A Note: Global Warming Threads

[Billy T]

Billy that's not the way this works.

I know of no reputable Climate Scientist or Scientific report that suggests that a possible outcome of our climate is what you describe: "Venus like, but slightly cooler, but with a thick steam atmosphere which makes the planet sterile".

Your assertion, you have the burden of proof. Arthur

It certainly does work that way. When someone suggests a process that violates some physical law, I* and many others will point that out to them. The fact that no one else has suggested that process is not proof it will not work.

You just don't want to discuss the process I have suggested may be possible, either because you don't think it would be a significant event that Earth could, by that process, turn into a cooler version of Venus OR it is an example of why one should be concerned, at least until we know a reason why it will not happen, and you are only interested in presenting POV that there is no reason for concern as if you were a shil for the petrochemical industry.

When you do reply, you only only attack me personally (question my qualifications etc.) Or mis quote me as saying some silly thing. Why not point out some reason the process that could make Earth sterile is impossible - a violation of some physical law, etc.?

Yes, in describing the process I have made many assertions, about the importance of OH radical in the troposphere being the main means of removal of CH4, that each CH4 removes four OH radicals, that OH is only produced in the stratosphere by harsh UV splitting H2O, so that OH- could be depleted in the troposphere IF the release rate of CH4 exceed the transport rate of OH down from the stratosphere, that if the OH were depleted then the lifetime of the CH4 in the atmosphere would greatly increase (producing the same effect on atmospheric concentrations of CH4 as if the surface release rate had increased by the same factor) plus many assertions about the mechanism of radiative transport, such as that the intensity can not exceed that of a black body at the same temperature - I.e. dozens of points where you could say: "No that is an error. This part of the process you suggest as possible is not possible." but the best you can do is to attack me personally or state no one else (you know of) has expressed concern that process may be possible. I.e. you behave exactly like a shil for the petroleum industry rather than a scientists who wants to discuss facts or refute others asserted facts.
-----------------
* I have done that so many times that I have earned the title: "Sheriff of Nonsense"

 

[adoucette]

Billy,
What you are saying is you've come up with a hypothesis on the possible future of the Earth's climate,

now they are rising too fast for all the CH4 being released to be destroyed by the O2. I.e. if we are in a positive feedback loop now, then earth is doomed to become a slightly cooler version of Venus. (Its other stable state)

The atmospheric destruction process for CH4 can be OH radical concentration limited but currently is not; however, once the OH concentration is reduced to make it limiting, then the CH4 lifetime in the air becomes many decades - I.e. at some point the temperature of earth explodes upward to approximately 100C, limited only by the thermal inertia of the oceans. It will take something on the order of a million years to boil all the ocean water into space and let the main temperate rise (to 700 or 800C?) of the surface begin again. Like Venus, which was once much like Earth, Earth also has two stable states, the current one and one with a very high pressure (at the surface) supper heated steam atmosphere, much thicker than the current one, so very little surface heat escapes thru it.

one supported by wild and unsupported assertions, like why Earth would eventually attain a temperature nearly 300 d C higher than Venus or that:

Adding a few ppm of CH4 would block even more radiation from escaping than 10,000 ppm of CO2 would

Because instead we read from the published climate science:

Methane absorbs infrared light between about 1250 and 1350 cm−1, a frequency range at which terrestrial radiation is less intense than it is in the absorption band of the CO2 bending mode about 600–700 cm−1. A massive increase in methane concentration therefore has a smaller impact on the radiative balance of the Earth than would a comparable increase in CO2

http://geosci.uchicago.edu/~archer/reprints/archer.2007.hydrate_rev.pdf

False assumptions about the existing climate science:

I am not disputing the IPCC's model for sea rise or claiming to know more than they do. What I am doing is considering that one of their assumptions (namely that CH4 concentrations are so small that they can be neglected) MAY be false.

Admission that though you make claims about what is in the IPCC climate reports you have NEVER READ THEM:

If CH4 is included in the IPCC studies, then I am wrong to state it is not but given the extremely low levels, now and for 40 years, there is no need to have included it as the errors on more important aspects are much larger than its total effects* - I.e. I assumed that they knew that and would not bother to include it any more than the heating by reflected moon light needs to be included. I have never read their reports.

