Guest Post by Willis Eschenbach
ABSTRACT
The IPCC says that the expected change in temperature arising from a change in forcing is equal to the change in forcing times the climate sensitivity. The IPCC provides values we can use to estimate the total human and natural forcing change since 1850. The IPCC also proves estimates for the climate sensitivity. These can be multiplied to provide the IPCC expected temperature change since 1850. The value derived (best estimate per IPCC numbers = 1.4 °C warming since 1850) is twice the observed warming (HadCRUT best estimate = 0.7°C warming since 1850).
Recently I became puzzled by what seems to be a glaring discrepancy in the official IPCC numbers. The IPCC estimate of climate sensitivity is +3 [+2 to +4.5] °C per doubling.
We also have the IPCC estimate of the change in forcing since 1750, in Watts per square metre (W m-2). The human contribution to that forcing is given by the 2007 IPCC Summary for policymakers as:
The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m-2.
This represents the best estimate plus [lower and upper bounds].
Now, a doubling of CO2 is estimated by the IPCC to produce a change in forcing of 3.7 W m-2. So if we divide the climate sensitivity (in degrees per doubling) by 3.7, we will get the climate sensitivity expressed in units of degrees per W m-2. This gives us the result:
Climate Sensitivity = +0.8 [+0.5 to +1.2] degrees per W m-2.
Finally, we know that sensitivity times the change in forcing gives us the temperature change. Using the IPCC estimates of both, this gives us:
+0.8 [+0.5 to +1.2] degrees per W m-2 times +1.6 [+0.6 to +2.4] W m-2
= +1.3 [+0.4 to +2.2] degrees of warming from human activities since 1750. (Errors throughout have been assumed to add in quadrature.)
Now, we don’t have very good temperature data before 1850, so we need to adjust for that. However, there was very little human effect on the climate from 1750 to 1850. CO2 levels were only slightly lower in 1750 than in 1850, the industrial revolution was in its infancy, little fossil fuels were burnt, sulfur emissions were negligible, no fluorocarbons were emitted. Since the 1750-1850 anthropogenic contribution is very small compared to the total anthropogenic forcing, that IPCC based calculation of temperature change from humans of +1.3 [+0.4 to +2.2] degrees can be taken as the best estimate and bounds of the human caused temperature change since 1850.
For our final estimate, in addition to the human forcings since 1850 we need to add the natural forcings. The IPCC includes only one of these, solar forcing. The IPCC estimates that changes in solar forcing in the ~250 years since 1750 was 0.12 W m-2. For our rough calculations, we can make a crude but adequate estimate that three fifths of this change occurred since 1850. Adding solar forcing to the earlier equations makes the IPCC calculated temperature change from human and natural forcings combined since 1850 slightly greater, at +1.4 [+0.4 to +2.3] degrees.
Now, here’s the problem with that, and it’s a very big problem. According to the HadCRUT dataset (monthly dataset here, with notes here), the total temperature change 1850 – 2006 is +0.7 [+0.5 to +0.9] degrees. In other words, the world has warmed by around three-quarters of a degree (best estimate 0.7°C) since 1850. That’s nowhere near 2.3°C, the high end of what the IPCC says should have happened since 1850. It’s only half of the IPCC’s most likely number. It is just above the IPCC’s lower bound. So the IPCC method, using the IPCC numbers, way overestimates the historical temperature rise.
What can we conclude from this mismatch between observations and calculations? There are a number of possible explanations, in no particular order.
1. The sensitivity numbers are too high, and the forcing numbers are correct. If that is the case, the sensitivity is +1.5 [+0.5 to +2.4] degrees per doubling of CO2, a much lower and narrower range than the +3 [+2 to +4.5] range espoused by the IPCC.
2. The forcing numbers are too high, and the sensitivity numbers are correct. That gives us a calculated change in forcing since 1850 of +0.9 [+0.5 to +1.4] W/m2. Again this is much lower and more narrowly bounded than the canonical IPCC range of +1.7 [+0.7 to +2.5] W/m2 including solar. Note that in both this and the previous case, the relatively narrow bounds of the temperature observations have constrained narrow bounds on the underlying forcings or sensitivities.
3. Both the sensitivity and the forcing numbers are too high. This would limit possibilities to values such that the product of the two give us +0.7 [+0.5 to +0.9] degrees of warming. If the reductions were proportional, the forcing and the sensitivity would each need to be cut to about 70% of the IPCC numbers.
4. There are other mechanisms at play (e.g. cosmic rays, plankton aerosol production, thunderstorms) that the IPCC is not accounting for.
5. I’ve made a foolish mathematical mistake.
6. Climate may not obey a linear relationship between forcing and temperature change. My calculations are based on the IPCC assumption that a change in temperature can be calculated as a constant called “climate sensitivity” times the change in forcing. However, climate sensitivity may not be (and in my view is not) a constant. Instead, in my view climate sensitivity is a function of T, which changes the equation.
