The Methane Issue

[blizzard1024]

Here is a fair and reasonable article on the potential for methane release from global warming. 

It IS from a reputable source.... Global Change... International Geosphere-Biosphere- Program. 

 

http://www.igbp.net/news/features/features/methanenotadampsquibnotyetatimebomb.5.19b40be31390c033ede80001011.html

 

They are a little skeptical of a catastrophe at this time stating the Earth in the distant past (last interglacial) was likely

2C warmer than today globally and probably warmer in the Arctic. Methane did spike but we did not have catastrophic consequences.

 

This is one scientists opinion.   

[csnavywx]

A chronic release appears more likely, though at least small explosive events can't be ruled out at least until we understand it better, due to the magnitude of the current forcing and the cold nature of Arctic waters. Even if the Arctic was consistently 1-2C warmer during the Eemian, it will not take long to cross that threshold. (The world was nowhere close to 2C warmer during the Eemian, btw.)

 

As far as the PETM is concerned, there is better evidence that the CO2 buildup in the atmosphere was actually pretty slow, on the order of 15-20 kyr. The maximum rate of emissions did not exceed 2 Pg of carbon a year, with the vast majority of the release probably far less than that (<.5 Pg per annum or <1-2 Billion tons of CO2 per year). We currently emit at rates more than an order of magnitude faster, using the optimistic CO2-only scenario for the PETM. It's likely that some significant chronic methane release was involved and in that case, this means our current emission rate exceeds that of the PETM by a ridiculous amount.

[blizzard1024]

A chronic release appears more likely, though at least small explosive events can't be ruled out at least until we understand it better, due to the magnitude of the current forcing and the cold nature of Arctic waters. Even if the Arctic was consistently 1-2C warmer during the Eemian, it will not take long to cross that threshold. (The world was nowhere close to 2C warmer during the Eemian, btw.)

 

As far as the PETM is concerned, there is better evidence that the CO2 buildup in the atmosphere was actually pretty slow, on the order of 15-20 kyr. The maximum rate of emissions did not exceed 2 Pg of carbon a year, with the vast majority of the release probably far less than that (<.5 Pg per annum or <1-2 Billion tons of CO2 per year). We currently emit at rates more than an order of magnitude faster, using the optimistic CO2-only scenario for the PETM. It's likely that some significant chronic methane release was involved and in that case, this means our current emission rate exceeds that of the PETM by a ridiculous amount.

Nice discussion here. Again, I am try to learn about this and I thought the above article was reasonable. Thanks for your comments. 

[blizzard1024]

Gonna have to take a break from these great discussions. Thanks to all...

even those who I don't see eye to eye with. I respect your opinions. I really

do. I have so much work to do in the next few weeks with my real job that

I just have to shed this for a while.

[TerryM]

An abstract of the latest paper from S&S.

 

The degradation of submarine permafrost and the destruction of hydrates on the shelf of east arctic seas as a potential cause of the “Methane Catastrophe”: some results of integrated studies in 2011 - Springer

 

If anyone knows where the full article can be accessed without the pay wall, I at least would be appreciative.

 

Terry

[dabize]

An abstract of the latest paper from S&S.

 

The degradation of submarine permafrost and the destruction of hydrates on the shelf of east arctic seas as a potential cause of the “Methane Catastrophe”: some results of integrated studies in 2011 - Springer

 

If anyone knows where the full article can be accessed without the pay wall, I at least would be appreciative.

 

Terry

Gee Terry, that looks ominous.

 

Were S&S's earlier obs from the SE Laptev?    I seem to remember that they were from further offshore.

 

If so, this would suggest the involvement of a larger part of the ESAS in the methane release party.......

[TerryM]

My recollection is that they were primarily concerned with the near shore features, then made their famed icebreaker run to track the reports of "boiling seas" being sent back by Arctic sailors.

 

Dr Munchow blogged a few days ago about the lengths Canada is going to in it's quest to keep Arctic research locked up by citing intellectual property concerns & I believe the US has  reopened it's case against the Alaskan scientist who had the temerity to mention drowned polar bears. 

