It seems depending on who you talk to, climate sensitivity is either underestimated or overestimated. In this case, a model suggests forcing is underestimated. One thing is clear, science does not yet know for certain what the true climate sensitivity to CO2 forcings is.
There is a new Paper from Tanaka et al (download here PDF) that describes how forcing uncertainty may be underestimated. Like the story of Sisyphus, an atmospheric system with negative feedbacks will roll heat back down the hill. With positive feedbacks, it gets easier to heatup the further uphill you go. The question is, which is it?
Insufficient Forcing Uncertainty Underestimates the Risk of High Climate Sensitivity
ABSTRACT
Uncertainty in climate sensitivity is a fundamental problem for projections of the future climate. Equilibrium climate sensitivity is defined as the asymptotic response of global-mean surface air temperature to a doubling of the atmospheric CO2 concentration from the preindustrial level (≈ 280 ppm). In spite of various efforts to estimate its value, climate sensitivity is still not well constrained. Here we show that the probability of high climate sensitivity is higher than previously thought because uncertainty in historical radiative forcing has not been sufficiently considered. The greater the uncertainty that is considered for radiative forcing, the more difficult it is to rule out high climate sensitivity, although low climate sensitivity (< 2°C) remains unlikely. We call for further research on how best to represent forcing uncertainty.
CONCLUDING REMARKS
Our ACC2 inversion approach has indicated that by including more uncertainty in
radiative forcing, the probability of high climate sensitivity becomes higher, although low climate sensitivity (< 2°C) remains very unlikely. Thus in order to quantify the uncertainty in high climate sensitivity, it is of paramount importance to represent forcing uncertainty correctly, neither as restrictive as in the forcing scaling approach (as in previous studies) nor as free as in the missing forcing approach. Estimating the autocorrelation structure of missing forcing is still an issue in the missing forcing approach. We qualitatively demonstrate the importance of forcing uncertainty in estimating climate sensitivity – however, the question is still open as to how to appropriately represent the forcing uncertainty.
h/t and thanks to Leif Svalgaard
With all the serious comments on this paper I am almost embarrassed to comment on Gary’s posting: “The really interesting question is: how do you get a cat to roll a watermelon in a lake?
The photo is obviously staged. You can see that the cat is standing on a stone, and its scared expression hints to me that it was released a small fraction of a second before the photo was taken. My wife, who is Japanese, tells me that inflatable balls are sold in Japan that look like melons. They are made as pool toys, and I suspect that this is one. Note how shallow the melon sinks in the water, not on the bottom, which is visible in the photo.
tallbloke (04:40:08) :
“H.R. (02:42:26) :
Anyhow, I’m 100% certain that once the big meteor hits, it won’t matter how sensitive the climate is to CO2.
Ah, but NASA will see it coming, and Bruce Willis, Big Al and Arnie will fly up and save the world by wedging Al in the hole they’ve drilled with the nuke at the bottom to make sure the energy is directed into the frozen heart of the meteor.
And if that fails Jim Hansen will adjust the trajectory data and it’ll miss us.
Oh. Wait a minute.”
Nah. Everybody knows Jim Hansen only does temperature.
However, the US Senate will leap into action and pass a law banning the meteor from hitting us. Oh, and raise taxes to to pay for the miss ;o)
The missing forcing that they are referring to is likely methane forcing.
Methane is a greenhouse gas much more potent than CO2, but it is oxidized in the atmosphere into CO2 with a halflife of about 12 years, by the hydroxyl radical.
They talk about a source of 3 or so trillion metric tons of C13 depleted carbon.
A source that fits this description is the five or so trillion tons of methane hydrates currently existing on the floors of the oceans, and in the Arctic.
What they appear to be saying is that CO2 forcing alone does not explain the PETM.
To explain the PETM, you have to also include methane forcing.
M. Simon (06:40:03) : said
““The greater the uncertainty that is considered for radiative forcing, the more difficult it is to rule out high climate sensitivity, although low climate sensitivity (< 2°C) remains unlikely."
The reason is that the lower bound is zero while the upper end is unbounded.""
This is incorrect since forcing is never expected to be zero when one expects a logarithmic relationship of CO2 to temperature. So, as one gets close to zero it is actually harder and harder to get closeer. The bounded "0.0" is actually undefined, not a boundary condition.
