Bishop Hill Doubt and assumptions
Apr 17, 2013 Climate: sensitivity James Hansen is also getting back into the climate sensitivity fray, posting up an Arxiv preprint that (surprise, surprise) comes up with a much more alarming figure than Lewis or Masters. The estimate is based on paleoclimate data, specifically δ18O data for foraminifera (a class of microscopic animals that got a mention in the Hockey Stick Illusion). However, as has often been noted in the past, these paleoestimates of climate sensitivity are fraught with difficulty as the quality of data on temperatures and forcings in the distant past is shaky indeed. Hansen alludes to these difficulties in his abstract, although his position seems to be that his new approach represents an improvement:
Cenozoic temperature, sea level and CO2 co-variations provide insights into climate sensitivity to external forcings and sea level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise paleoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity 3 ± 1°C for 4 W/m2 CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e., 3-4°C for 4 W/m2 CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state-dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapor elevates the tropopause. Burning all fossil fuels, we conclude, would make much of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change.
You get a flavour of the difficulties from this summary of the methodology:
We hypothesize that the global climate variations of the Cenozoic...can be understood and analyzed via slow temporal changes of Earth's energy balance, which is a function of solar irradiance, atmospheric composition (specifically long-lived GHGs), and planetary surface albedo. Using measured amounts of GHGs during the past 800,000 years of glacial-interglacial climate oscillations and surface albedo inferred from sea level data, we show that a single empirical "fast-feedback" climate sensitivity can account well for global temperature change over that range of climate states.
And then when you read the detail it starts to hit you:
To clarify our calculations, let us first assume that fast-feedback climate sensitivity is a constant (state-independent) 3°C for doubled CO2 (0.75°C per W/m2). It is then trivial to convert our global temperature for the Cenozoic (Fig. 4a) to the total climate forcing throughout the Cenozoic, which is shown in Fig. S4a, as are results of subsequent steps. Next we subtract the solar forcing, a linear increase of 1 W/m2 over the Cenozoic era due to the Sun's 0.4% irradiance increase (Sackmann et al., 1993), and the surface albedo forcing due to changing ice sheet size, which we take as linear at 5 W/m2 for 180 m sea level change from 35 Myr BP to the LGM. These top-of-the-atmosphere and surface forcings are moderate in size, compared to the total forcing over the Cenozoic, and partially offsetting, as shown in Fig. S4b. The residual forcing, which has a maximum ~17 W/m2 just prior to 50 Myr BP, is the atmospheric forcing due to GHGs. Non-CO2 GHGs contribute 25% of the total GHG forcing in the period of ice core measurements. Atmospheric chemistry simulations (Beerling et al., 2011) reveal continued growth of non-CO2 gases (N2O, CH4 and tropospheric O3) in warmer climates, at only a slightly lower rate (1.7-2.3 W/m2 for 4×CO2, which itself is ~8 W/m2 ). Thus we take the CO2 forcing as 75% of the GHG forcing throughout the Cenozoic in our standard case, but we also consider the extreme case in which non-CO2 gases are fixed and thus contribute no climate forcing.
You need to know temperatures in the distant past, ice sheet sizes in the distant past, solar irradiance in the distant past, and greenhouse gas levels in the distant past. You wouldn't want to bet the house on the results would you?
Reader Comments (24)
Assumption followed by assumption by assumption. If you were presenting this as an engineering report trying to justify $Bn's of spend you would be laughed at, why are they taken seriously at all.
BUT importantly it's a paper the "Team" can point to support their position it's all worse than we thought.
Additionally, I wonder who reviewed the paper? More pal review anyone???
Regards
Mailman
"Burning all fossil fuels, we conclude, would make much of the planet uninhabitable by humans," is speculation.
Not burning all fossil fuels would make much of the planet uninhabitable by humans - fact.
Science fiction author Isaac Asimov, didn't do reconstructed paleo climate sensitivity guess work...................but if he did..................
Re: Apr 17, 2013 at 11:43 AM | Breath of Fresh Air
"Assumption followed by assumption by assumption. If you were presenting this as an engineering report trying to justify $Bn's of spend you would be laughed at, why are they taken seriously at all."
Because it's political - to justify the tax take they can then dole out to their cronies who then go on to produce reports such as these!!!
What do they mean by "fast"?
While I haven't yet read the paper in depth, it seems to be merely a reiteration of this 2011 Hansen & Sato paper. [Which seems to be also here.]
Is there some novelty in the paper?
What ever else ends up on Hansen's grave stone, the words 'He was wrong right to the end ' should certainly be there .
Hansen is not going to stop his rent seeking, moral hazard ways whether he is retired or not.
So at least this nutter admits to Milankovitch cycles...