7. This is the “missing heat” that Trenberth referred to.
8. Something completely different that I haven’t thought of.
I couldn’t even begin to say which of those, or how many of those, if any of those, are actually going on …
Anyhow, that’s the oddity. If we multiply the IPCC historical forcing change since 1850 times the IPCC climate sensitivity to get the IPCC estimated temperature change since 1850, the result is nothing like the historical temperature change. The high IPCC estimate (2.3°C) is three times the actual change (0.7°C) since 1850. Clearly, something is wrong. Depending on which explanation we choose, we have different conclusions, none of which seems compelling.
Assistance and ideas welcome …
“What can we conclude from this mismatch between observations and calculations?”
Models vs. Reality = Models always lose
Thanks again for a clear-headed analysis. I suppose if one were to take out a UHI influence there may be little to no sensitivity/warming at all.
Wow. Why don’t we go back in time and “heat” our homes in the southwest using swamp cooler as “heaters”. Isn’t that what the idea of CO2 forcing and water system feedback does?
Or better yet, why not go back using swamp cooler in high humidity to cool our homes.
@Dave Springer
Well, the democRats can do a lot of damage during the lame duck session and they can pass all kinds of economy hobbling measures. Obama can agree to any treaty he wants to. One thing they can’t do is ratify any of these stupid treaties. The founders saw to that by requiring 2/3 of the senate.
Hopefully, the new house of representatives will shape a little of the future legislation to bring some of Pelosi’s stupidity home to roost on the morons in her district who keep re-electing her. That may be the only way to do anything about the entrenched ideologues who are working so hard to do away with the document that requires that inconvenient two-thirds majority.
A large radiative imbalance caused by ocean lag means there should be continuous warming of the oceans as they catch up to the equilibrium temperature. The data that shows they are not warming is in direct contradiction to the long lag time hypothesis.
Aerosols are so much fun. They can explain everything because our understanding is so poor. What is often missing from the aerosol discussion is the fact that black carbon could easily cause more warming then attributed and sulfites could cause less cooling then attributed making the climate sensitivity much less. Since when has ignorance become a convincing argument?
I can’t believe Willis didn’t know about aerosols, volcanoes, global dimming, and he was probably just testing his readership by feigning ignorance. Areas where warming has been suppressed, mostly in the northern hemisphere, include as a most obvious example the SE USA, where the obvious effects of anthropogenic haze have been increasing between the 40’s and 70’s in conjunction with the oil industry. Some claim the PDO and AMO caused all of this, but I dispute that on geographical grounds as regards the southeast, which dominates the US average cooling.
Willis, when it comes to trolling for trolls, you da best! Amazing how these folks hover over the site and jump in with their views ahead of normal human beings! Your posts seem to roil the bottom and bring these odd creatures to the surface. Thanks.
Mike Davis says:
October 23, 2010 at 5:35 am
Willis:
You are not using the correct “Math”!
Your math: 2+2=4!
3+3=6!
Climate Math: 2+2=6!
3+3=16!
There is an “Esoteric” formula for that and your not being among the enlightened is why you got it wrong!
😉
2+2=16 for very large values of “2”.
This post is perfectly timed for me. I have recently finished an analysis of the CO2 forcing and climate sensitivity and I found some serious flaws that cannot be reconciled. Using only AGW supplied information I have concluded that their sensitivity is much greater than possible. By only using their information.
Tomorrow I will post the analysis on my website. It is pretty good. Still touching up the article so I am giving myself time, but it should be a very good read. I am very curious what the response will be.
John Kehr
thank you for a step closer to truth! So sick of all the BS out there! love your blog.
I have a question for all you gw ‘computer ensemble’ programmers out there.
If the atmosphere contains 750 gigatons of carbon, and all 4,000 gT of known fossil fuel reserves were burned, the CO2 concentation would increase from 390 to 2,440 ppm, resulting in a logarithmic temperature increase of 1.5C. If we are burning 5.5 gT of carbon per year, the temp increase can only be about 0.002C.
How many people do you know own a thermometer that can measure this increase?
Willis,
You forgot to include natural recovery from the LIA. About half of the temperature rise occurred before 1940, and almost all of that is considered to be natural rise. After 1940 the temperature went down then up. It is fairly obvious that the drop is not due to aerosols, since cycles up and down occurred before and are occurring after that period. The long period ocean currents and or solar variation are the likely cause. There is a reasonable chance much of the rise over the 1940 level is related to CO2 and other human causes, but when the cyclical variation due to the oceans (or whatever the cause) is accounted for, the human effect is almost surely less than 0.3 C. The cycle down is started, and projecting out to a doubling of CO2, possibly 0.3 C more might be caused by human activity. By this time, the use of fossil fuels should be almost stopped (due to greater difficulty getting it and thus increased cost compared to say nuclear). The basic point I make is that including natural recovery from the LIA, most of 0.7 C has to be dropped to about 0.3 C, and the models are even more wrong.
Perhaps I’m missing something, but I’ve often wondered what is the point of error bands if everyone ignores them and assumes the ‘mean’ of ‘median’ or some other value is the ‘correct’ one.
Since the IPCC are correct (i.e. the real data is within the error bands) then the theory is OK – perhaps someone needs to work one reducing the error bands.