 

It's seemed to me that the ESAS methane situation hasn't been getting a lot of play for some time- but I'm sure it's for our own good.

 

Terry

[skierinvermont]

Arctic methane forms much less than 1% of all global methane emissions. Because methane is short-lived, unlike CO2 small changes in the methane budget do not cause large changes in methane concentration.

[salbers]

The percentages (current and potential future) as well as climate impact have been much discussed in the following thread:

http://www.americanwx.com/bb/index.php/topic/30926-this-is-not-good/

The threat is of a several order of magnitude increase in Arctic methane emissions. There would be both a short term spike in radiative forcing due to CH4 and a longer term increase when the CH4 converts to CO2.

I think Arctic ice shelf methane is a bit more than 1% of global methane emissions currently, and it seems to be increasing.

Incidentally if you scroll to the bottom of the page below, you can see a photo (second from bottom) of the posters that I viewed at the AGU 2012 conference, in fact yours truly is talking with Dr. Semiletov.

http://www.iarc.uaf.edu/research/highlights/2012/agu

[WeatherRusty]

Arctic methane forms much less than 1% of all global methane emissions. Because methane is short-lived, unlike CO2 small changes in the methane budget do not cause large changes in methane concentration.

 

However the addition of (X) number of CH4 molecules carries 20-25 times the global warming potential of the same number of CO2 molecules over a 100 year time horizon. This is mostly due to the fact of CH4 being so dilute compared to CO2. Relatively few additonal CH4 molecules are required to reach a doubling compared to the number of CO2 molecules.

[TerryM]

A question

 

CH4 has an atmospheric lifespan of ~12.4 yrs so why are 20 and 100 year GHG equivalencies always used?

 

All of the CH4 as measured is apparently <=12.4 years of age & is exerting a much stronger effect than either the 100 yr. or the 20 yr. measures indicate.

 

Since running the 100 and 20 year figures give disparate results I'm unsure of what the real time figure for CH4 would be.

I'm also unsure of why the 100 or 20 year figures give a better measure of what is being experienced under say a plume of CH4 rising from a seep under the ESAS.

 

Thanks in advance

Terry

[WeatherRusty]

A question

 

CH4 has an atmospheric lifespan of ~12.4 yrs so why are 20 and 100 year GHG equivalencies always used?

 

All of the CH4 as measured is apparently <=12.4 years of age & is exerting a much stronger effect than either the 100 yr. or the 20 yr. measures indicate.

 

Since running the 100 and 20 year figures give disparate results I'm unsure of what the real time figure for CH4 would be.

I'm also unsure of why the 100 or 20 year figures give a better measure of what is being experienced under say a plume of CH4 rising from a seep under the ESAS.

 

Thanks in advance

Terry

 

Terry,

 

Methane has a GWP of 72 if considered over a 20 year time horizon. 25 over a 100 year horizon. These values are relative to the same initial mass of CO2 used as the standard. CO2=1

 

When you consider the atmospheric lifetime of CH4 being ~12.5 years, we are referring to the average lifetime of any one particular molecule. CH4 decays at a rate such that if we start with a given mass, the chance is greatest that a particular molecule will be eliminated at 12.5 years. Some will still remain at 20 years, less will remain at 100 years and less still at 150 years.

 

Obviously the effect or GWP at 12.5 years will be greater than at 20 years, but the radiative forcing given by the starting mass will be deteriorating rather rapidly at that point.

[TerryM]

Terry,

 

Methane has a GWP of 72 if considered over a 20 year time horizon. 25 over a 100 year horizon. These values are relative to the same initial mass of CO2 used as the standard. CO2=1

 

When you consider the atmospheric lifetime of CH4 being ~12.5 years, we are referring to the average lifetime of any one particular molecule. CH4 decays at a rate such that if we start with a given mass, the chance is greatest that a particular molecule will be eliminated at 12.5 years. Some will still remain at 20 years, less will remain at 100 years and less still at 150 years.