The "unlikely" stands once again for ""we are unlikely to be continued with our funding if it is this low. ""
“Insufficient Forcing Uncertainty Underestimates the Risk of High Climate Sensitivity”
“…a willing suspension of disbelief.”
Tanaka is the Hillary Clinton of climate science.
Ah…. The more uncertainty the more we have to fear. But nevermind the possibility that there is nothing to fear, which is not included in our model.
Wow. And wow backwards. These brilliant people have come up with a cough-cough “scientific” justification for increasing the magnitude of the threat (since the current level has lost its steam) thus hoping that the populous will be fooled into once again believing in chicken little. At first it was the sky is falling. Now its the universe is collapsing. What next?
It has all become clear to me.
They are fishing for a new research budget.
In the mean time we have scientists who keep the threat of a possible run away climate
a live.
Earth has experienced several extinctions, probably caused by really big volcanic eruptions and/or meteorites/comets.
Each time the climate stabilized and life made a come back.
Local destruction caused by atom bomb tests took less than 40 years to recover.
The biggest risk humanity runs today is the onset of a new ice age and short term the accomplishments of our really disturbed political establishment.
Can I please have a budget for studying that?
Here is something I would like to understand about GHGs. If there is a feedback, shouldn’t we have already witnessed it? If CO2 is going to excite other gases in the atmosphere, like water vapor, why don’t other gases in the atmosphere set off the same effect? If water vapor is a feedback, why doesn’t it feedback off of itself?
Take the example of UHI. I live in a city that has a fair amount of this effect, so I would expect that the extra radiating would excite any feedback mechanisms that were present in the atmosphere around the city. There is also a fair amount of CO2 radiating from the city. Wouldn’t the feedback be noticed in this situation?
Given that:
1) The forcing due to changes in the Earth’s albedo (on decadal time scales) is multiple times greater than the forcing calculated for doubling CO2 ( http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/ )
and
2) Climate sensitivity, including feedbacks, is not dependent on what causes the forcing;
Therefore, since the Earth’s temperature hasn’t changed much in response, it appears that there is already enough data to conclude that sensitivity is quite low.
Any model that doesn’t take this data into account is seriously incomplete and can’t tell us anything about the real world.
Roddy Baird says:
The absorption spectrum has indeed been carefully measured and, from that, the radiative forcing due to doubling CO2 has been determined, a value of somewhere around 4 W/m^2 (+-10%) which is agreed to be basically all serious scientists (including “AGW skeptics” Roy Spencer and Richard Lindzen). The big question, as you allude to, is how the various feedback processes in the atmosphere operate to produce the value for the climate sensitivity.
A positive feedback does not necessarily lead to a run-away effect. It has to be sufficiently strong to do so. If it is not, it simply leads to amplification of the warming. (What you describe here is essentially mathematically expressed as an infinite series but, for example, the infinite geometric series 1 + 1/2 + 1/4 + 1/8 + 1/16 + … does not diverge but rather converges to the value 2.)
And, scientists who study paleoclimate have generally concluded that the climate is indeed quite sensitive to small perturbations, see e.g., http://www.sciencemag.org/cgi/content/summary/sci;306/5697/821
M. Simon (06:40:03) : “The reason is that the lower bound is zero while the upper end is unbounded.”
Simple and direct. I like that. Had the same thought just after hitting the submit button earlier. Went away and when I came back decided to read all the comments before adding anything. For once. Cheers!
“”” Insufficient Forcing Uncertainty Underestimates the Risk of High Climate
Sensitivity “””
What kind of gobbledegook is that ? Are they trying to tell us that more uncertainty would improve the accuracy of their wild A*** guesses.
These people are nutz.
George
The paper notes how a failure to fully account uncertainty causes the probability of high climate sensitivities to be underestimated, but it neglects to mention how failure to full account uncertainty also causes the probability of LOW climate sensitivities to be underestimated.
If low climate sensitivity proves out, it means that 20th century warming was not caused by CO2, and it bolsters the competing hypothesis: that it was caused by “grand maximum” levels of solar activity from the 1930’s through 2003. With solar activity now falling off, that means the real danger is global cooling. Funny how the authors fail to even mention the low sensitivity case.
As to “forcing uncertainty”; we know for certain that from place to place on earth the “radiative forcing” ranges over more than a decade; something like a 12:1 range simply due to the surface temperature, and the Stefan Boltzmann law.
