Methane is like the radical wing of the carbon cycle, in today’s atmosphere a stronger greenhouse gas per molecule than CO2, and an atmospheric concentration that can change more quickly than CO2 can. There has been a lot of press coverage of a new paper in Science this week called “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf”, which comes on the heels of a handful of interrelated methane papers in the last year or so. Is now the time to get frightened?
No. CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 60 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 90 miles per hour instead of 60. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it’s not the big story, nor does it look to be a game changer to the big story, which is CO2.
[Note: Edited Toyota velocities to reflect relative radiative forcings of anthropogenic CO2 and methane. David]
For some background on methane hydrates we can refer you here. This weeks’ Science paper is by Shakhova et al, a follow on to a 2005 GRL paper. The observation in 2005 was elevated concentrations of methane in ocean waters on the Siberian shelf, presumably driven by outgassing from the sediments and driving excess methane to the atmosphere. The new paper adds observations of methane spikes in the air over the water, confirming the methane’s escape from the water column, instead of it being oxidized to CO2 in the water, for example. The new data enable the methane flux from this region to the atmosphere to be quantified, and they find that this region rivals the methane flux from the whole rest of the ocean.
What’s missing from these studies themselves is evidence that the Siberian shelf degassing is new, a climate feedback, rather than simply nature-as-usual, driven by the retreat of submerged permafrost left over from the last ice age. However, other recent papers speak to this question.
Westbrook et al 2009, published stunning sonar images of bubble plumes rising from sediments off Spitzbergen, Norway. The bubbles are rising from a line on the sea floor that corresponds to the boundary of methane hydrate stability, a boundary that would retreat in a warming water column. A modeling study by Reagan and Moridis 2009 supports the idea that the observed bubbles could be in response to observed warming of the water column driven by anthropogenic warming.
Another recent paper, from Dlugokencky et al. 2009, describes an uptick in the methane concentration in the air in 2007, and tries to figure out where it’s coming from. The atmospheric methane concentration rose from the preanthropogenic until about the year 1993, at which point it rather abruptly plateaued. Methane is a transient gas in the atmosphere, so it ought to plateau if the emission flux is steady, but the shape of the concentration curve suggested some sudden decrease in the emission rate, stemming from the collapse of economic activity in the former Soviet bloc, or by drying of wetlands, or any of several other proposed and unresolved explanations. (Maybe the legislature in South Dakota should pass a law that methane is driven by astrology!) A previous uptick in the methane concentration in 1998 could be explained in terms of the effect of El Niño on wetlands, but the uptick in 2007 is not so simple to explain. The concentration held steady in 2008, meaning at least that interannual variability is important in the methane cycle, and making it hard to say if the long-term average emission rate is rising in a way that would be consistent with a new carbon feedback.
Anyway, so far it is at most a very small feedback. The Siberian Margin might rival the whole rest of the world ocean as a methane source, but the ocean source overall is much smaller than the land source. Most of the methane in the atmosphere comes from wetlands, natural and artificial associated with rice agriculture. The ocean is small potatoes, and there is enough uncertainty in the methane budget to accommodate adjustments in the sources without too much overturning of apple carts.
Could this be the first modest sprout of what will grow into a huge carbon feedback in the future? It is possible, but two things should be kept in mind. One is that there’s no reason to fixate on methane in particular. Methane is a transient gas in the atmosphere, while CO2 essentially accumulates in the atmosphere / ocean carbon cycle, so in the end the climate forcing from the accumulating CO2 that methane oxidizes into may be as important as the transient concentration of methane itself. The other thing to remember is that there’s no reason to fixate on methane hydrates in particular, as opposed to the carbon stored in peats in Arctic permafrosts for example. Peats take time to degrade but hydrate also takes time to melt, limited by heat transport. They don’t generally explode instantaneously.
For methane to be a game-changer in the future of Earth’s climate, it would have to degas to the atmosphere catastrophically, on a time scale that is faster than the decadal lifetime of methane in the air. So far no one has seen or proposed a mechanism to make that happen.
References
Dlugokencky et al., Observational constraints on recent increases in the atmospheric CH4 burden. GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L18803, doi:10.1029/2009GL039780, 2009
Reagan, M. and G. Moridis, Large-scale simulation of methane hydrate dissociation along the West Spitsbergen Margin, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L23612, doi:10.1029/2009GL041332, 2009
Shakhova et al., Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf, Science 237: 1246-1250, 2010
Shakhova et al., The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle, GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L09601, doi:10.1029/2005GL022751, 2005
Westbrook, G., et al, Escape of methane gas from the seabed along the West Spitsbergen continental margin, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L15608, doi:10.1029/2009GL039191, 2009
All I see is about radiative heat transfer. What about convection effects. Aren’t these significant espesially with el nino etc
David
Thanks for the post and thank you to all at Real Climate for your great work.
