Yes, our forebears started global warming by hunting the woolly mammoth. Right. Must be the mammoth albedo effect, much like the sheep albedo effect. Oh, wait, no it’s birch trees albedo calculated via pollen proxy. The mammoths stopped eating birch trees, that’s wot did it. And those hunters used cooking fires too. Gosh. I wish I had more time to refute this, travel beckons, but I’m sure readers can lend a hand in comments.
UPDATE: Carl Bussjaeger points out in comments that;
Just last month, USA Today told us that Felisa Smith of the University of New Mexico in Albuquerque discovered that…
Mammoth extinction triggered climate COOLING
http://content.usatoday.com/communities/sciencefair/post/2010/05/mammoth-extinction-triggered-climate-cooling/1
Man-made global warming started with ancient hunters
AGU Release No. 10–15 Link here
30 June 2010
For Immediate Release
WASHINGTON—Even before the dawn of agriculture, people may have caused the planet to warm up, a new study suggests.
Mammoths used to roam modern-day Russia and North America, but are now extinct—and there’s evidence that around 15,000 years ago, early hunters had a hand in wiping them out. A new study, accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU), argues that this die-off had the side effect of heating up the planet.
“A lot of people still think that people are unable to affect the climate even now, even when there are more than 6 billion people,” says the lead author of the study, Chris Doughty of the Carnegie Institution for Science in Stanford, California. The new results, however, “show that even when we had populations orders of magnitude smaller than we do now, we still had a big impact.”
In the new study, Doughty, Adam Wolf, and Chris Field—all at Carnegie Institution for Science—propose a scenario to explain how hunters could have triggered global warming.
First, mammoth populations began to drop—both because of natural climate change as the planet emerged from the last ice age, and because of human hunting. Normally, mammoths would have grazed down any birch that grew, so the area stayed a grassland. But if the mammoths vanished, the birch could spread. In the cold of the far north, these trees would be dwarfs, only about 2 meters (6 feet) tall. Nonetheless, they would dominate the grasses.
The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun’s heat, in turn heating up the air. This process would have added to natural climate change, making it harder for mammoths to cope, and helping the birch spread further.
To test how big of an effect this would have on climate, Field’s team looked at ancient records of pollen, preserved in lake sediments from Alaska, Siberia, and the Yukon Territory, built up over thousands of years. They looked at pollen from birch trees (the genus Betula), since this is “a pioneer species that can rapidly colonize open ground following disturbance,” the study says. The researchers found that around 15,000 years ago—the same time that mammoth populations dropped, and that hunters arrived in the area—the amount of birch pollen started to rise quickly.
To estimate how much additional area the birch might have covered, they started with the way modern-day elephants affect their environment by eating plants and uprooting trees. If mammoths had effects on vegetation similar to those of modern elephants , then the fall of mammoths would have allowed birch trees to spread over several centuries, expanding from very few trees to covering about one-quarter of Siberia and Beringia—the land bridge between Asia and Alaska. In those places where there was dense vegetation to start with and where mammoths had lived, the main reason for the spread of birch trees was the demise of mammoths, the model suggests.
Another study, published last year, shows that “the mammoths went extinct, and that was followed by a drastic change in the vegetation,” rather than the other way around, Doughty says. “With the extinction of this keystone species, it would have some impact on the ecology and vegetation—and vegetation has a large impact on climate.”
Doughty and colleagues then used a climate simulation to estimate that this spread of birch trees would have warmed the whole planet more than 0.1 degrees Celsius (0.18 degrees Fahrenheit) over the course of several centuries. (In comparison, the planet has warmed about six times more during the past 150 years, largely because of people’s greenhouse gas emissions.)
Only some portion—about one-quarter—of the spread of the birch trees would have been due to the mammoth extinctions, the researchers estimate. Natural climate change would have been responsible for the rest of the expansion of birch trees. Nonetheless, this suggests that when hunters helped finish off the mammoth, they could have caused some global warming.
In Siberia, Doughty says, “about 0.2 degrees C (0.36 degrees F) of regional warming is the part that is likely due to humans.”
