurate. So, I think the story is interesting, but beyond that I see no reason to make any additional speculation relating to global warming.
anna v,
These numbers are from model simulations were, for example, all CO2 is removed keeping all other gases constant and recording the change in the greenhouse effect. So, removing all CO2 from the atmosphere but keeping the water vapour concentrations constant reduces the greenhouse effect by 9%. This is no feedback.
But, as I mentioned, increasing the CO2 concentration does cause a reduction in water vapour.
There is a near infinite supply of greenhouse gases available to the atmosphere in the form of water vapor from the ocean to provide the greenhouse effect, but the relative humidity in the atmosphere is much less than one. Therefore, there must be some greenhouse equilibrium mechanism to control the relative humidity, and therefore the strength of the greenhouse effect. Otherwise, climate would be very unstable.
If some temporary disturbance adds a large amount of greenhouse gases into the atmosphere, temperatures will temporarily increase, as it did in 1998 due to the super El Nino. If one believes that a temperature rise will cause more water vapor, which will cause more temperature rise, and more water vapor yet again, one would expect temperatures to continue to rise after 1998, and result in a run-away effect. But the opposite happened, temperatures fell as the greenhouse equilibrium mechanism restored the balance. The extra greenhouse gases rained out to restore the equilibrium.
The new Miskolczi theory describes this missing greenhouse equilibrium mechanism. He shows that the classical theory does not include all the necessary energy constraints. When these constraint are included in a new theory, the strength of the GHE is determined analytically. The result shows that the Earth’s atmosphere is maintained at a nearly saturated greenhouse effect. The greenhouse sensitivity to a doubling CO2 is about 0.24 K.
This greenhouse equilibrium mechanism doesn’t care if an initial increase of greenhouse gases was water vapor or CO2. If somehow we suddenly released an amount of CO2 to the atmosphere equal in GHG effect of the 1998 El Nino water vapor, the temperature effect would be the same. Temperatures would increase by 0.6 Celsius, but would fall within a year to the original temperature, as the greenhouse equilibrium mechanism restores the greenhouse strength to the equilibrium value by raining out the excess greenhouse gases. Adding man-made CO2 to the atmosphere just rains out almost an equivalent amount of water vapor.
The first question I have is are the specific humidity data reliable? I’d like to know how it is measured, what parts of the planet are measured, how often, and what assumptions and extrapolations are being made. Are there any independent confirmations of this data? I am highly skeptical of any kind of global measurement. If the data aren’t good, then there’s not much point in trying to determine it’s meaning.
Please pardon my utter lack of knowledge here, but how can the amount of water vapour in the atmosphere be falling if the cloud cover is increasing?
Ok, I’ll throw my $.02 into this discussion:
First, about the 300 mB cutoff… Just a guess, but it probably represents an arbitrary, but convenient cutoff level, where the total amount of water vapor located at elevations higher (lower pressures) is simply negligible in comparison to what lies below. The upper 30% of the atmospheric mass simply can’t hold much water because of the low temperatures.
Second, with regard to Sea Level changes corresponding to the specific humidity changes… please check that math! A change of 0.03 g/kg dry air amounts to what… something around 0.3mm depth of water if you could possibly condense it all and bring it to earth… if you could then get all that water to the oceans, it would be less than 1/2 mm change in ocean depth. Remember that you’ve only got roughly 1kg of air above each square centimeter of earth’s surface.
Ok, so this was only about $.002
DaveK
Uh-oh. If adding CO2 decreases water vapor I can see the next scare as being “more CO2 causes less water in the atmosphere which means less rain”.
Or is it that, that means more rain as the excess water is rained out? However if we stop adding CO2 there will at equilibrium be less water in the atmosphere which surely means less rain in the long term.
No runaway greenhouse though.
See the update I made to this post regarding the “up to 300mb” humidity graph.
I took a look at what I think is the source of this data, and it shows specific humidity values at various levels from the surface up to 300 mB. There is no data above. It also allows you to “combine” data for several elevations. Therefore, I would presume it is a plot of the average specific humidity using the averaged value up to the 300mb elevation.
I didn’t take the time to actually do the plot, since it’s difficult to extract more than one year’s worth of values at a time.
Dave K
I believe the plot is derived from this
I hope that link worked!
DaveK
Oops, I’ll try again…
DaveK
“up to”? Surely that should be “around”? i.e. in the Stratosphere (did I mention that’s cooling, so you wouldn’t immediately expect it to have increasing WV levels?).
Yes there’s interesting research on stratospheric Wv trends, involving changes in CH4 (IIRC the levelling of CH4, that’s now ending), and stratospheric transport(Brewer-Dobson) changes. But as I’m busy with the Arctic right now, I can’t spare the time to discuss further.
And the answer is “not a great deal” as the major impact of changes in water vapour on GEB is in the IR blocking of the enhanced greenhouse effect below the effective radiating layer in the troposphere.