Being a farmer in the South West of Australia who is custodian of both sheep and cattle I tend to be sensitive to talk of methane. Could you put the production of methane from dams into some perspective? I have read that the it is estimated that we produce 120 million tonne of methane from dams around the world in one year.
[Response: Don’t know much about it but I don’t get the impression it’s a big deal. Sorry, David]
“They need to figure out where the methane is coming from and why. Then wait and see how it changes with time.” No proxy data with which to hindcast?
[Response: Maybe someone will come up with something. Human ingenuity is an amazing thing. Ice core data can shed some light via the North / South difference, but it’s crude. David]
“In fact both CO2 and methane varied cyclically through the glacial cycles, both probably as feedback to temperature which was originally driven by wobbles in the Earth’s orbit. CO2 had a larger impact on the radiative forcing than CH4 did. David”
I know David, thanks.But can the amount of methane that can be released by a variation of a few degrees be comparable to the amount of fossil carbon that is currently burnt by mankind (at least 1000 Gt, may be more )? if no, how could it trigger a runaway , and if yes, why has CO2 not reached this kind of level (500 ppm or so) in during interglacial periods? wouldn’t it be an extraordinary chance that the natural variations has never released it before,giving a high CO2 concentration after being oxidized ?
CFU :How does this make your statement
“Why is methane a serious problem, since methane is naturally emitted all around the world in much larger amounts than what has been observed in Arctic,”
true, then?
Because what is observed to rise is only the 0.01 g , not the 1g, so there is no sign that we are nearing a tipping point.
[Response: In the geologic past through the glacial cycles the climate feedback from methane has been smaller than that from CO2. However, as you note we’re pushing CO2 beyond the limits of what it has been for millions of years. The methane hydrates in the ocean take millions of years to grow. So we may be pushing the hydrates to melt down in the future. We did calculations that if the feedback were too strong you’d see the hydrates melting down spontaneous throughout Earth history. You don’t really see that, so the upper limit we predicted was that the hydrates could ultimately release as much carbon as we burn in fossil fuels. But the time scale for that is thousands of years, so the impact on climate over the next few hundred years would be small compared to that from fossil fuel CO2. David]
Over the last 7 years the ESAS has developed 100 ‘hotspots’ of Methane venting, as warming continues, seems fair to expect more ‘hotspots’ to emerge.
As the ESAS is estimated to contain 540 billion tonnes of Methane, it alone has the potential to cause substantial Global warming.
The only question would seem to be the rate at which it increases to vent over the coming years, as this permafrost is collapsing far sooner than expected it would seem that it is more sensitive to temperature than expected, suggesting a fast rate of collapse is likely.
Gilles: “Because what is observed to rise is only the 0.01 g , not the 1g”
No, that still doesn’t make “why is methane a problem when we’re getting it naturally” true.
Go look up the volume of methane in the atmosphere and the amount of methane trapped in the tundra and under the water.
[edit]. Do something real. Investigate.
Prof T Heidrick #151: of course climate modellers are aware of convection and it is part of the models. Just because it isn’t being discussed in this article doesn’t mean it’s ignored. Try the search box at the top of the page.
Haven’t Paleontologist found good evidence of catastrophic methane release in the past? What you are observing right now on the edges of the stability border of methane hydrate in the oceans might just be a precursor of future catastrophe?
[Response: The PETM is the poster child, but the combination of the carbon and oxygen isotopes seem to rule out methane as the source, you wouldn’t get enough carbon to get as much warming as the oxygen isotopes tell you, unless the climate sensitivity was something like 7 degrees for doubling CO2. So I don’t personally believe it could have been methane. David]
Thanks, David, for the response about the water vapor feedback question. I did not take into account the change in air pressure with altitude, but that seems to make things even worse. The number of H2O molecules per total number of gas molecules goes up with temperature, but the radiative effect of these molecules goes down, because they are warmer.
I imagine a “box” of air at any given altitude, which has a certain number of water vapor molecules depending on its temperature. If we now double the amount of carbon dioxide, the box gets warmer. So I move the box higher to get it back to the same temperature. But being higher, there are now less molecules in it, including water vapor molecules, than before. So it will have less radiative effect than before. This is true for a box of air at every altitude. The only new “boxes of air” are added near the surface, where they are warm and do make much difference to the greenhouse effect.
