The Loom

There’s nothing more grating for a science writer than see your work get cut and pasted to give people precisely the wrong impression. My latest irritation: “Ten Questions For Al Gore and the Global Warming Crowd”, which appeared Friday on the conservative web site

The author is John Hawkins, who describes himself as a professional blogger who runs Right Wing News. Hawkins claims that he is skeptical that humans are causing global warming because, in his words, “‘the Earth-is-going-to-burn-us-alive’ crowd cannot answer the most basic questions about the theory that they haughtily insist is so beyond reproach that there should be no more need for debate.”

He then offers ten questions for the “global warming crowd,” claiming that “if the proponents of the manmade global warming theory can come up with good answers to questions like these, you can expect everyone, including me, to accept their theory.”

Questions seem inherently innocent–they’re just simple quests for knowledge, right? But in the hands of someone like Hawkins, they also have the potential to spread quite a lot of misinformation…

Take, for example, Hawkins’s second question:

2) If greenhouse gasses produced by mankind are behind the roughly one degree increase in temperature over the last century, then why did the global temperature go down from roughly 1940 to 1975 even though mankind’s production of greenhouse gasses was skyrocketing during that same time period?

Funny how Hawkins doesn’t mention in his questions the well-established fact that burning fossil fuels creates emissions that can both absorb heat and cool the atmosphere (the latter happens when pollution seeds clouds that bounce incoming radiation back to space). Over the course of the twentieth century, cooling effects increased and then faded as dirty pollution was cleaned up and the lingering gases in the atmosphere got washed out. Meanwhile, however, heat-trapping gases continued their increase. In the mid-1900s the cooling and warming effect of human emissions roughly canceled each other out. Computer models that include the historical records of all these gases show a mid-century stall in the rise of global temperatures.

See this excellent picture, based on a 2004 study in the Journal of Climate. For a more recent update, see the new Intergovernmental Panel on Climate Change report, figure 4 (pdf). (via Real Climate.)

Before Hawkins delivered this question to the world, he could have found the answer with a few minutes of Googling. I don’t know if he didn’t have the time, or if he already knew and didn’t want to draw people’s attention to it. Hard to tell exactly what happened. But I do have a better idea of what happened when he invoked an article by me down in question nine. And it’s pretty ridiculous.

Indulge me as I quote Hawkins quoting myself–I do have a reason for it…

9) As Carl Zimmer has noted in Discover, at times in the earth’s past, we’ve had considerably more carbon dioxide in the air that we do today, and yet it’s debatable whether the temperature was significantly warmer,

“During the Ordovician Period, 440 million years ago, there seems to have been 16 times as much carbon dioxide in the atmosphere as there is today–and yet, judging from the gravelly deposits it left behind, there was also an ice sheet near the South Pole that was four-fifths the size of present-day Antarctica. The second exception is even more troubling. The Cretaceous Period, when dinosaurs ruled the Earth and CO2 levels were about eight times what they are today, has been one of the most popular case studies for global warming forecasters. And everyone knows what the climate was like during the dinosaurs’ heyday: steamy. Or was it? The latest evidence, reported just this past summer by British researchers, suggests that temperatures in the tropics 95 million years ago were no higher than they are now; and while it was a lot warmer at the poles than it is today, it was still freezing cold.”

Doesn’t this suggest that there isn’t anywhere near as much of a close relationship between greenhouse gasses like carbon dioxide and the temperature as many people seem to believe?

Now, if you read the article itself at the Discover web site, you’ll see–in the very next paragraph–that this paradox did not cause climate scientists to reject the link between greenhouse gases and climate. Why not? Because the Earth millions of years ago was different in a couple important ways. For one thing, it got less light 440 million years ago, because the sun was dimmer. For another, the geography was different. In the Ordovician, for example, many of the continents were rammed together and situated partly over the south pole. The climate scientists I wrote about in the article were running computer models that indicated that this arrangement allowed glaciers to grow even while the planet heated up. In the article I also explained how the arrangement of continents in the Cretaceous allowed cooling clouds to form over the interiors of the continents.

If the continents were going to slam into each other in the next century, the climate 440 million years ago might give us some pause about whether the planet is going to warm. But the continents are just going to creep along, while the carbon dioxide is going to shoot up, perhaps doubling or even tripling.

What makes quoting my article particularly funny is that it’s not–shall we say–springtime fresh. It may sound like I’m delivering the newest research with lines like, “the latest evidence.” But when I first saw myself quoted in Hawkins’s piece, I thought, “Hey–I remember that story. When did I write it?” Fortunately, the Discover web site reminded me.