 

Obviously the effect or GWP at 12.5 years will be greater than at 20 years, but the radiative forcing given by the starting mass will be deteriorating rather rapidly at that point.

I think I'm following you, but it begs the question, or quite possibly I'm not asking the question correctly.

 

What I'm concerned with knowing is the GHG effect of a rapid outgassing of CH4 that for a short period of time occupies a space close by the emission source.

 

If an amount of CH4 were suddenly released above the ESAS, and the cloud drifted over the Karla Sea raising local levels by a certain amount I'd assume that the GHG effect in that particular area would be greatly enhanced. The 20 year or 100 year effect might be negligible, but for that particular week, month or season I'd assume that the Karla Sea might lose ice or see enhanced SLT's in excess of what the 20 or 100 year numbers would indicate.

 

What I'm looking for is a number to put with these suppositions.

 

Terry

[WeatherRusty]

I think I'm following you, but it begs the question, or quite possibly I'm not asking the question correctly.

 

What I'm concerned with knowing is the GHG effect of a rapid outgassing of CH4 that for a short period of time occupies a space close by the emission source.

 

If an amount of CH4 were suddenly released above the ESAS, and the cloud drifted over the Karla Sea raising local levels by a certain amount I'd assume that the GHG effect in that particular area would be greatly enhanced. The 20 year or 100 year effect might be negligible, but for that particular week, month or season I'd assume that the Karla Sea might lose ice or see enhanced SLT's in excess of what the 20 or 100 year numbers would indicate.

 

What I'm looking for is a number to put with these suppositions.

 

Terry

 

What you are asking for is the immidiate or instantaneous greenhouse effect of methane rather than the time integrated radiative forcing which is implied by GWP. So to answer this question, and take it with a grain of salt, I would assume the impact to be very small. This question forces me to look to the absorption spectrum for CH4, which produces a narrow absorption feature at 1300 microns and one near 3000 microns. Water vapor produces such a strong instantaneous greenhouse effect partly because of its wide range of infrared absorption which CH4 lacks.

 

 

[TerryM]

Rusty

 

I'm aware of the narrow banding but would still expect the GHG effect to be increased over a shorter period of time rather than the opposite. Just as the 20 year figure is much higher than the 100 year figure, Id assume that a 10 year figure, when most of the gas is still viable, would be much higher than the 20 year figure & that the one month figure would be higher still.

 

I hope you won't be offended if I pose my question at some other blogs to see what responses it elicits since from what I have been able to find, the effect of all the GHG's diminish over various time periods & assuming that CH4 would act differently seems counterintuitive.

 

Terry

[WeatherRusty]

Rusty

 

I'm aware of the narrow banding but would still expect the GHG effect to be increased over a shorter period of time rather than the opposite. Just as the 20 year figure is much higher than the 100 year figure, Id assume that a 10 year figure, when most of the gas is still viable, would be much higher than the 20 year figure & that the one month figure would be higher still.

 

I hope you won't be offended if I pose my question at some other blogs to see what responses it elicits since from what I have been able to find, the effect of all the GHG's diminish over various time periods & assuming that CH4 would act differently seems counterintuitive.

 

Terry

 

The more the merrier!

 

What you are asking for pertains to the instantaneous greenhouse effect under an as of yet not fully dispersed emission of methane. This would be a localized condition at one moment in time.

 

Comparing that to a GWP time horizon which considers the Earth as a whole over an extended period of time to arrive at a radiative forcing value is asking a different question where the anwers obtained are not directly comparable.

 

The former is asking for the greenhouse effect under a localized methane cloud. The latter is asking for the globally averaged radiative forcing relative to a like mass of CO2 emitted at time X in the past.

[skierinvermont]

I don't really understand why the narrow banding would matter to the instantaneous effect. A narrow band means less of an effect than a wide effect for both the instantaneous GHE and GWP. Also how saturated that band and (I would imagine) how much emissions occur in that band. 

 

 

But the instantaneous effect is much less the GWP. I would imagine there is a constant scaling ratio from the latter to the former that is the same for all GHGs. It would also depend on the length of time and the areal coverage (global, regional, or local). 