Equally, the hockeystick, when shown with error bands, easily encompass the MWP, the LIA, and the missing recent increases, and in fact hardly looks like a hockeystick at all if you include the error bands.
So what are they for if they are always ignored?
Jim D says:
“Areas where warming has been suppressed, mostly in the northern hemisphere”
Actually it is the southern hemisphere that hasn’t been warming.
Thank you Willis. I have wondered at your patience to sift through these reports that are full of wild theories and outright fabrications. It occurs to me you have a natural inclination to teach. I appreciate the lessons you have brought forward and feel a small kinship with you in that in all things I want to see the numbers. Dont try to baffle me with discourses that imply I lack the intelligence to understand as I saw through that argument at the age of eight. What I see in the comments here does nothing to persuade me in agreeing to AGW. On the other hand I see Joe Lalonde qualifies for a grant worth camillions, the ocean heat sink theory needs a camillion dollar grant, etc. etc. I expect these reports to reach the high standard displayed by those paragons of virtue Hanson and Mann. I think I understand how the dark ages happened from watching what is going on today as these charlatans are at least with the likes of the al gores responsable for some of the dimming of the intellect of this generation.
steveta_uk wonders:
“Equally, the hockeystick, when shown with error bands, easily encompass the MWP, the LIA, and the missing recent increases, and in fact hardly looks like a hockeystick at all if you include the error bands. So what are they for if they are always ignored?”
Your recollection of events may be different from mine, but it seems that the Hockey team and IPCC made a bit of a fuss about the hockey stick.
I don’t recall Mann saying: “Hey, our conclusions are well within the error bands, you can fit in any curve you feel like! Nothing to look at here.”
I’m pretty sure Pielke Sr. has refuted the “heat in the pipeline” hypothesis (aka Trenbeth’s Travesty), mentioned by several posters above. I don’t have the ref handy, or the time to find it now. Anyone?
TIA, Pete Tillman
Jim D – I have lived most of my life in the SE US and have no idea what you’re talking about .
Jim D says:
October 23, 2010 at 8:54 am
Where did I say that my numbers did not include aerosols and the rest? Take a look at the SPM? The IPCC forcing figures are from all sources of forcing, not just CO2 …
One great thing about numbers is they only work well when properly used.
Did the IPCC include flatulence from cows and bulls, that could account for the missing heat.
When arguments rigged to support theory are acceptable by authority there is no need for fundamental physical laws. It is depressing to see people with obvious ability use it in such a fashion.
A number of people have said “it’s in the ocean”, which is possible. However, some numbers in this would be appreciated, showing exactly how that might work. I have provided the IPCC estimates. If you think it is in the ocean, exactly how does that work?
And if it is in the ocean and only half of the warming has shown up in one hundred and fifty years, what does that imply for the coming century? Doesn’t that mean that the warming during that period will only be half of that predicted by the IPCC as well.
tty is wrong. The minimum in the 70’s is clearly a northern hemisphere phenomenon. Recent differences in rate of warming between the hemispheres can be explained by the larger ocean area in the southern hemisphere that has more thermal inertia. Look at the GISS temps for example.
The IPCC cherry-picked the highest forcing examples it could find, and declared them to be the global average.
Since when has that bunch ever made an honest attempt at getting an acceptable number?
old construction worker says:
October 23, 2010 at 8:15 am
“Wow. Why don’t we go back in time and “heat” our homes in the southwest using swamp cooler as “heaters”. Isn’t that what the idea of CO2 forcing and water system feedback does?
Or better yet, why not go back using swamp cooler in high humidity to cool our homes.”
steveta_uk says:
October 23, 2010 at 9:51 am
“Perhaps I’m missing something, but I’ve often wondered what is the point of error bands if everyone ignores them and assumes the ‘mean’ of ‘median’ or some other value is the ‘correct’ one.
Since the IPCC are correct (i.e. the real data is within the error bands) then the theory is OK – perhaps someone needs to work one reducing the error bands.”
I guess we don’t use swamp coolers to heat our homes because we could never figure out in advance whether they would be heating or cooling today.
Willis,
You use the same approach, over the same time period, as Schwartz did in “Why hasn’t the earth warmed as much as expected” Journal of Climate 2010.
http://www.ecd.bnl.gov/steve/pubs/SchwartzJClimate10WhyHasnt.pdf
“The current best estimate and uncertainty range of
the earth’s climate sensitivity suggest an equilibrium
increase in the earth’s global mean surface temperature
for forcing by anthropogenic long-lived greenhouse
gases of 2.1 K (range 1.5–3.2 K, roughly 1 standard deviation),
well in excess of the observed increase relative
to preindustrial times, about 0.8 K. The discrepancy is
attributed mainly to uncertainty in climate sensitivity
and/or cooling forcing by anthropogenic aerosols, also
highly uncertain; countervailing natural cooling and
thermal lag in climate response seem to be relatively
small.”
Considering there remains to be no hotspot the tropical troposphere, it would seem this is consistent with an IPCC overestimate of climate sensitivity and WV feedback.