The upshot of which:
This doesn’t present the problem for consensus science that your post initially suggested, and from my re-reading still seems to imply.
Cobbly Out.
Confirm data is only available for pressures up to an altitude equivalent to 300mb.
250mb – no data is available
1000mb – I think this graph gives the global average value
http://www.holtlane.plus.com/images/specifichumidity.jpg
Ok, this should be a link to the underlying dataset…
Please let this be right this time! (and thanks for your patience with my miserable skills with this tag)
DaveK
I am so stupid! This dataset
DaveK
PS… any way we can get a preview button on this?
Trent- you say “On the issue of CO2 freezing out … The freezing point (solid/vapor) at atmospheric pressure is about -78 ºC, but this applies to pure CO2 vapor. Since the atmosphere contains only about 380 ppm CO2, the temperature would have to drop to about -142 ºC before CO2 would begin to condense out. So, there is no chance of any CO2 condensation on planet earth.”
I thought the total pressure above a solid or liquid is what determines the phase transition temperature, not the partial pressure. If not, can you provide me some information on this? I did some looking but could not find anything specifically addressing CO2. It is also interesting that the poles on Mars do not seem to get colder than about -140 C, both poles have condensed solid-phase CO2 during their respective winters, and the atmosphere on Mars is 0.007 bar of 95% CO2, all of which support your contention of a suppressed freezing point at low pressure (which is consistent with the CO2 phase diagram). But, that is not the same situation on Earth where the atmospheric pressure is 1 bar.
So the lower limit of the graph in terms of altitude is 8 miles up, where pressure is at 300 mb if you were standing at that altitude, and the upper limit is wherever pressure is 0, which in my mind equates to weightlessness if you were standing at that altitude. Is that right?
REPLY: Correct except you can’t stand in zero gravity
If the data comes from the PSD monthly-average multilevel dataset, there is no data at elevations above (pressures lower than) 300 mB. But perhaps it comes from another source?
DaveK
Sorry Anthony, you are still incorrect.
The graph you show in your post is the specific humidity at 300 mb. It is NOT from 0 mb to 300 mb. You can easily recreate this graph for yourself at the link I gave in my previous post, recopied here:
http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries1.pl
Unfortunately, the graph is not labeled with the elevation of the data (300 mb). You can create other graphs from this site of data of from surface up to 300 mb, (surface, 1000mb, 925, 850, 700, 600, 500, 400 or 300 mb). All of these graphs have exactly the same label.
If you click on the graph in your post to display only the graph from the NOAA site, you can see the full URL, which shows all the parameters used to create the graph, including “level=300”, meaning the graph is showing data at the 300 mb level. The “up to 300 mb only” on the graphs means that data is available from surface up to the 300 mb level only, so don’t try to plot the 200 mb level, as you will get a error message.
REPLY: Hmmm, so the “up to” portion of the label put there by ESRL is completely wrong and misleading. Thanks for the note.
This is annual data, so use “Seasonal data”, First month=Jan, second month=Dec. Use Area weight grids=Yes.
In my previous posting, I presented a graph of Relative Humidity at several levels, copies here: http://members.shaw.ca/sch25/FOS/GlobalRelativeHumidity.jpg
This shows that the relative humidity has dropped 21.5% from 1948 to 2007.
I will create a composite graph of Specific Humidity now and post it shortly.
Thanks for the reply. If the greenhouse gas, as I understand, works this way, then I don’t understand how there can be predictions of huge temperature increases. Although I must admit I am a lowly chemical engineer and not a fancy climate modeler. Perhaps the climate modelers have some special laws of thermodynamics that they use that I’m unaware of.
If we’ve survived the 100 ppm or so of CO2 increase in the atmosphere it would appear to me that the next 100 ppm shouldn’t be nearly as bad. Let’s see, the last 100 ppm resulted in an explosion of wealth and doubling or so of human life expectancy – we should be so lucky in the future.
This is highly disturbing, if part of a longer term trend. Combined with the era scale trend toward slow decline of CO2 (which man made GHGs may or may not ultimately be able to mitigate) this means two key factors for biosphere success are in decline. We should be plotting our exit strategy. It will either have to be terraforming right here on Earth, or, colonization of space.
REPLY: Check the update in the article – Anthony
Not to go overboard on the doom and gloom here (my main objective is to incite serious efforts to conquer space) when you consider the harsh realities regarding fossil fuel costs and apparent future supply curve, by a couple hundred years from now, unless we develop methods for cheaply synthesizing oil, our ability to add CO2 will no doubt be in steep decline. Barring mass burning of forests, or other highly drastic countermeasures, we are going to have to eventually face the music regarding the apparent long term CO2 trend, once it is reestablished.
200 years from now even coal will be in decline.