Part 1 of 5: A 175-year-old Puzzle

This is the first installment of a five-part series by Bill Chameides on How We Know Humans Cause Global Warming.

1. A 175-year-old Puzzle
2. What Chemistry Tells Us
3. Causes of Past Climate Change
4. The Medieval Warming Period
5. The Only Explanation Left

Most people these days accept that our planet is warming, but some find it hard to believe that mere humans could cause such a large-scale global change. How do we know that the warming is due to human activity? How can we be so sure?

Would it surprise you to know that the scientific community has been investigating the link between CO2 and global warming for more than 175 years? Scientists are born skeptics, and by no means accepted the theory as fact the first time it was proposed.

The idea that gases in the atmosphere could trap heat and warm the earth was first proposed in 1827, in an essay by French mathematician and physicist Joseph Fourier. He was trying to explain why the earth was warmer than physics would predict based just on distance from the sun.

The topic came up again 30 years later when Irish naturalist John Tyndall found clear evidence that glaciers once covered the Alps. The Earth had experienced ice ages. But how could the climate have changed that much? Tyndall was familiar with Fourier’s essay, and in 1859 did some experiments that showed water vapor and carbon dioxide (CO2) could both trap heat.

Nearly 40 more years passed before another scientist fascinated with ice ages did some investigating. In 1896, Swedish Nobel Prize winner Svante Arrhenius computed that halving the amount of CO2 in the atmosphere would lower the temperature by 7°F or more – ice age temperature. But he didn’t see how CO2 concentrations could change this much.

It was a colleague of Arrhenius, Arvid Högom, who discovered that burning fossil fuels could add significant amounts of CO2 to the atmosphere – as much as natural geochemical processes. But both he and Arrhenius saw this as something that could only cause warming over thousands of years – at first.

In 1908, when coal-burning was more widespread, Arrhenius published a book where he theorized that global warming might take centuries rather than millennia, but no one paid this much mind. It wasn’t the main point of the book, and no one believed it anyway.

For the next three decades, most scientists dismissed these ideas. The theories were often flawed or oversimplified, and in any case they thought that excess CO2 would be harmlessly absorbed by the ocean.

Then in 1938, an English engineer named Guy Stewart Callendar took another look. People had been talking about a warming trend, so he checked the record and found that CO2 concentrations had increased 10 percent over the last hundred years. His observation spurred further research.

Finally, in the 1950s, thanks to increased government funding for research after World War II, experiments confirmed the suspicions. There was an unmistakable connection between CO2 emissions from the burning of fossil fuels and global warming. Check out this short produced in 1958 by Frank Capra:

So you see, the greenhouse effect is not something scientists cooked up a few years ago, or even a few decades ago. We have been studying it for almost two centuries! After painstaking measurements and calculations by generations of scientists, the scientific community has reached a consensus: Global warming is caused by human activities. In the next posts in this series, I’ll tell you how the measurements and calculations lead us to that conclusion.

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  1. greenlady
    Posted June 14, 2007 at 5:00 pm | Permalink

    I have read this first part on global warming and ask “Why is it that every site I have visited on global warming (including this one) only shows one side of the ‘coin’?”(Maybe the information I am including will be in a later part of the article.) Emissions is only half of the story! During this same time that emissions (CO2 and H2O) from burning fossils fuels has been on the rise, nature’s carbon sink (the forests of the world) that removes CO2 from the atmosphere have been decreased by 90% and are expected to be gone by 2050! Global warming can be reversed by a two-fold approach– 1)reducing emissions (CO2 and H2O) and 2) increasing the carbon sink (removal of the CO2 from the atmosphere) by replanting the world forests. Do the lumber megaindustries have so much clout that this aspect of the equation never comes before the public?

  2. K.C. Weber
    Posted June 14, 2007 at 10:36 pm | Permalink

    As the old saying goes, “There are two sides to every story.” One web site (among many) that has a long list of scientists that present different views about global warming is:

    Some believe that global warming is not occurring. Others believe the accuracy of climate projections is inadequate. Many believe that global warming is caused by natural processes. Still others believe the cause of global warming is unknown.

    I don’t know the complete story myself. As I have stated before, I think the sun’s interaction with the Earth and its atmosphere has something to do with global warming. But that is my view.

    I think it is necessary to study both sides of the issue to take the proper steps. Many say that if man is the cause of global warming, what if we don’t act on it? True. But if something else is the caue and we don’t act on that cause, it could be disastrous also.

    All I am saying is we need to completely know the facts, not just look at one side.

    K.C. Weber

  3. Posted June 15, 2007 at 11:12 am | Permalink


    I don’t quite agree with the percentages you quote, but I do agree that deforestation – especially in the tropical rainforests – is a significant part of the problem. About 20 percent of global greenhouse gas (GHG) emissions currently come from deforestation. It’s also true that land management practices that increase the carbon sink by terrestrial plants can make a huge contribution toward offsetting GHG emissions.