Earlier research indicated that prehistoric farmers changed the climate by slashing and burning forests starting about 8,000 years ago, and when they introduced rice paddy farming about 5,000 years ago. This would suggest that the start of the so-called “Anthropocene”—a term used by some scientists to refer to the geological age when mankind began shaping the entire planet—should be dated to several thousand years ago.
However, Field and colleagues argue, the evidence of an even earlier man-made global climate impact suggests the Anthropocene could have started much earlier. Their results, they write, “suggest the human influence on climate began even earlier than previously believed, and that the onset of the Anthropocene should be extended back many thousands of years.”
This work was funded by the Carnegie Institution for Science and NASA.
Notes for Journalists
As of the date of this press release, the paper by Doughty et al. is still “in press” (i.e. not yet published). Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this paper in press.
Or, you may order a copy of the paper by emailing your request to Maria-José Viñas at mjvinas@agu.org. Please provide your name, the name of your publication, and your phone number.
Neither the paper nor this press release are under embargo.
Title:
“Biophysical feedbacks between the Pleistocene megafauna extinction and climate: The first human‐induced global warming?”
Authors:
Christopher E. Doughty, Adam Wolf, and Christopher B. Field, Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA
======================
Readers, I urge you to write to newspapers and magazines that carry this story.
Was this proven or just logical speculation? Don’t wolves eat beavers? Could wolves really depopulate the caribou to such a huge extent that the number of saplings decreased so dramatically? Maybe the wolves too to secretly stocking the streams because they really enjoy fishing?
Global Warming got ketchup on my tie.
—
this article makes perfect sense to me — I am not kidding. Our world is so interconnected, it seems plausible to me that one action (killing mammoths) could lead to a completely unforeseen result (climate change). As an example: Not too long ago environmentalists re-established the gray wolves in Yellowstone National Park which had the effect of increasing the population of trout in nearby streams. Yes you heard right — more wolves meant more trout. You see more wolves meant less caribou and dear eating fewer saplings which meant more trees for the beavers to make more dams which meant more spawning of trout. So which story — mammoths or wolves — is more outlandish?
“Was this proven or just logical speculation? Don’t wolves eat beavers? Could wolves really depopulate the caribou to such a huge extent that the number of saplings decreased so dramatically? Maybe the wolves too to secretly stocking the streams because they really enjoy fishing?”
No the wolves had a plan…eat a beaver….save a tree!
Paging Dr. Paul Martin, Paging Dr. Paul Martin, please come to the library and see what a hash someone has made of your over-kill hypothesis.
I really hope that this is, as mentioned above, a test balloon sort of article written to encourage discussion and further research.
It makes no sense to me, the leaves on trees are darker because they are able to absorbing more solar energy, converting it to stored energy and would therefore be cooler than grassy areas where the soil/rainfall is unable to support tree growth. Forests are cooler than grassy areas for that reason and transpiration.
Just because something is darker does NOT mean that it is closer to behaving like a black-body, there’s photosynthesis going on. I think landsat imaging of IR band intensity ought to prove or disprove what I’m asserting.
Nuke, even today mankind is part of nature despite the crap known as gospel according to the Church of the Gorbal Warming err, I mean climate change.
I concur with Frank Haney (6/30 6:56PM) and JeffKrob (7/1 6:06AM) that this sounds completely backwards — on a sunny day, a dark leaf feels a lot cooler than a nice white beach.
My guess is that this is a combination of both photosynthesis and transpiration — the leaf is absorbing solar energy, but instead of being converted to heat as in a lifeless black body, most of it is convered to chemical energy in the form of hydrocarbons. Meanwhile the leaf is transpiring, causing latent heat (in the form of vaporized water) to rise to the upper troposphere and thereby reducing the amount of GHGs the heat has to pass through radiatively to return to space. The net result is cooling, even aside from the reduced atmospheric CO2 caused by the increased living and fossil biomass.
I also suspect that at night the leaves act as relatively efficient IR radiators, causing perhaps even more nighttime cooling. (Whence the tendency of dew and frost to land preferentially on plants that are actually cooling the atmosphere, not being cooled by the atmosphere.)
But what do I know in comparison to these AGU-certified experts?
