Sensitive to sensitivity at WUWT

The latest article at Anthony Watts' denier blog is about climate sensitivity. (Archived here.)

The author is Jeff L., which I guess means that he is only half an "anonymous coward" by Anthony's standards and is therefore half okay. The half that Anthony is okay with, when it comes to Anonymous Cowards.  The Anonymous half.

Jeff wrote about how he went about estimating what he thought was the equilibrium climate sensitivity (ECS). It wasn't.  He was estimating transient climate response.

Some definitions from IPCC AR5:

Climate sensitivity In IPCC reports, equilibrium climate sensitivity (units: °C) refers to the equilibrium (steady state) change in the annual global mean surface temperature following a doubling of the atmospheric equivalent carbon dioxide concentration. Due to computational constraints, the equilibrium climate sensitivity in a climate model is sometimes estimated by running an atmospheric general circulation model coupled to a mixed-layer ocean model, because equilibrium climate sensitivity is largely determined by atmospheric processes. Efficient models can be run to equilibrium with a dynamic ocean. The climate
sensitivity parameter (units: °C (W m–2)–1) refers to the equilibrium change in the annual global mean surface temperature following a unit change in radiative forcing.

The effective climate sensitivity (units: °C) is an estimate of the global mean surface temperature response to doubled carbon dioxide concentration that is evaluated from model output or observations for evolving nonequilibrium conditions. It is a measure of the strengths of the climate feedbacks at a particular time and may vary with forcing history and climate state, and therefore may differ from equilibrium climate sensitivity.

The transient climate response (units: °C) is the change in the global mean surface temperature, averaged over a 20-year period, centred at the time of atmospheric carbon dioxide doubling, in a climate model simulation in which CO2 increases at 1% yr–1. It is a measure of the strength and rapidity of the surface temperature response to greenhouse gas forcing.

Jeff claimed he came up with a number that was less than the IPCC estimate.  He didn't.  His number was slap bang in the middle of the IPCC estimate.

Read on.

What Jeff L. did was take the HadCRUT4 surface temperature anomaly and the CO2 record.  He spliced the Law Dome CO2 measures to the Mauna Loa record to get a series back to 1850.

Then he created a bunch of temperature plots using the equation:

 ∆T = ECS* ln(C2/C1)) / ln(2)

where :

∆T = Change in temperature, ° C

ECS = Equilibrium Climate Sensitivity , ° C /doubling

C1 = CO2 concentration (PPM) at time 1

C2 = CO2 concentration (PPM) at time 2

He did this at intervals of one year. He plotted the resulting temperature anomalies on a chart together with HadCRUT4. Here is his result:

Source: WUWT



Based on the above and, after discussing and doing some "goodness of fit" calculations on each of the "ECS" plots, Jeff settled on what he called an "ECS" of 1.8°C.

It's a simplistic approach but it's got some appeal as a quick and dirty estimate.  (An even simpler approach using Jeff's numbers and formula, would be to say that temperature rose by 0.86°C, with a 40% rise in CO2, which also gives the result as 1.8°C.)

However there are a few wrinkles.  Most of these will be obvious to the reader.



Transient climate response and equilibrium climate sensitivity

Firstly, Jeff L. isn't calculating equilibrium climate sensitivity because he hasn't allowed time for the earth system to reach equilibrium. Not even short term equilibrium.  He is attempting to calculate the transient climate response. The surface temperature at the time of CO2 doubling.

To my way of thinking that's the biggest thing wrong with what he's written.  As a rough estimate and making assumptions that other forcing are negligible, you could argue that it's okay.  Especially when you compare it to other estimates - it's in the ball park.

Other forcings in the first half of the twentieth century aren't negligible though, particularly the rise in solar radiation and pollution.  And it's likely that some forcings in more recent years aren't negligible either. I'm thinking about the drop in solar radiation and pollution (aerosol forcing).  But as long as you aren't wanting any more than a rough estimate, it's okay.

The IPCC AR5 WG1 report states:

With high confidence the transient climate response (TCR) is positive, likely in the range 1°C to 2.5ºC and extremely unlikely greater than 3°C, based on observed climate change and climate models (see TFE.6 for further details).

So, despite what Jeff claims to the contrary (see below), Jeff's number is slap bang in the middle of the IPCC estimate.

If you read his article, you'll see he's made other assumptions as well as misrepresented the IPCC report.

For example, Jeff reported that the AR5 report estimated ECS as 3.4°C. In fact the IPCC estimate is that ECS is "likely" between 1.5°C and 4.5°C, while not giving a "best estimate", unlike previous reports.  But as I've just said, Jeff didn't work out the ECS.  He worked out the transient climate response and got an estimate in the middle of the IPCC estimate.

Another thing.  Being WUWT it's no surprise that Jeff divides people into "alarmists" and "sceptics". Early on he writes:

All potential “catastrophic” consequences are based on one key assumption: High ECS (generally > 3.0 ° C/ doubling of CO2). Without high sensitivity, there will not be large temperature changes and there will not be catastrophic consequences. As such, this is essentially the crux of the argument : if sensitivity is not high, all the “catastrophic” and destructive effects hypothesized will not happen. One could argue this makes ECS the most fundamental quantity to be understood.

