The 'social cost of carbon' may have just gone negative

Estimates of the Social Cost of Carbon (from Jesse Jenkins, forthcoming) Values in 2012 US$ per ton CO2

Estimates of the Social Cost of Carbon (from Jesse Jenkins, for illustration purposes only Values in 2012 US$ per ton CO2

Ross McKittrick writes on his personal web page: (h/t to David L. Hagen)

I have just released a working paper with Kevin Dayaratna and David Kreutzer of the Heritage Foundation in Washington DC which recomputes standard Social Cost of Carbon (SCC) estimates using updated empirical estimates of the equilibrium climate sensitivity (ECS).

We applied the 2015 Lewis and Curry ECS distribution to the widely-used DICE and FUND Integrated Assessment Models. Previously the developers of these models (and others) have relied on model-simulated distribution of ECS values, especially from a 2007 paper by Roe and Baker. The Roe-Baker distribution underpins the US government’s current SCC values used for regulatory purposes. We critique this aspect of SCC computation, explaining why the Roe-Baker distribution is unsuitable. A major reason is that simulated ECS distributions have been superseded by a suite of empirically-estimated distributions. Using a recent, well-constrained empirical ECS distribution we find the estimated SCC drops substantially in both the DICE and FUND models, and in the latter there is a large probability it is no longer even positive.

The paper:

EMPIRICALLY-CONSTRAINED CLIMATE SENSITIVITY AND THE SOCIAL COST OF CARBON Kevin Dayaratna Heritage Foundation Washington DC Ross McKitrick Department of Economics, University of Guelph Frontier Centre for Public Policy David Kreutzer Heritage Foundation Washington DC


Integrated Assessment Models (IAMs) require parameterization of both economic and climatic processes. The latter include Ocean Heat Uptake (OHU) efficiency, which represents the rate of heat exchange between the atmosphere and the deep ocean, and Equilibrium Climate Sensitivity (ECS), or the surface temperature response to doubling of CO2 levels after adjustment of the deep ocean. Due to a lack of adequate data, OHU and ECS parameter distributions in IAMs have been based on simulations from climate models. In recent years, new and sufficiently long observational data sets have emerged to support a growing body of empirical ECS estimates, but the results have not been applied in IAMs. We incorporate a recent observational estimate of the ECS distribution conditioned on observed OHU efficiency into two widely-used IAMs. The resulting Social Cost of Carbon (SCC) estimates are much smaller than those from models based on simulated parameters. In the DICE model the average SCC falls by 30-50% depending on the discount rate, while in the FUND model the average SCC falls by over 80%. The span of estimates across discount rates also shrinks considerably, implying less sensitivity to this parameter choice”

Draft copy: Empirically-Constrained Climate Sensitivity and the Social Cost of Carbon.SSRN-id2759505 (PDF)

“Substituting an empirical ECS distribution from LC15 yields a mean 2020 SCC of $19.52, a drop of 48%. The same exercise for the FUND model yields a mean SCC estimate of $19.33 based on RB07 and $3.33 based on the LC15 parameters—an 83% decline. Furthermore the probability of a negative SCC (implying CO2 emissions are a positive externality) jumps dramatically using an empirical ECS distribution. Using the FUND model, under the RB07 parameterization at a 3% discount rate there is only about a ten percent chance of a negative SCC through 2050, but using the LC15 distribution, the probability of a negative SCC jumps to about 40%. Remarkably, replacing simulated climate sensitivity values with an empirical distribution calls into question whether CO2 is even a negative externality. The lower SCC values also cluster more closely together across difference discount rates, diminishing the importance of this parameter.”