And without any actual calculataions or meaningful data to support your hypothesis:

Indeed YOU admit:

I have no way to know what rate of CH4 release is needed to make the positive feedback loop have a gain greater than unity but some rate can. If that feedback loop does get a gain of unity, then it is quite probable than that Earth will switch to the hot stable state.

More importantly, given your demonstrated lack of knowledge of climate science and the fact that you can't point to any support from even a single example of this hypothesis written up in the mainstream climate science literature and though you are clearly not a climate scientist and have never even bothered to read the IPCC reports, you think your half baked idea deserves consideration simply because a small handful of posters on an internet site aren't willing to take the significant amount of time and effort that it would likely take to show your idea is not possible?

LOL

No Billy, that is NOT how science works.

Or decent discussion boards.

Put some science into it Billy, at a minimum you need to at least show how much CH4 has to be released at what rate for how long to swamp the OH radical supply and then show what the projected rate of CH4 buildup in the atmosphere would be and what the additional forcing of that buildup would be and then show what that would mean as far as an increase in average atmospheric temperatures would be.

Arthur

 

[Billy T]

Billy, What you are saying is you've come up with a hypothesis on the possible future of the Earth's climate, one supported by wild and unsupported assertions, like why Earth would eventually attain a temperature nearly 300 d C higher than Venus...

No again you are mis-quoting and or mis reading. That is definitely not my assumption or assertion.

I assumed that other things were possible and if they did happen that would be the consequence. Try to point out at least one of the things I did assume or facts I used, is wrong or "wild and unsupported", not continue to mis represent what I said.

The conclusion that you do not want to discuss facts or processes and probably are a shil for the petrochemical industry is gaining support.

 

[adoucette]

No again you are mis-quoting and or mis reading. That is definitely not my assumption or assertion.

I'm not misquoting you Billy, and I supported my assertions by direct quotes from your previous posts:

The atmospheric destruction process for CH4 can be OH radical concentration limited but currently is not; however, once the OH concentration is reduced to make it limiting, then the CH4 lifetime in the air becomes many decades - I.e. at some point the temperature of earth explodes upward to approximately 100C, limited only by the thermal inertia of the oceans. It will take something on the order of a million years to boil all the ocean water into space and let the main temperate rise (to 700 or 800C?) of the surface begin again. Like Venus, which was once much like Earth, Earth also has two stable states, the current one and one with a very high pressure (at the surface) supper heated steam atmosphere, much thicker than the current one, so very little surface heat escapes thru it.

As to: "Try to point out at least one of the things I did assume or facts I used, is wrong or "wild and unsupported",

I did:

Adding a few ppm of CH4 would block even more radiation from escaping than 10,000 ppm of CO2 would

Because Billy, if adding a few ppm of CH4 would be worse than 10,000 ppm of CO2 then the focus on avoiding future AGW would be on reducing CH4 far more than reducing CO2.

And INDEED, three of the IPCC scenarios (yes, I know you don't read their reports) include increases in this century of ~a few ppm of CH4 and yet most of the scenarios only include an increase of ~300 ppm of CO2, yet the climate control focus is far more on reducing CO2 then it is on reducing CH4.

Arthur

 

[Billy T]

Billy, ... wild and unsupported assertions, ...
Because instead we read from the published climate science:http://geosci.uchicago.edu/~archer/reprints/archer.2007.hydrate_rev.pdf...

You quoted: from your link: “Methane absorbs infrared light between about 1250 and 1350 cm−1, a frequency range at which terrestrial radiation is less intense than it is in the absorption band of the CO2 bending mode about 600–700 cm−1. A massive increase in methane concentration therefore has a smaller impact on the radiative balance of the Earth than would a comparable increase in CO2”

I agree that this is true. As there is less terrestrial escaping radiation in the CH4 band to absorb than in the CO2 band a “massive amount” of both CO2 and CH4 will block less energy flux trying to escape in the CH4 band as it can only block 100% of what is trying to escape. But I did not speak of a “massive increase” in CH4. I spoke of a few PPM increase and said that that few percent increase in the CH4 concentration would be more important than a much large increase in the CO2 concentration.

