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Long-term warming, short-term variability: why climate change is still an issue

A new study published today suggests that the short-term warming due to increasing greenhouse gases may be less than previously feared. However, when we look at the bigger picture, we still find that climate…

Warming may be slower than we expected, but it’s still happening. Marc Samson

A new study published today suggests that the short-term warming due to increasing greenhouse gases may be less than previously feared. However, when we look at the bigger picture, we still find that climate change is an issue that demands our attention.

The new work by Alexander Otto of Oxford University and colleagues, published in the journal Nature Geoscience, uses observations of surface temperature and Earth’s heat budget spanning the last 40 years. This differs from many previous studies, which have been based on computer models of the climate system.

The sensitivity of our planet to a doubling of the atmospheric carbon dioxide concentration can be expressed using two different measures. One measure, the transient climate response, describes the immediate, short-term warming. This figure is the one that really matters to policy makers. The other measure, the equilibrium climate sensitivity, describes the long-term commitment once the climate system has come into balance with the enhanced level of greenhouse gases.

Using observations from the period 2000 to 2009, a decade when global warming appeared to slow down, Otto and colleagues obtain a “best estimate” for the transient climate response: 1.3ºC. This is smaller than the value of 1.6ºC obtained when they look at observations from the 1990s instead. We might conclude from this that we need to reduce our estimates of the climate sensitivity.

However, natural variability needs to be considered as well. Internal variations within the atmosphere and oceans matter when we look at just ten years of observations. When Otto and colleagues look at the entire period from 1970 to 2009, the last decade starts to look less unusual. Their best estimate for the transient climate response is now 1.4ºC – just 0.1ºC greater than the value estimated from the last ten years.

This suggests that it might be the 1990s that was unusual, rather then the first decade of the 21st century. Indeed, another recent study by Myles Allen and colleagues evaluates a long-term climate model projection made back in 1999. That projection turned out to be extremely accurate. However, the real world warmed faster than the model prediction during the 1990s, before returning to the predicted long-term trend during the decade that followed.

So natural variability might have caused Earth to warm a little faster than expected during the 1990s. Then, during the following decade, it had the opposite effect, cancelling out some of the warming due to increasing concentrations of greenhouse gases. The period from 2000 to 2009 may therefore have seen the climate system “pausing for breath” before the long-term warming trend continues in future.

Using observations from the past decade, Otto and colleagues derive a best estimate for the long-term equilibrium climate sensitivity of 2.0ºC. This is consistent with the estimates obtained when they look at observations over longer periods of time, including the whole of the period from 1970 to 2009. The apparent slow-down in global warming over the past decade has therefore done nothing to change our best estimates of the long-term response.

This new work by Otto and colleagues refines our estimates of the climate sensitivity, but the overall picture remains unchanged. Even medium-range climate scenarios suggest that the atmospheric carbon dioxide concentration will have doubled, relative to pre-industrial levels, well before the end of the current century. If our emissions of greenhouse gases continue unabated, we still face an uncomfortable future.

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  1. Mark Pollock

    Analyst

    Hold on here. I thought the science was settled. Ah that's it. This paper is based on observational data not the set in stone models that only deniers question. So, all very good in practice but completely disrespects the theory.

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    1. Mike Hansen

      Mr.

      In reply to Mark Pollock

      So Mark Pollock, Sean Lamb, Greg North, Peter Lang.

      Can we take it that this paper is your stake in the ground? This is what you believe to be the "correct" science on AGW?

      So no more "pending ice age", "scientists conspiracy new world order", "no greenhouse effect", "blah, blah, blah" that you have been ranting about here for a while.

      If so, you will be happy to endorse the author's comments and we can get on with decarbonising the economy.

      "We would expect a single decade to jump around a bit but the overall trend is independent of it, and people should be exactly as concerned as before about what climate change is doing," said Dr Otto.
      http://www.bbc.co.uk/news/science-environment-22567023

      Oh look - pigs flying over head - I venture to suggest that you will all be back to denying climate science once this paper disappears down the memory hole.