Thank you, Mr. Hawkins, for taking me back to my cub days as a science writer, to the early days of the Clinton administration, to the year that Netscape Navigator was released and Dakota Fanning was born.

I just have to wonder, why did you have to reach back thirteen years for the latest understanding on climate science? Did you think that climate scientists shut their computers off in 1994? Did you think that they stopped looking for better estimates for temperatures and carbon dioxide levels in the past? You might have looked at this 2006 study on the Cretaceous, or this 2004 model of the Ordovician (pdf), which is far more complex than anything done in 1994, and sheds more light on how glaciers form in a high-CO2 world.

Scientists still have a lot to learn about the climate of the ancient world. The further back in time they go, the worse their record of temperature and greenhouse gases becomes. Drifting continents make the problem even more complex. But they are making headway, not by rejecting the role of greenhouse gases in the climate but by learning more about the other factors at play in the past. The most revealing features of Earth’s climate history come from the more recent past–the past few million years, for which scientists have found some excellent records in ice cores and other materials. The more recent past is also useful because the continents were in the same arrangement as they are today. And studies on the recent past support computer models that project a 3 degree C rise in response to a doubling of carbon dioxide.

It’s nice to know that someone’s still digging back into my archives. Too bad it’s Hawkins, slicing and dicing them so that readers end up misinformed.


  1. #1 Sally Grafton
    April 2, 2007

    I’m disappointed that you seem to be following the crowd on the “carbon dioxide is the problem” bandwagon. I have a great admiration for your writings – I have most of your books – but here you seem to have lost your way. My recommendation is that you look behind the quasi-political documents from the IPCC and the rigid line that one finds at real climate and follow the more questioning sites such as I think you will find that the science is not so supportive of the position you have been espousing.

  2. #2 Carl Zimmer
    April 2, 2007

    Sally–I just linked to four different papers published in peer-reviewed scientific journals in this post. I am aware of the science.

  3. #3 Blake Stacey
    April 2, 2007

    Apropos of nothing, I bought Parasite Rex and Soul Made Flesh on Saturday, figuring I could read them in pieces before bed or when I’m just tired of work. Not a chance: I read all but the last chapter of Soul Made Flesh Saturday afternoon, finished it Sunday morning, and devoured Parasite Rex before teatime Sunday afternoon.

    You set a high bar to clear, sir.

  4. #4 Jim RL
    April 2, 2007

    You may be aware of the actual science, but are you aware of the junk science that rips your actual science to shreds? See, apparently science is a big crock. The best minds in fields like climate modeling and evolution create theories that any right-winger without any scientific training can tear apart with a quick trip to conservipedia. But, billionaire atheists and environmentalist suppress the truth by paying off the scientists. That’s why the anti-science crowd always seems backward and ignorant. If they were smarter, they’d be paid off too.

  5. #5 Blake Stacey
    April 2, 2007

    Jim RL:

    How many times do I have to say that the correct way of spelling that site’s name is Conservapaedia? (-;

  6. #6 Joshua
    April 2, 2007

    As long as we’re heaping praise on Carl, I read Parasite Rex earlier this year, myself, and spent a couple of hours on the phone shortly after I finished it telling one of my friends all about bombing cassava fields with wasps and the interplay of parasites and the reproductive habits of snails. The book’s so good, it’s even fascinating second hand. ;)

    I’d comment on what Sally said, but your own response pretty much covers it. The claim that global warming can only be accepted by ignoring scientific evidence is ludicrous on its face. The deniers may be able to point out one or two papers here and there, but those are completely overwhelmed by the vast majority of studies that point toward not only warming trends but human influence on those trends — four of which Carl already linked, just as a side effect of an average post. Not even as a concerted effort on his part to “prove” global warming, just during his normal blogging.

  7. #7 Brian
    April 2, 2007

    Do we currently measure/estimate the atmosphere’s albedo from space (by satellite I mean)? I know we’ve recently put up satellites that get a image of cloud cover with depth rather than surface only, but it seems to me it would be useful to have a baseline for the amount of energy radiated back into space to check against.

    Every time I read a brief for this or that model it always strikes me that either they are not sharing the many variables they are taking into account or the models are severely simplified.