At your link at the end of page 522 / start of 523 is the following quote, which directly supports my claim that a few PPM increase in CH4 is more important than a massive increase in CO2 as the radiation in the CO2 bands is already nearly 100% blocked from escape and that the absorption by CH4 is far from being 100% blocked. See graph at end, which is also from your link and note that the CO2 is already in the flat part of the curve but CH4 absorption is not.

“The most significant practical distinction between the gases is that CO2 is more concentrated in the atmosphere than is methane. For this reason, in the strongest absorption bands of CO2, most of the outgoing longwave light from the ground as already absorbed. An increase in CO2 concentration tends to make the absorption bands a bit wider, but they cannot get any more intense. Methane is less concentrated than CO2, and its absorption bands less saturated, so a single molecule of additional methane has a larger impact on the radiation balance than a molecule of CO2, by about a factor of about 40…”

That was the point I was making, when stating that a:
“Adding a few ppm of CH4 would block even more radiation from escaping than 10,000 ppm of CO2 would”

Your attempted to show that is not correct with a quote about a MASSIVE INCREASE in CH4 concentrations totally fails and is very likely DISHONEST rather than just your ignorance / misunderstanding of what your link is stating.

I of course am not disputing that the absorption bands are different or that the terrestrial radiation in the absorption bands of CH4 is less intense than in the CO2 bands. Thus I agree with your quote at the top of this post that a MASSIVE increase in CH4 would block nearly 100% of a smaller terrestrial flux of energy escaping.

SUMMARY: Far from refuting my “wild and unsupported” claim you link confirms it!

Sorry I can not post the graph as it is in a .pdf paper but anyone interested in seeing it can go to page 522 of your link. It is at top of that page.

 

[Billy T]

I'm not misquoting you Billy, ... Arthur

You certainly did again mis quote me in your post 642. You said I had asserted something when in fact I have said exactly the opposite, namely that I don't think it probable, only that it may be possible, and "hopefully with low probability of happening" that Earth will switch to a cooler version of Venus. Here from your post 642 is the most recent example of your putting words in my mouth:

[post 642} Billy .... wild and unsupported assertions, like why Earth would eventually attain a temperature nearly 300 d C ... Arthur

Again I never asserted the "Earth would eventually attain a temperature nearly 300 d C " as you falsely claim I did.

BTW I agree that "climate control focus is far more on reducing CO2 then it is on reducing CH4." That is because most of the rapid CO2 increase is man-made and we can do something about that by burning less fossil fuels, switching to electric or sugar cane alcohol fuel for them, etc. but most of the CH4 is either natural increase which we have no control over.

 

[adoucette]

You quoted: from your link: “Methane absorbs infrared light between about 1250 and 1350 cm−1, a frequency range at which terrestrial radiation is less intense than it is in the absorption band of the CO2 bending mode about 600–700 cm−1. A massive increase in methane concentration therefore has a smaller impact on the radiative balance of the Earth than would a comparable increase in CO2”

I agree that this is true. As there is less terrestrial escaping radiation in the CH4 band to absorb than in the CO2 band a “massive amount” of both CO2 and CH4 will block less energy flux trying to escape in the CH4 band as it can only block 100% of what is trying to escape. But I did not speak of a “massive increase” in CH4. I spoke of a few PPM increase and said that that few percent increase in the CH4 concentration would be more important than a much large increase in the CO2 concentration.

At your link at the end of page 522 / start of 523 is the following quote, which directly supports my claim that a few PPM increase in CH4 is more important than a massive increase in CO2 as the radiation in the CO2 bands is already nearly 100% blocked from escape and that the absorption by CH4 is far from being 100% blocked. See graph at end, which is also from your link and note that the CO2 is already in the flat part of the curve but CH4 absorption is not.

“The most significant practical distinction between the gases is that CO2 is more concentrated in the atmosphere than is methane. For this reason, in the strongest absorption bands of CO2, most of the outgoing longwave light from the ground as already absorbed. An increase in CO2 concentration tends to make the absorption bands a bit wider, but they cannot get any more intense. Methane is less concentrated than CO2, and its absorption bands less saturated, so a single molecule of additional methane has a larger impact on the radiation balance than a molecule of CO2, by about a factor of about 40…”

That was the point I was making, when stating that a:
“Adding a few ppm of CH4 would block even more radiation from escaping than 10,000 ppm of CO2 would”

Your attempted to show that is not correct with a quote about a MASSIVE INCREASE in CH4 concentrations totally fails and is very likely DISHONEST rather than just your ignorance / misunderstanding of what your link is stating.