I have now conjured up a negative water vapor feedback. Please explain the error in my reasoning.
“I have now conjured up a negative water vapor feedback. Please explain the error in my reasoning.”
The problem is here:
“So I move the box higher to get it back to the same temperature. But being higher, there are now less molecules in it, including water vapor molecules, than before.”
But you have more boxes. Therefore the total may go up or down.
Blair,
That’s an utterly bizarre formulation. What matters is the number of potential ghgs between a photon and space. It’s not that you cease to have radiation at lower levels, but that it just doesn’t escape. Try looking at the atmosphere in columns rather than boxes.
Re 160 – CFU, I am saying the new boxes are all at the bottom of the atmosphere, where they do not have much impact on the greenhouse effect.
Re 161 – Ray, my understanding is that the greenhouse effect depends on the temperature of the gas from which the radiation escapes into space. If a low altitude ghg radiates directly into space, its temperature is about the same as the surface, so it makes little difference to how much energy is lost. If the radiation is intercepted by another molecule, than the lower molecule no longer matters.
I tried to look at the atmosphere in a column. Given constant relative humidity and lapse rate, increasing carbon dioxide raises the entire column to a higher level. There is no change in the temperature structure. A warmer layer is inserted below it, so the surface warms.
Thanks for your response. I know there must be something wrong with my understanding, and I appreciate any help you can give.
“Re 160 – CFU, I am saying the new boxes are all at the bottom of the atmosphere, where they do not have much impact on the greenhouse effect.”
Then you say you lift them up.
How can this leave them at the bottom of the atmosphere?
Interesting example [methane generating?] of the morphs that lead to contrarian hysteria – the study “Large-Scale Controls of Methanogenesis Inferred from Methane and Gravity Spaceborne Data” leads to headline “Arctic permafrost leaking methane at record levels, figures show” [Guardian of course], which leads to “Methane Madness”. The comments at the Guardian and “American Tinker” are entertaining, but depressing. Seems more attention to public education on the range and interaction of all greenhouse gasses is needed.
This viz mechanism for methane release:
The 3000 km3 Storegga submarine landslide occurred c. 8150 years ago from an area rich in gas hydrates off the western coast of Norway. A synchronous increase of 80—100 ppb in atmospheric methane concentrations is recorded in the Greenland GRIP ice core. This increase is hypothesized to reflect methane releases from the Storegga slide debris at an estimated rate of 20—25 Tg/yr for several hundred years following the slide. Methane is a powerful greenhouse gas, and methane release from the Storegga submarine landslide may have contributed to the rapid termination of the brief but intense 8200 yr cold event and the subsequent evolution of Holocene climate.
Earthquakes or simple destabilization of shelves could lead to a possible methane release; couple this with increasing water temperature, and I could see how there could be a sudden surge in greenhouse effects…
[Response: The Storegga slide could have released about a gigaton of carbon as methane at most, which would have increased the atmospheric concentration by maybe a third, about the same climate perturbation as a large volcanic eruption but warming rather than cooling. The slide coincided more or less with the 8.2k climate event, which was a cooling driven by ocean circulation and the methane concentration went down, not up. Anyway, an increase of 100 ppm would be a very small climate impact. I think you’d need simultaneous storeggas all around the world to get a climate kick from the methane. David]
I think this is your problem:
> If the radiation is intercepted by another molecule,
> than the lower molecule no longer matters
“no longer matters” is wrong. It’s the delay time you’re omitting.
Hmmm, a venture into recreational typing, top o’ my head version:
The added greenhosue gas molecules near the surface are _delaying_ the transfer of heat, extending the time it takes moving out from the surface, spreading the heat to the surrounding air, which conveys heat back to greenhouse gases and to the surface by conduction, convection, and radiation. Meanwhile above those warming lower layers, the higher layers have more CO2 intercepting less heat from below, and the upper layers cool.
But Blair, what happens is that the ghg in the new radiating layer is colder, and so radiates less than the gas in the the old one. Stefan-Boltzmann Law.
By formulating the problem as boxes, instead of masses, you forgot to preserve mass balance. By adding a new box at the surface, the box “jacked up” at altitude has fewer molecules, but the left over molecules don’t disappear. They go into a new box, at altitude, so the statement “The only new ‘boxes of air’ are added near the surface,” is wrong.
To really understand what happens, you gotta run a line by line and layer by layer calculation (model), and compare them against others models. see http://www.ametsoc.org/atmospolicy/documents/071029Soden.pdf
What about the danger than James Hansen highlights, of methane release triggering a PETM-type warming event on top of the warming caused by other GHG emissions?
