THEGREENGROK

Copenhagen Climate Primer


by Bill Chameides | December 14th, 2009
posted by Erica Rowell (Editor)

Permalink | 18 comments

Did you hear? The Copenhagen talks have been suspended. Another walkout. The disagreement is over policy, not science (and some call the move tactical and a possible sign of progress). But since there’s been a kind of walkout over here in public opinion, here’s some basics on the science to keep in mind for when folks walk back in.

Amid all the debate about e-mails between scientists and emissions from China, let’s not lose sight of the basics.

The evidence of global warming and the role of human activities in that warming is strong. And it goes well beyond whether temperatures over the past 1,000 years are shaped like a hockey stick or whether climate models can accurately reproduce climatic variations.

As in all areas of science, the proof is in the data from observations.

Global Temperatures Are on the Rise

Our record of global temperatures from direct measurements goes back about 150 years. It shows a clear, long-term upward climb in global temperatures — today’s average global temperature is some 0.9 degrees Fahrenheit above that of 1880. And despite all the claims that global warming has stopped since 1998, it appears that the period from 2000 to 2009 will prove to be the warmest decade on record.

Some have challenged this global temperature record. Despite the best efforts of scientists to filter out confounding effects such as urban heat islands, many skeptics continue to challenge the trends derived from the record.

Fine, you don’t have to be a statistical maven of global temperature measurements to appreciate that the globe is warming. Glaciers and sea ice the world over are melting. Case closed.

A Role for Humans

All too often scientists explain the evidence of human interference in climate change using results from climate-model simulations. This explanatory technique is unfortunate because these models, while highly sophisticated, are in the end just numerical representations of the way we think our planet works. And the evidence of human interference is a lot more basic than model simulations — as basic as the most fundamental law in physics, the conservation of energy.

Conservation of energy demands that any increase in temperature for any body including the atmosphere must be accompanied by a source of extra energy or heat. If atmospheric temperatures are rising, if glaciers are melting, excess heat must be coming from somewhere. This applies to all possible causes of global warming. Natural causes of climate change, so-called internal oscillations, manmade climate change — nothing gets a pass from the law of the conservation of energy.

So, what is the source of heat causing global warming? It turns out that scientists have been asking themselves that question for decades and have been using advanced instruments and satellites to get answers. And here are the answers:

  • It’s not the Sun. Satellite data show that over the past ~ 30 years, there has been no net change in the total solar irradiance (the amount of energy emitted by the Sun). The same is true of cosmic rays and the solar wind.
  • Not heat from the ocean. For the ocean to have supplied the heat needed to cause global warming, the heat content of the ocean must have decreased. Why? Conservation of energy: if the ocean is supplying heat to the atmosphere, its own heat content must be decreasing. But measurements data show that, if anything, the heat content of the ocean has increased while the atmosphere’s heat content has increased. It seems that whatever is driving an increase in atmospheric temperatures is also warming the oceans.
  • Not reflection. Much has been made of clouds as a possible driver of global warming. Changing cloudiness can have a huge impact on the climate by changing the Earth’s reflectivity or albedo. Other processes such as changing land-surface characteristics or changing the atmospheric load of scattering aerosols can also affect albedo.

    If the Earth’s albedo has been slowly decreasing, then it would cause the planet to absorb extra energy from the Sun and explain global warming. But here again we have direct observations that appear to rule out this possibility. The Earth’s albedo has at times increased and other times decreased, but has not steadily decreased in the way needed to explain global warming.

  • Greenhouse gases supply the heat. Unlike the other putative sources of global warming, greenhouse gases and specifically carbon dioxide (CO2) have been observed to be heating the atmosphere.

    Satellites looking down on the Earth detect a hole or dip in the infrared radiation emitted by the Earth and sent into the space at exactly that part of the spectrum that corresponds to where CO2 absorbs radiation. Since the Earth emits infrared radiation to balance the absorption of energy from the Sun, blocking the emission of this radiation acts effectively as a source of heat to the planet and leads to global warming. That this occurs is not a theory; it is directly observable from space.

So, by the process of elimination, we are left with only one viable explanation for global warming — greenhouse gas pollution. To advance any other explanation requires that a source of heat be identified and thus far, as hard as scientists have tried, no such source has been found.

Let me repeat:

  • The evidence that humans are causing global warming is not a theory.
  • It is not based on a model simulation.
  • It is founded in the law of conservation of energy and direct observations of the Earth.