I of course am not disputing that the absorption bands are different or that the terrestrial radiation in the absorption bands of CH4 is less intense than in the CO2 bands. Thus I agree with your quote at the top of this post that a MASSIVE increase in CH4 would block nearly 100% of a smaller terrestrial flux of energy escaping.

SUMMARY: Far from refuting my “wild and unsupported” claim you link confirms it!

Sorry I can not post the graph as it is in a .pdf paper but anyone interested in seeing it can go to page 522 of your link. It is at top of that page.
I agree I this is true. As there is less terrestrial escaping radiation in the CH4 band to absorb than in the CO2 band a “massive amount” of both CO2 and CH4 will block less energy flux trying to escape in the CH4 band as it can only block 100% of what is trying to escape. But I did not speak of a “massive increase” in CH4. I spoke of a few PPM increase and said that that few percent increase in the CH4 concentration would be more important than a much larger increase in the CO2 concentration.

At your link at the end of page 522 / start of 523 is the following quote, which directly supports my claim that a few PPM increase in CH4 is more important than a massive increase in CO2 as the radiation in the CO2 bands is already nearly 100% blocked from escape and that the absorption by CH4 is far from being 100% blocked. See graph at end, which is also from your link and note that the CO2 is already in the flat part of the curve but CH4 absorption is not.

“The most significant practical distinction between the gases is that CO2 is more concentrated in the atmosphere than is methane. For this reason, in the strongest absorption bands of CO2, most of the outgoing longwave light from the ground as already absorbed. An increase in CO2 concentration tends to make the absorption bands a bit wider, but they cannot get any more intense. Methane is less concentrated than CO2, and its absorption bands less saturated, so a single molecule of additional methane has a larger impact on the radiation balance than a molecule of CO2, by about a factor of about 40…”

That was the point I was making, when stating that a:
“Adding a few ppm of CH4 would block even more radiation from escaping than 10,000 ppm of CO2 would”

Your attempted to show that is not correct with a quote about a MASSIVE INCREASE in CH4 concentrations totally fails and is very likely DISHONEST rather than just your ignorance / misunderstanding of what your link is stating.

I of course am not disputing that the absorption bands are different or that the terrestrial radiation in the absorption bands of CH4 is less intense than in the CO2 bands. Thus I agree with your quote at the top of this post that a MASSIVE increase in CH4 would block nearly 100% of a smaller terrestrial flux of energy escaping.

SUMMARY: Far from refuting my “wild and unsupported” claim you link confirms it!

Bull,

Nothing you posted supports your assertion that a few ppm increase in CH4 is equal to a 10,000 ppm increase in CO2.

And as I showed, the IPCC is already presuming a CH4 increase this century of several ppm and if that WAS equal to 10,000 ppm of CO2 then THAT would be where our focus on reducing GHGs would be because that would be so much easier than reducing CO2 levels by a significant amount.

Arthur

 

[Billy T]

... Billy, if adding a few ppm of CH4 would be worse than 10,000 ppm of CO2 then the focus on avoiding future AGW would be on reducing CH4 far more than reducing CO2. ... Arthur

I think that a false argument too as it is possible, but admittely hard to cut the CO2 release by 50%* as it is mainly man made but there is no way man can cut the CH4 release by 50% as it is more natural in its origins.

-----------------
*For example generate electric power ONLY from nuclear or solar sources and drive only electric or sugar cane alcohol powered cars.
How would you make an equal reduction in CH4? Mankind should focus on what can be reduced significantly and that is the CO2 release.

BTW, I was making a little understood point that a few PPM increase in CH4 is much more important than a much larger increase in CO2 - Admittedly I have no idea what increase in CO2 would make the same the same increase in global warming as 10 ppm increase in CH4 would make. That is too complex for me to attempt to calculate. Perhaps 1000 ppm increase, instead of 10,000 ppm of CO2 would do it. Telling the exact number was not my point. My point was that CH4 absorption is currently far from near saturation and each added molecule of CH4 is about 20 times more effective than an added CO2 molecule.