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    2. Sean Lamb

      Science Denier

      In reply to Mike Hansen

      "Can we take it that this paper is your stake in the ground? This is what you believe to be the "correct" science on AGW?"
      Not at all, I take it is part of the Great Climate Science Tap Dance - the process by which the industry concedes its models and projections are going to fail massively and try to distance themselves from them without an explicit repudiation.
      My figure for the doubling of CO2 is around 0.7 C - although I think I have erred on the alarmist side as well. I am confident that…

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    3. Mike Hansen

      Mr.

      In reply to Sean Lamb

      Expand that comment a bit Sean and you could have the makings of an article for WUWT. ;-)

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    4. Sean Lamb

      Science Denier

      In reply to Mike Hansen

      Well, Mr Hansen, I guess having a more sophisticated model than the IPCC is a very low bar to surmount.

      To the IPCC, this is a sophisticated model:
      http://www.youtube.com/watch?v=lj3iNxZ8Dww

      The wonderful thing about models is you judge how good they are by how accurately they predict. And with CO2 climate sensitivity, the lower you go the better your model is going to predict.

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  2. Sean Lamb

    Science Denier

    Ahhh, is this the start of the Great Climate Science Tapdance?

    By coincidence I wrote this earlier today on the British edition of The Conversation. Reposting:
    Its worth quoting from the Weekend Australian
    "In his recent book on millennialism, Richard Landes argues that millennial movements become more extreme the more they fail, and it will certainly be the case that this is what happens with the climate change lobby. Empirical evidence will have little effect on their views and they will…

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    1. Michael Marriott

      logged in via Twitter

      In reply to Sean Lamb

      Sean, the religion/Lysenko analogy is a fail.

      These tactic is pretty much identical to what creationists use.

      Quoting the Australian on climate science, also a fail.

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  3. Mark Pollock

    Analyst

    I think the author is honestly trying to reconcile the yawning gap between his belief structure and the harsh light of reality - rather like Gosse and his Omphalos. He should be given credit for clutching at straws rather than than denying that the ship is sinking.

    At this point he is still wistfully hoping that the "End of Days " is still imminent - though not as imminent as it was before the mercury headed south. "We still face an uncomfortable future". The revised climate sensitivities indicate that maybe it's not the end of the world, just the beginning of the end of the world, at a time yet to be announced.

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    1. Sean Lamb

      Science Denier

      In reply to Mark Pollock

      97% of climate scientists believe in AGW - even it is just a soupçon of AGWarming

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  4. Greg North

    Retired Engineer

    It is pleasing to see some recognition of variability, something that climate change proponents have often claimed is fully covered in modelling, just like all the volcanic and other gaseous emissions that nature creates.

    Where it can get even more interesting is to ask about the really longer term variation or ask about science always being an expanding field of knowledge and that will get you labelled as a denier no problems at all.

    " Using observations from the period 2000 to 2009, a decade…

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    1. Mark Pollock

      Analyst

      In reply to David Arthur

      10s of metres? Is that like 20 or 30 or even more metres?

      I thought the IPCC was predicting about 80 centimetres by 2100 with an nst rise of 3 centigrade?

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  5. Osk Archer

    Chemist/Maltster

    Now hold on; I keep hearing about these doomsaying "climate scientists" (a nebulous term if ever there was one) who brandish their unquestionable Models aloft like stone tablets and will never waiver in the message of CAGWy devastation which we face.

    To read the deniers type, peer reviewed research should be following lock-step with the 97% consensus - don't rock the boat!

    And don't publish results which might appear to "weaken" CAGW!

    I see 14 institutions, most atmospheric or environmental, represented here, who are just doing science. Adding, refining and improving knowledge. I hope at the end of it they find out AGW isn't something to worry about, but the best science right now says that's not the way to bet.

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    1. Michael Marriott

      logged in via Twitter

      In reply to Osk Archer

      97-99% of scientists accept evolution.

      Are they also afraid to rock the boat?

      How many astrophysicists reject the big bang theory - a basic tenant of cosmology.

      Are they also afraid to rock the boat.

      People reject the consensus because it contravenes values and a preferred world view.

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    2. Osk Archer

      Chemist/Maltster

      In reply to Michael Marriott

      Those are interesting comparisons, but in my scientific experience researchers don't actually think like that, especially those with established reputations. Cautious, maybe, but not afraid.