87 thoughts on “The 'social cost of carbon' may have just gone negative

    • Great now the nonsense flows on all sides of the argument! I can’t stand any more studies good, bad or indifferent to the skeptical cause they are all ridiculous nonsense created by people with nothing but time on their hands because some stupid university or government or government created monopoly is taking or manipulating the system to take my hard earned money that should be going to my family and friends and community and spending it to pay them to make stupid nonsensical advertisement studies to boost a stupid f***ing political agenda designed to steal more of my hard earned money!!!!!! Government propped Corporate types, Academic types and Political types you are all a drain on society you should take a good long look in the mirror and ask yourselves who the f*** is paying my salary really and what do I actually do to deserve it. The every day hard working honest caring people in this world are losing all they work for because everyone else is pissing it away on total gobbledygook and nonsense. go get a real job, go build something, go start a business, go do something of value and leave the rest of us alone!

      • Not to add fuel to the fire Bob, but today is “Tax Free” day in Canada. Today is the day that after all taxes (income, sales, property, payroll, gasoline, etc) are paid, you actually get to keep what you earn. Average in Canada – 43%. But we have decent health and education. (Note I said decent, not good.)

      • Yes, Bob. Many of us feel the frustration of what often seems a losing battle. If we do not keep up with the push-back, the alarmists get everything their own way, and disaster ensues.
        The old Yankee adage of a good neighbor is the fellow who wishes to be left alone, and in turn wishes to leave others alone. If only life were so simple.
        Remember, just because you have no interest in them, does not mean they have no interest in you.
        Remember, greenies, tax-and-spend types, those who would regulate, and a whole host more, are all parasites.
        Remember, the proper response to a parasite infestation is not to shout “Leave Me Alone”, it is to reach for the insecticide.

      • So we have entered a “wordsmithing” arms race that will eventually lead to mutual assured destruction

      • How would “dethroning” the Cagw hypothesis lead to mutual destruction, do you figure, Neo? Seems to me that’s the only real hope we have to preserve even the right to wordsmith as we wish . .

      • TonyL says: June 7, 2016 at 1:07 pm
        … tax-and-spend types, …

        They’re not the dangerous ones. The dangerous ones are “don’t tax but spend like crazy anyway”.

      • Bob Boder, just so you know, this study was apparently privately funded and essentially says that CO2 is likely net beneficial.

      • David A
        I get it, but I just can’t take another study where someone lines up stuff in the good column and in the bad column and then says this one cost this much and that one saves that much and thinks they actually know anything about anything. Its ridiculous and no matter who is doing it or why, its the same crap the other side uses to justify spending my money on every ridiculous program they want. I can’t take it any more someone needs to put a stop to it and call all of these studies out as total propaganda and just because the propaganda fits in this case is for the proper side of the argument its still made up BS.

      • “don’t tax but spend like crazy anyway”.
        They are equally bad. They just destroy the economy in different ways.

      • Commie Bob
        The dangerous ones are the ones that don’t understand that taxing is inherently evil, it maybe a necessary evil but its is still evil. when you decide that the benefits of my labor belong to you or someone else you are enslaving me.
        I am not wealthy by any stretch and I have to balance everything I do so that my family is taken care of, it is getting to the point where every step I turn the system is being rig so that either the government or some government bought stooge is getting every dollar I make except for the barest minimum for my families survival. Its a rig game and no matter how much we give up things only get worse not better, somehow in less than one hundred years this country was able to rise to the point where most people could live in some for of comfort and freedom and since then we have been told we need to give more so that we can fix whats left and all we do is go backwards. I have less freedom each year, I have less disposable income each year and this sacrifice I am making is not make the world safer, the poor wealthier, the sick healthier, the oppressed less oppressed its only getting worse, but the powerful are getting more powerful and the wealthy government connect people are getting wealthier, yet if I am told all we need is a little more to fix the problem. you no how things get better? when people are in charge of their own lives and when the work I has a benefit to me and gives me a reason to get up and work hard.

