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
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Oh oh… the drop in water vapor can’t be a good omen. Ice age water vapor was very low… could we be heading towards another Maunder or Dalton Minima?
So, how long will it be before the US Supreme Court declares water (in vapor form) a pollutant?
So much for hydrogen fuel alternatives.
I see where you’re trying to take this argument, but I have a few comments.
The major assumption going in here is a syllogism – that specific humidity (which, as a reminder for those of you who don’t know, is simply the ratio of water vapor to dry air in a parcel) is directly proportional to temperature which is logarithmically proportional to CO2 concentration. I won’t fault the logical argument, but I will point out something that I think contradicts this notion:
Extending this argument one step further, higher specific humidity equals a higher amount of precipitation dispensed from the atmosphere. However, this is not a prediction of global warming – climate models have no consensus on what the global precipitation change will be, although there is some consensus on certain regional effects. To illustrate this, look at 1998 on the first graph; why does the warmest year on record not have the highest average specific humidity?
In reality, the water vapor feedback is much more complicated than being acknowledged here. As has been already brought up, water vapor varies dramatically by region and time. It has an extremely short residence time in the atmosphere compared to CO2.
You hypothesize that decreased water vapor means less energy reflected away from the atmospheric system and subsequent warming. Then why is an apparent decrease in average water vapor correlating, as skeptics point out at every chance right now, to a decrease in global temperature rather than an increase?
REPLY: ?? Your last question: It is explained clearly in the article. Note this is up to 300mb so while there may have been an increase in near surface humidity in 1998, it was likely manifested mostly at lower levels of the atmosphere.
Wow! Anthony if graphs can provide food for thought you just gave us a 6 course meal. That graph on electromagnetic absorption is one I’ve been looking for. (I would also like to have the original source for that if possible.) But if I’m reading it right it says in the wavelengths that water or CO2 can absorb, they are already absorbing nearly 100%. So adding more would not make much difference.
And the graph showing water vapor content is also very surprising. The decreasing trend from 1960 to 1975 more or less agrees with temperature drops during that time. But the drop from 1990 to 2000 runs counter to the temperature trend. It sure seems that increasing temperatures would cause more evaporation but the graph from 1990 to 2000 shows the opposite.
Wow- Lots to think about.
Well, how can the realclimate boys claim a positive feedback from increase in CO2 to increase in H2O vapour? It is obviously non-existance.
[snip]
Anthony,
So this chart has been available all along, for those who cared to look??
So much for due diligence on the part of the model makers when they “assumed” that CO2 induced warming was causing the atmosphere to hold more water vapor.
Anthony – I am pretty sure the graphs are for the specific humidity at that atmospheric level and the reason it is listed as up to 300 mbars is because they don’t have data for higher atmospheric levels. If you check the plot of specific humidity at 1000 mbar,e.g., you get values of around 7.7 g/kg, at 925 mbars, listed values are around 5.9 g/kg, while at 300 mbars, the values are around 0.2 g/kg. Obviously, this decrease in value with height makes sense since the atmosphere can’t hold as much water vapor at higher altitudes.
I did a quick download of the data for each listed level (1000, 925, 850….300) and summed the annual average values (I do not know if this is the right way to do this analysis! since I am not a meteorologist). What it showed was a modest increase (~2.5%) in the total specific humidity from about 23.4 g/kg to about 24 g/kg for the summed values from 1000 to 300 mbar for the period from 1950 to 2007. I have the data file and a graph but do not have anyway of posting it on the site.
BobN
REPLY: Bob check your email, I’m interested in determining if this data plot from ESRL is “at level” or “up to” as they state. The values you cite are right for levels, but I viewed this as an anomaly plot for up to 300mb rather than absolute values for that level.
But the question needs to be settled, I may be in the wrong as to my interpretation.
MattN (07:33:48) ,
Here is my understanding of why regional differences matter to the climate:
Regional patterns matter because physical processes take place at the temperature, pressure, humidity, etc. at the location they are happening. They do not take place based on the average temperature of the earth or any other averages.
Having more or less water vapor on average is useful for tracking trends but not for determining what physical processes are taking place in a certain region.
For instance if cold dry air comes out from high latitude (a cold front) and causes water to be removed from the warmer, more humid air over a warm part of the ocean, more radiation will escape into space from that area of the ocean than from another area of the ocean that still has humid air above it (assuming the ocean temperature is the same in both regions). This is called weather and may not affect the average water vapor in the air if water is evaporating elsewhere and replacing the water vapor that has rained out, but it is important to the radiation budget of the earth.