      For example, the Theory of Evolution is not considered set in stone, and can absorb new information, even resurrected old ideas, once strong evidence is found - http://en.wikipedia.org/wiki/Lamarckism#Current_views

      I'll allow that saying "97% consensus!" isn't evidence or even a valid argument, but it is a fact that shouldn't be dismissed, and more importantly it represents a vast network of trained experts and specialists (as exemplified by the 14 institutions I mentioned) who do the damned work. Ascribing hidden agendas, biases or corruption to them is also not an argument (though one the deniers are often guilty of), it is disingenuous and a disservice to their hard work and skills.

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    3. Peter Lang

      Retired geologist and engineer

      In reply to Osk Archer

      Osk Archer,
      '
      You are partly correct in your defence of course. However, climate scientists have brought the discredit on themselves. They have continually exaggerated, misrepresented and tried to scare the population to get the action the scientists think should be implemented. The scientists have been advocates for totally ridiculous policies - like carbon pricing and renewable energy. they advocate for policies that are totally outside their area of expertise. By these practices they have…

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    4. David Bentley

      logged in via LinkedIn

      In reply to Peter Lang

      Surprising then, don't you think Peter, that given the enormous amounts of money behind organisations who would benefit from AGW being debunked and, according to you, the almost impossibly low hurdle for publishing peer reviewed research in this area, that such a tiny number of peer reviewed research papers have been published which cast doubt on the AGW hypothsis.

      What are you so called sceptics doing? C'mon the door is wide open to publish pretty much anything and then to get it onto the Conversation....the sceptics are either lazy or stupid not to be making the most of this opportunity.

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    5. Sean Lamb

      Science Denier

      In reply to David Bentley

      "the sceptics are either lazy or stupid not to be making the most of this opportunity."
      I can only speak for myself: lazy, stupid, indifferent and more than a touch of schadenfreude.
      As a Science Denier why should I be trying to stop this glorious trainwreck of scientific hubris?
      You won't find me trying to dispute that 97% of climate scientists endorse IPCC projections - rather I shall be proclaiming it gleefully!

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    1. Geoffrey Henley

      Research Associate

      In reply to Lee Emmett

      "So in the event where 97% of scientists agree that global warming and climate change are real"

      I think you quote the 97% figure without any understanding of how it is derived. In fact, there is no credible survey that comes close to estimating the true proportion of scientists/climate scientists who adopt a particular position on AGW. The 97% figure is a myth conjured up through statistical trickery. It is not supported by any credible research.

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    2. Peter Lang

      Retired geologist and engineer

      In reply to Geoffrey Henley

      >"The 97% figure is a myth conjured up through statistical trickery. It is not supported by any credible research. "

      Dead right. This explains how:
      http://rankexploits.com/musings/2013/on-the-consensus/

      And for anyone with common sense they'd realise how silly is the result by considering this comment posted elsewhere by Latimer Alder:

      "97+% of practising homeopaths believe that homeopathy works
      97+% of members of the Catholic Curia believe in transubstantiation
      97+ % of drunk drivers…

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    3. Michael Marriott

      logged in via Twitter

      In reply to Peter Lang

      Peter, I'm surprised that you claim to be a geologist yet equate the scientific consensus with religion and pseudo science.

      How old is the earth Peter? 5,000 years or 4.5bn.

      Because if you answer the later, I can introduce you to some creationists who call you're making a faith statement and that "It's Just a theory".

      http://evolution.berkeley.edu/evosite/misconceps/VBisreligion.shtml

      You're argument is identical: X people believe in Y belief > theory A is like Y belief > therefore A is like Y

      Classic association fallacy – your premise is deeply flawed.

      http://en.wikipedia.org/wiki/Association_fallacy

      You and I know the difference between a faith position and testable scientific facts that buttress a theory.

      -1 logic

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    4. Geoffrey Henley

      Research Associate

      In reply to Michael Marriott

      So Michael, can you provide me a reference to a single survey that provides credible evidence to support the 97% figure? I doubt it.

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    5. Jennifer Norton

      statistician, researcher, entrepreneur

      In reply to Geoffrey Henley

      You might find this article interesting Michael:
      http://asr.sagepub.com/content/75/6/817.full.pdf

      It is about how consensus is formed and measured in all areas of science. By the authors reckoning, consensus was achieved on ACC around 1993.