      • Bob I do understand the sentiment. I happen to think that the benefits are underestimated, and the harms over estimated, even in this study. Yet time and again M and M have hurt the CAGW alarmist in their own field with facts instead of modeled speculation. From showing UHI to be under estimated, to demolishing the bad science of Mann and Gavin, and many other pro CAGW studies. neither of them gets any funds from government, and Climate Audit is as grass roots as you can get. (Big Oil being conspicuous by their absence)
        Christopher Monckton did an excellent article using the IPCCs own inflated estimate of ECS and demonstrated quite adequately that even if all the nations followed their insane demand/requests, GMT would be reduced just a fraction of a degree. Now did he give credit to the inflated IPCC ECS estimate. IMV no, as he clearly articulates its failure in the real world observations, but he demonstrates what a futile exercise the entire CAGW proponents engage in as far as climate is concerned.
        if I could not point to peer reviewed CAGW skeptical science compiled and summarized from groups like Climate Audit, the NIPCC, CO2 Science, WUWT, Poptech, etc… all grass roots organizations non big oil funded, then my small personal ability to contradict alarmists would be considerably weaker. Unfortunately combatting CAGW alarmism takes money.

      • I couldn’t agree more. The quality of these “studies” is pathetic. We are in a decline in our universities it is apparent. The attempts to redo papers in all sciences shows that fully half of papers in virtually all sciences are irreproducible. I am sure 90% of the ones in Climate Science are bogus. We need to fix this.

  1. I’ve always felt that there is no “social cost of carbon” — so, effectively zero. But the mathematics in the article’s analysis is above my pay grade. 😉

      • Simply using some basic philosophy here instead of sophistry would suggest you are right, even suggesting such a thing as “social cost” of CO2 is ludicrous. Absolutely ludicrous. It is literally proposing that life and society was better off in 1800 than it is today.
        Perhaps next, Climate Inc., will use the same sophistry to tell us the societal cost of oxygen in the atmosphere, after all, there is solid evidence that oxidation is why we ultimately become old. Stop killing Earth, reduce the oxygen! /s

      • The idiots who think there’s a cost would stand around with a hurt look on their face until they starved to death if we ever had to do without it.

      • Doug, that is, IMV, an articulate comment illustrating the mistake of linear thinking which cannot be universally applied. The benefits of CO2 are indeed fairly linear to well over 1000 PPM. The suppose failing to manifest harms of CO2 decrease exponentially with every increased CO2 molecule, yet the CAGW alarmist case is worse then that;
        The exponential decrease in CO2 to warm does not I believe account for the fact that the energy required to sustain the world one degree warmer at say 15 to 16 degrees, is much less then the energy required to increase the GMT an additional one degree from say 17 to 18 degrees. Both are a one degree increase, but the ladder takes more energy to sustain, just as your gas mileage decreases far more going from 70 to 80 MPH, then it does going from 20 to 30 MPH.

      • “It is literally proposing that life and society was better off in 1800 than it is today.”
        That is nonesense. I suggest you look it up before you comment. I cannot imagine what you are thinking, it makes so litttle sense.
        The social costs and/or benefits are simply the externalities. Do you say that there are no such things as externalities in economics? Externality is cost or benefit that is not included in the price. CO2 fertilising crops is a positive externality, since nobody decides how much to pay for fuel based on whether global greening occurs. We all get that benefit “for free”.
        You may argue that the social cost of carbon is zero, or even negative (that is there is a social benefit), but proposing that there is a social cost has no bearing at all on whether society was better of in 1800.

    • The social cost of carbon is a construct built to justify anti-CO2 policies on an economic basis. I have found that most EPA calculations that support increased regulation are technically flawed with not-on-planet-Earth assumptions as their starting point. I have since concluded they are merely window dressing so EPA can say, “See we are real scientific! We have calculations with numbers in them and everything!” Most people are not capable of understanding this and EPA ignores the rest of us.

  2. Added CO2 is worth $trillions to the economy from increased crop and forest growth. If the +1C from doubling CO2 ever shows up, that will be more $trillions in expanded habitable land, increased growing seasons and lowed heating costs. If the NW Passage ever materializes, that’s more $billions.

  3. None of this will come as a suprise to most people at this site, but to convince the rest of the world may take some doing, even if the evidence is staring them in the face.