Let’s hope there are lots of comments submitted by those more knowledgeable than myself.
MartinGAtkins: July 1, 2010 at 7:35 am
Are you sure about that?? Elephants sleep standing up. I’m not sure I’d be too keen to try that with a flint axe.
They do indeed, sleep standing up, and a flint axe isn’t just a sharp hammer, as depicted in those B-movie caveman flicks — a well-made flint axe is sharper than a surgeon’s scalpel. It’s certainly sharper than the panga poachers use, and the tip of an elephant’s trunk is the most vulnerable part of the animal — and the most-sensitive.
North of 43 and south of 44 says:
July 1, 2010 at 9:44 am
Nuke, even today mankind is part of nature despite the crap known as gospel according to the Church of the Gorbal Warming err, I mean climate change.
And we could bet any Al Baby follower if She/He can find a single not natural “chemical”.
The warmistas claim that more trees act as a storage mechanism for CO2 and more trees will reduce atsmospheric [CO2], thereby reducing temperature. Now we have;
The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun’s heat, in turn heating up the air.
So, I guess the solution is to paint trees white. /sarc off
Paul Vaughan says:
July 1, 2010 at 5:00 am
Trivial misunderstandings arising from such press releases are no cause for alarm. (Alarm is for alarmists.)
[–snip for brevity–]
One option is to chill and watch the debate comfortably.
What the climate debate (in general) needs at this stage is more civility. Goofy rabid hyperpartisanism has become the tiresome big yawn du jour. (One can go on screaming like an irritated irrational protester, or opt to chill calm, composed, & collected.)
Well, I dunno, Paul.
Because you see? Whilst we might all go and ‘chill out’ as you’ve suggested, there’s a far larger and more serious issue which you’ve seemingly neglected to consider, and that’s this: There are other elements whom have it in mind to use every last bit of leverage –however corrupt and/or ill defined/conceived– to further their agenda.
So then, whilst we might kick back and watch the charade with calm amusement, we do ourselves no great favor by remaining on the sidelines, unengaged. Because by the time we figure out what they’ve been up to, it will be too late to do much of anything, and they’ll use our inactivity as the sine qua non –the essential element– of our disinterest to further their plans.
So, no thank you to the invite to do nothing.
In fact, at every turn of the CAGW/CC worm, I’ll be there poking it mercilessly.
Enneagram says:
July 1, 2010 at 6:02 am
It would be advisable, instead, to promote the inmediate extinction of those institutions which sponsor this kind of stupid research. That would increase the spiritual albedo of the human societies involved and it would clean up the atmosphere of noxious political contaminants which impede a clear vision of reality.
My Gawd, Man!
Are you fully cognizant of the implications of such a move?!?!
Why, the U.S. national debt could be paid-off in but a few short decades, we could repeal the 16th Article of Amendment (the income tax and IRS), recall the troops from the far-flung reaches of the EMPIRE, and actually concentrate on the things which really matter: Family, friends, fraternity, and space exploration with a gusto heretofore unknown!!
But then I woke up …
Perhaps the issue here is not the truth or falsehood of this study, but whether this was a reasonable expenditure of public treasure (if this was public funded research) and the life work of the scientists involved.
As this has become a major political issue, I personally think that *no* grants of public money should be allowed for any research project with any wording that implies government a priori acceptance of the danger of catastrophic anthropogenic global warming. I think this is the only way to avoid claims that the results of any such research were grantor driven.
“The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun’s heat, in turn heating up the air. ”
Ahem, wait, isn’t photosynthesis endothermic? Could somebody explain the concept to the researchers?
As for the physiological aspects of this, darker leaves have pigments other than chlorophyll that can act to store energy, but mostly as protection from insects or as antioxidants. The latter act in the plant to protect cellular activity by reflecting light in wavelengths that would normally be absorbed (uv as in blue grape skins, high energy blue, etc.) and allowing the plant to keep the chloroplasts functioning.