 

[adoucette]

Admittedly I have no idea what increase in CO2 would make the same the same increase in global warming as 10 ppm increase in CH4 would make. That is too complex for me to attempt to calculate. Perhaps 1000 ppm increase, instead of 10,000 ppm of CO2 would do it. Telling the exact number was not my point.

Then WHY did you give it an EXACT number? Indeed you suggested that 10,000 PPM of CO2 was equivilent to the lower boundry of increasing CH4 by just a few ppm.

My point was that CH4 absorption is currently far from near saturation and each added molecule of CH4 is about 20 times more effective than an added CO2 molecule.

Yet you used an example that put the ratio at over 5,000 to 1.

Why is it that you can't admit that you were wrong?

And No Billy, your example about the reason we try to cut different GHGs is WRONG.

Man is only ~3% of the CO2 cycle, but that doesn't mean the atmospheric buildup isn't because of the additional CO2 we produce.

The buildup of CH4 is also from our actions and YES we could reduce it, indeed we have been reducing it which is one of the reasons the growth of CH4 has slowed to nearly a flat line.

Arthur

 

[Billy T]

Then WHY did you give it an EXACT number?... YES we could reduce it, indeed we have been reducing it which is one of the reasons the growth of CH4 has slowed to nearly a flat line. ... Arthur

I have already explained / answered your questions about the 10,000 number and further more it should be obvious that one is not making a exact equation betweem 10,000 and a "few" - but just trying to illustrate one is much larger than the other. Or perhaps you know the magnitude of "few" to four significant figures so that is why you thought I was giving an exact relationship? :shrug:

Are you in quote above claiming that man could reduce CH4 release as much as he could CO2 release by steps I mentioned? If so, I again I ask what measures would reduce CH4 release the same fraction* as making all electric power from nuclear or solar sources and switching to only EV or sugar cane alcohol cars?

How has man significantly reduced or held steady the release of CH4? Give some examples of what man has done to hold its atmospheric concentration flat for a few years before it started to climb again.
----------------
*I said "cut release by 50%", but again I am not giving an exact fraction that my suggestions would make - only indicating that the reduction would be large. Perhaps my suggested measures would only make a 30% reduction (or a 60% reduction) - I don't know, but tend to guess numbers to make it clear what I mean by vague terms like "large."

 

[adoucette]

Billy,
It wasn't an issue of being an exact equation and you know it.
Indeed you used 10,000 ppm as the LOWER BOUND of the effect of CO2 equal to 2 ppm of methane, but even the lower bound is a 5,000 to one ratio, but NOW you say it's a 40 to 1 ratio.

Do you not see how WRONG your original statement was?

Guess not. (And it's friggin amazing what you will do to defend your indefensible statements).

As to Methane, yes we have cut the growth rate:

How?
Simple, reduce pipeline leaks.
Reduce flaring of unburnt CH4.
Reduce losses at oil pumping sites.
Reduce emissions in coal mining operations.
Reduce emissions by changing rice growing operations
Reduce emissions by capturing/using gas from landfills.
etc etc

Approximately 500 participants from over 30 countries, representing
government, private sector, andnon‐governmental organizations,
met in Indiatoshare expertise and develop strategies
to advance cost‐effective, near‐termprojectsto reduce
methane emissions.

http://www.epa.gov/cmop/docs/spring_2010.pdf

One of many such projects.

And from our own emission inventory in the US, we've cut Methane by 46 TgCO2 Equivalent since 1990.

http://epa.gov/methane/sources.html

And of course from what I've already posted on this thread:

The long-term growth rate of methane has declined steadily over the past 20 years, from about 15 ppb per year in the mid-1980s to about zero over the past six years. The reason for the decline is uncertain, but possibly involves a reduction or stabilisation in methane release from the oil and gas industry, as methane is now considered a valuable resource; in the 1960s, unwanted methane was commonly either burnt (flaring) or released under high pressure (venting). A worldwide trend to minimise leaks from natural gas reticulation networks, particularly in the former Soviet Union, might also have contributed to the trend.

http://www.environment.gov.au/soe/2006/publications/commentaries/atmosphere/climate-change.html

Arthur

 

[Billy T]

... As to Methane, yes we have cut the growth rate:

{note this graph ends in 2005}

... Yes Arthur, you're absolutely right, average atmospheric methane leveled off between 2000 and 2005, however, between 2005 and 2009 they again increased.