 

 

The GWP for doubling methane is ~.5C (including medium-term century-scale feedbacks). The methane increase alone without feedbacks, but with the long-term accumulation of heat is .25C. So even a massive methane release in the arctic that brought concentrations from 1900ppb to 3800ppb would be what a .1C instantaneous warming if a permanent global increase would be .5C. 

 

That's just a a WAG. Would not be surprised if it's much less than that or slightly more. Remember the atmosphere is constantly mixing, so a regional or local forcing agent must constantly warm the air mixing in from the surrounding area. 

 

 

 

It takes a couple years to get to just half of the GWP for a moderate change in global forcing (I'm thinking of Pinatubo here it took 1-2 years to reach the maximum cooling, and by that time much of the SO2 had already diminished). Perhaps a century to reach the full GWP. Bigger forcing takes longer.  

[salbers]

I would recall that the the longer time horizon of CH4 GWP is composed of two components. First, the decaying amount of CH4 that has a half-life of roughly 10 years. Secondly, the conversion of CH4 to CO2 (a gas that lasts much longer). So the GWP of CH4 at 1000 years can even be significant despite almost all of the CH4 being gone by then.

Note that GWP is related just to radiative forcing and doesn't take into account things like the lag due to the heat capacity of the ocean. That is a different part of the discussion of global warming.

It's a good question about how much local radiative forcing there is in the Arctic. Generally I hear values of 1900-2000ppb of methane in the Arctic, so it seems to be an enhancement of order 0.1C compared with the earth globally. Maybe more localized plumes would be different though.

More general info here:

http://en.wikipedia.org/wiki/Global-warming_potential

[WeatherRusty]

I don't really understand why the narrow banding would matter to the instantaneous effect. A narrow band means less of an effect than a wide effect for both the instantaneous GHE and GWP. Also how saturated that band and (I would imagine) how much emissions occur in that band. 

 

 

But the instantaneous effect is much less the GWP. I would imagine there is a constant scaling ratio from the latter to the former that is the same for all GHGs. It would also depend on the length of time and the areal coverage (global, regional, or local). 

 

 

The GWP for doubling methane is ~.5C (including medium-term century-scale feedbacks). The methane increase alone without feedbacks, but with the long-term accumulation of heat is .25C. So even a massive methane release in the arctic that brought concentrations from 1900ppb to 3800ppb would be what a .1C instantaneous warming if a permanent global increase would be .5C. 

 

That's just a a WAG. Would not be surprised if it's much less than that or slightly more. Remember the atmosphere is constantly mixing, so a regional or local forcing agent must constantly warm the air mixing in from the surrounding area. 

 

 

 

It takes a couple years to get to just half of the GWP for a moderate change in global forcing (I'm thinking of Pinatubo here it took 1-2 years to reach the maximum cooling, and by that time much of the SO2 had already diminished). Perhaps a century to reach the full GWP. Bigger forcing takes longer.  

 

What Terry is asking for is the strength of the greenhouse effect in the same sense as what happens when a humid air mass replaces a dry one. How does the local temperatue respond to an isolated cloud of methane passing over? I am saying very little, since the absorption bands of methane near 10 microns are few and narrow. Water vapor acts strongly on the instantaineous greenhouse effect because it absorbs a broad range of wavelength near 10 microns.

 

10 microns is the wavelenght the Earth's suface radiates most strongly, the peak of the Planck thermal radiation bell curve.

[TerryM]

What Terry is asking for is the strength of the greenhouse effect in the same sense as what happens when a humid air mass replaces a dry one. How does the local temperatue respond to an isolated cloud of methane passing over? I am saying very little, since the absorption bands of methane near 10 microns are few and narrow. Water vapor acts strongly on the instantaineous greenhouse effect because it absorbs a broad range of wavelength near 10 microns.

 

10 microns is the wavelenght the Earth's suface radiates most strongly, the peak of the Planck thermal radiation bell curve.

 

You've phrased my question perfectly.