Absorption of blue light by photosynthetically inactive or less
active pigments resulted in reduced photosynthetic activities
under blue light for white pine (2) and Scots pine (6). A third
potentially important photosynthesis-screening mechanism is
species differences in leaf relative spectral reflectance. These
various effects fall into three independent classes of potential
photosynthesis-screening mechanisms, viz., (a) metabolic
screening caused by selective stimulation of photorespiration
by certain wavelengths; (b) absorption screening resulting from
the presence of photosynthetically inactive or less active pigments;
and (c) physical screening attributable to selective light
filtering at the leaf surface.
They can also have a greater [chlorophyll]/unit area. In general, the debate is still raging whether plants compensate for lower photosynthetic rates by increased leaf area index. Keep in mind that whatever the vegetation, very little reaches the ground, and agronomic crop yields have been increased by other mechanisms, not increasing photosynthesis/unit area.
Regardless, without knowing the vegetation that was alledgedly replaced by the birch trees, in each specific location, population density, other herbivore population and their eating preferences, etc. etc., which the authors don’t know either leaves me with one comment:
B.S.
drewski says:
July 1, 2010 at 6:37 am
this article makes perfect sense to me — I am not kidding. Our world is so interconnected, it seems plausible to me that one action (killing mammoths) could lead to a completely unforeseen result (climate change). As an example: Not too long ago environmentalists re-established the gray wolves in Yellowstone National Park which had the effect of increasing the population of trout in nearby streams. Yes you heard right — more wolves meant more trout. You see more wolves meant less caribou and dear eating fewer saplings which meant more trees for the beavers to make more dams which meant more spawning of trout. So which story — mammoths or wolves — is more outlandish?
Well then, that makes perfect sense to me as well, because you see? If –IF– Man was responsible for the decimation of the mammoths, then that could only have been a good thing, because –as with your example above– the said mammoths were no longer around polluting the ground with their huge piles of meadow muffins, the run-off of which thence no longer polluted the waterways, and the saplings which formerly had been consumed by the ‘dead mammoth tribe’ were actually allowed to grow into big trees which meant that more beavers would build dams which meant more spawning of trout.
That meant that the fish would thence thrive, and the beavers not being deterred by de turds of de mammoths, things got better and better all around for everyone.
Hey! Gotta love it! Work for me!!
Now there is something I can’t understand.
Humans have gradually warmed the planet since the time mammoths were plenty. So we can conclude the planet is now much warmer than at that time. So we conclude that arctic ice extent is way lower than at that time. The question is: Why do we find mammoths frozen in the ice? What were they eating in the ice?
I always thought the mammoths were dead during a cold year and the cold had persisted.
MartinGAtkins says:
July 1, 2010 at 7:35 am
Bill Tuttle says:
However, the usual method of killing an elephant without using a firearm involves stalking one of the outliers of the herd while they’re asleep, using an axe to lop off the tip of the trunk,
Are you sure about that?? Elephants sleep standing up. I’m not sure I’d be too keen to try that with a flint axe.
So, it’s elephant-tipping, then?
You’ve heard of cow-tipping, right? Sneaking up on a sleeping cow and pushing it over?
🙂
Given that we’ve now had back-to-back 13 cycles of ice age (90,000 year average), each followed by a warming (“interglacial”) period (10,0000 year average), it seems that we must have killed off the mammoths during these earlier eras as well – or at least some similar big animal.
Or could it be that the wooly mammoths will somehow resurrect themselves during this current thaw, in preparation for yet another slaughter? (I sense the possibility of a good paper in this, following peer-review of c0urse, perhaps even a PHHHdegree.)
Cassandra King says:
July 1, 2010 at 8:06 am
The more I think about it the more I am convinced that the underlying principle of ‘research’ of this type is to paint a picture of human existence as anthropogenic in nature, a dangerous and destructive enemy of the percieved(by some)pure Gaia balance and harmony that humanity upsets by its very existence.
We become the enemy of the planet, we become the infection that harms the planet and we become the problem, the narrative is clear here. We humans are a burden on the planet which would be far better off without us polluting it.
If you think about it the idea is very old and starts with the garden of Eden where God bestows a paradise and human nature gives in to desire and ruins the paradise given.
I am sure we are seeing the deliberate deconstruction of the historical record and the building of a new one that fits the anthropogenic narrative.