Is runaway climate change possible? Hansen’s take
[Response: Or carbon release from peats, or soil carbon, or biomass, or the ocean somehow-like-it-did-during-the-glacial-cycles. Methane is not the only game in town. David]
Some people take comfort from the fact that there have been times in the history of the planet when greenhouse gas concentrations were much higher than now. The world was very different, but there was no runaway greenhouse and life endured. James Hansen devotes the entire tenth chapter of Storms of My Grandchildren to considering whether this assessment is valid. Three things give him pause:
1. The sun is brighter now than it was during past periods with very high greenhouse gas concentrations. The 2% additional brightness corresponds to a forcing of about 4 watts per square metre and is akin to a doubling of CO2 concentrations.
2. For various reasons, the greenhouse gas concentrations in past hot periods may not have been as high as we thought.
3. We are introducing greenhouse gases into the atmosphere far more quickly than natural processes ever did. This might cause fast (positive) feedback effects to manifest themselves forcefully, before slower (negative) feedback effects can get going.
He also explains that the sharp warming that took place during the Paleocene–Eocene Thermal Maximum (PETM) were not caused by fossil fuels (which remained underground), but rather by the release of methane from permafrost and clathrates. If human emissions warm the planet enough to release that methane again, it could add a PETM-level warming on top of the warming caused by human beings.
In this post, are you saying that is unlikely to happen at all, or just that it would be likely to take a long time? What do you think about his concerns about methane kicking off runaway warming? Hansen says that: “While that is difficult to say based on present information, I’ve come to conclude that if we burn all reserves of oil, gas, and coal, there is a substantial chance we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.”
Hank, I am trying to use a radiation balance model. The Earth receives a certain amount of radiation from the sun, and must radiate the same amount out to keep its temperature in balance. So the only greenhouse gas molecule that matters is the one that radiates into space.
This is like managing your bank balance, all you do is subtract withdrawals from deposits (assuming you trust the bank). You do not pay attention to all the transactions that happen inside the bank with the money you deposit. I view your discussion of conduction and convection as internal transactions which can be ignored when calculating radiation balance. In reality, convection may affect the lapse rate, but I am assuming a constant lapse rate for now.
For water vapor feedback to add to the greenhouse effect, you need to get more water vapor molecules up to a higher altitude, where they will radiate at a lower temperature, so less energy is “withdrawn” from the earth system. The only mechanism (I am ignoring convection, maybe that is the problem) to get the water there is the Clausius Clapeyron law, basically saying warmer air holds more water vapor.
A column of air has a certain temperature profile, determined by the lapse rate.
Doubling carbon dioxide simply raises that temperature profile of a vertical column of air higher into the atmosphere, assuming constant lapse rate. That is what lapse rate means.
Assuming water vapor concentration depends only on temperature, the proportion of water vapor will not change. The amount of water vapor will be less, because the air is thinner. So there are less water molecules to intercept radiation, and re-radiate at a cooler temperature.
Mass balance is maintained by the new warmer layer at the surface (underneath the “raised” column of air), which will have more water vapor that was there before. So there is more total water vapor in the atmosphere, but the additional water vapor is all near the surface, where it will radiate at a high temperature, and have little greenhouse effect.
I hope this makes my thinking clearer, and I hope someone will point out specifically where the problem is. I appreciate the help so far.
Hello again.My comment is #27.I just read up to comment # 172.There are many excellent comments which quickly educated me even further.That’s why I like this site.Tons of highly educated people commenting on things I care about deeply.So, thanks to everyone here for their time and comments.
Geez Louise, folks it sure does look like there is a lot to be concerned with.Notable are comments #165,#169 and #170 among many other notable comments.Also,Hansen has it right.No question at all on that.
Mark J.Fiore
markfiore50@hotmail.com
Re Blair Dowden 171:
Well, the vapor pressure of water vapor increases roughly exponentially with increasing temperature for constant RH. Thus, assuming constant RH, a temperature increase will increase the water vapor pressure.
For the sake of the argument, if the RH profile shifts upward with the temperature profile (let’s say it shifts upward by an amount h), the water vapor pressure profile shifts upward, which generally means more water vapor at a given height level. (PS Note that the same water vapor pressure at lower atmospheric pressure actually means an increase in mixing ratio (specific humidity).) In that case, the water vapor would be at the same temperature relative to a coordinate that shifts upward by h, but there is then the additional water vapor near the surface. But with the temperature increasing at the bottom of the temperature profile, there is a greater temperature difference between the water vapor above h from the surface and the surface and water vapor beneath h. Aside from some variations in line broadenning, the water vapor reduces the upward LW flux at the tropopause more not because it is colder but because the surface and lowermost water vapor are warmer (or if the lowermost water vapor completely blocked surface radiation, then the effect of the water vapor above that would not have changed, since the temperature at the top of the lowermost water vapor would be the same as the surface temperature before, but then there would not have been any increase in the outgoing LW flux in response to warming – actually there would be some increase due to the nonzero LW albedo at the surface, but anyway…). Thus the increasing temperature has not increased the net upward LW flux as much as it would have if water vapor were held constant relative to atmopheric pressure or geometric height.
