New paleoclimate study: pace of global warming beats anything since the Ice Age

A study of world temperature since the last Ice Age, published this month, shows we are in the midst of a dramatic U-turn: gradual cooling ended in the early 20th century and turned to relatively rapid warming.

The climate scientists who wrote the study say it provides further evidence that warming is caused mainly by carbon dioxide emissions since the industrial revolution, and not naturally.

The study, led by Shaun Marcott of Oregon State University and published in Science magazine, reconstructs temperature changes over the past 11,300 years. It is based on 73 sets of climate data, mostly built up from analysis of the fossils of pollen, plankton and other marine micro-organisms.

Previously, continuous temperature reconstructions only went back 2000 years. The most well-known of these, published in 1998 by Michael Mann of Penn State University and his colleagues, included the so-called “hockey stick” graph, showing a steady downward trend in temperature over two millennia, with a sudden spike upwards in the twentieth century.

Marcott et al’s new study, based mainly on data from marine fossils, confirms Mann et al’s results, that were based mainly on data from tree rings, ice cores and sediments from lakes. (Marcott et al. write, using scientists’ jargon, that their results are “indistinguishable within uncertainty” for the last 1500 years from Mann et al’s).

And that’s significant because, after the Intergovernmental Panel on Climate Change (IPCC) used Mann et al’s “hockey stick” graph in their 2001 Third Assessment Report, it became the target of every demented climate denialist in the American political establishment and media.

Marcott et al’s publication (i) confirms the basic findings of the “hockey stick” research, but extends the record back from 2000 years ago to 11,300 years ago, and (ii) provides yet more proof that the denialists’ claims were bogus.

The science

Marcott et al, summing up their results, write that the global mean temperature for 2000-09 did not exceed the warmest temperatures of the early Holocene period (5000-10,000 years ago) – but they DID exceed the temperature in at least 72% of the 11,300-year period studied. And the global mean temperature in 1900-09 was cooler than 95% of the period studied.

“Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began [about 5000 years ago].”

Marcott, quoted by the Associated Press here, said: “In 100 years, we’ve gone from the cold end of the spectrum to the warm end of the spectrum. We’ve never seen something this rapid. Even in the ice age the global temperature never changed this quickly.”

The study indicates that in the 4000 years after the end of the Ice Age, the world warmed about 1.25 degrees on average. After that there was a plateau of warm temperatures, and then a long period of cooling that went on until about 200 years ago. Then the cooling reversed, with a vengeance.

Climate scientists quoted by AP praised the methods used by Marcott and his colleagues, although they said they might be a bit too oriented to the Northern Hemisphere. Jeff Severinghaus of the Scripps Institution of Oceanography said there could have been an abrupt shift in climate about 12,000 years ago, i.e. just before the period studied by Marcott et al.

There is a useful report on the Climate Central site here. Unfortunately the article in Science magazine is subscriber-only (although remember that many libraries are subscribers). The supplementary material is open-access.

The politics

The study by Marcott and his colleagues is welcome not only as another step forward in scientific research, but also as yet another rebuttal of the pseudo-scientific, political attacks on climate science that were so intensely concentrated on the “hockey stick”.

Michael Mann, the lead author of key articles proposing the “hockey stick”, tells the grim story of the denialist campaign – and the fight back against it – in his book, The Hockey Stick and the Climate Wars: Dispatches from the Front Line (Columbia University Press, 2012), which I strongly recommend. (It’s currently going for less than 20 US dollars on Amazon).

Mann gives a lay person’s introduction to paleoclimatology, i.e. the study of “proxy records” such as tree rings, fossils and ice cores, which have enabled scientists to ascertain temperatures for thousands of years prior to the 1880s, when measurements began to be recorded. From the 1980s, paleoclimatological research deepened scientists’ understanding of long-term climate trends, enabling them to interpret current climate and make predictions about future possibilities with greater confidence.

Mann also traces the growth of climate denialism in American political culture during the 1990s, and the response to it at the highest levels of government during the George Bush administration (2000-08). He explains very clearly the distinction between scientific debate and scepticism on one hand and the battle with the denialists, whose methods undermine science.