Star Trek (TOS) had an episode which addressed almost that very same theme:
http://www.imdb.com/title/tt0708482/
Except they were looking for the ‘Garden of Eden.’
my question is : who paid and how much for this junk
Well I followed that “Sheep Albedo” link over to Real Climate to discover Peter Humbug trying his hand at some humor. I’d stick to computer modelling if I were in his place.
But while I was over there, I somehow found a relatively rational discussion of water vapor as GHG or “feedback”.
Well let’s say it was relatively courteous to the posters; including some relatively dissenting; but the arguments on the case subject itself; were hardly any more enlightening than anything else we have seen on the subject.
I was highly tempted to try submitting my own analysis of the questions raised; but given that site’s well established reputation for simply censoring contrary inputs; I thought better of it; and refrained from doing so; but I did read the complete file well for at least the first several pages.
I have to say it is quite tiresome to see the same argumants over and over again cited as fact without ever any supporting evidence.
Take the prime question of the discussion. Is H2O in VAPOR form a “Greenhouse Gas” LIKE CO2 IS ? Or is it simply a FEEDBACK ENHANCEMENT of a primarily CO2 causation.
Well of course their view is that it is NOT a GHG but simply a feedback enhancement of a CO2 driving force.
So out they trot the old saw, that H2O vapor is a short lived intruder into the earth atmosphere while CO2 is a long term permanent resident.
Of course this is complete nonsense; both of them are permanent residents of earth’s atmosphere and have been as far back as we can determine reliably; and H2O has always exceeded whatever amount of CO2 there is in the atmosphere; anywhere where they both occur, at least below the 14 km level. And the global average abundance of each is reasonably stable, although it is possible that H2O is a bit more variable than CO2.
There’s not a jot of difference in the behavior of CO2 and H2O vapor as regards the capture of LWIR radiation emitted from the earth surface in the roughly 5-80 micron wavelength range; other than that they absorb somewhat differnt parts of that spectrum.
The H2O absorption bands they claim are often “Saturated”, while of course the CO2 band is not. Well the exact same argument can be made for H2O as is made for CO2. A cascade of multiple absorption/ re-emission (from a warmed atmosphere) takes place in either case; and the effect of “saturation” of any particular band simply thins the layer of atmosphere that captures the emissions.
And as Phil has pointed out several times; the high resolution spectra of CO2 and H2O are such that they do not necessarily overlap, even though they occupy a similar range. Now I am sure that line broadening due to Temperature (Doppler) and pressure (collision) broadening tend to smudge that separation somewhat; and I suspect that Phil would not greatly disagree with that.
The point is that there is absolutely no way to separate the increased evaporation of H2O from the oceans, or the “outgassing” of CO2 from a warmer ocean; into components that are initiated by ATMOSPHERIC WARMING caused by CO2 and that caused directly by H2O vapor. CO2 is just as much a feedback amplification of H2O atmospehric Warming, as is the reverse.
raypierre, even performed an experiment (computer) where he removed all the atmospheric H2O, and then his computer replaced it all in about three months. Not at all unlike the “Birdseye experiment I have often proposed; except Ray did not apaprently drop the temperature as well to aid in removing the H2O. Hardly matters though the recovery is the same.
Say raypierre, now that you have done that experiment; why don’t you do the converse.
Remove ALL the CO2 and other GHG, leaving only the H2O, and then tell us where your computer model settles out (keep the GHG out permanently). I’m quite sure that even your computer models will restore the temperature to about its present value, but with the right amount of cloud cover.
The point is that the choice of whether H2O or CO2 is a GHG (yes) or a “feedback” is a totally arbitrary choice.
Eli Rabbett tries to minimize the arid desert cooling rate, as a glaring demonstration of the complete ineffectiveness of CO2 to maintain a warm atmosphere; but his argukents are quite unconvincing. How could they be, in light of the simple fact that everybody who has ever been out at night in an arid desert environment, has experienced for themself, that it simply does not remain warm, without H2O (which of course is not a greenhouse gas, so could not keep the atmosphere warm).