What About the Future

Ah, you say, maybe humans are causing global warming, but how do we know what will happen in the future? If you agree that models are not all that trustworthy and models provide the only way to predict the future, then you can’t be sure how the climate will change in the future if we continue to emit greenhouse gases.

And I agree: predicting the future is a bear. We really don’t know what the climate will do in the coming decades.

But don’t forget that uncertainty cuts both ways. Maybe the models have overestimated the effects of greenhouse gas pollution, and maybe they have underestimated the effects. With every extra megaton of carbon dioxide we add to the atmosphere, the chances of serious adverse consequences increase.

And there’s the rub for the folks in Copenhagen. Come to a global agreement about greenhouse gas emissions or place your bets, ladies and gentlemen, on the well-being of future generations.

filed under: carbon dioxide emissions, climate change, faculty, global warming, temperatures
and: , , , , , , , , , , , , , , ,

18 Comments

All comments are moderated and limited to 275 words. Your e-mail address is never displayed. Read our Comment Guidelines for more details.

  1. Barnes B.
    Dec 17, 2009

    It is very important for people to have at least a layman’s understanding of how carbon dioxide (and other gases) absorb and re-radiate infrared energy in the atmosphere. This fundmental mechanism is what keeps earth from being an ice ball; that it operates to heat earth is clear, and that too much of this effect from having too much of these gases in the atmosphere is equally clear. Getting bogged down in abstruse arguments about ice core data and the like is unnecessary, while getting back to this fundamental mechanism is vital, because too many people involved in the fray don’t appreciate its significance (and many scientists don’t use this information as a starting point). To repeat the old saw, nothing is so simple that it cannot be made way too complicated to understand. In this regard, it’s great to have Grok reviewing this satellite information that helps show what is going on at its most basic. There are in addition some nice animations on the internet showing how carbon dioxide molecules vibrate as they absorb infrared energy, and then re-radiating it as they return to a ground state. It would be good to show some links to these web sites. (I like one at rkm.com.au/ANIMATIONS/carbon-dioxide-global-warming.html, but there are others, I’m sure.)

  2. D Kelly O'Day
    Dec 15, 2009

    Dr. Chameides: In your excellent post, you state: “Satellites looking down on the Earth detect a hole or dip in the infrared radiation emitted by the Earth and sent into the space at exactly that part of the spectrum that corresponds to where CO2 absorbs radiation.” Can you please provide a link to your data source for this statement? I would like to see the actual spectrum. Thanks…

  3. Justin
    Dec 15, 2009

    How can you be so wrong, on so many facts, in such a short article! The only correct thing you say here “We really don’t know what the climate will do in the coming decades.”. But we do know how scientists have cooked the books, fudged the data, lied, attacked, evaded FOI requests and generally behaved badly. While you all worry about CO2, there are millions of people dieing right now from starvation, AIDS and disease. And you are worried about what might happen a hundred years in the future? Because of a possible temperature rise of 2 degrees? Get real, stop trying to waste our money on your faith. I am so pleased your Copenhagen Love In will fail. It will give you time to find some sense.

    • MattN
      Dec 16, 2009

      There are so many errors here, I simply quit reading half way through. CO2 simply can NOT heat the oceans to any great extent. CO2 “warms” through infrared radiation and infrared simply does not have enough energy to penetrate more than a few cm into the ocean. Visible and UV, however, does. CO2 *may* warm the ocean surface, true, but ocean heat content (measured down to 700m by Argo bouys)is simply not affected by CO2. It can’t…

      • Bill Chameides
        Dec 16, 2009

        MattN: Once again I am disappointed in your response — come on, MattN, you know better than that. Greenhouse gases heat the atmosphere. Some of the heated molecules in the atmosphere come in contact with the ocean and some of that heat diffuses/is conducted into the ocean — just as some of the heat melts glaciers. First the surface is heated and then that heat is in turn transported downward. Simple physics. How do you think the water in a pot on a stove heats up? Obviously the flame does not penetrate through the pot into the water. No, the heat from the flame increases the temperature of the pot and the heat from the pot is transported to the water, and not just the water in contact with the pot but all the water. Some of the heat is even transported into the air above the water. Check it out yourself — but please don’t put your hand too close. But I guess you know that.