Mann describes how climate scientists logically and repeatedly demolished the denialists’ arguments – which were usually published by non-scientists, or scientists in other fields, in journals not adhering to standard review processes. Nevertheless, the denialists’ quackery was recycled endlessly in the media. The hand of oil and coal companies, who funded – and still fund – climate-denying lobbying organisations, was never far away.

Mann points a frightful picture of the vilification of climate scientists by politicians such as Texas congressman Joe Barton, and the uncritical repetition of denialist arguments by journalists who should have known better. At the height of these “climate wars”, Mann and other climate scientists set up the Real Climate site, to explain their work to non-scientists and counter the denialist barrage in cyberspace. Bookmark it!

Reading Mann’s account made me rethink an analogy I used in a review of a book by another leading climate scientist, James Hansen. I compared Hansen’s stand against the Republican denialists with Galileo Galilei’s refusal to accede to the insistence by the Catholic church in the seventeenth century that the sun goes round the earth. But now I am thinking that that is a little unfair on Pope Urban VIII and the torturers of the Holy Inquisition.

After all, the heads of the seventeenth-century Catholic church were usually acting from profoundly-held beliefs. The idea that the sun, and all other celestial bodies, went round the earth was an essential part of the religious ideology that held together the social and political system of their times. Present-day climate denialists usually have no such illusions of a higher calling. They act from much baser motives – often simply because their quack “research” is funded by fossil fuel industries, who are only concerned to preserve their ability to churn out profit over the very short term, whatever science says about the inevitability of a transition away from fossil fuels.

Mann reminds us in his book, and in interviews and articles on his web site here, that although the Bush presidency is over, the climate denialists are still hard at work. The peak of their efforts to undermine science was the notorious “climategate” episode in the run-up to the failed Copenhagen climate summit of 2009. Even serious newspapers gave unduly respectful coverage to this denialist witch-hunt, based on misquotations carved from a mountain of hacked emails. A report here shows that even now, in 2013, fresh bundles of hacked emails are still being served up to the denialists.

… and the level of carbon dioxide emissions

Marcott et al’s findings arrive along with news that the increase in the level of carbon dioxide in the atmosphere in 2012 was the second-fastest on record, the New Scientist pointed out in its report.

Monitoring stations in Hawaii recorded that between January and December 2012 the level of CO2 in the atmosphere rose by 2.67 parts per million to 393.81 parts per million (ppm). When these records began in 1959, there were 315.97 ppm of CO2 in the atmosphere. The only jump bigger than 2012’s was in 1998, when the level rose by 2.93 ppm.

Many climate scientists believe that CO2 levels need to plateau at 450 ppm for humanity to have a reasonable chance of avoiding dangerous global warming of two degrees centigrade or more. But others believe that the level needs to be pushed back down to 350 ppm – as does, for example, the campaign group founded by American environmentalist Bill McKibben. GL.

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13 Responses to New paleoclimate study: pace of global warming beats anything since the Ice Age

  1. [...] by Gabriel Levy People and Nature, March 24, 2013 [...]

  2. guenier says:

    To fully understand this important matter, it might perhaps be noted that there’s no significant link between the actions of the “climate denialists” and the recently accelerated increase in atmospheric CO2 – almost wholly due to what’s happening in the world’s emerging economies. Over the past six years, for example, China has increased its CO2 emissions by an amount equal to the USA’s total emissions. And, as may be seen from this diagram (of proposed coal-fired plants), that trend seems likely to strengthen:

    That is underscored by an International Energy Agency forecast of how things will look by 2035, compared to the Copenhagen Accord targets:

    The harsh reality of today’s world is that CO2 emissions will continue to rise – probably at an increasing rate. And there’s really nothing the so-called developed economies can do about it. I’m no scientist, so am not qualified to judge whether those who are sceptical about catastrophic anthropomorphic global warming are right. But we must hope they are.