    Don’t get me wrong, I understand the potential magnitude of the data involved, and the necessary shortfall of computational power, but I’d like to feel a bit more confident in current models (I personally think pollution and sustainability is an issue outside of the specter of global warming is extremely important to humanity–but I’ve not yet seen anything which gives me confidence in our ability to accurately model the climate).

  8. #8 ed
    April 2, 2007

    Hi Brian
    Try this link:

    I got that by typing ‘earth albedo’ into a common search engine. If you do some searches on climate models you should come up with a history of their development and what variables they include.

  9. #9 Brian
    April 2, 2007


    I appreciate the link… Though I’ll admit I was looking for more targeted information. There are a lot of different models of different quality out there and I was operating under the assumption that someone reading may have an informed starting point.

    …Results 1 – 10 of about 6,050,000 for long term climate model. (0.37 seconds)…

    Though the link in the article gives more information than I gave it credit for originally; an odd line break means I glanced over the more relevant, if incomplete, bits of this description:

    For this purpose we used a climate model of intermediate complexity to perform a large set of equilibrium runs for (1) pre-industrial boundary conditions, (2) doubled CO2 concentrations, and (3) a complete set of glacial forcings (including dust and vegetation changes).

    But of course that’s (1) subscription-only data and (2) a model specifically targeted at historical data.

    Although, of course, I appreciate the snarkiness in assuming I was baiting and/or ignorant of Google.

  10. #10 David B. Benson
    April 2, 2007

    Brian — Use Real Climate as a resource to discover about climate. For example, there are useful sidebar links, such as the one to the AIP history of climatology. Also, there are many knowledgeable posters who are often ready to help others find interesting information…

  11. #11 Brian
    April 2, 2007

    I’ll give it a look David, thanks.

  12. #12 Pat
    April 2, 2007

    The one question the global warming alarmists haven’t answered is why the cause of the slight warming over the last century should be any different than the warming that occurred during the medieval warm period and the warming that occurred during the Holocene maximum. These warm periods occurred while the continents were very close to their current position.

    The default state of the Earth over the last million years has been ice age. We are currently enjoying a respite from that default state. The little ice age was a dreadful time in human history – plagues, wars and famine devastated the population of Europe during that period. That was bad enough. Imagine the impact of a real ice age when mile-deep ice sheets covered much of North America and Europe.

    The global warming alarmists imply that if we carry on burning fossil fuel, global warming will accelerate until we are all fried. They forget where the carbon in fossil fuels came from; the ancient atmosphere of the Carboniferous period when CO2 concentrations were an order of magnitude higher than today. Burning oil and coal is really just a form of recycling :).

    Computer models of anything other than a simple, closed system, have as much predictive value as a clairvoyant. They might help understanding of the dynamics of a complex system but they can predict nothing. If you run the models starting from a million years ago, do they predict the cycle of ice ages and inter-glacial periods? If they don’t, what use are they?

    Can we actually do anything to stop global warming, if, in fact, it is partially human induced? Probably not. India and China aren’t going to stop their march forward. The best we could do is encourage them to do it cleanly. Actually, switching SE Asia from burning cow dung and plant material to electricity would be a good thing. The Asian Brown Cloud has a nasty impact on the region. It is “a 2-mile-thick blanket of pollution over South Asia, [that] may be causing the premature deaths of a half-million people in India each year, deadly flooding in some areas and drought in others, according to the biggest-ever scientific study of the phenomenon.” Be that as it may, human emissions of CO2 are a tiny fraction of a gas with a concentration measured in PPM.

    Look on the bright side. A warmer Earth is a happier, more productive Earth. The land lost to minuscule rises in sea levels is more than compensated for by land made productive in Siberia and Canada. Just pray that the current inter-glacial doesn’t end anytime soon.

  13. #13 bybelknap
    April 2, 2007

    OT {I’m in the middle of At The Water’s Edge . It’s a wonderful read.)

    Now, this may also be a bit off topic, but finding the silver lining in the Cloud of Hawkins. At least he isn’t a YEC. He seems to accept The Ordovician was 440 million years ago and not 4,000. Baby steps.

  14. #14 Richard Simons
    April 2, 2007

    Pat: as far as I can make out, the medieval warm period was a local European affair and during the Holocene warm period the northern hemisphere summers were warmer and that was it.

    Climatologists who are concerned about the effects of CO2 do not forget where the carbon in fossil fuels came from and do not necessarily argue that a warmer world is a worse world. The problem is the rate of change, which is apparently unprecedented.

    human emissions of CO2 are a tiny fraction of a gas with a concentration measured in PPM.

