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
Ken,
Look at the date on the American Geophysical Union article. It’s dated 2005 and it says that it looks at data from 1995 to 2002.
The Beacon eSpace article talks about “Recent simultaneous observations of upper tropospheric”
“derived this graph before we jump to conclusions”….I could be wrong but I think the graph is from NOAA
Ooops sorry! Mr Watts, with an “s”.
Just before I go, this might better display what I mean:
The original URL from this article:
http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries.pl?ntype=1&var=Specific+Humidity+(up+to+300mb+only)&level=300&lat1=90&lat2=-90&lon1=-180&lon2=180&iseas=1&mon1=0&mon2=11&iarea=0&typeout=2&Submit=Create+Timeseries
And the same url with the value for “level” changed from 300 as above to 1000:
http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries.pl?ntype=1&var=Specific+Humidity+(up+to+300mb+only)&level=1000&lat1=90&lat2=-90&lon1=-180&lon2=180&iseas=1&mon1=0&mon2=11&iarea=0&typeout=2&Submit=Create+Timeseries
Anthony,
Great, was lookin’ for that data for quite some time.
By the way, I use in a spreadsheet the data (global, ocean, temperature anomaly) from:
http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt
versus the Pacific warm water volume from:
http://www.pmel.noaa.gov/tao/elnino/wwv/data/ (wwv.dat)
– I am using this one, because global ARGOS datas have still too less years to be valuable –
Interesting – especially – is the year 1997/1998, when the Pacific – lost or
supplied to atmosphere – around 24% of its warm water volume.
I assumed when I read it that “up to 300 mb” meant 0-300 mb – ie above 8 km.
“Up to 300 mb” may be referring from 0 mb to 300 mb, which would equate to ~6 miles on out to space.
Anthony,
addendum to my 18-06-2008 14:24:29,
as far as know, the heat capacity of – oceanic – water versus atmosphere, is
more than 3000:1 (if I am wrong, please, I should be corrected).
So the year of ’98 – with it’s temperatures – is caused by the oceans switching
from collecting of heat energy to emitting heat energy, until it fell to it’s lower
threshold, causing the not so warm ’01/’02 temperatures, because after several
months of emmiting heat energy, the fallback to collection of heat energy – re-occured.
I couldn’t say, it’s reasoned end-to-end from my side, I simply stumbled over it.
I was able to find Create a monthly/seasonal mean time series from the NCEP Reanalysis Dataset
Thanks, Jared. Do you have a reference? Interested for obvious reasons.
CoRev, editor
http://globalwarmingclearinghouse.blogspot.com
‘Up to 300mb’ I think means from 0 mb up to 300 mb. Not from the surface up to where the pressure is 300.
OK now I’m confused. This graph has all the same labels but shows a completely different graph. http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries.pl?ntype=1&var=Specific+Humidity+%28up+to+300mb+only%29&level=1000&lat1=-90&lat2=90&lon1=-180&lon2=180&iseas=1&mon1=0&mon2=11&iarea=0&typeout=2&Submit=Create+Timeseries
I am beginning to see several nested loops here:
Water vapor balance is driven by two primary factors: evaporative input and precipitated output.
Solar output affects evaporative input by heating exposed water and heating surfaces containing pore water, driving osmotic evaporative surface drying.
Solar output reduction therefore directly reduces evaporative inputs, by reducing surface heating.
If the cosmic ray cloud-seeding hypothesis is correct then reduced solar output, also increases ionized condensation nuclei. That increases low clouds, increasing albedo, which further reduces heating and lowers evaporative input further.
Increased condensation, with lower surface temperatures, means that the a larger proportion of precipitated condensate does not return to the vapor load in the atmosphere but to surface water and pore water.
This means the coincidence of several negative vapor balance factors.
Seas are rising, which might be in part explained by additions of net unvaporized precipitate, as well as, or perhaps better than the volumetric thermal change (which heating isn’t happening anyway, at least not in the upper 700 m).
Sea levels are rising (less than the GCM’s predict) so that may actually be a vapor volume loss signal (they mostly hold water vapor constant, and therefore would naturally misinterpret that as heating signal, an artifact of that bad assumption on a basic gas law issue).
Seems an easy thing for a basic correlation analysis:
What is the comparison of the balance of the mass of water in the reliably observed sea level rise data to the mass of lost vapor represented in the declining specific humidity?
Anthony:
Good thought provoking stuff.
Is it possible that what you are talking about is the reduced evaporation rate that has been recorded worldwide (albeit at the surface). This is a well known effect and was noted in Australia initially and is probably caused by increased atmospheric particulate pollution. There are mountains of data on this.
It is interesting that global warming would be probably worse if this effect was not present. By the way evaporation rates are measured worldwide by farmers interested in soil moisture for planting and there is a fairly good data record going back quite a way. Also, if I remember correctly evaporation is as dependant on the “photon density” impinging on the water as ambient temperature. Hence a smoky atmosphere slows evaporation even with no ambient temperature change. – But now I am stretching my memory so I need to check.
I cant help thinking that the Earths temperature would significantly influence humidity. Lower temperatures mean less evaopration and what water vapour is in the atmosphere will in fact more readily form clouds at lower temperatures.
Naturaly air pressure would influence this formation.
In fact their may be an interesting investigation in whether temperature could be measured from global humidity information.