No amount of argument; whether by rabbett, or Stephen Schneider is going to convince those night desert dwellers, that H2O vapor is a very weak GHG compared to CO2; yet somehow H2O “feedback” is the major warming effect caused by CO2.
Well they can’t have it both ways.
H2O vapor is quite capable of maintaining a comfortable earth Temperature above the black body equilibrium temperature, without any help or trigger whatsoever from CO2 or any other GHG; and raypierre can easily show that with his computer model; so long as he has properly included the cloud modulation effect that is clearly demonstrated in the experimental results of Frank Wentz et al in SCIENCE for July-7-2007; “How Much More Rain Will Global Warming Bring ?”
And I would invite raypierre to perform the “Venus” experiment as well, by taking the temperature (atmosphere) up to say 50 deg C, and placing total cloud cover from the ground to maybe 15-20 km from pole to pole; and then let his computer model the recovery from that condition.
And then perhaps he can explain why he does not end up in the exact same place, as his H2O removal experiment ended up (if that turns out to be the case).
Like I said; I was tempted to post a response there; but I’m not interested in silly political games for whatever rationale one has. I have only one interest; and that is to have the real science correctly presented.
I was quite surprised to find that even Gavin, was not able to present convincing arguments to substantiate the notion that H2O vapor is NOT a GHG. It’s a quite arbitrary choice; the Physics is in no way different; and the only substantial difference between H2O and CO2, is the very simple and quite important fact that H2O alone exists permanetly in the atmosphere at about the same global average level in ALL THREE PHASES of ordinary matter; and as a vpor it has clearly demonstrable positive feedback warming behavior, as well as negative feedback cooling behavior; but as a liquid or solid form in clouds, it ALWAYS results over climate time scales in a cooling for increased cloud coverage.
The argument that high clouds being cold, and low density, that can only radiate weakly to space (thereby cooling the planet) so increased ground level insolation results in warming; is simply a diversion. For the very same reason, those high low density clouds intercept very little ground level LWIR radiation; and they DO NOT radiate back towards the surface any more readily than their weak radiation to space. So get over it. We already know, that NO CLOUDS results in a warmer surface;a nd we know that low density cold high clouds only block or reflect outwards a small amount of either solar or ground level LWIR but they also don’t re-radiate much towards the surface; and THEY DO block some solar radiation from the surface; so THEY DO COOL over NO CLOUDS.
I’m afraid that raypierre did not make a very convincing case; well he made essentially no case. I don’t know anything about his computer models; so I am not going to comment on them.
But if the can’t replicate what Mother Gaia does in HER laboratory; then he needs to amend them until they do.
George E. Smith says:
July 1, 2010 at 4:10 pm
[–big snip–]The point is that there is absolutely no way to separate the increased evaporation of H2O from the oceans, or the “outgassing” of CO2 from a warmer ocean; into components that are initiated by ATMOSPHERIC WARMING caused by CO2 and that caused directly by H2O vapor. CO2 is just as much a feedback amplification of H2O atmospehric Warming, as is the reverse.[–snip rest–]
In the Earth’s atmosphere, there is no such thing as ‘positive feedback.’
In fact, the whole idea is a myth.
In order for any such thing to exist, there of necessity MUST exist a mechanism which puts MORE energy into the system than which was put into it to begin with.
That “MORE” amount MUST be significant such that even without the external influence, the system is SELF-PERPETUATING.
Since the Sun is the ONLY source of SIGNIFICANT energy external to the Earth, then removing it will eliminate ALL SIGNIFICANT energy imparted to the atmosphere.
Echoes DO NOT overtake –much less equal– the original sound.
Marc77 says:
July 1, 2010 at 1:58 pm
Now there is something I can’t understand.
Humans have gradually warmed the planet since the time mammoths were plenty. So we can conclude the planet is now much warmer than at that time. So we conclude that arctic ice extent is way lower than at that time. The question is: Why do we find mammoths frozen in the ice? What were they eating in the ice?
I always thought the mammoths were dead during a cold year and the cold had persisted.
There is a logical reply: Said animals were feeding when caught in an avalanche of snow, and eventually the snow turned to solid ice.