I had to go back thru a lot of posts (11 pages), before finding this one. As I went back, and noticed that you dis-hontestly reposted your out of date (ends in 2005) graph and claim that methane release was flat six times more AFTER this graph from Trippy was posted.

That is exactly what a shil for the oil industry would do. I am not say you are one but there is something about things that walk like a duck, ... etc.

 

[adoucette]

No Billy, I posted the one graph that showed the long term growth rate (the RED line which is NOT in the graph you posted) has been on decline, I also posted a graph of GLOBAL rates, you posted a graph from a single SITE.

The slight increases in CH4 in the three years since the end of that graph (0 ppb in 06, 8 ppb in 07 and 4 ppb in 09) do NOT change the slope of that line or change the fact that there has been a long decline in the annual increase in CH4 (indeed they start the line in 1985, but in the 70s the annual increases were of the order of 20 ppb per year).

So yes, considering the considerable increase in global population putting upward pressure on the production of CH4 by increasing the amount of rice cultivated, the amount of cattle grown, the amount of coal mined, the amount of oil produced, YES we have most definately cut the growth rate of Methane, which was the issue.

Arthur

 

[F-X]

This thread is awesome.

 

[adoucette]

The conclusion that you do not want to discuss facts or processes and probably are a shil for the petrochemical industry is gaining support.

Billy you know that is a lie, so why go there?

We have debated on the Electric Vehicle thread for months and my support for electric vehicles was clearly obvious to you, and the whole point of that was to move the energy we use for our transportation system from oil to Electricity, where a high percent can come from Nuclear and Renewables.

The net is we use too much oil and we only produce about 1/3 of our needs, so reducing oil imports whether it’s by converting part of our transportation system to electricity (which only about 1% comes from oil) or by increasing the mileage of the cars by Extended range (Volt) or hybrid technology (Prius) or higher CAFE levels, are all means to the same end.

Clearly not something a shil in the petrochemical industry would be supporting.

So quit making up BS stories about me when you know they aren't true.

Arthur

 

[iceaura]

See you in 24hrs when you've had a chance to think it through.

Thanks for the break.

When you are ready to apologize, public will be necessary for acceptance.

Back to the actual issues, as adoucette reminds us of the denialist agenda:

So yes, considering the considerable increase in global population putting upward pressure on the production of CH4 by increasing the amount of rice cultivated, the amount of cattle grown, the amount of coal mined, the amount of oil produced, YES we have most definately cut the growth rate of Methane, which was the issue.

No.

The local issue was the potential of a positive feedback loop getting started in vulnerable deposits of methane, in the high arctic or deep ocean, touched off by the anthro CO2 buildup but amplifying it and possibly self-sustaining at least short term.

Such a loop adds to the simple danger of the CO2 boost melting some methane, and amplifying itself that way - which is a serious enough problem itself.

The outside chance of a Venusian catastrophe illustrates some of the risk of such a loop. The improbability of that event in the next couple of hundred years seems to be the reassurance we are offered - although without estimation of the actual odds, the extraordinary nature of such a thing is still worrying. The odds of negligently annihilating the known biological world need to be very, very long against, and projected out much farther than a couple of hundred years. Perhaps the observation that it hasn't happened naturally already, at least not for a very long time, is the best argument for relaxation - but then, we have no examples of the current extraordinarily rapid and continuing CO2 boost to compare with.

But regardless of the actual odds - currently unknown, presumably small - of that ultimate disaster, we have the fact of an unprecedented and continuing boost in CO2 apparently showing signs of touching off some kind of methane boom as feared, most likely a smaller one than Venus unleashed, but nevertheless worrisome. The circumstances are there - shallow water and permafrost methane deposits held in place by barely adequate temperature regimes, a waiting atmosphere scant of methane, various relevant factors (water currents, landslide potential, etc) poorly understood, etc.

The overall issue, in this thread about global warming, was the greenhouse effects of the ongoing CO2 buildup. This extra methane risk is one of them, and maybe the possibility of a Venusian catastrophe makes a reasonable if dramatic touchstone for considering it, but using its drama to deflect and minimize consideration of the root problem - the CO2 buildup - should be recognized and avoided.