 Jeff is wrong in a number of ways.  For one thing, the consequences depend on the amount of emissions as well as on climate sensitivity.  If sensitivity were, say, 2°C but we ended up with four times the amount of pre-industrial atmospheric CO2, then temperatures would rise by 4°C.  This would have very big consequences and is a huge risk to take.  If sensitivity were 4°C and we quadrupled CO2, then we'd be looking at a rise of 8°C.  That would render a lot of currently inhabited land uninhabitable.


Thing is, for safety's sake we've got to keep total emissions under 1,000 gigatonnes of carbon.  We're almost halfway there already and annual emissions are increasing each year.  Some people argue that 1,000 gigatonnes will take us above the safe level.

Adapted from Figure SPM.10: Global mean surface temperature increase as a function of cumulative total global CO2 emissions from various lines of evidence. Source: IPCC AR5 WG1 Summary for Policy Makers

Jumping to wrong conclusions for all the wrong reasons

You'll not be surprised to read Jeff's conclusion because it's probably the whole reason for his article.  He wrote in part:

Furthermore and most importantly, any policy changes designed to curb “climate change” are also unsupportable based on the data. It is assumed that the need for these policies is because of potential future catastrophic effects of CO2 but that is predicated on the high ECS values of the IPCC.

Most deniers don't want to shift to clean energy.  Whether it's because they fear change or because they know it requires actions by governments and changes in some industries it all boils down to the same thing. They just don't want change and will fudge and misrepresent evidence and reject science to try to justify their stance.

From the WUWT comments

There was a mixed reaction at WUWT.  There were people who said, variously:

• Jeff's workings were wrong
• Jeff is right and the science is wrong  
• HadCRUT4 isn't reliable
• The physics of CO2 is wrong so Jeff's work is meaningless
• Jeff needs to compute things in a different way
• Law Dome CO2 data is faked
• James Hansen has used paleo data to estimate ECS
• James Hansen hasn't used paleo data to estimate ECS
• The rise in CO2 is caused by warming, it doesn't cause warming
• There is no warming
• It's all too hard and there are too many unknowns so we shouldn't even try to understand climate
• It's cycles
• The pause proves that climate sensitivity is low
• Temperature is caused by gravity
• Everybody is wrong about everything
• Jeff is right and has proved we don't have to cut CO2 emissions and that climate science is a giant hoax committed on we, the sheeple, by greenie, nazi, Lysenkoist, commie, warmist, alarmist, eco-tard, cultist, watermelons. So there.

Okay, I threw in the last one myself :)  It's the sort of thing you'll read any day of the week on denier blogs.

Here is a sample of comments from the archived article.


Alex Hamilton says (excerpt):

February 13, 2014 at 3:13 pm
Continuing from my comment at 2:16pm, the inevitable conclusion is that it is not greenhouse gases that are raising the surface temperature by 33 degrees or whatever, but the fact that the thermal profile is already established by the force of gravity acting at the molecular level on all solids, liquids and gases. So the “lapse rate” is already there, and indeed we see it in the atmospheres of other planets as well, even where no significant solar radiation penetrates.

cnxtim says:

February 13, 2014 at 2:22 pm
The simple fact is this; warmists believe that traces of CO2 generated at ground level by the burning of so called “fossil fuels” make the implausible journey to the upper atmosphere and cause CAGW – they have NO other position whatsoever, and since despite their mantra and models, recent GW has ceased for 17.5 years, they have NO position whatsoever.
Case proven and closed, time to get a real job and stop wasting the taxpayers money!

albertalad says:

February 13, 2014 at 2:42 pm
I always suspect calculations based on 100 plus years which eliminates the historical earth climate. Other warm periods in time plus the various ice ages. However I do understand in the AGW camp CO2 as THE factor. What I don’t get is why we always fall into the AGW trap and only concentrate what the AGW camp wants us to talk about, CO2. Something melted each ice age long before man ever existed. I know, I know – trying to prove man is entirely responsible is the buzz words. With respect – I don’t trust any temperature massaged so many times none of us know what real temperature were or supposed to be anymore. Even the different data collected by different device cannot agree with each other and have to be massaged.

Dr Burns says:

February 13, 2014 at 2:53 pm
Here’s Siple vs Mauna Loa. I wouldn’t be surprised if Law Dome has also been faked.

Dr Burns says:

February 13, 2014 at 2:55 pm
The article ignors the fact that CO2 changes are a result of warming rather than a cause.

Stevek says:

February 13, 2014 at 3:09 pm
The most significant evidence we have of low sensitivity is the pause. The alarmist need the heat to be in the ocean. They need it or they know it is game over.
If we have perfect measurements from satellites of the input and output heat radiation budget then we will know if heat is in ocean.
My guess is that there is a big negative feedback mechanism we do not fully understand. There is some type of release valve , throttle as Willis says. It has to do with water cycle or wind in my opinion.

Leonard Lane says (excerpt):

February 13, 2014 at 4:29 pm
Thank you for your research and publication.

I feel that if the HADCRUT, and other temperature records, including the satellite data, have been so grossly adjusted to reduce warming periods before CO2 started its rapid increase and to increase warming as the atmospheric CO2 levels increased, that they are false. This dishonest and criminal tampering with the data to suggest global warming that just never happened means that accurate and true measured temperature to compute global temperature simply do not exist.

Thus, we have no measured data to compare with modeling results. Unless something like another little ice age (which I hope does not occur) cools to the extent that future data cannot be adjusted upward without it being obviously and criminally altered, then we are stuck with adjusted data.