And since there isn’t any global network to actually measure the radiative forcing all over the globe in accordance with the usual rules for sampled data systems; then they can’t have the foggiest idea what the overall radiative forcing is for the earth as a whole (the earth knows). And that is before they even consider how the atmosphere reacts with that 12:1 radiative forcing source.
So it is pretty hard to imagine how they could actually have more uncertainty than they actually have; i would say they have total uncertainty; so that must presumably give them the greatest accuaracy to their predictions.
And I pay for this rubbish with my tax dollars ?
“”” Joel Shore (09:55:43) :
Roddy Baird says:
Why is the heat retention of different combinations of gases not tested directly? Or has that been done? A positive result, i.e. CO2 being shown to considerably effect the heat retention of a parcel of gas representative of the earth’s atmosphere would not, on its own, prove the AGW hypothesis as you’d still need to examine the various feedback processes but a negative result would falsify it. Has this been done?
The absorption spectrum has indeed been carefully measured and, from that, the radiative forcing due to doubling CO2 has been determined, a value of somewhere around 4 W/m^2 (+-10%) which is agreed to be basically all serious scientists (including “AGW skeptics” Roy Spencer and Richard Lindzen). The big question, as you allude to, is how the various feedback processes in the atmosphere operate to produce the value for the climate sensitivity. “””
So just what “absorption spectrum” has been measured; and under what conditions has it been measured ?
But more importantly; whatever GHG absorption specra have been measwwured, no matter how carefully; they are pretty much useless, if you haven’t also measured just as carefully the RADIATION SPECTRUM that interracts with the
Hmmm, using greater uncertainty to narrow a conclusion. Is there any other endeavor that this works? I mean, other than in the mind of the “Intellegencia”?
In debugging code or electronics, I usually remove uncertainty (check and eliminate possible causes one at a time) and thereby narrow my focus until I find the error (conclusion). Apparently, although I’ve been successful at doing this for 30 years now, I’ve been doing it all wrong!
That’s not a cat rolling a watermellon into a lake; its a cat rolling a watermellon out of harms way, and into the house, to escape from the rapidly rising sea level, coming up behind it; as a result of too much uncertainty in the radiative forcing.
George
I thought the “science was settled”. Now I find out it’s not settled, it’s “worse than settled.” Would somebody please stop the merry-go-round?
Why is the kitty pushing the watermelon by the shoreline?
tallbloke (06:02:05) :
TSI from the sun at ~1365.2 to ~1366.6W/m^2 is divided by four to get the incident insolation on the curved sun facing side of earth sorted sorted out, but isn’t the tropical area right under the sun going to feel the full effect of the ~ 1.4(PMOD)-2.2W/m^2(Neptune/ACRIM) swing between solar max and solar min, rather than a quarter of it? Plus of course the 8W/m^2 swing induced by earth’s eccentric orbit.
For me, it is simpler to correct for the curved Earth [and albedo and night and day] at the end [or not at all, if you are using percentage changes]. Then the ‘swing’ is more like 90 W/m2.
So in percentages you have a swing of 7% and a solar cycle effect of 0.1% [or almost a hundred times smaller]. That translates into a quarter [S-B law, not round vs. flat] temperature change, so 1.7% of 285K = 5K annual swing and 0.025% of 285K = 0.07K for the solar cycle effect [also almost a hundred times smaller].
OK, greater uncertainty means “we” can’t rule out higher sensitivity, bur for some unknown reason “can” rule out lower sensitivity.
Haven’t people started to laugh at this kind of “grant money propaganda” doubletalk by now?
David (08:56:20) :
The role of water in earths climate is certainly the most central and least understood factor. Water exists on earth in three phases, it has a complex absorption spectrum, it stores and releases vast quantities of heat energy and it has great effects on albedo in the form of clouds , snow and ice. Without the assumption of a positive feedback from water, the vaunted computer models show no frightening scenarios. CO2 is a simple gas and an climatological open book by comparison. Conclusion: nobody is close to pinning down the role of water in climate regulation.
J.Hansford (02:28:04) :
My hopeful take on that was a skeptical tide (the truth) coming in on both Cap and Trade (the CaT) and the watermelons (those who are green on the outside and red on the inside). Notice that the CaT has its back to the sea. Not a good idea. 8^)
Then, I found this (and please no one link the OTHER one on YT)-
A cat pushing a watermelon on a lake. Sheer genius.