 

[iceaura]

To separate out, and use a link already established here above ("The fact that he was quoting another source, I thought was quite clear from this statement:
"From your link, (Just skimmed it so far, but it looks good I'll read in closely later, thanks) a couple of summary points stood out:" "):

The proximity of structural hydrate deposits to the waters
of the ocean allows them to be affected by anthropogenic
warming without waiting thousands of years for heat to diffuse
into the sediment column (Fig. 3). However, these deposits
are still covered with hundreds of meters of ocean water.
Throughout most of the ocean, the stability depth is of
order 500–700 m, shoaling to perhaps 200m in the Arctic.
Surface warming is expected to take order a century to reach
these depths. Presumably any melting response to this gradual
warming would be gradual as well, slower than the atmospheric
lifetime of methane and therefore by our definition a
chronic methane release rather than a catastrophic one.
- - - -
On the timescale of the coming century, it appears that most
of the hydrate reservoir will be insulated from anthropogenic
climate change. The exceptions are hydrate in permafrost
soils, especially those coastal areas, and in shallow ocean
sediments where methane gas is focused by subsurface migration.
The most likely response of these deposits to anthropogenic
climate change is an increased background rate
of chronic methane release, rather than an abrupt release.
Methane gas in the atmosphere is a transient species, its
loss by oxidation continually replenished by ongoing release.
An increase in the rate of methane emission to the atmosphere
from melting hydrates would increase the steady-state
methane concentration of the atmosphere.

The lifetime of of methane in the atmosphere was considered, by that author, to be about ten years, but we know he is not really adopting a decade as his cutoff for "abrupt" - his demarcation between "abrupt" and "chronic" is elsewhere indicated to be hundreds, rather than thousands, of years. And he ignores feedback effects, as well as the effects of the water vapor and CO2 that methane oxidizes into. But we see even there that some significant share of the methane currently sequestered in permafrost and shallow ocean deposits is universally considered to be vulnerable now and soon, and accepted as a likely significant contributor to the global warming effects of the CO2 boost.

The question of significant net positive feedback in the Arctic remains - which would be my cutoff for "disaster" versus "serious problem".

 

[Billy T]

Perhaps it is possible to make a simple crude model of what release of CH4 is likely to lead to positive feedback runaway to "cooler version of Venus" Earth along the following lines:

(1) Accept the period 2000 to 2005 in which as adoucette likes to point out had stable CH4 atmosphere concentrations as a dynamic equilibrium between the production of OH- in the stratosphere and the surface release of CH4. If adoucette, who has read much more of the literature than I have can tell what was the global surface release of CH4 during this period, then it seems reasonable to me that the OH- transport into the troposphere was 4 times greater in molecular terms. One molecule of CH4 takes four OH to convert it to 4H2Os (and one CO2, but I assume the very abundant O2 can oxidize the carbon in CH4 without any aid from or destruction of OH)

Thus we could learn the flux of OH into the troposphere and assume it is an invariant as the harsh solar UV, the H2O distribution in the stratosphere are invariants.

(2) We could assume that the OH concentration at the surface was during this period was zero and had it maximum at the top of the troposphere, with a linear gradient between. Likewise we could assume thqt the CH4 concentration was maximum at the surface and reduce linearly to zero at the top of the troposphere. I.e. a model with two counter fluxes, one going up and the other going down that exactly destroy each other as they travel thru the troposphere.

(3) Then, for example, if the flux of CH4 were to double, we could model that as an elevation from the surface where the OH was reduced to zero. I.e. up to that altitude the concentration of CH4 is uniform – just a flow moving up without any destruction. I would suggest that elevation (for double CH4 ground level flux) should be that elevation in the troposphere where half of the troposphere mass is below and half is still above. i.e. is the altitude where the pressure is ~7 psi (Assuming the stratosphere make makes 0.7 psi on the top of the troposphere, at the surface the atmosphere pressure is 14.7 psi) Furthermore, we continue to assume that all the CH4 is destroyed by the time it reaches the top of the troposphere.