  4. I forgot the cost savings from milder storms as the polar/equatorial heat differential is reduced. Then the is the value of increased rainfall.

  5. I predict a large number of people covering their ears an saying “LALALALALALA … I can’t hear you” in response to this paper.

  6. Activists will never admit to a positive effect of CO2 – it ruins their message. If the damage from CO2 is halved, than the excuse for green subsidies is reduced, the emergency is lessened, regulations are not needed, EPA becomes exposed as non-scientific, and of course, cats start sleeping with dogs. This can’t be happening.
    However, if a person were to consider the impacts, more food has to be positive, and all vegetation is food to something. We are raising the amount of energy available to living things. We should also be increasing the rate that carbon is being sequestered in new dirt and at the bottom of the ocean. Hmm, just like a natural cycle!

    • More food is only a positive if you don’t believe that humans are a plague and that are numbers need to be reduced.

      • They are the enlightened ones, who’s job it is to save the rest of us from ourselves.

      • Mark W, if I may rephrase,,,
        “They are the enlightened ones, who’s job it is to save the rest of THEM from ourselves.”

  7. So the government is going to pay people to breath. That is completely unprecedented! Oh Wait…

  8. In the past I’ve posted here at WUWT a couple of examples using the IPCC’s own figures showing that global warming is a net benefit for at least the next 200 years, even under the worst case model.

  9. Here’s a better way to calculate the social cost of carbon:
    Compute a dollar value for total the health, wealth, and overall well-being of the world’s population, then assign a negative value. Finally, assume any actual costs from AGW reduce this total.
    Our entire way of life exists because of energy use.

  10. Tech question here:
    Does anybody know what the absolute physical effects claimed for the “Social Cost Of Carbon” are. All I have ever seen is hand waving about “Externalities”. Does anybody know what these “Externalities” are claimed to be, such as SLR, storms, floods, drought, anything that can be objectively measured?
    {Yes, I know the whole concept is bogus, but I would like to know what is actually claimed. Note that SSC is a justification and basis for the EPAs latest round of regulations in their War On Coal. Yet they seem to have little besides “Externalities”}

  11. So has anybody “computed” the social cost of concrete? Or the social cost of steel? Or the social cost of Tarmac? Or bricks? Or the social cost of an iPhone?
    They are none of them independent, even if any of them exist in a meaningful way. Greens invented the concept of a “social cost of carbon” essentially because it helps them to get the answers they weren’t getting by traditional calculations.
    Real money is still the best measure. And for a good reason.

    • They have computed the social cost of tobacco and it’s gigantic. It continues to this day, but at a lower rate because people have reduced smoking, at least in the U.S.A.. You folks sound like the tobacco lobby, except you don’t get paid. You should send the fossil fuel industry a bill for your services.

      • I keep sending them a bill … they never pay. Maybe I should send them to collection.
        I’m guessing you might be familiar with a few good collection agencies; can you give me a few suggestions who I could use.

      • bobthebear, Does tobacco increase the growth of every crop on the planet while using the same amount of water and the same amount of land?

      • The cost of tobacco is only huge if you don’t look at the whole picture.
        The dishonest activists who came up with that number took the cost of caring for tobacco related illnesses and assigned them to tobacco. Fine and good.
        What they didn’t do was remember that everybody dies of something eventually, and whatever they would have died from also costs money. Not to mention the costs of keeping someone alive as they age slowly.
        If you are going to add the cost tobacco related illnesses, it’s only fair to include the cost savings for these now avoided costs.
        There’s also the fact that Social Security and pension funds save lots of money when people die younger.
        Like most warmistas, bobthebear is at his core, totally dishonest.

    • Social cost of concrete:
      Social costs of road surfacing. Not quite tarmac, but related.
      I think someone has probably done iphones.
      “Real money is still the best measure. And for a good reason.” Real money is a very poor way to measure social costs. This is because social costs are defined as being outside the “real money” part of the transactions.
      The road surfacing paper is a good example. The social cost of re-surfacing is partly increased travel time for drivers. This would not be included in any “real money” measure of surfacing costs.