 

If I'm lying in bed for 100 min with two blankets over me and after 12.4 min, one of the blankets is removed the effect that the second blanket had over the first 20 min, or over the whole 100 min period might be of far less importance than the effect it was having while it was actually in place.

 

What I'm looking for is a figure similar to the albedo ratio that would indicate what ratio of outgoing long wave radiation could be expected to be redirected earthward for each increase of say 100 ppb of CH4. This would be independent of any concerns regarding oxidization rates & would indicate the real time effect of a particular measured concentration.

 

When we're concerned with how the Arctic ice is behaving during a particular melt season, and being cognizant of the fact that much of the radiative energy won't be measurable as sensible heat & may in fact be hidden in the following season's freeze, having a number that we can plug in indicating how much additional long wave radiation will be trapped because a cloud of CH4 is over an area might be helpful.

 

I have noticed that over anomalously warm Arctic areas there seems always to be a high methane concentration. While it's certainly possible that this is simply because more methane is released due to the high temperatures, I think it's also possible that we're seeing a positive feedback where the increased CH4 levels are heating the area causing more outgassing ect.

 

I do think that the relatively narrow window blocked by CH4 is less important than the fact that this window is fairly transparent to other greenhouse gasses. My understanding is that because of this CH4's contribution to the greenhouse effect can be measured linearly as opposed to CO2 which has to be measured on a logarithmic scale due to saturation concerns. I can't think of any reason for the 10 year effect of CH4 to be less than the 20 year effect and would in fact expect it to be far more powerful in the short term.

 

I do agree with what I understand is the consensus opinion in that in the long term CO2, because of it's longevity is far more important than short lived CH4. However when we're considering the albedo changes that the loss of Arctic ice will bring the effects of CH4 might be far more important in the immediate future.

 

Terry

[WeatherRusty]

You've phrased my question perfectly.

 

If I'm lying in bed for 100 min with two blankets over me and after 12.4 min, one of the blankets is removed the effect that the second blanket had over the first 20 min, or over the whole 100 min period might be of far less importance than the effect it was having while it was actually in place.

 

What I'm looking for is a figure similar to the albedo ratio that would indicate what ratio of outgoing long wave radiation could be expected to be redirected earthward for each increase of say 100 ppb of CH4. This would be independent of any concerns regarding oxidization rates & would indicate the real time effect of a particular measured concentration.

 

When we're concerned with how the Arctic ice is behaving during a particular melt season, and being cognizant of the fact that much of the radiative energy won't be measurable as sensible heat & may in fact be hidden in the following season's freeze, having a number that we can plug in indicating how much additional long wave radiation will be trapped because a cloud of CH4 is over an area might be helpful.

 

I have noticed that over anomalously warm Arctic areas there seems always to be a high methane concentration. While it's certainly possible that this is simply because more methane is released due to the high temperatures, I think it's also possible that we're seeing a positive feedback where the increased CH4 levels are heating the area causing more outgassing ect.

 

I do think that the relatively narrow window blocked by CH4 is less important than the fact that this window is fairly transparent to other greenhouse gasses. My understanding is that because of this CH4's contribution to the greenhouse effect can be measured linearly as opposed to CO2 which has to be measured on a logarithmic scale due to saturation concerns. I can't think of any reason for the 10 year effect of CH4 to be less than the 20 year effect and would in fact expect it to be far more powerful in the short term.

 

I do agree with what I understand is the consensus opinion in that in the long term CO2, because of it's longevity is far more important than short lived CH4. However when we're considering the albedo changes that the loss of Arctic ice will bring the effects of CH4 might be far more important in the immediate future.

 

Terry

 

Let's look at what I am saying graphically:

 

 

If we increase atmospheric CH4 8X we get a radiative forcing of only 1.95W/m^2. But again, a radiatve forcing applies to the whole Earth tropopause boundary, rather than an isolated geographical area.

[salbers]

What I'm looking for is a figure similar to the albedo ratio that would indicate what ratio of outgoing long wave radiation could be expected to be redirected earthward for each increase of say 100 ppb of CH4.