Blair, did you do the exercise recommended by Brian Dodge’s pointer at 168 yet?
When you “run a line by line and layer by layer calculation (model), and compare them against others models. see http://www.ametsoc.org/atmospolicy/documents/071029Soden.pdf ” — where does your model fall compared to those charted there? I’d guess it’s well outside (below) the bunch of them?
But those as shown are in the range of what’s observed; how would the chart drawn from your model correspond?
Seems like “do the math, show the work” is the answer — people can comment on the work once they see it, but not by imagining what it would look like.
PS, some of these are ‘fill in the blank’ approaches as I recall
http://www.google.com/search?q=simple+climate+model
[Response: The relative humidity stays about the same, but the absolute humidity, the number of H2O molecules per total number of gas molecules, goes up with temperature. It goes up proportionally to the change in saturation vapor pressure. David]
This is totally off topic…but a lil curiosity i havnt been able to google the answer too… but what you say here is what i lean towards..
I guess this is global, but optical depth seems variable on air pressure, its an old farmers weather prediction method. So during a high pressure, distant objects(mountains etc) appear more distant, with less visible definition to the details, and appear closer with greater visble detail pre a change in the weather… Is this the result of the SW light being scattered/or absorbed by the greater density o water molecules in the atmosphere during a high pressure system?
Random i know, but im curious.
Blair Dowden, in your conceptual model, presume that the outgoing radiation comes from three separate IR bands, a CO2 band emitted from its effective emission height, an H2O band emitted from its effective emission height, and a window band emitted from the surface. When the CO2 amount increases, the effective emission height for CO2 lifts, warming the entire temperature profile for radiation balance. The warmer profile now holds more H2O, so the effective emission height for H2O lifts as well, and the temperature must get warmer again.
bandwidth(CO2)*(T(surface)-gamma*height(CO2))^4 +
bandwidth(H2O)*(T(surface)-gamma*height(H2O))^4 +
bandwidth(window)*(T(surface))^4 = constant
Re Blair Dowden 171 – part II
More generally, the absence of water vapor feedback is when the mixing ratio and thus the vapor pressure (setting aside the minor effect that adding water vapor increases total atmospheric mass just a little) doesn’t change at any level. In that case, warming increases the net LW flux out at the tropopause level (cooling of the stratosphere would do the same thing; effects of changes in stratospheric temperature in response to radiative forcing before any response are included in the tropopause level radiative forcing with equilbrated stratosphere; both the stratosphere and troposphere and surface, etc, change farther in the total response (the stratosphere adjusts to tropospheric changes, that is another source of feedback)).
Now, after the temperature changes, add water vapor at any level within the troposphere (or for that matter, the stratosphere – in spite of stratospheric cooling, changes in the troposphere could inject more water vapor into the stratosphere (a generally dry place to begin with, due to the cold of the tropopause level)). That will reduce the net outgoing LW flux at the tropopause level. Water vapor at all levels (and all places and times) is not equal, and in some conditions the opposite could be true (water vapor on top of a low-level inversion), but it is generally true (and it would be odd if the only increases in water vapor were at the tops of low-level inversions).
And so on for other feedbacks…
Re 170 – I agree bad things would happen, but I’m a little surprised by the Venus reference.
It’s been a while since I’ve read this stuff but I vaguely recall:
Earth would start to lose signficant amounts of the ocean to space when specific humidity (volumetric mixing ratio) ~ 20 % (presumably at the surface), which would correspond to a temperature of …? (factor of ~ 1.2 increase per 3 K, … um, um, … approx 30 K warmer?) and that would take awhile. We’ll have a lot to deal with before we ever get into Venus territory, I think.
I think James Kasting wrote some things on this topic, perhaps in response to “Rare Earth”.
[Response: I don’t disagree with any of this. But I’m not trying to “downplay the threat” by pointing out that so far the methane sources from hydrates are small. David]
Comment by ccpo — 8 March 2010 @ 3:19 AM
I don’t think I specifically said you were trying to, per se, only that you are. I said in at least one of my posts on this topic that scientists are held back by the scientific rigor and the unwillingness to take leaps of faith, intuition, etc.