  12. Now all you’ve got to do is convince Climate Community that some of their more outlandish ECS estimates should be discarded. They don’t tend to do “empirical” :-).

    • Not at all. If the cost of something is unclear but essentially zero, one would expect a distribution that spans from small negative values to small positive values.

  13. How about the social costs of the entire CAGW fiasco? Those would be astronomical.

    • Yeah, just look at what a few little lies by the Climate Change Gurus have done to the world. Small input, huge effect.

  14. When I rule the world …
    Countries that make use of inventions, technology and developments that were pioneered in the west by processes that gave rise to CO2 should be required to make offsetting payments back to me.
    Currently, others are benefitting from things like cars and computers but the “social cost of carbon” all falls to us.

  15. I wonder if the same reasoning could be applied to cows farting. In my country they are trying to stop cows from releasing methane in this untoward manner! Trouble is that humans fart also, possible from eating beef so the culprit is clearly identified.
    But if it is a positive for the emissions producer, why we could have farting parties or windy pubs which may even pay for the beer.

  16. Social cost of carbon estimation is computer-aided sophistry. Its political function is to persuade the gullible that fossil fuels are unaffordable now matter how cheap, and renewables a bargain at any price:
    So I can understand Bob Boder’s frustration. If I catch his drift, he’s saying that quarreling over SCC values implicitly concedes the validity of SCC analysis, whereas the entire enterprise is hogwash.
    But as a practical matter, some people won’t be persuaded it’s junk until they see what happens with the same models are run with more realistic alternative assumptions. That’s what Ross, David, and Kevin do here.

    • Social cost analysis is the basis of all policy decisions: You have to know if it is worthwhile spending money on a new road (for example) based on the the number of lives saved, the number of minutes shaved off a journey time, the reduction of fuel used etc. compared to the cost of the road, the increase in traffic and whatever else you can think of. Applying this to CO2 in the atmosphere is the only way policy makers can make any decision which can be justified under cross examination.
      Now, you can say that the current level of knowledge about the social cost of CO2 in the atmosphere is so pathetic that the answer is meaningless (and many here would agree), but the process is the only thing policy makers have to go on and if you don’t question the alarmist figures then you cannot argue against the policies that are being put forward.
      CAGW is a political issue and has to be fought with political weapons. A social cost analysis is the weapon that brings this issue down to where politicians can understand what it is all about (dollars).

      • the reduction of fuel used etc. compared to the cost of the road
        the social cost of carbon does not include the trillions of dollars in increased worldwide food supply due to 15% increase in plant growth. that single figure alone would dwarf all others.

      • It is all political.
        Cost/benefit analysis of roads is also political. If “we” want the road (because the congestion is obvious to the majority) then the wetland impacts are acceptable. If “we” don’t want the road (because of “urban sprawl”) then the deaths over the next 20 years on the 2-lane crap highway are ignored and the wetland loss is deemed unacceptable.
        Social cost analysis is too easily manipulated. The only way to win with respect CAGW hysteria is to make the direct costs obvious to the masses. But It is tough to make the (future) direct costs of losing carbon based energy sources obvious to the idiots. It is easy to frighten them with predictions of indirect cost predictions.

  17. The “Social Cost of Carbon” is another Orwellian neologism implying all the usual assumptions — carbon pollution instead of CO2 being the climate ‘control knob’ etc. — they must have teams of cognitive psychologists working full-time on this stuff.
    If there is a social cost of carbon, meaning the IPCC RCP8.5 temperature prediction, then it follows there are social benefits to falling global temperatures although I can’t imagine what they might be.

  18. The social costs of high CO2 may be incalculably beneficial. Flowering plants only evolved when CO2 levels were 4X higher than they are today. The argument can be made that our plants today are CO2 starved. No plants, no food. What is the social cost of mass starvation?