....

I can't think of any reason for the 10 year effect of CH4 to be less than the 20 year effect and would in fact expect it to be far more powerful in the short term.

 

I do agree with what I understand is the consensus opinion in that in the long term CO2, because of it's longevity is far more important than short lived CH4. However when we're considering the albedo changes that the loss of Arctic ice will bring the effects of CH4 might be far more important in the immediate future.

 

Terry

Below is a link to a graph that shows the radiative forcing for different concentrations of methane. This is fairly consistent with Weather Rusty's graph above for an 8x CH4 increase. I suppose it can apply either locally or globally, though local effects might depend on the local vertical distributions of methane and temperature.

http://www.intellectualtakeout.org/library/chart-graph/radiative-forcing-methane

I agree the 10 year CH4 effect should be more than at 20 years, and a large pulse of CH4 will be an issue in the short term. However the Global Warming Potential (GWP) value might do something different (relative to CO2) if CO2 has short-term rapid decay involving a fraction of that gas. GWP compares two rates of decay (CH4 and CO2) that aren't really simple exponential curves.

It's interesting that CH4 overall has more long term effect (per unit mass) than CO2, because a given mass of CH4 will convert to a greater mass of CO2. I'm unsure why the long term (500yr) GWP of CH4 is around 7 though (on this scale where CO2 is defined as 1).

Here's a somewhat related paper on methane pulse radiative effects, though it covers time scales longer than the methane decay time:

http://www.falw.vu/~renh/methane-pulse.html

More background is in my post #18.

Steve

[salbers]

Here are some formulae for radiative forcing:

http://www.esrl.noaa.gov/gmd/aggi/

Table 1. Expressions for Calculating Radiative Forcing*

Trace Gas Simplified Expression

Radiative Forcing, ΔF (Wm-2) Constant

CO2 ΔF = αln(C/Co) α = 5.35

CH4 ΔF = β(M½ - Mo½) - [f(M,No) - f(Mo,No)] β = 0.036

N2O ΔF = ε(N½ - No½) - [f(Mo,N) - f(Mo,No)] ε = 0.12

CFC-11 ΔF = λ(X - Xo) λ = 0.25

CFC-12 ΔF = ω(X - Xo) ω = 0.32

*IPCC (2001)

The subscript "o" denotes the unperturbed (1750) abundance

f(M,N) = 0.47ln[1 + 2.01x10-5 (MN)0.75 + 5.31x10-15M(MN)1.52]

C is CO2 in ppm, M is CH4 in ppb

N is N2O in ppb, X is CFC in ppb

Co = 278 ppm, Mo = 700 ppb, No = 270 ppb, Xo = 0

[WeatherRusty]

Below is a link to a graph that shows the radiative forcing for different concentrations of methane. This is fairly consistent with Weather Rusty's graph above for an 8x CH4 increase. I suppose it can apply either locally or globally, though local effects might depend on the local vertical distributions of methane and temperature.

http://www.intellectualtakeout.org/library/chart-graph/radiative-forcing-methane

I agree the 10 year CH4 effect should be more than at 20 years, and a large pulse of CH4 will be an issue in the short term. However the Global Warming Potential (GWP) value might do something different (relative to CO2) if CO2 has short-term rapid decay involving a fraction of that gas. GWP compares two rates of decay (CH4 and CO2) that aren't really simple exponential curves.

It's interesting that CH4 overall has more long term effect (per unit mass) than CO2, because a given mass of CH4 will convert to a greater mass of CO2. I'm unsure why the long term (500yr) GWP of CH4 is around 7 though (on this scale where CO2 is defined as 1).

Here's a somewhat related paper on methane pulse radiative effects, though it covers time scales longer than the methane decay time:

http://www.falw.vu/~renh/methane-pulse.html

More background in my post #18.

