Climate Sensitivity Estimates Trending Down? Less Future Warming?

How much the globe will warm depends crucially on how sensitive the climate is to additional atmospheric concentrations of greenhouse gases, chiefly carbon dioxide emitted from burning fossil fuels. As I explained elsewhere:

The term climate sensitivity conventionally refers to how much warming can be expected from a doubling of carbon dioxide concentrations in the atmosphere...

With regard to climate sensitivity, in 2007 the Fourth Assessment Report of the United Nation’s Intergovernmental Panel on Climate Change (IPCC) estimated that “climate sensitivity is likely to be in the range of 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.” In IPCC parlance, likely means that there is a 66 percent probability that climate sensitivity falls between 2 and 4.5°C (3.6 to 8.1°F), with 3°C (5.4°F) as the best estimate.

Some researchers suggest that temperatures could in fact rise well beyond the IPCC's best estimates by more than 6 degrees Celsius (13 degrees Fahrenheit).

Over at the New York Times' excellent DotEarth blog, science reporter Andrew Revkin rounds up a bunch of recent studies that suggest that climate sensitivity is somewhat less than the IPCC's old estimate. In his post, "A Closer Look at Moderating Views on Climate Sensitivity," Revkin reports that for this ...

...one critically important metric — how hot the planet will get from a doubling of the pre-industrial concentration of greenhouse gases, a k a “climate sensitivity” — some climate researchers with substantial publication records are shifting toward the lower end of the warming spectrum....

But while plenty of other climate scientists hold firm to the idea that the full range of possible outcomes, including a disruptively dangerous warming of more than 4.5 degrees C. (8 degrees F.), remain in play, it’s getting harder to see why the high-end projections are given much weight.

This is also not a “single-study syndrome” situation, where one outlier research paper is used to cast doubt on a bigger body of work — as Skeptical Science asserted over the weekend. That post focused on the as-yet-unpublished paper finding lower sensitivity that was inadvisedly promoted recently by the Research Council of Norway.

In fact, there is an accumulating body of reviewed, published research shaving away the high end of the range of possible warming estimates from doubled carbon dioxide levels. Chief among climate scientists critical of the high-sensitivity holdouts is James Annan, an experienced climate modeler based in Japan who contributed to the 2007 science report from the Intergovernmental Panel on Climate Change.

Apparently, the best estimate of climate sensitivity is converging on a value a bit less than 2 degrees Celsius.

Revkin makes it clear that he nevertheless believes that even if truly catastrophic future warming can be ruled out that humanity should still make the transition to a low-carbon and no-carbon energy future to mitigate warming consequences like sea level rise, shifting weather patterns, and ocean acidification. He ends by observing:

I can understand why some climate campaigners, writers and scientists don’t want to focus on any science hinting that there might be a bit more time to make this profound energy transition. (There’s also reluctance, I’m sure, because the recent work is trending toward the published low sensitivity findings from a decade ago from climate scientists best known for their relationships with libertarian groups.)

Nonetheless, the science is what the science is.

Yes, it is.

For more background see my column, "The Sky is Falling Less?" and my post, "Man-Made Warming Likely Benign, Reports WSJ Columnist Matt Ridley."

Update: Revkin asks me to alert H&R readers to go click over to his post for an addendum response from the RealClimate folks.

Editor's Note: We invite comments and request that they be civil and on-topic. We do not moderate or assume any responsibility for comments, which are owned by the readers who post them. Comments do not represent the views of Reason.com or Reason Foundation. We reserve the right to delete any comment for any reason at any time. Report abuses.

  • R C Dean||

    it’s getting harder to see why the high-end projections are given much weight.

    No, it's really not.

  • Russell||

    It is hard to know the quantitative truth because climate sensitivity to CO2 has been a moving target since the Victorian era.

    In 2008 I collated this running account of the dozens of bona fide estimates that have appeared in the peer reviewed literature since 1896 ,

    http://adamant.typepad.com/sei.....-fear.html

    I invite Ron to add the latest published estimates to it , and tell us where ,in their light he thinks the trend may lie-- it isn't exactly a convergent series.

    Getting it to converge on a single , uncontroversial value may be the most serious climate science challenge extant.

  • ||

    And the slow backing away from the bullshit begins. How long did it take Rachael Carson or the Population Bomb people to weasel out of responsibility for being utterly fucking wrong?

    Oh wait, they never had to, because they've never been held to account for being so wrong they should be laughingstocks. I'm sure the same will apply here.

  • Cytotoxic||

    We can make their lives harder. We already did ex CRU leaks. We have the technology.

  • tarran||

    Remember the famines and rioting Erlich predicted? The dork is still feted despite being utterly wrong because he was saying what people wanted to hear.

    Same deal here.

  • Brett L||

    I don't know. I stopped taking Erlich seriously long ago. Others on that list include Michael Mann and Hanson from NASA. Those are the three off the top of my head that I am personally sure are more interested in putting their reputation ahead of good science.

  • Ron Bailey||

    E: Carson and Ehrlich have too both been held to account.

  • Rasilio||

    Sorry Ron, Carson should be in held up there next Stalin and Mao as one of the worst Mass Murderers in History, a single negative article in a not very well read magazin hardly counts as holding her to account.

  • Ron Bailey||

    R: "Not very well read" - ouch!

  • robc||

    Compared to, say, Playboy.

  • Tulpa (LAOL-PA)||

    How on earth does Playboy survive in the age of ubiquitous net.pr0n?

  • BakedPenguin||

    By having exceptionally hot chicks?

  • Rasilio||

    Because stopped being primarily an outlet for Porn long before the internet.