  19. The quickest way to calculate the social cost of carbon is to turn off all fossil fuel usage and see how much better off you are. The difference before and after is the social cost of carbon.
    Does anyone seriously believe that for example, we turned off all gasoline and diesel supplies in the US that the US would benefit? Well according to the EPA millions of lives would be saved without the dangerous CO2 that fossil fuels emit. So it stands to reason that the death rate in the US would drop dramatically if gasoline and diesel supplies were cut off.
    So why doesn’t Obama outlaw gasoline and diesel if the Terror Formerly Known as Global Warming is such a threat? What about the millions of Coal Black Lives lost as a result? Don’t they matter?

  20. The best part of this is the terminology. If we say that the social cost of carbon is negative, wouldn’t it be better to say that the social benefit of carbon is positive? Love to see the cagw panic community digest that.

  21. That has been my thought all along. Increased crop yields, less (% wise) cold mortality, less heating costs, less winter-related expenses, etc, etc. IF those things were actually occurring (certainly the crop increase has).

  22. Seriously, the “social cost of carbon”?
    Carbon can be very expensive especially when it’s in the form of diamonds.
    The cost of carbon dioxide is nada. Anyone that tries to tell me there’s a social cost for exhaling can stick their papers in a place where there’s minimal solar radiation 🙂
    These arguments (on both sides of the fence) are just plain silly!

  23. A 40% chance CO2 ‘harm’ is negative is more than the 38% confidence Gavin has that 2015 was the warmest year evah.

  24. Horrible, nasty carbon. Maybe instead of decrying it, teachers should start by telling young students that around 18% of our bodies are comprised of the stuff (second only to oxygen). Then go on and tell them how much is in the natural world around us. It is even safe as a drinking water filter. Mind, the majority of adults probably do not know this either. So many are so blind to the latest paradigm to which they flock in droves

  25. Yesterday, here in the UK, I switched on the BBC radio service, Radio 4 for just two minutes.
    A woman was being allowed to explain how in Rajastan, people were dying in the extreme heat whilst they suffered from dismally unreliable electricity supply of as little as 2 hours per day.
    The proposed solution?
    YES, you guessed it. Her organization was going to assist in providing Rajastanis with, in here words, “access to clean energy” in the form of solar panel, batteries and inverters.
    Here in the UK, the propaganda and brainwashing program is now so all encompassing and so persistent that black is white and night is day – and the problems of access of the world’s poor to reliable energy can be solved by providing them with access to more expensive and more unreliable energy.
    In the minds of the useful idiots, all of the third world should be targeted with expensive unreliable energy.
    Meanwhile for the same useful idiots – big hydro should be obstructed by all possible means.
    Because, whilst clean – it is too cheap and too reliable – I suppose.
    The environmental movements and third world aid movements may have started out with good intentions.
    They have seemingly since morphed into a force for foolish, destructive and wasteful cruelty.
    These monsters and their agenda must be halted before they can do any more damage.
    (P.S. I am always puzzled by the contention that providing households in the third world with millions of lead acid batteries is a promotion of “clean energy”. Doesn’t the title hold some clues – lead and acid? AND, does it never occur to these NGO/eco warrior idiots that household in india already have access to lead-acid batteries and a vast range of cheap UPS and inverter technologies, since they have been living with unreliable power provision for decades. In my experience indian villagers know more about inverters, UPS and AVR technology than the average westerner. They also know more about diesel generators. Which they use. Especially after dark. Because diesel works out cheaper than battery storage in most situations.)

    • IF Rajastan has a poor electric distribution system because of government corruption or rebellion, off-the-grid solutions like solar panels and inverters are a good plan. It isn’t the most efficient plan, but it may be the only plan available in that POLITICAL environment. Remember ALL of this garbage is about politics and one of the chief tools of politics is conflating unrelated cause and effect to create alarm and clamoring for safety amongst the citizenry to increase the power and importance of the politician.
      If there is a stable government, the charities would be far better off investing in the expansion of the electric grid. Of course the problem in that is it is harder to connect the photo of a child to the expansion of the grid in a fund-raising campaign, and since most of the big charities are better termed big fund-raising organizations (not necessarily good at effective distribution in a way the really helps people – after all if there were no victims out there, there would be no fund-raising efforts to skim 40% off the top of!)