I suggest you embrace them, instead.
There is a degree of semantics and interpretation here, certainly, but when we take all the evidence we have collectively, the methane seepage thus far is dang alarming. I see your article above as not providing full context and accepting the purely scientific, verified evidence as all of the evidence.
What we know of non-linear systems and the much-faster-than-expected progression thus far tell us that underestimation is likely a very bad idea.
Cheers
PS. In case i don’t say it often enough, I love you guys, man!
Actually, work by Sowers reported in Science (v 311, 838, subsequent work since by Petrenko Science 324, 506)and even several others all show that hydrates did not contribute to, or even noticeably respond to, any of the post glacial warming episodes. The best example where this might have happened is the PETM, and even there, the evidence is not conclusive.
Comment by Dennis Denuto — 8 March 2010 @ 7:00 PM
It was pointed out above, by David, I believe, that GHG levels are higher than at any time coming out of an ice age in the past. They’re higher than for a very, very long time. Also, that bit about the 1.8 parts per whatever for methane?
This is not Kansas, Toto.
First, let me be clear that I do not believe my “result” that there is no water vapor feedback. I am aware that both modeling and empirical results indicate that it is significant. I am trying to understand how it works so I can explain it to others. This should be possible without doing a line by line calculation.
Does anyone have a problem with the following: Low altitude water vapor has little impact on the greenhouse effect from a radiation balance point of view. This water vapor may absorb every single photon in its absorption band, but Kirchhoff’s Law says they will be emitted again at the same wavelengths. They are at about the same temperature as the Earth’s surface, so this re-emission does not change the energy balance. (See page 152 of this Pierrehumbert paper.) However, this process may affect convection, which change the temperature distribution of the atmosphere.
Patrick 027, you said “water vapor reduces the upward LW flux at the tropopause more not because it is colder but because the surface and lowermost water vapor are warmer.” I do not understand this statement. Temperature difference affects convection, but not radiation.
Imback, I agree with your statement up to the conclusion. The effective emission height for H2O is raised, but so is its temperature. I fail to see how that changes the radiation balance.
I think the problem is that the atmosphere is not saturated with water vapor, so Classius Clapeyron is not sufficient to determine moisture content. Relative humidity may change, perhaps differently at different altitudes. Also, changes in convection may be important. It would be nice to have some idea how all this works.
Blair wrote:
Imback, I agree with your statement up to the conclusion. The effective emission height for H2O is raised, but so is its temperature. I fail to see how that changes the radiation balance.
I do understand you want a heuristic model. The situation is tricky because H2O depends on temperature and temperature depends on H2O, so we have to think in simultaneous equations.
Let’s start from the radiation balance equation (bottom of post 177). (Note gamma is the lapse rate.) —
bandwidth(CO2)*(T(surface)-gamma*height(CO2))^4 +
bandwidth(H2O)*(T(surface)-gamma*height(H2O))^4 +
bandwidth(window)*(T(surface))^4 = constant
Let’s assume constant RH and a linearized Clausius-Clapeyron (here the baseline heights and temperatures are subtracted, and chi is the linearized C-C slope) —
(height(H2O) – height(H2O)@t=0) = (T(surface) – T(surface)@t=0)*chi
So now we raise height(CO2). Algebraically we can see that T(surface) will increase, holding more H2O so height(H2O) goes up, which will force a further increase in T(surface) to keep the radiation balance.
Re Blair Dowden – it should be clear from my subsequent comment (first increase the temperature, then add water vapor and see what that does).
154.”No, that still doesn’t make “why is methane a problem when we’re getting it naturally” true.
Go look up the volume of methane in the atmosphere and the amount of methane trapped in the tundra and under the water.
[edit]. Do something real. Investigate.”
Obviously David’s answer is much more relevant to my question than your comment. Thanks David.
The main points seem to be:
1) Right now, the methane from the Arctic is a small percentage of total methane sources.
2) There is no clear mechanism for sudden, catastrophic release of all this methane.
Even if we set aside problems with these assertions, it seems to me that if this is the beginning of a new vast (how vast? anyone have the latest estimates?) source of carbon emissions into the atmosphere, this is a bad thing, whether in the long or short term. The researchers themselves say that studies in the ’90 found no such methane release, so either the release now is part of some cyclical pattern we don’t understand, or it is the beginning of something new.
So this in turn leads to two questions:
1) Is there any evidence or theory of what kind of cyclical event this could represent?
2) Is there any kind of negative feedback that would likely stop this, if it is a new trend.