If the average is done properly (i.e. perhaps a geometric average is necessary for the particular physics of a process — just an example), then the trend can give us some clues about what is happening overall. For instance, if CO2 continues its increasing trend but water vapor continues its decreasing trend we can conclude (assuming all other things are equal, which is the catch) that an increase in CO2 does not induce an increase in water vapor in the atmosphere.
Lyman Horne
Well, so much for one of the pillars of positive feedbacks in AGW. As I recall the IPCC treatment of feedbacks in FAR claims a huge amount of ‘warming’ influence from increased water vapor caused by increased CO2 warming. If this is not the case, then the IPCC calculations are in deep trouble.
It does fit with NOAA data that shows an increase in precipitation in the US since 1900 though.
There is one aspect of this that bears scrutiny. IF water vapor is decreasing and water vapor is overlapping a a goodly portion of the CO2 absorption band, then wouldn’t this allow CO2 to absorb more long wave radiation? This would be only true if the remaining water vapor did not still absorb all the radiation available at those wavelengths.
Let’s see here:
IPCC can’t calculate the sensitivity of the climate to CO2 (nobody really can) and may have overstated it by a factor of 3-4.
Water vapor is not providing a positive feedback
Aerosols are not providing a ‘dampening’ of the warming.
Overall not looking good for the AGW crowd.
CoRev-
Yes, temperatures in the tropics are currently at their lowest levels since 1989…with anomalies lower than any other region on earth.
Doesn’t decreased water vapour fly in the face of positive feedback in global warming theory.
Yes.
And now we know why the AquaSat data is being swept under the carpet:
Not only less vapor (cooling via less GHG), but more low-level cloud cover (increased albedo).
So much for positive feedback.
Can someone with more knowledgable put some perspective to the increments in specific humidity on the left side of the graph? The graph shows flucuations from a high of just over 0.21 to a low of about 0.172 over the course of 60 years. How significant is that?
Austin- you say “CO2 does not do this.”
Actually, there may be a place on Earth where CO2 can condense to its solid phase during cooling and sublimate during subsequent warming. But I don’t know how often Amundsen Station in the Antarctic has dipped below -78.5 C!
: )
It does happen.
http://hypertextbook.com/facts/2000/YongLiLiang.shtml
OOPS. Well maybe I was to hasty in assuming that less water in the air means there was less evaporation. Of course that is one possibility but it is also possible that there has been more precipitation, which drains moisture from the air.
BTW does anyone know if molecules in the atmosphere can gain enough energy to escape the earth’s gravity? That would provide another means by which energy could leave the earth, besides radiation.
Counters:
“As has been already brought up, water vapor varies dramatically by region and time. It has an extremely short residence time in the atmosphere compared to CO2”
I fail to see what relevance of residence time to what is an on-going process. So one particular molecule of H2O may not stay in the atmosphere for long, but it’s the total concentration at any point in time that has any effect.
Besides, the concentration of CO2 also varies quite widely by region and time. The diurnal range over woodlands can be in excess of 100ppm.
The new humidity data causes me to wonder if there is a correlation between it and the period of time that atmospheric CO2 is retained. As I understand it, the GCMs assume that CO2 is retained in the atmosphere for about 100 years. This assumption supports the hypothesis that CO2 and water vapor interact so that an exponential increase in temperatures occurs as a result from prolonged long wave retention in increasing amounts.
Conversely, 50 years worth of empirical research indicates that retention is between 4 and 12 years. Does the new data falsify the GCM assumption about the length of the cycle for retention of CO2?
Am I missing something? I look forward to reading new comments on this thread.
Just noting that Global Warming theory relies on the assumption that “Relative Humidity” would remain constant (the amount of water vapour the atmosphere can hold given the temperature – as relative Humidity approaches 100%, it rains).
In Global Warming theory, as atmospheric temperature increases, the amount of water vapour the atmosphere can and does hold will increase although the Relative Humidity would remain constant.
Anthony’s chart relates to “Specific Humidity” which is the actual mass of water vapour in the air. Specific Humidity should be increasing according to Global Warming as the warmer air is able to hold more water vapour.
So not only is Specific Humidity not increasing with the supposed increase in atmospheric temperature, it is actually falling (which is the nail in the coffin for the +3.5C increase in temperatures for a doubling of CO2 sensitivity estimate.)