  3. Gabriel Levy says:

    In response to Robin Guenier. Why the sarcasm? Climate science denialists, as I should have called them, are not responsible for CO2 emissions – but they clearly are partly responsible for ensuring that the leading capitalist nation, and one of the largest carbon dioxide emitters, the USA, set a policy course AGAINST doing anything significant about tackling emissions. The stats mentioned do indeed show the huge part played in this by China and its coal-fired power, and the IEA’s dire forecast is to be noted. But why can’t “the so called developed economies” do anything? China is to some extent a machine to provide them with cheap goods. Their governments prevail over an international system which serves short-term profiteering, not humanity’s long-term interests. If those governments cared about parts of Bangladesh, or New Orleans, going under water, they would put a gradually-rising tax on carbon emissions. And as for “those who are sceptical about catastrophic anthropomorphic global warming” – Robin hopes they are right … but they are not right, for the same reasons that creationists are not right. They don’t “believe” science. Calling them “sceptical” is a misuse of that word. Scepticism is a healthy desire to check facts, challenge assumptions and research more deeply. By contrast, the climate science deniers are fundamentalist and dogmatic.

  4. guenier says:

    Gabriel: thanks for your response.

    There are two issues here: the attitude of the developing world and what you term “climate science denialists”. I think it would be best to comment on each separately. This is the first comment.

    I suspect you may not understand what’s happening in China – or for that matter in India or other emerging economies. Since I first visited many of them over thirty years ago, the change has been near miraculous. China’s economy has grown by more than 10% per annum, and it seems likely to surpass the US as the world’s premier economy by 2020. And trade with the West is an increasingly small part of this: they welcome it, but they no longer need it.

    One result is that China has, according to the UN, “generated the most rapid decline in absolute poverty ever witnessed” and, by 2008, had already achieved “the goal of halving the number of people in extreme poverty by 2015 set by the UN as one of eight Millennium Development Goals.” Nearly 400 million people have benefited – getting access to clean water, proper sanitation, fresh food, adequate health care, better education, etc. It’s a pattern repeated throughout the emerging economies. See, for example, this: Read the whole piece, but note this extract:

    “… the essentiality of electricity to modernity is incontrovertible. The countries that can produce cheap, abundant, reliable electricity can grow their economies, educate their citizens and pull their people out of poverty. And those that can’t, can’t.”

    All this is the direct result of the massively increased availability of cheap, reliable electric power, something we comfortable people in the West take for granted. It’s light years away from being a “system which serves short-term profiteering”. Note: over 1.2 billion people have no access to electricity and another 2 billion have inadequate access. Despite the above successes, there’s still a lot to be done – but doing it will truly serve “humanity’s long-term interests”.

    As the article says, “Global leaders should give up their fixation on cutting carbon dioxide emissions. Significant cuts will not happen voluntarily anywhere. And to make certain political leaders understand the need to eradicate energy poverty, the UNFCCC should hold its next meeting in Hanoi.” That’s why I believe we must hope that those who are sceptical about the dangerous climate change hypothesis are right.

    A footnote: there’s evidence (I’ll provide the links if you’re interested) that the Chinese are not convinced that climate change is the result of industrial emissions– indeed one view, seemingly supported by the government, is that the whole thing is little more than a Western plot to keep developing countries poor and undeveloped.


  5. guenier says:

    Gabriel: this is my promised second comment.

    You said: “those who are sceptical about catastrophic anthropomorphic global warming” are “not right, for the same reasons that creationists are not right. They don’t “believe” science. Calling them “sceptical” is a misuse of that word. Scepticism is a healthy desire to check facts, challenge assumptions and research more deeply. By contrast, the climate science deniers are fundamentalist and dogmatic.”

    And that’s why you call them “climate science denialists”.

    Well, I’m in touch with a lot of people who are sceptical of CAGW and I know that most share the following understanding: (1) that the climate changes, has always done so and will continue to do so; (2) that the most recent example of change is the slight temperature increase (about 0.8 deg. C) experienced since the mid 19thC; (3) that mankind’s CO2 emission levels have risen markedly in recent years and especially since the end of WW2; (4) that basic physics shows that CO2 is a so-called “greenhouse” gas and therefore that additional CO2 may warm the atmosphere – although vast natural forces (cosmic, solar, orbital, atmospheric, hydrological, cryospheric, tectonic, oceanic etc. and their interactions) are hugely influential on the global climate; and (5) that, nonetheless, mankind’s CO2 emissions probably contributed to the marked warming observed at the end of the 20thC. They query, however, whether mankind’s CO2 emissions, and not natural influences, were the principal cause of that warming and – in particular – whether, if such emissions are not reduced, the consequence will be catastrophic climate change.