      What delays the broad recognition of consensus in many areas of study is obfuscation. This occurs where there are strong vested interests against the "new" theory/discovery.

      The same thing happened with tobacco. There was recognisable consensus among researchers that tobacco caused cancer in humans well before that consensus was recognised outside the field. And it was even longer before governments acted on the data. All because big tobacco had a lot of money to spend on counter-studies and counter-lobbying.

      It's common sense--look where the *big* money is for where the obfuscation is most likely to occur.

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    6. Michael Marriott

      logged in via Twitter

      In reply to Geoffrey Henley

      A single study?

      How about three:

      1) Oreskes / The Scientific Consensus on Climate Change (2005) http://cmbc.ucsd.edu/Research/Climate_Change/Oreskes%202004%20Climate%20change.pdf
      2) Doren et al / Examining the scientific consensus on climate change (2009) http://cmbc.ucsd.edu/Research/Climate_Change/Oreskes%202004%20Climate%20change.pdf
      3) William Anderegg et.al / Expert credibility in climate change (2010) http://www.pnas.org/content/early/2010/06/04/1003187107.abstract

      From the Anderegg…

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    7. Geoffrey Henley

      Research Associate

      In reply to Jennifer Norton

      Jennifer, the big money is in belonging to the AGW gravy train. Any money received by sceptics is a mere pittance to the billions of dollars in funding foisted upon AGW doomsayers. The IPCC only exists by making exaggerated claims and painting doomsday scenarios.

      The tobacco analogy is irrelevant here. I dare say that the vast majority of sceptics would agree that smoking increases the chances of lung cancer. Even Lewandowsky's fatally flawed moon landing paper puts the figure of well in excess of 90%.

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    8. Michael Marriott

      logged in via Twitter

      In reply to Geoffrey Henley

      Evidence?

      You know pharmaceutical companies, governments, researchers and universities spend billions of dollars on researching a cure for cancer.

      Does that mean people are making up a disease just to grab funding?

      Does the Australian Cancer Council exist merely to raise funds for a non-existent problem?

      Or is it – just maybe – the IPCC and scientific community are researching climate change because – just like cancer – it is a real world problem?

      But hey: must be a global conspiracy including the UN, IPCC, researchers, activists, socialists, bankers, the alternative energy industry, the world's military planners, governments…

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    9. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      "The IPCC only exists by making exaggerated claims and painting doomsday scenarios."

      LOL. Never get between a climate science denier and his tinfoil hat.

      The very paper that we are currently discussing was authored by many of the lead authors of the IPCC WG1.

      According to some of your colleagues here and the climate denial blogs, this paper is now suggesting no more than a few balmy Sunday afternoons.

      Get your stories straight please.

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  6. Comment removed by moderator.

    1. Mike Swinbourne

      logged in via Facebook

      In reply to Peter Lang

      Well Peter, it looks as though you read neither the article, nor the paper concerned, before you decided to post your usual denier nonsense.

      The study does NOT show that climate sensitivity is much lower than stated in the IPCC reports. The study clearly states that, based on the last decade alone, that the rate of atmospheric temperature increase over the next few decades may be slightly lower than forecast, but over the longer term the rate of increase will be consistent with what has been…

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    2. Peter Lang

      Retired geologist and engineer

      In reply to Mike Swinbourne

      >""Well Peter, it looks as though you read neither the article, nor the paper concerned, before you decided to post your usual denier nonsense. The study does NOT show that climate sensitivity is much lower than stated in the IPCC reports."

      Wow, talk about denial.

      IPCC AR4 gives central estimate for 2xCO2 = 3.1C
      This paper gives central estimate for 2xCO2 = 2.0C
      Get the difference?

      You doomsayers are unbelievable. And the extent you are prepared to go to to mislead others is outstanding…

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    3. Mike Swinbourne

      logged in via Facebook

      In reply to Peter Lang

      Yes Peter - we are talking about denial. So before I go on, let's get a couple of things clear first.

      It looks as though you may actually have read the paper (or got a couple of quotes elsewhere). So I will apologise for suggesting that you hadn't.