    I mean seriously, someone who was looking for porn in the 80's, would they be buying Playboy or something with a LOT more porn in it like Penthouse or Hustler?

    Meaning that by 1980 if anyone told you they read Playboy for the articles they were probably telling the truth.

  • Rasilio||

    Well it's not like I have EVER walked into a waiting room of any sort and found a copy laying around and most of my non libertarian friends have never even heard of it, the few who have are occupy types who just dismiss it as a wing of the Kochtopuss.

    I mean I'd LOVE it if you guys had a bigger circulation but it just isn't there.

  • Tulpa (LAOL-PA)||

    Every prediction of doom eventually turns out to be false.... except the last one. The question is, is this the last one.

  • Homple||

    No. Apocalyptic raving has gone on for centuries and will continue as long as human gullibility.

  • Paul.||

    It'll certainly go on until the first apocalyptic event.

  • robc||

    Not entirely true. Some predictions of doom are more localized, like say Obadiah's prediction of the destruction of Sela.

  • Concerned Citizen||

    100 years of burning fossil fuels can fuck up a 4 billion year old planet? And the only solution is more gov't?

  • Homple||

    To the Manns, Ehrlichs, Club-of-Rome hucksters and the like, more government is the solution to everything.

    Most of all, the solution for getting a chance to push the rest of us around.

  • Canman||

    Mann has a blurb by Ehrlich on his book's jacket and in it he calls Ehrlich a personal hero.

  • Paul.||

    And yet liberals keep telling me that everything I have is because of government. My SUV, my fossil fuels, my Roadz...

  • Tulpa (LAOL-PA)||

    It may well be that backing off the high-end numbers actually makes people more likely to work to cut emissions.

    As long as the AGW-asserters are saying we have to lower CO2 emissions to 1850 levels or the planet will become Venus, most people aren't going to bother, because there's simply no way to achieve that goal. If they just come out and say, look, just don't increase emissions above where they are now, THAT's doable, as developed nations can decrease their emissions to make up for developing nations' increases.

  • Overt||

    No.

    1) The constant downward revisions of climate sensitivity should give people more and more faith that the original claims of catastrophe were overblown. This has happened many times in history when scientists have reported findings based on flawed data, and it took a lot of scientists time to converge on the real value.

    2) There is no way that we can reduce our emissions enough to allow the developing world to grow and maintain planetary levels. China exceeds the US emissions with per capita income a fraction of ourse. 300 million people in the US cannot cut emissions enough to allow 4 billion developing citizens to continue emitting. Peoples' inability to grasp these basic facts is what makes this climate debate go on.

  • BlueBook||

    Meh, the machines will be taking over around 2045, I doubt a few extra degrees will make much difference to their liquid nitrogen cooled computronium minds.

  • Tulpa (LAOL-PA)||

    Anyone else getting malware warnings about this page? I just got one from Chrome about something from cmi.netseeker.com.

  • Homple||

    Earlier this morning, Firefox warned me about a Breitbart page being an attack site.

    I expect progressives have found a new way to foster information sharing and debate.

  • ||

    I got that from Sloopy's link to Breibart last night, but from Crome.

  • ||

    *Chrome

  • Cytotoxic||

    I got that at Breitbart.

  • Loki||

    There’s also reluctance, I’m sure, because the recent work is trending toward the published low sensitivity findings from a decade ago from climate scientists best known for their relationships with libertarian groups.

    OH NOS!!!! TEH KOCHTOPUS!!!1111!!!!1

  • tarran||

    The Gavin Schimdt response is telling... He essentially is saying "hey, we never peddled the 20ft sea rise in a decade bullshit - the numbers are areound what we've always said they would be"

    Of course, this is mendacious horseshit. His masters at Fenton Communications *have* been scaremongering and he's been keeping quiet because there is so much money at stake. Oh sure, the rewriting of history he's attempting is not at a Skeptical Science Credulous Superstitions level of dishonesty, but he is being intentionally deceptive none-the-less.

  • Ron Bailey||

    t: He also misstates Ridley's view (Schmidt says it's 1.0 degree Celsius). Actually Ridley thinks that climate sensitivity hovers around 1.6 - 1.7 degrees Celsius.

  • ||

    Ron, you heard anything about the leaked report (supposedly from the UN) that up to 25% of the post industrial warming is because of solar activity?

    Supposedly buried in Chapter 11 of said report. Didn't catch the official title.

  • Raston Bot||

    Al Gore showed a map of the US at night and the fracking flareoffs in North Dakota were nearly as bright as Chicago. Therefore fracking is harming the environment.

  • ||

    I saw that. He also said Sandy was caused by AGW.

    That man's credibility is shot.

  • Ron Bailey||

    FdA: See this Fox News piece:

    Some skeptical climatologists say that the statement in the U.N. draft report is important, but not game-changing.

    “The solar component is real but not of sufficient magnitude to have driven most of the warming of the late 20th century,” Pat Michaels, the former president of the American Association of State Climatologists, and current director of the Center for the Study of Science at the Cato Institute, told FoxNews.com.

  • ||

    thx

  • Raston Bot||

    Oyster lovers want to hear more about this ocean acidification stuff.

GET REASON MAGAZINE

Get Reason's print or digital edition before it’s posted online

  • Progressive Puritans: From e-cigs to sex classifieds, the once transgressive left wants to criminalize fun.
  • Port Authoritarians: Chris Christie’s Bridgegate scandal
  • The Menace of Secret Government: Obama’s proposed intelligence reforms don’t safeguard civil liberties

SUBSCRIBE

advertisement