    Perhaps you missed it, but we’ve covered both these issues in previous posts. Please check out these links:

    Slicing the greenhouse gas pie: What gases?
    Slicing the greenhouse gas pie: Where from?
    Agricultural Offsets
    Comment from Annie Petsonk on Deforestation

  4. John Hartz
    Posted June 16, 2007 at 12:08 pm | Permalink

    There’s no way for any human being on earth to know all the facts about climate change and probably will never be.

    If all the facts about global warming were to assembled into a single document, it would probably:

    a. require a small army of of experts to gather all of the facts, quasi-facts and fiction about climate change out there.

    b. take a Papal decree to properly sort items into “facts”, “quasi-facts”, and “fiction” (It is virtually impossible for the scientific community to reach 100% agreement on anything. — which is intrinsic to the scientific process and mind-set.)

    c. take a Supreme being to distill all of the facts into a document that could be read and digested by a human being in a single lifetime.

    Therefore, gathering all of the facts about and looking at all sides of the Climate Change issue reuslts in “Paralysis by Analysis.”

    Unfortunately, the negative effects of climate change are accelerating and the human race does not have much time left to mitigate against those changes and to address the forces driving the climate change that we are experiencing.

    Hats off to Dr. Bill and scientists like him who are willing to accept and endorse what the majority of scientists have concluded through the sifting and winnowing process started by the UN in 1988 when it created the the Intergovernmental Panel on Climate Change (IPCC) to analyse and report on scientific findings about climate change.

    Under the uspices of the IPCC, scientis will continue to analyse and report on scientific findings about climate change through a rigorous and deliberative process.

    Millions of people throughout the word and hundreds of institutions in both the public and private sectors have accepted and embraced the finidngs issued to date by the IPCC. They have all concluded that the time to take action is now!

  5. Brian
    Posted June 19, 2007 at 4:07 pm | Permalink

    It’s true that we don’t know all of the factors that combine to drive climate change, much less how those causes interact. But does that mean we shouldn’t take action to eliminate from the equation the ones we do understand and can exert direct control over?

    We don’t know every minute detail of the inner workings of cancer, but that doesn’t stop us from spending many millions of dollars each year to find a cure.

    Cutting GHG emissions is a step that can be implemented (relatively) quickly and have fairly well-understood results. Other solutions, including reforestation, would take much longer (read: possibly centuries) to take effect. Saplings don’t exactly absorb a lot of CO2.

  6. Posted June 20, 2007 at 3:58 pm | Permalink

    Hi Brian,

    You’re right that we need to cut GHG emissions as soon as possible. That includes emissions not only from fossil fuels but also from deforestation, particularly in the tropics. We’re working to develop incentives for developing countries to reduce deforestation (for more, see here).

    However, don’t count reforestation out. Young forests can sequester a lot of carbon. In fact, the rate of carbon storage generally decreases as forests mature. Parts of North America and Europe are net carbon “sinks” (i.e., they take up carbon) because forests are reclaiming abandoned agricultural fields.

  7. greenlady
    Posted June 23, 2007 at 8:05 pm | Permalink

    Hi, Bill Chameides,

    Thanks for listing your previous articles! I may never have found them, but I have read them all through and left a comment under ‘Comment from Annie Petsonk on Deforestation’.

    I read all of your articles (that I can find). They are easy to read and very informative. However, I think the idea of farmer/forester offset would escalate out of control. I assume the offset concept is that I run my vehicle and pay a farmer or forester to plant 250 trees to take up the CO2 my vehicle produces in a year. Now the way I see this is that there is only a limited amount of land upon which to plant trees while the population is increasing with more cars being put into service each year. Eventually, all the land that can have trees (ideally) will have trees but the emissions will continue to rise. Reducing emissions, in reality, is only a bandaid to stop a hemorrage. It seems to me that ultimately (sooner, hopefully than later) a change in fuel from oil to some clean fuel (which research Congress nixed to pay for at the Oil Giant’s expense) will have to occur. Possibly even some major lifestyle changes. However, in the meantime, I shall continue planting trees!

    Love, Peace, and Joy!

  8. srk1970
    Posted June 27, 2007 at 5:34 am | Permalink

    Hi Bill

    I got this thought which I was pondering on for a long time, I assume we all are thinking that Human race survives on O2 along with ofcourse other gases and we cannot survive on CO2, now this spills over into Biology, but what if this change is environment will spur evolution in human race or for that matter other species inhibiting earth, what if this environmental change, changes our Physiological condition and allows us to adopt to the changing environment, all this has got nothing to do with my support to conserve nature, that thing has to be done.