    You may consider an increase of around 50% (so far) to be a tiny fraction; I do not.

    A warmer Earth is a happier, more productive Earth. The land lost to minuscule rises in sea levels is more than compensated for by land made productive in Siberia and Canada.

    This is just wishful thinking. A large part of the land that could be lost to rises in sea level is currently highly productive. The land in Canada that could benefit from increased temperatures is mainly thin soil on bedrock. You are also forgetting that higher temperatures increase the water demands of crops and can also reduce yields, for example by stopping pollination of wheat and corn. They would also have a significant impact on the distribution of pests and diseases.

  15. #15 Brad Arnold
    April 3, 2007

    Mr Zimmer, thank you for your explaination of the Cretaceous period’s seemingly contradictory high CO2 levels, and modest temperture increases. On the other hand, I just imagine how chilly it would be with no CO2 in the air (approximately minus 18 degrees C), then imagine doubling it from today’s levels-simple!

    Global warming is like cancer: pain will eventually force the patient to seek an accurate diagnosis and good advice on treatment. Hopefully, the denial won’t delay the treatment until the condition is fatal.

    I believe that it is unlikely that mankind will cut their emissions so fast and severely that runaway global warming will be avoided. Therefore, I recommend removing the CO2 from the air by improving nature’s ability to fix the carbon. Perhaps seeding a GMO into the ocean-it maximizes cost and scale.

  16. #16 Pat
    April 3, 2007

    Richard Simons,

    Sea levels rose 400 feet since the end of the last ice age. The IPCC, in its more reasonable projections estimates sea level rises of less than 3 feet. Not much land would be lost if such a rise occurred. Valuable land can be protected, as the Dutch have done for centuries. We already know that a warmer climate opens up more land for agriculture. It happened during the MWP and it could happen again.

    The idea that the MWP was a local European affair is an unsubstantiated assertion. Greenland was inhabitable and that is not part of Europe. The MWP and LIA occurred in Japan , which is also not part of Europe.

    The Vostok Ice Core sample shows “a strong correlation between carbon dioxide content in the atmosphere and temperature”. Concentrations varied between 180 (ice-age) and 300(inter-glacial) ppm over the last 400,000 years. So, while you claim concentrations have risen over the last century, you haven’t separated the natural increase that always occurs during an inter-glacial period from the human contribution.

    Brad Arnold,

    You don’t have to imagine what would happen if CO2 concentrations doubled. All you have to do is check how high concentrations were in the Earth’s earlier history. This graph is useful in that regard. the world survived concentrations an order of magnitude higher than they are today.

    If there wasn’t any CO2 in the atmosphere then photosynthesis would stop. All terrestrial plant life would die along with all the animals. i.e. we’d all be dead.

  17. #17 Thomas R. Holtz, Jr.
    April 5, 2007


    The world has indeed survived much higher carbon dioxide levels and such.

    Of course, that wasn’t a world where there were human beings trying to feed greater than 6 billion of their fellows on plants evolved and domesticated in Holocene climates…

    Or a world where we needed reliable patterns of rainfall and other freshwater sources for those same people.

    Of course non-anthropogenic climate change happens. But through our activities we have additionally liberated copious amounts of carbon that has been sequestered for tens to hundreds of millions of years.

  18. #18 Brian Schmidt
    April 8, 2007

    “Before Hawkins delivered this question to the world [cooling up to the 1970s], he could have found the answer with a few minutes of Googling. I don’t know if he didn’t have the time, or if he already knew and didn’t want to draw people’s attention to it.”

    Hawkins has written extensively about climate change over the years, and is not a fool. There’s no reasonable possibility that he does not know about the role of aerosols. He asked the question, knowing what the answer was but hoping it would appear significant.

    I’ve challenged him repeatedly to bet me over global warming, without receiving an answer.

    He’s now working on the presidential campaign for Duncan Hunter.

  19. #19 Aaron Legler
    April 8, 2007

    Just to join in the discussion…

    The major issue I have with all “global warming” data is that it is attempting to account for very small changes in temperature by comparing real measured data, which we have today thanks to actual surface temperature readings, to extrapolations of temperatures hundreds of years ago from a CO2/Temperature ratio.

    This doesn’t seem to be a scientifically sound method. You might be able to say that higher CO2 levels = higher temperatures, but to try to pinpoint such a small shift in temperature as is being discussed is certainly stretching the credibility of the relationship.