"We hypothesize that the global climate variations of the Cenozoic...can be understood and analyzed via slow temporal changes of Earth's energy balance, which is a function of solar irradiance, atmospheric composition "
Then gets it arse about face, as usual, by ranting about greenhouse gases and the dreaded CO2.
Hasn't this bozo realised yet that at glacial inception/terminations temperature changes precede those of CO2?
See this paper- and many others
Siegenthaler, U., Stocker, T., Monnin, E., Luthi, D., Schwander, J., Stauffer, B., Raynaud, D., Barnola, J.-M., Fischer, H., Masson-Delmotte, V. and Jouzel, J. 2005. Stable carbon cycle-climate relationship during the late Pleistocene. Science 310: 1313-1317.
KnR - Perhaps Hansen would want "λ = 0.75 K/(W/m2)". Certainly he does not seem willing to revise this estimate.
At least - with its claim that there are sufficient fossil fuels remaining to enable humanity to make the earth uninhabitable - this paper gives the lie to that other popular eco-myth, that fossil fuels are about to run out.
I too have always found it almost humorous that people seem to think that we can get a more accurate estimate for 50 million years ago than for the recent past. Given the huge uncertainty, this just doesn't pass the smell test. Surely, estimates based on the recent past have far smaller uncertainty bounds.
Tom Wigley summarizes why no-one should believe Hansen's paleo-based ECS estimate:
http://wattsupwiththat.com/2011/11/28/senior-ncar-scientist-admits-quantifying-climate-sensitivity-from-real-world-data-cannot-even-be-done-using-present-day-data/
"date: Fri, 30 Jun 2000 12:30:43 -0600 (MDT)
from: Tom Wigley...
subject: Re: ...
to: Keith Briffa...
Keith and Simon (and no-one else),
Paleo data cannot inform us *directly* about how the climate sensitivity
(as climate sensitivity is defined). Note the stressed word. The whole
point here is that the text cannot afford to make statements that are
manifestly incorrect. This is *not* mere pedantry. If you can tell me
where or why the above statement is wrong, then please do so.
Quantifying climate sensitivity from real world data cannot even be done
using present-day data, including satellite data. If you think that one
could do better with paleo data, then you’re fooling yourself. This is
fine, but there is no need to try to fool others by making extravagant
claims."
My summary:
1. We don't know the temperature or its first derivative during that time.
2. We don't know what thermal forcings existed during that time.
3. We don't know if stationarity is a valid assumption.
4. We don't know how much snow and ice was around during that time.
5. We don't know the ocean temperature profile during that time.
Therefore, we KNOW climate sensitivity to +/- 0.01 C/W/m^2. Sure.
"Burning all fossil fuels, we conclude, would make much of the planet uninhabitable by humans"
Is that burning all fossil fuels this week? Or all at the same time? Or all of them at the current rate? Or over the next 1 million years?
And exactly how do we find and extract all fossil fuels?
In fact, does the sentence has any content whatsoever?
Heh, this guy will be spectacular on the witness stand.
=================
Politicians will ultimately believe what they want to believe and this guy certainly knows how to keep them in their comfort zone. A sure-fire recipe for success any day. Expensive for those who ultimately pay the bills though to put it mildly, in more ways than one.
Hansen deserves to be the object of more study than his papers get. But the possibility* that relevant materials related to him are being destroyed at NASA has been raised and is a worrying one since it would interfere with what I think deserves to be an area of scholarly endeavour for years to come: 'Hansen Studies'.
*http://junkscience.com/2013/04/16/is-nasa-destroying-records-related-to-the-retiring-jim-hansen/
Did he start with an assumption of 3c warming to get his climate sensitivity number?
"Additionally, I wonder who reviewed the paper? More pal review anyone???"
Arxiv isn't reviewed. Hansen usually avoids even pal review these days. He's a little bit too far out even for "the team".
Hopefully there might, one day, be an independent way of actually measuring climate sensitivity. Then we will cease to plagued by such useless papers.
No paleo person has published results of experiments designed to show that their proxies are unreliable. That tells scientists all they need to know.
chris y -
Yes, Wigley had it right. There are some advantages to trying to assess climate sensitivity via paleo studies:
1. Can assess equilibrium response; modern era can only monitor transient response.
2. Large change in forcing in the before-and-after of the glacial termination; modern era has a smaller change in forcing.
Against those are the disadvantages which Wigley set out, namely much larger uncertainties in the global state. As well as your comment that it is not at all certain that the sensitivity as of the last glacial maximum, is in fact equal to the current sensitivity. Biological feedbacks, in particular, would seem to be much different. It may be that sensitivity isn't much changed, but right now that seems to be postulated rather than proven.
Judith Curry has a detailed overview of recent papers on climate sensitivity - http://judithcurry.com/2013/04/17/meta-uncertainty-in-the-determination-of-climate-sensitivity/#more-11524