Amplification of Global Warming by Carbon-Cycle Feedback Significantly Less Than Thought, Study Suggests
from ScienceDaily (Jan. 28, 2010) — A new estimate of the feedback between temperature and atmospheric carbon dioxide (CO2) concentration has been derived from a comprehensive comparison of temperature and CO2 records spanning the past millennium.
The result, which is based on more than 200,000 individual comparisons, implies that the amplification of current global warming by carbon-cycle feedback will be significantly less than recent work has suggested.
Climate warming causes many changes in the global carbon cycle, with the net effect generally considered to be an increase in atmospheric CO2 with increasing temperature — in other words, a positive feedback between temperature and CO2. Uncertainty in the magnitude of this feedback has led to a wide range in projections of current global warming: about 40% of the uncertainty in these projections comes from this source.
Recent attempts to quantify the feedback by examining the co-variation of pre-industrial climate and CO2 records yielded estimates of about 40 parts per million by volume (p.p.m.v.) CO2 per degree Celsius, which would imply significant amplification of current warming trends.
In this week’s Nature, David Frank and colleagues extend this empirical approach by comparing nine global-scale temperature reconstructions with CO2 data from three Antarctic ice cores over the period ad 1050-1800. The authors derive a likely range for the feedback strength of 1.7-21.4 p.p.m.v. CO2 per degree Celsius, with a median value of 7.7.
The researchers conclude that the recent estimates of 40 p.p.m.v. CO2 per degree Celsius can be excluded with 95% confidence, suggesting significantly less amplification of current warming.
Journal Reference:
- David C. Frank, Jan Esper, Christoph C. Raible, Ulf Büntgen, Valerie Trouet, Benjamin Stocker, & Fortunat Joos. Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate. Nature, 2010; 463 (7280): 527 DOI: 10.1038/nature08769
Full story here at Science Daily
steven mosher (13:46:43) :
before everybody gets all hot and bothered read the SI
http://www.nature.com/nature/journal/v463/n7280/extref/nature08769-s1.pdf
When we get the whole paper we’ll have to see what role the previous studies
jones98, briffa, mann03, mann08, and others had in final answer
It is quite simple: There was a drop of about 6 ppmv of CO2 in the highest resolution ice cores (Law Dome) for the MWP-LIA drop in temperature.
If you take Mann’s 1998/99 hockeystick, the temperature drop MWP-LIA is about 0.2°C, thus the influence of temperature on (pre-industrial) CO2 levels is about 40 ppmv/°C. But we all know the validity of Mann’s hockeystick…
If you take Moberg’s “bathtube”, where treerings have less influence, the temperature drop MWP-LIA is about 0.8°C, which gives about 7.5 ppmv/°C
The very long term influence of temperature on CO2 levels is about 8 ppmv/°C, according to the Vostok ice core (420,000 years):
http://www.ferdinand-engelbeen.be/klimaat/klim_img/Vostok_trends.gif
And the short term influence is about 4 ppmv/°C, as can be seen in the variability of the CO2 uptake around the trend (1992 Pinatubo, 1998 El Niño).
Ferdinand Engelbeen did this study on his own yrs ago, and, IIRC, got ~7 ppm/degC:
http://www.ferdinand-engelbeen.be/klimaat/climate.html
Sorry, Ferdinand, you beat me to it.
The positive feedback element is missing.
http://www.sciencemag.org/cgi/content/abstract/science.1182488
http://www.nytimes.com/2010/01/29/science/earth/29vapor.html?partner=rss&emc=rss
Leo G (19:50:23) :
Deech, are you saying that if we started at 1 ppm, doubling that would add approx. 1C warmth to the globe?
So by the time we got to 356 ppm about 9C of our average temp of 15C would be solely from CO2?
This doesn’t seem right to me.
Or is that added to the 15C? then we should be on average about 24C.
Arrgghh, this is why I refuse to get off the fence! I don’t understand this logic!
there has to be a starting point. Gavin suggested maybe the first 50 ppm raised the temp 1C, then the doubling starts, but again, where is the research on this? How can we say how much effect a doubling of CO2 will have on this planet if we don’t know where the starting point is???
For a dilute sample of CO2 the absorption is linear i.e. follows Beer’s Law, as the concentration increases the effects of broadening occur which leads to a logarithmic response. The difference shows up as follows:
Say you start at 1ppm an increase to 2ppm would double absorption whereas in the log regime it would only increase by 30%. So the first few ppm of CO2 in the atmosphere have a stronger effect than those added now, I don’t the transition point for CO2 but Gavin’s suggestion of ~50ppm sounds reasonable. Note that this is not special to CO2, this can happen with any gas, an example of ones which are still in the linear phase are the freons (which is why their contribution to Hansen’s Scenario A is so strong).
So does this mean instead of CAGW, we will have MAAGW (Mildly Annoying Anthropogenic Global Warming)?