[…] 18, 2008 · Filed under Climate crap Anthony at Watts Up With That has some interesting graphs regarding water vapor and planetary temperature. As he points out: It […]
Talking of planetary temperature, the Hadley global temperature for May is in. Are these the wrong figures or have they been Hansonised?
http://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly
2008/01 0.053
2008/02 0.192
2008/03 0.430
2008/04 0.254
2008/05 0.278 UP???
Anthony,
At 8 miles up, isn’t that in the upper troposhere, above the height where most of the water vapor in the atmosphere is? In fact, according to the RSS data, that’s up in the TTS (very slight warming) and TLS (very distinct cooling) temperature bands as measured by the satelites. So if temps are cooling that high up, you’d expect to see water vapor decrease.
Another question. What is the data collection method behind that graph? Given that the trends start in 1940s, I’m guessing radiosondes. There have been bigger discrepencies in the radiosondes with changing instruments, changing locations, time of day, etc… then there have been with the surface temperature stations. You should look into that.
Also, CO2 becomes more important at higher attitudes, because it’s well mixed throughout the atmosphere, unlike water vapor, which is more important near the surface. So increasing the amount of CO2 is going to block more outgoing longwave radiation higher up in the atmosphere, which is going to have an impact on the radiation budget. The planet is going to have to warm up to equalize the amount of radiation received.
Ken,
“At 8 miles up, isn’t that in the upper troposhere”, but it says “up to” 300mb not “at” 300mb.
Can we assume they are measuring the “specific humidity” from sea level up to 8 miles as an average?
Mr Watt,
From your link: …&level=300…. That’s in the stratosphere, which is cooling.
Go to here: http://www.cdc.noaa.gov/cgi-bin/Timeseries/timeseries1.pl
try it again at say 1000mb height.
Then you get specific humidity going up.
It helps to look in the troposphere (where there’s warming) rather than at 300mb in the stratosphere. Yes the dataset goes up to 300mb, but you selected 300mb as the analysis level.
Well when I use the datasets linked to by Anthony to examine the surface specific humidity trend since 1948 I get:
http://www.cdc.noaa.gov/cgi-bin/GrADS.pl?dataset=CDC+Derived+NCEP+Reanalysis+Products+Surface+Flux&DB_did=40&file=%2FDatasets%2Fncep.reanalysis.derived%2Fsurface_gauss%2Fshum2m.mon.mean.nc&variable=shum&DB_vid=1109&DB_tid=20632&units=grams%2Fkg&longstat=Mean&DB_statistic=Mean&stat=&lon-begin=0.00E&lon-end=358.13E&lat-begin=88.54S&lat-end=88.54N&dim0=time&year_begin=1948&mon_begin=Jan&year_end=2008&mon_end=May&X=lon&Y=lat&output=plot&bckgrnd=white&use_color=on&cint=&range1=&range2=&scale=100&maskf=%2FDatasets%2Fncep.reanalysis.derived%2Fsurface_gauss%2Flsmask.19294.nc&maskv=Land%2FSea+Mask&submit=Create+Plot+or+Subset+of+Data
which tells a different story to the one posed by Anthony’s plot. You can mess around with the data here to see different trends:
http://www.cdc.noaa.gov/cgi-bin/db_search/DBSearch.pl?Variable=Specific+Humidity&group=1&submit=Search
Dave,
“Can we assume they are measuring the “specific humidity” from sea level up to 8 miles as an average?”
I don’t know what we can presume from that graph, which is why I asked the question. The graph Anthony presents isn’t consistent with the results from peer reviewed science. Take a look at these three articles:
Water Vapor Feedback is Rapidly Warming Europe
http://www.agu.org/sci_soc/prrl/prrl0538.html
Trends and variability in column-integrated atmospheric water vapor
http://www.springerlink.com/content/v164l177374p1445/
Enhanced positive water vapor feedback associated with tropical deep convection : new evidence from Aura MLS
http://trs-new.jpl.nasa.gov/dspace/handle/2014/40309?mode=simple
Water vapor feedback is clearly increasing, and in some cases, much more than predicted by models.
Anthony has used incorrect methods before (his comparison of the anomalies of the different surface and satellite temperature datasets without first putting them on a common baseline for example). I think we should know what his methods are and how he derived this graph before we jump to conclusions.
Ken