        • MattN
          Dec 17, 2009

          http://www.noc.soton.ac.uk/bilko/module7/m7_l7.php?PHPSESSID=8308c451bc0e3f3bd7089edce35bcee4 “When light penetrates water, its intensity decreases exponentially with increasing depth. The rate of attenuation differs with the wavelength. The red part of the visible spectrum attenuates more rapidly than shorter wavelength blue light and infrared light hardly penetrates water at all.” Again, IR from CO2 re-radiation *may* warm the surface, but it does NOT have enough energy to penetrate much beyond a few cm. IR CANNOT heat the deep ocean to 700m, and ocean het content to that depth is THE MEASURE of global warming (According to a WHOLE LOT of credible scientists on both sides of this issue).

          • MattN
            Dec 17, 2009

            Try heating a pot of water with a torch from the top and let me know how far you get. Now, if CO2 could magically heat from the bottom of the ocean, then it might get somewhere….

            • Jim
              Dec 17, 2009

              Once again MattN, you fail to include the effect of CO2. If you go with your blowtorch and pot of water analogy, the reason the water does not heat much is because the heat rises and the heat escapes the pot. Now if you cover the pot and leave a hole for the blowtorch, then the heat eventually makes it way down into the water. The CO2 in the earth’s atmosphere is preventing the heat from escaping, so eventually the ocean waters warm, just as with the covered pot with the blowtorch.

              • MattN
                Dec 17, 2009

                I’d have better luck explaining this to my dog. The blowtorch IS the CO2 in the analogy. It’s the IR source. /out

                • Jim
                  Dec 17, 2009

                  CO2 is not and can not be an IR source in and of itself. The IR source is the sun. The CO2 simply traps the heat from radiating out once it is deposited by the IR source. Claiming that the blow torch is CO2 is an IR source simply is fallacy, a gas is not a source of heat, but it can trap heat. I don’t know where you learned your science.

                  • Bill Chameides
                    Dec 21, 2009

                    Jim, A few clarifications. 1. Gases are sources of energy – like all material above absolute zero temperature they radiate electromagnetic radiation. And CO2 when at ambient temperatures most definitely radiates in the IR and so by definition is an IR source. That’s basic physics, my man. 2. Actually the IR radiation related to the Greenhouse Effect does not come from the sun, it comes from surface of the earth and lower atmosphere, which is absorbed by atmospheric CO2 and re-radiated by that same CO2 back to the Earth’s surface. 3. Of course you are correct in one sense, and that is that virtually all the energy that drives the climate system does come from the sun. But most of that energy comes in the visible part of the spectrum not the IR.

                    • Jim
                      Dec 22, 2009

                      In the mean time I’ll get a basic book on physics and stick to computer science. My confusion came in because of the terms “Green house gasses” and “heat trapping gasses”. To me that implies that the radiation comes in, then the heat is trapped by the gasses, not that the CO2 actually acts as a source of IR. If the CO2 is a source of IR, does it radiate in all directions, including into space? From what I understand the sattellites have detected less and less of IR radiation in the spectrum that is absorbed by CO2, which would imply that the CO2 radiates back down to earth, but not into space. But it could be my incomplete understanding of the process.

                    • Bill Chameides
                      Dec 28, 2009

                      Jim: Good question. Yes, CO2 does radiate in all directions. But even so it acts to warm the planet. The simplest way to understand this is to realize that CO2 molecules in the middle of the atmosphere encounter more IR coming from below than from above. So in absorbing the upwelling and downwelling radiation and reraditaing it — ~50% downward and ~50% upward — less ends up going upward and more ends up going downward; i.e., back to the Earth’s surface.

                    • Jim
                      Dec 24, 2009

                      I just found this wonderful post over at science blogs that helped explain how greenhouse gasses work: http://scienceblogs.com/gregladen/2009/12/global_warming_the_blog_epic_0_9.php

                • Bill Chameides
                  Dec 21, 2009

                  MattN: I believe that your dog would believe you.

            • Bill Chameides
              Dec 21, 2009

              MattN: Actually that is exactly the way the ocean is heated – from above by the sun. Photons absorbed in the surface are converted to heat and the heat is then transported downward. And I guarantee you that if you blowtorched a pot of water from the top (for the record I do not suggest you do this), the water would heat up.

          • Bill Chameides
            Dec 21, 2009

            MattN: Think heat transport not photon transport.

©2015 Nicholas School of the Environment at Duke University | Box 90328 | Durham, NC 27708
how to contact us > | login to the site > | site disclaimers >

footer nav stuff