Steve

 

I must mention again, for clearity, comparing a radiative forcing to global warming potential is like comparing apples to oranges. They are not directly equivelant. The radiative forcing difference between CO2 and CH4 is based off of a doubling or other multible of the starting consentration. On the other hand GWP assumes an equal initial mass of each is spontaineously emitted and allowed to decay over a given time interval. The immediate effect of CH4 will be stronger because given the same mass release, the CH4 will produce a larger radiative forcing, simply because there is so little of it to begin with, but with advancing time the CH4 decays more rapidly than does the CO2 so it's strength dwindles relative to the same inital mass of CO2. A kilogram of CH4 will deliver a much greater global waming potential than a kilogram of CO2 simply because there is so little of it to start with, and thus represents a larger percentage of the new total.

 

 

I have tried to answer Terry's question given one instant in time, or as the instantaneous greenhouse effect. The effect should be small. If the cloud of methane is a semi-permanent feature over a limited geographical area, then that obviously changes how we would have to look at the effect, as one evolving over time.

[salbers]

Yes it's good to clarify that radiative forcing is instantaneous (W/m**2) and GWP is integrated over time (relative to the CO2 benchmark). On the other hand, looking at GWP values can help give a sense (in the absence of more direct information) of how the instantaneous radiative forcing will change over time.

It still seems to be true that kg of CH4 has more long term GWP than a kg of CO2 because 1kg of CH4 actually converts chemically over time into more than 1kg of CO2. There may be other factors in the accounting though as Weather Rusty alludes to. Whatever significant short term effects there are from a pulse of CH4 there will also be long term effects that are important to consider.

One can note that the methane concentrations we're talking about are pretty small right now relative to CO2, though that could change in the event of a major and sustained release. The Java Climate model I recall we posted on in another thread had some good illustrations of how this all plays out over time. Whether the effect in the short term is small or large depends on the magnitude and pace of the release.

Here are some additional radiative forcing formulae:

http://acd.ucar.edu/textbook/ch15/table15.2.html

Table 15.2. Simplified Expressions to Calculate Radiative Forcing Delta FR (W m-2)

Resulting from Changes in Atmospheric Concentrations

1. CO2 Delta FR = a ln (µ / µ0) where µ and µ0 are new and initial CO2 mixing ratios.

2. CH4 Delta FR = a [squareroot µ (CH4) - squareroot µ0 (CH4) - f (µ (CH4), µ0 (N2O)) - f (µ0 (CH4), µ0 (N2O))], where µ (CH4) and µ0 (CH4) are new and initial CH4 mixing ratios (ppbv) and µ0 (N2O) is the N2O mixing ratio (ppbv).

3. N2O Delta FR = a [squareroot µ (N2O) - squareroot µ0 (N2O) - f (µ0 (CH4), µ (N2O)) - f (µ0 (N2O), µ0 (CH4))], where µ (N2O) and µ0 (N2O) are new and initial N2O mixing ratios (ppbv) and µ0 (CH4) is the CH4 mixing ratio (ppbv).

4. CFCs and

HCFCs Delta FR = a (µ - µ0), where µ and µ0 are new and initial mixing ratios (ppbv), respectively.

Function f (x, y) is defined by (IPCC, 1990) f (x, y) = 0.47 ln [1 + 2.01 × 10-5 (xy)0.75 + 5.31 × 10-15 x (xy)1.52]

Values of factor a Clear sky Cloudy conditions

CO2 7.6 6.7

CH4 0.044 0.036

N2O 0.16 0.14

CFC-11 0.27 0.21

CFC-12 0.35 0.27

CFC-113 0.38 0.29

HCFC-22 0.20 0.15

Values of factor a calculated by the 2D model of Brasseur et al. (1990). In the case of cloudy conditions, fractional cloud amounts are 0.23 for high clouds (10 km), 0.09 for middle clouds (4 km), and 0.31 for low clouds (2 km). Optical depths are 1.5, 6.1, and 16.3, respectively (from Manabe and Wetherald, 1967).