If this is a new trend, and the answer to the second question is no, then even if this may not represent some kind of Hollywood doomsday in an hour scenario, long term it will greatly exacerbate (at least) already very bad prospects for the planet.
Re:142 Thanks Brian
You explained the slow storm effect very well. Because the tropics are warming at a slower rate than the sub tropics and temperate zones the whole world is indeed entering the ‘greenhouse effect’ scenario very clearly. Ok the earth will probably never resemble the extremes of venus but it’ll still too hot hot for intelligent life to flourish.
Thanks ccpo that that bit of plagerism. If I was writing for a newpaper I’d sue you..haha!
Least I know we’re on the same wavelength.
Blair (162),
If you like, I can send you a tutorial I wrote on column atmosphere models (directed originally at deniers on an amazon.com forum, thus the occasionally sarcastic tone). I plan to incorporate it in a book, so I can’t publish it on the web. You’ll require a programming language to follow the examples; the one I use in the tutorial is Just Basic, which is a free download.
Blair,
The vapor pressure of water is higher as temperature climbs. Check out the Clausius-Clapeyron relation.
Manabe’s team used the equation RH = 0.77 * (P/Ps – 0.02) / 0.98 for relative humidity at different altitudes (I think this overestimates it in the stratosphere, but that’s another story). Here P/Ps is atmospheric pressure relative to sea level. There’s an unphysical discontinuity at P/Po = 0.02, so above that they just assumed RH = 0.000003.
Actual vapor pressure = RH x saturation pressure, and Clausius-Clapeyron gives the saturation pressure.
Imback and Patrick 027, we all agree that water vapor at every level will increase when carbon dioxide is increased. The issue is that its temperature is also increased, so it is not clear what the net radiative effect will be.
Observation shows that the increase is large enough to have a net positive radiative effect. I am trying to understand why. I am saying that if relative humidity and lapse rate are held constant this will not happen, and no one has shown that logic is wrong. Something else is happening.
Blair, your conceptual model should work even keeping relative humidity and lapse rate constant. We can see it in the algebraic argument, so it must work in the heuristic argument. Your logic error may be that you are double counting the first temperature increase. The first temperature increase perfectly offsets the increase in CO2. It’s already in balance without changing the H2O. Now raise the H2O due to Clausius-Clapeyron. The radiation becomes unbalanced again even with the first temperature increase. So a second temperature increase is necessary for balance.
Blair, define what you mean by “net positive radiative effect”. Are you saying that it’s a positive feedback or that it’s emitting more radiation?
Slightly o.t., as roughly 25% of the current rise of atmospheric Methane is due to increased Wetlands emissions wouldn’t there be a similar rise of Methane during the ‘Medieval warm period’, if it was as warm as the current period? The levels of Methane for the last thousand years have been pretty much constant until recently, as shown here, http://joseph44.users.sourceforge.net/climate/graphs/ch4-etheridgeetal-reconstruction-1008-1993.JPG
“Historic CH4 Records from Antarctic and Greenland Ice Cores, Antarctic Firn Data, and Archived Air Samples from Cape Grim, Tasmania”
[Response: Interesting question. It was very dry during the Medieval time, maybe that slowed down methane production in wetlands. Today the methane is high not because of the warm temperatures but because of livestock farting, rice farming, and leaking fossil fuels. David]
Ok the earth will probably never resemble the extremes of venus but it’ll still too hot hot for intelligent life to flourish. – Lawrence Coleman
Whatevergate would seem to indicate that it already is :-d
David said: “But the time scale for [total methane hydrate release] is thousands of years, so the impact on climate over the next few hundred years would be small compared to that from fossil fuel CO2.”
Somehow, I don’t find this very comforting. I guess I’d like to know the sober assessment of the likelihood that the releases reported in the Science article are in fact a new feedback that, over whatever timescale, will eventually lead to carbon releases on a par with all ff sources of atmospheric carbon to date.
Even if it on a timescale of thousands of years, that does not bode well, to my mind, for the future of life on earth.
Yes, some of us do care about the future long after we and everyone we knows are long gone. Perhaps more need to start thinking on these timescales.
And again, thanks for all the good work you do here.
Thanks for the post David. I was wondering if you might be interested in posting on RC a response to David Archibald’s recent post at WUWT:
http://wattsupwiththat.com/2010/03/08/the-logarithmic-effect-of-carbon-dioxide.