    And what is the bet and how would you propose to say who won?

  20. #20 pough
    April 9, 2007

    extrapolations of temperatures hundreds of years ago from a CO2/Temperature ratio

    Really? That’s the first I’ve ever heard of that method. Do you have any links explaining it?

  21. #21 David B. Benson
    April 9, 2007

    Aaron Legler — The science of how greenhouse gases, such as carbon dioxide, warm the surface has been well understood for over a century.
    Being a regular reader of Real Climate, I doubt that a CO2/T ratio is ever used.

    I recommend not only Real Climate but also the side bar link to the AIP history of climatology site. Reading that ought to remove misconceptions, IMO…

  22. #22 Aaron Legler
    April 9, 2007

    Pough – Perhaps in an attempt at brevity I was too brief. Historical atmospheric carbon dioxide levels are correlated with global temperatures through ice core sampling. The temperature is derived from oxygen isotope ratios in the air bubbles in the ice. This is probably the method you are familiar with reading about.

    David – Real Climate seems to have far too much investment in global warming to be a reliable source of information. I have no misconceptions about climatology. The planet gets warmer, the planet gets colder. I feel that this is natural variation and the historical record shows this.

    The flaw in the “global warming crisis” argument is that until the last 50 years or so we had very little actual data about global surface temperatures. As more and more information is able to be gathered through actual measurements, and not through proxies, you begin to zone in on reality.

    When I say that I am not convinced that global warming is manmade, that does not mean that I take every opportunity I can to club a baby panda. Do humans cause environmental damage? Absolutely. Should we limit the amounts of pollution that we produce? Absolutely. It is not a matter of global warming, it is a matter of not p**ping where you eat.


  23. #23 pough
    April 10, 2007

    Pough – Perhaps in an attempt at brevity I was too brief.


    Historical atmospheric carbon dioxide levels are correlated with global temperatures through ice core sampling. The temperature is derived from oxygen isotope ratios in the air bubbles in the ice. This is probably the method you are familiar with reading about.

    Yes and no. You seemed to be discussing the recent past (hundreds of years) and not the distant past. From what I’ve read, ice core sampling has been used more for thousands of years of temperature data and it’s proxies like tree rings and coral growth that are used for more recent temperature reconstructions. It did a similar red flag thing that creationists dissing paleontology because carbon-dating isn’t accurate past 40,000 years does.

    As for natural variation, it’s not the temperatures that are causing alarm as much as the rapidity of increase. At least, that’s the impression I’ve gotten. You seem to have understood something quite different from the available information.

  24. #24 David B. Benson
    April 10, 2007

    Aaron Legler — Then try just reading the AIP history of climatology.

    Briefly, carbon dioxide warms the planet as a so-called greenhouse gas. It is easy to find many separate ways to determine that, especially in the last 50 years, humans have put a huge slug of carbon dioxide in the air by burning fossil carbon. Therefore it is already warmer than natural, but it is going to get worse.

    See the IPCC reports.

    pough — Yes, the rate of increase appears to be without precendent in the paleoclimatological records. The last time anything approaching this rate of increase was PETM. Carl Zimmer can tell you better than I what happened to the large mammals ( > 5 kg) of that age…

  25. #25 Nick
    April 11, 2007

    Given the uncertainty about current aerosol levels (see e.g. ), how accurately do we know historic aerosol levels, say, from 1940-1980? If the answer is “not very”, how do we know that aerosols largely accounted for the global cooling of 1940-1980?

  26. #26 Aaron Legler
    April 12, 2007

    The argument that the increase is happening at an unprecedented rate is flawed because we lack true measurements of what the temperature was in the past. Tree rings and coral growth are good natural indicators of climate, but they do not tell you an actual measurement. They are simply an indicator that some years it was warmer, some it was colder. These things are also affected by other factors – fire (not the coral, obviously), disease.

    David – as for the PETM, who was generating the carbon dioxide emissions that caused that? Or was it the other many greenhouse gases that nobody seems to care about?


  27. #27 pough
    April 12, 2007

    Ah, I see. 90% certainty of all the climate scientists = I dunno.

    Nobody cares about the other greenhouse gases? That surprised me until I recalled that you consider the RealClimate guys nobody.

  28. #28 David B. Benson
    April 12, 2007

    Aaron Legler — You clearly haven’t done your reading assignment: paleotemperatures are estimated by combining a collection of proxies. The science is solid and the estimates quite good.

    As for PETM, try Wikipedia for starters…