A naive POV would suggest that if there is twice the 2000/2005 CH4 flux up from the surface and that there is no increase in the flux of OH into the troposphere then all of the OH would be destroyed and the concentration of CH4 would be at least equal to that of the 2000/2005 era to the very top of the troposphere. This however neglects that fact that it is the gradient in OH concentration which drives the OH downward. If the OH is reduced to zero at the altitude of 7 psi then the gradient in the upper “pressure half” (altitude between 7 and 0.7psi) of the troposphere is also doubled.* So the OH comes down twice as fast and we assume there is an infinite supply of OH in the stratosphere.

I.e. doubling the CH4 flux does not “overwhelm” all the OH with unlimited continuous increase of CH4 in the troposphere in this model, but only fills the lower “pressure half” with uniform (No reduction as no OH there) CH4 concentration equal to that at the surface. I.e. instead of the altitude with psi =7 having only half the on centration of CH4 as the surface as it had in this model when the CH4 flux was not doubled, it will have the full surface CH4 concentration all the way up to the psi = 7 altitude. This will reduce the escape of the IR that CH4 can absorb, but not, by itself make a run-away instability as the naive POV might suggest. I.e. the effect is that the surface is warmer and this increases the surface CH4 release rate, but by how much is hard to evaluate.

SUMMARY at this point I will stop my outline of how one might crudely approach the problem of estimating at what increase over the 2000/2005 era CH4 surface flux into the troposphere the system does go unstable with positive fed back loop gain greater than unity. If others think there is some merit in this model (or see serious flaws in it) please comment.

Obviously, many hard parts remain and there would be great uncertainity, but it does seem possible to get some idea as to what CH4 release rate may cause Earth to switch to a cooler version of Venus, by this approach. Thus, far I have only said that there is no known reason why that switch is impossible (Assuming there is unlimited CH4 to be released by surface warming.) So it would occur if the CH4 release rate becomes high enough. It would be nice to have a crude estimate of how far we currently are from the “point of no return”

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* This is not correct unless perhaps the gradient is expressed per increment of pressure instead of the more conventional per unit of altitude; but I don't want to be fully correct now as that is too complex, as I am only trying to outline the method. As the altitude range of the "top pressure half" of the troposphere is much larger than the altitude range of the lower half (14.7 to 7.7psi) the gradient per unit of altitude is less than doubled.

 

[adoucette]

The outside chance of a Venusian catastrophe illustrates some of the risk of such a loop. The improbability of that event in the next couple of hundred years seems to be the reassurance we are offered - although without estimation of the actual odds, the extraordinary nature of such a thing is still worrying.

No ice, the odds of a Venusian catatrophe on the earth in the next TEN THOUSAND years is ZERO.

There is in fact NO CHANCE of that occurring.

To put it in perspective, it would take over 10,000 years with the average annual temperature of the planet running 20C above current just to melt the East Antarctica ice sheet, and yet we have no conceivable climatic model which would yield +20C.

That's not to say that climatic changes which COULD occur aren't very serious, but it doesn't help to create impossible scare stories and have them shot down and thus for people to think that if we can't become like Venus then there is no problem.

HYPE does not actually help.

Arthur

 

[iceaura]

No ice, the odds of a Venusian catatrophe on the earth in the next TEN THOUSAND years is ZERO.

There is in fact NO CHANCE of that occurring.

No argument capable of supporting such a blanket assertion is visible here.

Your links do not support it, ignoring as they do feedback effects, changes of ocean currents, and other considerations. They rest their assurances on such matters as the depth of the ocean over the typical hydrate source, and the assumption of the millenia necessary to warm all that water at current rates of temperature increase. These are reasonable assumptions, but they are not certainties - they do not support a conclusion of zero probability.

To put it in perspective, it would take over 10,000 years with the average annual temperature of the planet running 20C above current just to melt the East Antarctica ice sheet, and yet we have no conceivable climatic model which would yield +20C.

That's not perspective, that's deflection. Much less than 20C will melt the shallow water hydrates - quite rapidly.

- it doesn't help to create impossible scare stories and have them shot down and thus for people to think that if we can't become like Venus then there is no problem.

So it makes a difference exactly how the scare stories are shot down.

Claiming there is no threat behind the methane release in the Arctic would not be one of the better ways - agreed?