P Gosselin points to an interesting issue. New York Times is heralding the Solomon, et al., paper with this headline:
Less Water Vapor May Slow Warming Trends
http://www.nytimes.com/2010/01/29/science/earth/29vapor.html?hpw
On the surface, the premise that water vapor changes in recent years may be responsible for the “apparent” plateau in temps since [pick a year from 1998 on] would seem to tie in well to the AGW theory that CO2 itself largely drives water vapor changes which do most of the “damage” (in terms of atmospheric temperature increase). But I still have doubts that it’s really that simple. Frankly I’m also not sure how the CO2 numbers have tracked. In any case, I have not read the actual article by Solomon, et al., but would like to.
My initial questions follow:
* Is there contrary evidence? Not?
* Is there a statistically meaningful correlation in observed data?
* Are the data available?
* Do the data appear to provide both a correlation and evidence of causation?
* If CO2 concentrations have changed, have they changed in a manner and on a timeline that would seem to discount or confirm the assertions by Solomon, et al.
Also, something I’ve always wondered about the GCMs: Does the modeled system of CO2 leading to water vapor changes lead inevitably to a level of water vapor that would be unrealistic in the atmosphere?
The Solomon et al. paper is talking only about stratospheric H2O. Ordinarily H2O is prevented from passing from the troposphere to the stratosphere by the temperature at the tropopause being so cold that water just drops to such a low vapor pressure that the stratosphere is extremely dry. As I recall the main bypass to the tropopause is very large tropical storms breaking through. I recall a paper several years ago which pointed to methane increases in the troposphere becoming a major source of water in the stratos. (it’s stable enough to make it through the tropopause but once there breaks down to CO2 and H2O). The paper’s results would suggest that leakage of H2O to the stratos. by whichever route has reduced recently.
Gene L. (10:34:48) :
P Gosselin points to an interesting issue. New York Times is heralding the Solomon, et al., paper with this headline:
Less Water Vapor May Slow Warming Trends
http://www.nytimes.com/2010/01/29/science/earth/29vapor.html?hpw
It seems that stratospheric water vapor is acting independently from greenhouse gases: CO2 stays on increasing and while methane is about stable in the past decade, it still is at high levels, thus can’t be responsible for the decline in water vapor of the stratosphere.
Thus something natural is at work, maybe connected to the PDO or other ocean/atmosphere cycles. And maybe correlated to “global dimming”, which is not related to aerosols (as the “warmers” suspect) but more probable to water vapor.
Anyway, if this is right, that decreases the influence of CO2 as part of the warming 1975-2000 and thus any future “projections” based on increased CO2…
“Gene L. (10:34:48) :
[…]
Also, something I’ve always wondered about the GCMs: Does the modeled system of CO2 leading to water vapor changes lead inevitably to a level of water vapor that would be unrealistic in the atmosphere”
They don’t compute that. They SET the humidity to a constant, assumed, chosen value. Usually called “parameterization” or so, leading to different scenarios. They then run a number of simulations with different setting and make an average to get a more robust result. Really. Don’t laugh. It’s like asking 3 soothsayers instead of one.
BTW they also don’t do clouds. They set the cloud cover to a fixed value. Research is ongoing into how cloud formation can be simulated. Ok, you can stop giggling now.
Phil…
However the molecule in the lower atmosphere experiences about 10 billion collisions/sec with other molecules so that the excess energy is lost before the molecule has time to radiate it away.>
OK. Instead of losing it via radiance it loses it by conductance. We agree that it does lose it though. saturated or not. and when it loses it, the energy can go in any possible direction. so as it propogates through the system… some heats the earth, some heats the atmosphere and some escapes into space. point being that saturation or no…some energy escapes into space.
The earlier post was unclear because blockquote didn’t work as I intended.
A molecule has no temperature. Temperature is a macroscopic concept and requires an aggregate for which to determine an energy distribution or a mean value–then you can speak of temperature.
There are many posts to this site, on every other thread it seems, about the unusual summer in New Zealand, and everyone of these, I think, is explainable by the large mass of anomalously cold water parked near NZ right now.
That was astounding. Don’t you think it would have been more interesting the look at the temperature gradient within the ice so that one could quantify heat flow magnitude and direction?
So it seems possible that some influence which humidifies the atmosphere, even in the absense of any CO2 generated warming, could also warm the planet, say something like El Nino, and this is quite beyond our control.
Dave in Delaware (07:08:41) :
You have stated that part backwards about humidity in Climate models. The models ASSUME constant relative humidity.
I worded my comment very carefully. The reason being I raised this very question some time ago and was assured by a climate modeller that constant relative humidity was a result of the models, i.e. it was NOT assumed by the models.
If you have proof that this is not the case then I am happy to be corrected.
stephen richards (04:30:08) :
John Finn (02:59:43)
John, what you premise here does not sound unreasonable but I do wonder how the el niño waters at 2°C and above affect these emissions of CO². Remember that most outgassing will be from the oceans and not the land, I am somewhat in the dark as to how ‘global temp anomoly’ can be used to define the rate and quatity of outgassing. What do you think ?
I think there is evidence that there is less CO2 uptake in El Nino years and more in La Nina years. If you look at Henry Galt’s post above (Henry Galt (04:23:47) : ) there was an increase in atmospheric CO2 concentration of 2.93 ppm in 1998 (the big El Nino year). The increase in 1999, a La Nina year, was only 0.94 ppm.