    The latter uncertainty (increasingly shared by many scientists and, for example, by the Royal Society – see paragraphs 46-50 of its “summary of the science”) is born precisely of the “healthy desire to check facts, challenge assumptions and research more deeply” you mention. You’re right: “they don’t “believe” science”. Belief is a matter for religion, not science. Doubt, uncertainty and keeping an open mind are the essence of science.

    What, Gabriel, are these people denying? In what sense are they “fundamentalist and dogmatic”? How are they comparable to creationists? There may, I suppose, be some people with the characteristics you describe (just as there are some people who are fanatical in their “belief” about global warming). But I’ve never come across any.


  6. guenier says:

    Further to my comment at 6:30 pm yesterday (unpublished when this was written), an article in the current edition of the Economist (a publication not noted for climate change scepticism) provides further evidence of uncertainty about the consequence of failure to reduce CO2 emissions. It illustrates how such uncertainty is shared by some climate scientists and that fears of catastrophe may be ill-founded. It confirms my opinion that describing CAGW sceptics as “climate science denialists” is unwarranted and gives further force to the questions I posed in my final paragraph.

    The article can be found here:


  7. BitBucket says:

    Robin, have you really never come across any “deniers”, as characterised by Mr Levy? As you are a regular contributor to the comments on Bishop Hill, where denial and scepticism mix freely, I would have thought you and denial were well acquainted. You can’t possibly have missed those who question the “greenhouse effect” or who deny that the instrumental temperature record is accurate (it is all urban heat islands etc) or who question the position of CO₂ instruments on a volcano, etc. And that is quite apart from those, including the host of BH, who accuse any and all climate scientists of fraud and worse. Why do you say such things? Are you ashamed of the company you keep?

  8. BB: it’s true that I’ve come across contributors to the Bishop Hill site who do not share all the understandings I spelled out in my post at 6:30 pm on March 26. But you’ve missed my point. It’s this: most of the CAGW sceptics with whom I’m in touch do share those understandings, are “sceptical about catastrophic anthropomorphic global warming” and, as such, are described by Gabriel as “climate science denialists”, despite the fact that scientific uncertainty about the consequences of AGW is increasing – see the RS overview and the recent Economist article.

    I’m still awaiting his answers to my questions about these people: What are they denying? In what sense are they “fundamentalist and dogmatic”? How are they comparable to creationists?

    The views of some BH contributors are another matter: yes, some may question the “greenhouse effect” but, if so, they’re very few (I’ve never come across any) and, yes, some (not many) do question the accuracy of the instrument record and the positioning of CO₂ instruments – but having such concerns hardly makes them “demented climate denialists”. As for accusations of “fraud and worse”, they’re fortunately rare on BH. And I’d be most interested to see your evidence that Andrew Montford has accused “all climate scientists” of these things. I believe that’s simply untrue.

  9. [...] previous article I asserted that climate science deniers are “fundamentalist and dogmatic”. In the comments section, Robin Guenier questioned this and advanced a supposedly “sceptical” argument. This is my [...]

  10. BitBucket says:

    By the way, your suggestion that scepticism is a “healthy desire to check facts, challenge assumptions and research more deeply” is in stark contrast to ‘sceptics’ attacks on anyone who attempts such research and to suggestions in your favourite blogs that money-grabbing researchers promote CAGW just for the research dollars. Shut-down the research and shut-up the researchers is more the ‘sceptic’ line.

  11. BitBucket says:

    I should make it clear that my earlier suggestion that the host of the Bishop Hill blog accuses “any and all climate scientists of fraud and worse” is overblown rhetoric and is clearly untrue. My apologies.

  12. BB: 6:15 pm – I agree.

    BB: 7:10 pm – well done.

  13. Paula C. says:

    I strongly recommend reading what Roger Pielke Jr has to say on this story:

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