      • I see what you are saying. But we are not talking about Afghanistan.
        The only problem is that the govt. has not ramped up the supply side to keep up with demand.
        Instead they waffle on about piecemeal clean energy solutions.
        They do have nuclear and coal and a grasp of how to operate a grid.
        They just need more supply, because there are more people using more energy.
        Powercuts are not the correct answer to rising demand.
        And personal batteries and inverters are just about the most expensive approach in the grand scheme of things.

  26. ever heard about
    thesis, antithesis and synthesis.
    – thesis: yes CO2 is bad.
    – antithesis – no, think of CO2 advantages.
    – synthesis – move along , nothing with CO2 here.

  27. The Government of Ontario is releasing its climate action plan today. Does anyone know if McKitrick’s SCC paper had any influence?
    Stupid question of course, In Canada if you are not on board with the AGW “scare” narrative you are politically irrelevant.
    As always, we live in interesting times.

  28. Temperature drives CO2 and water vapour concentrations and evaporative and convective cooling independently. The whole CAGW – GHG scare is based on the obvious fallacy of putting the effect before the cause. Unless the range and causes of natural variation, as seen in the natural temperature quasi-periodicities, are known within reasonably narrow limits it is simply not possible to even begin to estimate the effect of anthropogenic CO2 on climate. In fact, the IPCC recognizes this point.
    In plain English, this means that the IPCC contributors have no idea what the climate sensitivity is. Therefore, there is no credible basis for the WG 2 and 3 reports, and the Government policy makers have no empirical scientific basis for the entire UNFCCC process and their economically destructive climate and energy policies.
    The whole idea of a climate sensitivity to CO2 (i.e., that we could dial up a chosen temperature by setting CO2 levels at some calculated level) is simply bizarre because the response of the temperature to Anthropogenic CO2 is simply not a constant, and will vary depending, as it does, on the state of the system as a whole at the time of the CO2 introduction.
    In fact, the range of outcomes depend almost entirely simply on the RCPs chosen. The RCPs depend on little more than fanciful speculations by economists. The principal component in the RCPs is whatever population forecast/speculation will best support the climate and energy policies of the IPCCs client Western governments. This entirely imaginary exercise is then further removed from reality by the use of whatever discount rate will produce a SCC appropriate to the needs on the governments funding the study – as in the Stern reports’ mystical musings .
    For a more complete discussion see