It happens quite frequently in parts of the country where –in the spring months– the high snows on steep hillsides slough into the lower regions and the occasional human or other creature gets trapped underneath.
We might consider that in an ice age –where the thaw time is quite reduced– the snow which buried the unfortunate never melts, and they instead becomes permanently encased.
Of course there’s always that ‘quick-freeze’ theory, but I’ve not bought into that for a number of reasons.
“You’ve heard of cow-tipping, right? Sneaking up on a sleeping cow and pushing it over?”
Great fun, but even better is the tipping of the little shack with the crescent moon in the door.
“”” 899 says:
July 1, 2010 at 5:04 pm
George E. Smith says:
July 1, 2010 at 4:10 pm
[–big snip–]The point is that there is absolutely no way to separate the increased evaporation of H2O from the oceans, or the “outgassing” of CO2 from a warmer ocean; into components that are initiated by ATMOSPHERIC WARMING caused by CO2 and that caused directly by H2O vapor. CO2 is just as much a feedback amplification of H2O atmospehric Warming, as is the reverse.[–snip rest–]
In the Earth’s atmosphere, there is no such thing as ‘positive feedback.’
In fact, the whole idea is a myth. “””
Well 899, if you believe that; then perhaps I should state more explicitly exactly what I mean by the use of that term “Positive feedback”; same goes for “negative feedback”.
Let’s take “positive feedback” in the sense that I mean it, relative to H2O in the atmosphere. H2O is known to capture LWIR emitted from the surface in several bands in the 5 to 80 micron spectrum. That intercepted energy is transferred to the ordinary atmospheric gases by molecular collisions (in the lower troposhphere at least) and that results in a warming of the atmosphere. The atmosphere in turn radiates LWIR isotropically, at an elevated level due to whatever atmospheric temperature rise occurs. some of that radiation reaches the surface (I bleieve a bit less than half of it) and that LWIR emission from a warmer atmosphere is absorbed mstly in the top 10 microns of the oceans or other water surfaces; since oceans are about 70+ % of the surface area (and even more in the tropical areas where most of this energy is manipulated. The surface absorption of the LWIR tends to result in prompt evaporation of MORE WATER VAPOR, thereby increasing the amount of atmospheric water vapor; which will result in even more LWIR capture due to H2O GH effect. In that sense it is a positive feedback; and the principal one raising earth temperature above the equilibrium BB temperature in earth’s solar orbit.
The H2O vapor “negative feedback” effect results from H2O vapor capture of incoming solar spectrum energy from about 760 nm wavelength to about 4 microns. That captured solar spectrum energy therefore does not reach the surface; so it results in surface cooling which will tend to reduce the amount of H2O vapor in the atmosphere. That is clearly a negative feedback.
Now that captured solar energy certainly DOES warm the atmosphere; BUT !! the resultant re-emission of LWIR by that wared atmosphere is necessarily isotropic, so about half of it heads outwards towards space, and only half of it returns towards the surface. The net result of the solar spectrum capture, and the isotropic emission of that energy as LWIR means an overall net LOSS to the total surface energy. So it clearly IS a surface cooling effect due to H2O vapor.
Now of course there is additional negative feedback due to cloud fomation.
CO2 of course does the same sort of atmospheic warming as H2O vapor just at different wavelengths. But CO2 has a much weaker interraction with the incomin solar spectrum; but not totally zero, so that too is a surface cooling effect but small compared to the H2O component.
As to is there an overall positive feedback; well I think it is clear that there has to be DUE TO GHG VAPORS ALONE; or else we would be a frozen ice ball; but it is the magic of cloud formation that only H2O brings that turns on the massive negative feedback to clamp the positive feedback off and shut down that regenerative heating mechanism.
So I wouldn’t try to defend than no positive feedback position; that’s a shaky ground; and more importantly it disguises the simple fact that the turn on of the cloud formation is the regulatory mechanism that defeats any attempt by CO2 or any other GHG (including H2O) to continue to raise the temperature. And if it gets too cold; then precipitation dissipates the cloud, and allows more solar energy to reach the ground.
It’s a quite stable self regulating mechanism.