But there is always an increase.
DirkH (11:49:00) :
“Gene L. (10:34:48) :
[…]
Also, something I’ve always wondered about the GCMs: Does the modeled system of CO2 leading to water vapor changes lead inevitably to a level of water vapor that would be unrealistic in the atmosphere”
They don’t compute that. They SET the humidity to a constant, assumed, chosen value. Usually called “parameterization” or so, leading to different scenarios. They then run a number of simulations with different setting and make an average to get a more robust result. Really. Don’t laugh. It’s like asking 3 soothsayers instead of one.
BTW they also don’t do clouds. They set the cloud cover to a fixed value. Research is ongoing into how cloud formation can be simulated. Ok, you can stop giggling now.
And you should stop making it up!
if feedback is much smaller than expected, but still positive, wouldn’t that mean oceans are outgassing more co2 than they receive from the atmosphere plus what the biosphere absorbs through increased plant growth ?
then, if co2 solved in oceans is reduced by warming. how can the theory of so-called ocean acidification through global warming still exist ?
Manfred (22:59:59) :
if feedback is much smaller than expected, but still positive, wouldn’t that mean oceans are outgassing more co2 than they receive from the atmosphere plus what the biosphere absorbs through increased plant growth ?
then, if co2 solved in oceans is reduced by warming. how can the theory of so-called ocean acidification through global warming still exist ?
In all cases, the oceans are absorbing more CO2 than that they emit. The increase in CO2 over time is about 55% of human emissions. A small addition from increasing ocean temperatures is included in the trend, hardly distinguishable in the total increase, but readily visible in the year by year variability of the absorption rate.
For the partitioning of CO2 sinks between oceans and vegetation see:
http://www.agu.org/journals/gb/gb0504/2004GB002410/2004GB002410.pdf Bender e.a. and
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/BenderGBC2005.pdf until 2002
George E. Smith (17:32:15)
“We have since the precambrian some 600 million years ago, some sort of proxy data for CO2 in the atmosphere covering a range from around 7000 ppm to a low of well below the recent 280 ppm which is considered sacrosanct. That is maybe five octaves of CO2 doubling, so that should yield a wing ding logarithmic graph versus temperature.
So please SOMEBODY show us a plot of any such logarithmic relationship, ever having been observed.”
You are forgetting that the world was created in 1850. You just don’t discuss climate before this date. I have posted several times on the Ordovician era (just after Cambrian) having 8-20 x higher CO2 than now but ending not in runaway warming but in a snowball earth ice age (glaciers in Sahara) but stony silence the only response. Also, amusingly, corals which are supposed to be killed off by CO2-induced ocean acidification, did the opposite in the Ordovician – they evolved! It was a good era generally for calcified marine life.
If we hypothesise that the climate posesses nonlinear / chaotic behaviour, then positive feedback will not cause runaway change, but instead it will establish oscillation – see the following paper by Kim et al 2001:
http://www.sciencemag.org/cgi/content/abstract/292/5520/1357
The last 2 sentences in the abstract are key:
“The global feedback further led to the development of cluster patterns and standing waves and to the stabilization of uniform oscillations. These findings are reproduced by theoretical simulations.”
Reference my paper at
http://icecap.us/images/uploads/CO2vsTMacRae.pdf
The spreadsheet is at
http://icecap.us/images/uploads/CO2vsTMacRaeFig5b.xls
There is strong correlation between Lower Troposphere Temperature (“LT”) and the rate of change with time of atmospheric CO2 concentration (“dCO2/dt”). These AVERAGES correlate with very little lead or lag time.
The integral of dCO2/dt is the atmospheric concentration of CO2 (“CO2”), and CO2 lags dCO2/dt and LT by about 9 months.
So it may be that the Nature study has the numbers approximately right, but not the science.
CO2 does not correlate best with temperature; dCO2/dt correlates best with temperature, and CO2 correlates less well, with a 9 month lag.
Ferdinand Engelbeen;
The main thing to remember is that the ice-cores do not allow direct measuring of historic CO2 levels. They are telling us the CO2 concentration of the ice-core today. Consequently they are nothing but a proxy.
I find it hard to believe the CO2 will not interact with the ice since CO2 so easily dissolves i water.
In addition, my engineering experience is that if you wish to contain a gas you must use metal as a barrier. “All” other materials are permeable to some degree. Re. the ice, we are talking about hundreds of years or more.
As mr. Beck points out, the ice is not a sterile environment and there will be bacteria present; some consuming CO2, some expelling CO2.
How these factors affect the CO2 concentration is as far as I have been able to see unknown.
Therefore, one should treat the ice-core data with caution.
I think its fair to say that the AGW argument for catastrophic climate change has been ‘sexed up’. We just had this with Iraq, they all ferverently believe some narrative and it ends up biting everyone.
The IPCC and career climate scientists have sexed up the evidence for political advantage.
No conspiracy required, just a general lack of moral fibre.