  9. Posted June 27, 2007 at 12:28 pm | Permalink

    There is evidence of evolution in some species – birds, squirrels and mosquitoes are best studied – in response to global warming. However, scientists predict high extinction rates because many species will not be able to adapt quickly enough.

    Evolution isn’t the main issue for humans, since we can adapt our behaviors and built environments. The danger to humans is more indirect – damage to the ecosystems that we depend upon for life, loss of places to live as land is submerged under rising oceans and shortages of important resources such as fresh water.

  10. Qwerty
    Posted June 29, 2007 at 6:56 am | Permalink

    Interesting articles … I think I’ll set a bookmark.

    @greenlady and @Brian –
    “planting trees will solve the problem” is one of the most powerful myths out there. Some facts against this myth are:
    1. forests tend to take in the most carbon when they’re young – old forests are pretty much neutral if not overall sources. Not so bad really, plant a tree and cut it for timber in 50-200 years. Point here is you need to keep planting those trees year after year. One word: cost.
    2. ever try planting thousands of trees? The pine timber industry does it in many countries but in many ex-hardwood forests which have simply been destroyed and abandoned the topsoil is gone and you’re left with some pretty horrible rocky stuff that is awful for trees. In other places such as Queenstown in Tasmania, the environment had been destroyed by sulfuric acid from ore processing operations; aside from topsoil washing away, what little soil there is doesn’t seem to support much.
    3. trees die – even if you’re extremely good with plants, a large part of every 1000 you plant simply won’t make it to maturity.
    4. people are greedy – you can bet people plant maybe 10,000 trees then tell 100 different parties that they’ve planted 10,000 trees on their behalf. If you don’t plant and look after it yourself, you can’t trust the numbers.
    5. even deliberate reforestation isn’t going to get anywhere near compensating for the ever-growing release rate of CO2

    @greenlady – H2O is not important in the sense that it can rain out or more can go into the air with an increase in temperature. It varies very rapidly and we have little control of it. We can control CO2 (at least in principle, I think in praxis people prefer to squabble than to do real work).

    @srk1970 – evolution is an extremely slow process. With a very slow change in temperatures then species and individuals which have a genetic tolerance for extremes of heat and cold will do better than others and may become dominant over numerous generations. With fairly rapid changes as we’re seeing, evolution hasn’t got time to do its work. Well, maybe the fruit flies will have a chance since generations breed so quickly, but they won’t have any fruits to feed off so they’d better learn to eat other fruit flies.

    Peeking at the next article, a changing 13C/12C isotope ratio is only one proof that burning fossil fuels is causing an increase in CO2. Far more shocking than that is the estimate of anthropogenic CO2 emissions. In 2007 the oceans (and other sinks) will essentially absorb all of the CO2 produced by nature (plants, animals, volcanoes) plus half of what we pump into the atmosphere. The most basic fact (which gets overlooked when people argue about the silly toy models) is that humans are essentially responsible for 100% of the currently observed annual increase in atmospheric CO2. You can laugh at the models all you want – I think they are a useless waste of time and money – but you can’t deny facts (unless you’ve got a religious inclination).

  11. self-reliant
    Posted July 6, 2007 at 10:08 pm | Permalink

    @qwerty While I think we all can agree there is benefit in reducing emissions and reforestation, you apparently have a religious inclination. That religious inclination would be called the Church of Man-Made Global Warming. Anyone who dares question it is burned at the stake. Where has your sense of inquiry gone? We all want a cleaner environment, but your squelching of discussion should not be tolerated.

    Everyone knows that we need to return earth to being a pristine planet. We do not need your tone of “preachiness”, since this does not advance our cause of a social move toward eco-friendly policy.

  12. Fred Sanford
    Posted July 8, 2007 at 2:24 am | Permalink

    I find it funny how the man made global warming crowed have to lie about climate change and what happen in the past. First of all I will state the climate is changing. It has been in all of recorded history and it is in th geological recorded. The climate has been much warmer and much colder. This is fact and it is also a fact the human had nothing to do with it. It is also a fact that the temperature has been rising steadily for over a 1000 years.

    Now as to the hypothesis of human induced global warming. And if you are and honest scientist you will have to admit the it is hypothesis not a theory or a law. Since the is not enough evidence to make it to a theory. If you were to take the evidence and weigh it you can say the following.

    The climate is warming. C02 is increasing. With these two facts and they are facts, you cannot say the following. CO2 is causing the warming. You can say CO2 may be causing the warming and that some evidence leads you to beleive it is human induced. The evedence is years from being proven or verified. If you are honest you also have to say there is some evidence the CO2 is a follower not a leaded on warming. If you are honest you wouls also have to it is a fact (and I did mean fact) CO2 is not a good predicator on how warm or how cold the earth will be at given l level. The evidence supports that CO2 level have little to do with warm or cold. As most of you should know. The earth climate had been colder with high level of CO2 and it been much warmed with lower levels of CO2 These are facts. From the evidence I have seen CO2 is a poor predicator of the earth temperatures.