He’s using the Modtran data again, this time to hind-cast a bit and suggest that the “IPCC models” (obviously run from the vast underground layer at the IPCC World Domination Headquarters) make anthropogenic warming fundamentally different from natural warming – thus that AGW is all rubbish. It’s attracted a lot of ooo’s and ahhh’s from Watts’ crowd, so I would love to hear your treatment of the matter.
As a plant ecologist, my favorite part is “Plant growth shuts down at 150 ppm, so the Earth was within 30 ppm of disaster [during the ice ages].” Say what?!! How many ACi response curves have you actually looked at, Mr. Archibald?
[Response: Yeah, this guy is over the line. Of course the radiative forcing from CO2 is logarithmic, I pointed out the same thing in my global warming textbook, and I’ll be teaching it to a full classroom of undergraduates in about a month. It’s not news, the models know all about it. I’ve seen Mr. Archibald’s work before. It’s weird he’s using the model I posted on line (for the class, actually), but, hey, transparency, what’re ya gonna do? David]
Are there simulations of the climate which include a methane hydrate dissociation model (like tough+hydrate) in their ocean-atmosphere coupling ?
Ray, by the poorly chosen term “net positive radiative effect” I mean that a positive feedback is observed in the real world.
Imback, I am saying that after I “raise the H2O due to Clausius-Clapeyron”, the water vapor is warmer, so it will radiate at a higher temperature, and more heat will be lost from the Earth system. More water molecules, but less effect from each. The mathematically inclined may want compare the exponential gain in water molecules with the fourth power of temperature in the Stefan Boltzmann law. I suggest that any layer is equivalent to a previously lower layer, except maybe fewer overall molecules. Always assuming constant relative humidity and lapse rate.
But back to the real world, the atmosphere is not saturated with water vapor, so Clausius-Clapeyron does not actually drive anything. The changes in water vapor must be driven by other forces, such as convection.
Re Blair Dowden – what Imback 191 said; or in other words:
The water vapor feedback is the change in LW flux (tropopause level or top-of-atmosphere or …, depending on context, but the first is of key importance) at a given temperature distribution, after the temperature has changed and before the temperature changes again in response to the feedback (or it can be described in terms of the further temperature change that results).
A radiative forcing occurs; to restore radiative balance, a change in temperature must occur. Without any other changes, x K warming increases net outward LW flux. But then water vapor increases, reducing the net outward LW flux from what it would be if only the temperature changed. Thus the temperature has to change more to restore balance.
@ Blair Dowden — 9 March 2010 @ 10:54 PM “It would be nice to have some idea how all this works.”
background info –
http://en.wikipedia.org/wiki/Lapse_rate
http://www.ipcc.ch/ipccreports/tar/wg1/266.htm
http://www-das.uwyo.edu/%7Egeerts/cwx/notes/notes.html
http://www-das.uwyo.edu/%7Egeerts/cwx/notes/chap08/moist_cloud.html
https://www.realclimate.org/?comments_popup=2817#comment-161863
http://svs.gsfc.nasa.gov/vis/a000000/a003600/a003648/index.html
Data to play with –
http://weather.uwyo.edu/upperair/sounding.html
http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
http://www.humidity-calculator.com/index.php
complications to consider –
Smaller droplets are in equilibrium at higher vapor pressures – the surface energy change caused by the curvature of the surface causes small droplets to require supersaturation for formation and growth; if the water vapor pressure is below that required for a small droplet, and above that required for a larger droplet, mass will transfer from the smaller to the larger by evaporation and condensation.
The moist adiabatic lapse rate varies depending on the mass of water available to supply heat by phase change, therefore varies with temperature and pressure(altitude).
Orographic and frontal lift/sinking, and momentum of moving masses of air sum with convective lift. The convective + momentum lift of tropical thunderstorms probably plays a role in injecting water into the stratosphere – http://svs.gsfc.nasa.gov/vis/a000000/a000800/a000831/a000831.mpg
Precipitation moves water and latent cool of melting/evaporation down in the atmosphere.
Winds have a significant influence on ocean evaporation, by removing the high humidity near surface layer, increasing the evaporative surface by ripple/wave formation, and creating spray(large highly curved surfaces) at high wind speeds. And surface winds are turbulent at a wide range of scales – spend a day sailing with an experienced skipper (like me &;>) and have him show you how to visualize the wind variations by ripple patterns. Also, since the troposphere is only ~ 10 km thick, turbulence at 1km scales is 3 dimensional, but at 100km plus, the flow is approximately 2 dimensional. large scale flow can couple into smaller scale turbulence – http://paranoicmrbrain.files.wordpress.com/2008/06/72.jpg http://www.colorado.edu/geography/class_homepages/geog_3251_sum08/07_rotor_clouds.jpg