[skierinvermont]

What Terry is asking for is the strength of the greenhouse effect in the same sense as what happens when a humid air mass replaces a dry one. How does the local temperatue respond to an isolated cloud of methane passing over? I am saying very little, since the absorption bands of methane near 10 microns are few and narrow. Water vapor acts strongly on the instantaineous greenhouse effect because it absorbs a broad range of wavelength near 10 microns.

 

10 microns is the wavelenght the Earth's suface radiates most strongly, the peak of the Planck thermal radiation bell curve.

 

Yes and I'm suggesting that this instantaneous effect would be 1/5th or less of what would occur if the concentration were raised that much globally permanently. So a pool of methane concentrated air at 3800ppb passing over the Kara sea might raise temperatures .1C. I could see anywhere from less than .01C to .2C. This is just a WAG.

[skierinvermont]

What I'm looking for is a figure similar to the albedo ratio that would indicate what ratio of outgoing long wave radiation could be expected to be redirected earthward for each increase of say 100 ppb of CH4. This would be independent of any concerns regarding oxidization rates & would indicate the real time effect of a particular measured concentration.

 

 

That's easy. .05W/m2 per 100ppb.

 

Doubling methane concentration provides about .8W/m2 of forcing. 100ppb is a 1/20th increase. That comes out to about .05W/m2. 

 

So a 100ppb increase is .05W/m2. Which if applied permanently and globally is enough to raise temperatures .016C. Applied regionally and temporarily, perhaps a mere .001C. 

 

 

.001C per 100ppb? Negligible. 

 

 

 

The correlation you say you have observed is either non-existent, coincidence, or you have causation reversed because the methane plumes at present are no where near dense enough to cause detectable warming. 

[PhillipS]

That's easy. .05W/m2 per 100ppb.

 

Doubling methane concentration provides about .8W/m2 of forcing. 100ppb is a 1/20th increase. That comes out to about .05W/m2. 

 

So a 100ppb increase is .05W/m2. Which if applied permanently and globally is enough to raise temperatures .016C. Applied regionally and temporarily, perhaps a mere .001C. 

 

.001C per 100ppb? Negligible. 

 

The correlation you say you have observed is either non-existent, coincidence, or you have causation reversed because the methane plumes at present are no where near dense enough to cause detectable warming. 

 

Keep in mind that the Barrow Observatory was reporting transient methane readings as high as 2,500 ppb in May 2012, shortly before NOAA pulled the plug on in-situ methane observations at Barrow.

 

 

 

A 600 ppb CH4 increase at Barrow, hundreds of miles from the ESAS, would almost certainly indicate a higher concentration nearer the source.

[skierinvermont]

Keep in mind that the Barrow Observatory was reporting transient methane readings as high as 2,500 ppb in May 2012, shortly before NOAA pulled the plug on in-situ methane observations at Barrow.

 

 

 

 

A 600 ppb CH4 increase at Barrow, hundreds of miles from the ESAS, would almost certainly indicate a higher concentration nearer the source.

 

Why so certain the methane came from the ESAS? The arctic is one big melting swamp right now. 

[WeatherRusty]

That's easy. .05W/m2 per 100ppb.

 

Doubling methane concentration provides about .8W/m2 of forcing. 100ppb is a 1/20th increase. That comes out to about .05W/m2. 

 

So a 100ppb increase is .05W/m2. Which if applied permanently and globally is enough to raise temperatures .016C. Applied regionally and temporarily, perhaps a mere .001C. 

 

 

.001C per 100ppb? Negligible. 

 

 

 

The correlation you say you have observed is either non-existent, coincidence, or you have causation reversed because the methane plumes at present are no where near dense enough to cause detectable warming. 

 

If we bring CH4 to 14,000ppb or an increase of 12,250ppb which would be 3 doublings, we get 1.95W/m^2 of radiative forcing which produces a global Planck warming of about 0.6K. In order for CO2 to bring about the same forcing and temp response the gas must increase by about 150ppm from it's 280ppm pre-industrial concentration.

 

The addition of just a relatively tiny bit of CH4 equals the addition of a whole lot more quantifiable CO2. Still, the addition of just a few 100ppb CH4 will produce very little forced temperature increase as you suggest.