    As to the computer climate models. For someone whom has made his living in the computer industry for the last thirty years. Garbage in garbage out. I computer is only as good as it programing and what I have seen with must programing it is low quality. I will only trust a computer to tell me what I can check directly. In weather models you can only make suppositions on what you think is happing and program on that bases. I know that the models are incorrect since the have failed to accurately predict the changes in the last ten years. The programs have contently overstate the rise. Granted the rise has been in the low end of computer models bus as to that.

    I not a climatologist or a computer programmer. But I could have created a model the would have been able to do what the present day models have predicated.. It been a good bet that if you created a module that predicated a temperatures increase following the line of what has been averaging in increase for the over the last 1000 years you would be right. And you know the actual temperatures rise is right in those lines and they do look dramatic in the last 20 years since we did have a minor cool down in the fifties sixties ans the early seventies. Now that that trend has ended and we are making up those losses the rises do now look pretty dramatic. Yet they are not out of the norm for the last 1000 years.

    From what I can see the present state of so called science in my adult life it that science is dead and it been replace a a pseudo or political science. Far to many hypothesis or theories are accepted laws when the are not.

    I find it funny the the global warming crowd has to lie about what happen in the past to prove the hypothesis or theories. When people like me point that out we are consider Luddites of low beings not worthily of you appointed knowledge. Yet I can take solace in that, these were also science considered facts. The earth was the center of the universe. A vacuum could not exist. Radio wave traveled on ether. And all all time good one is that the earth was flat.

    So I will state on other fact for you enlighten man made global warming worshipers should know yet will refuse to beleive. The climate is going to change and there is not a thing you or we can do about it. It will either get warmer or colder. I sincerely hope if it when it changes it gets warmer for if it get colder where I presently live, Ten thousand years more or less there was a sheet of ice covering it. Warm I can cope with colder that a far different problem, or are going to tell me that that also incorrect. Since you have already eliminated the little ice age and the medieval warming period. Now are you going to tell me glaciers never covered the over half of the North American continent!

    Oh by the way it seem that if glaciers did exist here ten thousand years ago life adapted pretty well to the climate change since when I look out my door I do not see bare earth covered only in lichens. I also know the plants and animals that are present in this area today were not here then. So much for plants and animals not being able to adapt.

    the globl warmin crowd have to lie about what happen in the past to prove the hy

  13. Posted July 8, 2007 at 7:41 pm | Permalink

    Hi, I’m a young nieve environmentalist that started a new job at a company that supports eco-responcibility and I’m the new PR guy. I’vbe spent my whole weekend trying to find sources of viable information. Dr. Balls paper “Global Warming: The Cold Hard Facts?” led me here, and simply put, you are the most credible looking forum I’ve found yet, and if anyone has the time, I would greatly enjoy learning what you know. I don’t know if they post it, but my e-mail is

  14. self-reliant
    Posted July 10, 2007 at 11:03 pm | Permalink

    Stevenson, you will need to learn to spell responsibility correctly to be taken seriously as a P.R. person. And, yes, you will even have to learn to spell naive correctly if any of your environmental-science references are going to be acknowledged by others.

  15. MeOfCourse77
    Posted July 30, 2007 at 2:57 am | Permalink

    In interest of full disclosure, don’t you think you should point out that the little film strip you played is from the Bell Science Series that aired in the late 50’s. Oh yea, almost forgot, THEY ARE NOT SCIENTIST. Frank C Baxter is not a scientist. This is nothing but more propaganda from the Global Warming quasi-religion. He may be one of your disciples, but he is not a scientist. Frank Capra and Richard Carlson are also a director and actor respectfully. Neither seen fit to include in their body of work, this masterpiece.

    I am not quite ready to get behind a movement that is far from conclusive in their science. I also think that we should not be making world economic decisions based on theories. Remember, people were punished for saying the world was round at one time in history. We should learn from the past, not repeat it.

    Computer models are only as good as the info put into it. You could make one say we will burst into flames next week and by next month be froze solid. My B.S. radar says proceed with a grain of salt in hand.

  16. Posted July 30, 2007 at 3:54 pm | Permalink

    >I am not quite ready to get behind a movement that is far from conclusive in their science.

    Funny you should say that. We just did a post on scientific uncertainty that I think you’ll find interesting.

    >Computer models are only as good as the info put into it.

    Actually, the most vulnerable part of computer models of climate is the models themselves. The data going into it is accurate. There are excellent measurement tools today. We did a post about climate modeling that explains how it works. You might want to take a look:

    Climate Models: How Good Are They?