I would also like to see what the links between humidity and relative cloud cover at different altitudes are.
David Segesta wrote: “OK now I’m confused. This graph has all the same labels but shows a completely different graph.”
Actually David, the Spicific Humidity scale on the left side is quite different than that on the original graph. Other than that, it looks like a typical NASA adjusted graph.
Jack Koenig, Editor
The Mysterious Climate Project
http://www.climateclinic.com
Some very rough figures:
Greenhouse effect = 30 degrees Celsius.
Water = 70% of 30 degrees = 21 degrees.
Reduction in water vapour content from graph = 10% (from about 0.2 to 0.18)
Predicted reduction in temperature based on water vapour greenhouse effect from graph = 2.1 degrees.
Either my logic is off, or that graph is wrong, or the temperature has cooled a huge amount since 1990 without being detected by our thermometers. Or something else has caused a 2 degree warming at the same time to compensate.
De-lurking for a quick comment to clear up apparent confusion on the meaning of the specific humidity graph data.
Looking at the inputs to the graph, there are two main ones: the actual variable to be plotted, and the “analysis level”.
The variable you are plotting is “Specific humidity (up to 300mb only)”, but you are plotting the 300mb analysis level. If you were to try to plot the 250mb level, you’ll find that you get an error page stating that there is no data for that level.
In other words, the “up to 300mb only” means that the data cuts out at that pressure/height – there is no data for any altitude with lower pressure levels. But when you choose an “analysis level” you are plotting the level at that specific level, not a cumulative level.
Gabriel
The subject of trends in atmospheric water vapour is critical to the whole climate debate. If you dig around you will find that real work is being done in this area of study.
A reference that might be useful in this discussion is:
Mieruch, S et al 2007. Analysis of global water vapour trends from satellite measurements in the visible spectral range. Atmospheric Chemistry and Physics Discussions 7: 11761-11796.
Then have a dig around in the references they cite.
Cheers
Rob R
Syl (Lutnes) (15:13:58 ) : I think the original plot is at 300mb
I went back and replotted the data and noticed that when you choose different ranges, you get different results
300mb – 300mb shows a downward trend for last half 20 century
400mb – 300mb shows a downward trend for last half 20 century
500mb – 300mb starting to flatten
600mb – 300mb flat trend
700mb – 300mb flat trend
850mb – 300mb flat trend
925mb – 300mb flat trend upward trend around 95 on
1000mb – 300mb downward trend ’til 70’s then upward trend on
IMO, what it really shows is that anthropogenic GHG increase causing water vapour increase doesn’t correlate all that well no matter how you’re measuring it.
Perhaps I am missing something here but specific humidity cannot be measured at a single altitude as it is the measure of humidity in a volume. A two dimemsional plane, at any altitude, has no volume.
Anthony,
I think you’ve read the data incorrectly (hey, it happens) and I look forward to your clarification.
The Miskolczi paper, “Greenhouse Effect in Semi-Transparent Planetary Atmospheres” adds energy constraints to the standard greenhouse theory and shows that the strength of the greenhouse effect is near the maximum. This implies that adding CO2 to the atmosphere would reduce the relative humidity, as CO2 emissions replace water vapour to maintain a constant greenhouse effect, assuming a constant external forcing (Sun and albedo). So, has relative humidity been falling with increasing CO2 concentrations?
Here is a graph of global average annual relative humidity at various elevations in the atmosphere expressed in milli-bars (mb) from 1948 to 2007. The data is from the NOAA Earth System Research Laboratory http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries1.pl.
This shows that the relative humidity has been dropping, especially at higher elevation allowing more heat to escape to space. The bottom curve labeled 300 mb is at about 9 km altitude, which is in the middle of the predicted (but missing) tropical troposphere hot spot. This is the critical elevation as this is where radiation can start to escape without being recaptured. The average annual relative humidity at this altitude has declined by 21.5% from 1948 to 2007! This explains why the computer model predicted hot spot, which assumes a constant relative humidity, is absent from observations.
To follow up my last on the mass balance issue on water vapor loss to sea level rise :
Just back of the envelope, but the mass of water vapor represented by the recent downtrend (1990-2008) in specific humidity (~.03 g/kg) compares to the uptrend (satellite measure – 1993-2005) of ~45mm rise in sea level over 361 sq. km of ocean to within about 95% of the same mass of water.
I’m just sayin’ …
On another forum there is a discussion of greenhouse effect on Mars.
This has a 95% CO2 atmosphere and nearly no water vapor or clouds to confuse the issue. Much the same axial tilt as Earth and same length of day. This ought to be a good natural experiment.
Of, yes, there’s 30 times as much mass of CO2 over each square meter of Mars as on Earth.
Estimates of greenhouse effect on Mars seem to be around 5 to 10C warming. I’m not sure how this was calculated. A back of the envelope calculation got me 10C with some simple assumptions based on Earth – Mars comparisons.
Searching for Mars “greenhouse effect” gets you lots of hits by people who want to Terraform it!
Seems to me until somebody figures out the greenhouse effect on Mars to better than a factor of 2 we’re wasting our time debating the CO2 contribution on Earth.
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.
Can someone explain why my graph did not appear in my message above?
What is the procedure to insert an image? Here is the graph URL
http://members.shaw.ca/sch25/FOS/GlobalRelativeHumidity.jpg