      So as you have read it, do you accept the findings of the paper? if so, why? If not, why not?

      That should be fairly simple. And when you have responded to that, we can continue with the details.

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  7. John Newton

    Author Journalist

    Have the denailists below really read the article? Here is the concluding par:

    This new work by Otto and colleagues refines our estimates of the climate sensitivity, but the overall picture remains unchanged. Even medium-range climate scenarios suggest that the atmospheric carbon dioxide concentration will have doubled, relative to pre-industrial levels, well before the end of the current century. If our emissions of greenhouse gases continue unabated, we still face an uncomfortable future.

    What has changed? Every national scientific organisation on the planet and 97% of peer-reviewed papers accept AGW.

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    1. Peter Lang

      Retired geologist and engineer

      In reply to John Newton

      That's a laughable comment. Climate sensitivity is lower than previous projections, and you are still trying to continue the scaremongering. Who are the deniers?

      And regarding the 97% joke surely you weren't so gullible as to fall for that one were you?

      Do you realise the dodgy analysis that was done?

      Do you realise Cook, the author is an academic specialising in communications (i.e .a spin doctor) who is totally committed the CAGW doomsday cult. The paper is a classic case of a predetermined…

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    2. Glenn Tamblyn

      logged in via Facebook

      In reply to Peter Lang

      No Peter, I know first hand how 'undodgy' the analysis was. I was a part of it.

      Have you actually read the paper?

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    3. Michael Marriott

      logged in via Twitter

      In reply to Peter Lang

      I repeat Peter:

      Peter, I'm surprised that you claim to be a geologist yet equate the scientific consensus with religion and pseudo science.

      How old is the earth Peter? 5,000 years or 4.5bn.

      Because if you answer the later, I can introduce you to some creationists who'd say you're making a faith statement and that "It's Just a theory".

      http://evolution.berkeley.edu/evosite/misconceps/VBisreligion.shtml

      You're argument is identical: X people believe in Y belief > theory A is like Y belief > therefore A is like Y

      Classic association fallacy – your premise is deeply flawed.

      http://en.wikipedia.org/wiki/Association_fallacy

      You and I know the difference between a faith position and testable scientific facts that buttress a theory.

      -1 logic

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    4. Michael Marriott

      logged in via Twitter

      In reply to Glenn Tamblyn

      Would it matter if a sceptic read it?

      They'll do what they do and cherry pick the relevant facts and read into it what they wish to see.

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    5. Peter Lang

      Retired geologist and engineer

      In reply to Glenn Tamblyn

      >"No Peter, I know first hand how 'undodgy' the analysis was. I was a part of it. "

      I know. That is one excellent reason why it is dodgy. It's group think and motivated reasoning by propaganda agents. How more dodgy could it be?

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    6. Geoffrey Henley

      Research Associate

      In reply to Glenn Tamblyn

      Glenn, I have read the paper and it clearly states that for 66% of the papers included in the study, the authors provided no specific endorsement of AGW. Therefore John's statement that '97% of peer-reviewed papers accept AGW" is clearly false.

      Besides, does not this study relate to the endorsements of the authors themselves and not whether the paper itself provides ant evidence of AGW. From my point of a view, a lot of papers provide some evidence of warming but provide no evidence of a specific link between global temperatures and human induced CO2 emissions.

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    7. Michael Marriott

      logged in via Twitter

      In reply to Geoffrey Henley

      Geoffrey, papers by geologists DO NOT affirm the fact the Earth is kinda round, orbits a thing called "the sun" and is maybe - give or take - 4.5bn years old.

      It's just a given.

      Like biologists DO NOT have to recount the history of evolutionary theory since the publication of the Origin of the Species last century. It's a given in biology evolution is true.

      Like...

      Oh never mind.

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    1. Peter Lang

      Retired geologist and engineer

      In reply to Glenn Tamblyn

      Motivated reasoning. You go with what supports your beliefs even when they prove to be consistently wrong. That's true denial.

      But I guess you don't take with a pinch of salt your mate, John Cook's non-science analysis of '97% climate scientists believe in ...' do you?

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    2. Michael Marriott

      logged in via Twitter

      In reply to Peter Lang

      Peter - care to list how many scientific associations in the world reject the consensus? Can you name one? The Royal Society? The US National Academy of Sciences? What's their view – or that of any national science body? Care to enlighten us?