  29. I sent an email to the three authors of this study on May 12, 2016. Most of it is copied below:
    I have reviewed your paper “EMPIRICALLY-CONSTRAINED CLIMATE SENSITIVITY AND THE SOCIAL COST OF CARBON” here. Your study uses estimates of equilibrium climate sensitivity (ECS) from a paper “Lewis and Curry 2015” (LC15) and the two Integrated Assessment Models (IAM) DICE and FUND to calculate new estimates of the Social Cost/Benefit of Carbon (SCC).
    I agree that the ECS estimates used by the IWG are far too high and should be based on a realistic empirically based estimate. However, I find your paper deficient on account of the following four reasons;
    1. The use of the DICE model is inappropriate because that model fails to account for the CO2 fertilization effect and it assumes that the optimum climate for humanity was the pre-industrial climate of 1900, which was near the end of the Little Ice Age. CO2 fertilization is an known physical effect documented by thousands of published papers. The failure to account for this important effect disqualifies this model for consideration in the calculation of social cost/benefit of greenhouse gas emissions. Testimony by Dr. Mendelsohn shows that there is no evidence that the temperature increase since 1900 caused any damages, and such damages would be easily detectable. The model does not include most benefits of warming, which should disqualify the use of it. The DICE model produces future sea level rise values that far exceed mainstream projections and exceed even the highest end of the projected sea level rise by the year 2300 as reported in the AR5 report. Your paper should not include the DICE model. The FUND model is the only IAM that should be used to determine a SCC.
    2. The climate sensitivity estimated in LC15 is too high for three reasons giving estimates of SCC that are too high. A study by Nic Lewis used new estimates of aerosol forcing. Nicholas Lewis writes, “a compelling new paper by Bjorn Stevens estimating aerosol forcing using multiple physically-based, observationally-constrained approaches is a game changer.” Using the new aerosol estimate reduces the mean estimate of ECS from 1.64 to 1.45 ºC. By failing to use the best and most current aerosol forcing estimates you have overestimated climate sensitivity.
    3. Dr. Ross McKitrick with Steve McIntyre published excellent papers that broke the “hockey stick” and restored the Medieval Warm Period and Little Ice Age natural temperature variability to history. Numerous peer reviewed papers show the large natural millennium scale climate cycle. It is indefensible to ignore natural climate change due to the millennium cycle. Climatologist Dr. Richard Lindzen writes, “Lewis does not take account of natural variability, and, I suspect, his estimates are high.”
    4. The HadCRUT4 temperature index used in LC15 is contaminated by the urban heat island effect (UHIE), and this effect must be subtracted from the recorded temperature change to determine the effect of greenhouse gases. Numerous studies show the this UHIE contamination, most notably, McKitrick and Michaels 2004 and McKitrick and Michaels 2007. Correcting for the effects of points 2, 3 and 4 reduces the ESC to 1.02 ºC as shown in my report.
    Applying the four corrections listed above would reduce the SCC best estimate to -$16.6/tCO2. The likely range is -19.3 to -11.5 US$/tCO2, and it is extremely likely to be less than -4.3 US$/tCO2. The benefits of CO2 fertilization, reduced cold weather related mortality, lower outdoor industry costs such as construction costs, increased arable land area and reduced heating costs greatly exceed harmful effects of warming on a global basis. High and improbable values of the SCC as reported by you and others may lead to very damaging policy decisions as evidenced by the Alberta climate change plan. [Note, the values of SCC in this paragraph were updated to those in my revised paper at the link above. The previous best estimate of SCC was -$17.7tCO2 as reported on WUWT on May 21.]

  30. Of course the SCC is negative. That is what a net benefit looks like. Boy would that screw up the EPA clean power plan!!!
    Just reference the recent papers of greening of the Earth and rising crop yields, and then think about power blackouts, and it all becomes clear.

  31. I have a nice idea that I believe everyone will hate. Think it through before trashing it. I won’t really care. I very seldom come back to posts.
    We should produce 6 months to a full year of MREs, or some other non-perishable rations, in sufficient quantity to feed the entire US population for that period. Add 10% for incidentals. Tell everyone far ahead what will happen. Then, on a specified day at a specified time (you know D-day, H-hour, M-minute) all coal-fired, natural gas, and nuclear powerplants would be shut down and mothballed for that 6 month to 1 year period. Everyone would have time to stock up on rations, bottled water, essential meds for the chronically ill, etc. The only electrical generation allowed for that time would be renewables. NOTHING else. Give them their chance to show what they can do in the real world. And give the Greens what they claim to want. When the time was up, bring the power back, unless the people don’t want it any longer.
    I figure there would be riots to get the power back on after about 2 days. All the “progressives” and “Greens” would be going insane without their smart phones by that time. If you doubt me, have you never seen one of them misplace their phone? I watched a guy leave work solely because he forgot to charge his phone the night before. 2 hours without it and he was starting to fray at the edges.
    I know. It’s a bad idea. BUT, if we tried it and advertised that we were going to give them what they say they want, no one would support their agenda for generations.
    A little bit /sarc, but I bet not nearly as much as you think. Enjoy!

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