      Let's talk about "flawed" surveys– and put a stop to the attempts to undermine the very good work of Cook et.al.

      Lets turn this conversation around get down to the "evidence" sceptics use to try and undercut the public's perception of consensus…

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  8. Alice Kelly
    Alice Kelly is a Friend of The Conversation.

    sole parent

    "the overall picture remains unchanged", this part of the conclusion must be terribly hard to read for arm-waving denialists, however there is a new tome available from heartland, ( the imaginary state devoted to the promotion of fossil fuels ).
    http://www.guardian.co.uk/environment/climate-consensus-97-per-cent/2013/may/20/heartland-institute-scientists?commentpage=1%0D
    I'm sure those lucky enough to get one will either laugh, experience some sort of anger, or bore us all with more stupidity, as shown in the usual commentary today.

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  9. Peter Lang

    Retired geologist and engineer

    This comment by Chris Uhlmann (ABC) seems to be applicable to those clinging to the CAGW cause:

    >"American Civil War author Shelby Foote often told the story of a ragged Virginian private captured by Northerners.

    "What are you fighting for anyhow?" his captors asked. They were genuinely puzzled for he obviously owned no slaves and seemingly could have little interest in states' rights or even independence.

    "I'm fighting because you're down here," the Virginian said.

    Protecting your home, or way of life, or simply believing that this is what you are doing is a powerful cause."

    http://www.abc.net.au/news/2013-05-17/uhlmann-labor-finds-itself-without-a-homeland-to-defend/4696656

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  10. Andrew Glikson

    Earth and paleo-climate scientist

    Steven

    Original estimates of the CS factor by the IPCC AR4 were 3.0+/-1.5. For the current relation between CO2 level (~400 ppm) and pre-industrial CO2 level (280 ppm) the increase in MGT of ~0.9C and continental temperatures by ~1.5 (Berkeley Temperatures http://berkeleyearth.org/results-summary/) would suggest a Climate Sensitivity value of ~2.1C (global) to 3.6C (continental) respectively. Depending on the magnitude of positive feedbacks from methane release, fires and warming water bodies…

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    1. Peter Lang

      Retired geologist and engineer

      In reply to Andrew Glikson

      >"The implication is that mean global temperature would about double"

      Wow. Is that what the scientists are trying to tell us now? Temperatures are going to double eh? From 288 K to 576 K (thats 15 C to 303 C. What are you guys going to come up with next to try to scare the pants off the world?

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    2. David Bentley

      logged in via LinkedIn

      In reply to Peter Lang

      I think he's talking about the mean global temperature anomaly. But of course you knew that and were just trying to be smart. Fail.

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    3. Michael Marriott

      logged in via Twitter

      In reply to Andrew Glikson

      Thanks Andrew, of particular concern is this: "Depending on the magnitude of positive feedbacks from methane release, fires and warming water bodies, changes in temperature may be non-linear."

      The vast quantities of CH4 under the northern tundra - which is being released - is of concern. A CH4 induced warming "pulse" seems a credible risk.

      I don't think enough people - at least among the general public - appreciate the risks of positive feedbacks. Out of interest, would you include the reduced albedo effect from the shrinking Arctic ice in your list?

      Also: if BAU continues and we hit ~500ppm mid-century (+/- a few years) one wonders how the possible Antarctic ice sheet collapse will effect the rate of SLR…

      The risks inherit in the vast geophysical experiment humanity is conducting are truly concerning.

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  11. Comment removed by moderator.

    1. Michael Marriott

      logged in via Twitter

      In reply to Peter Lang

      And yet here you are, posting freely?

      Do we sand on the precipice of left wing totalitarianism - a new Marxist world order?

      Really Peter, talk about alarmist!

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    2. In reply to Peter Lang

      Comment removed by moderator.

  12. Andrew Glikson

    Earth and paleo-climate scientist

    Where I wrote in my comment:

    "The implication is that mean global temperature would about double without the sulphur aerosol factor,"

    Of course it was meant to say the "mean RISE in global temperature would about double without the sulphur aerosol mitigating factor,"

    Namely the mean rise since the 19th century.

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