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An open letter to Steve Levitt

Filed under: — raypierre @ 29 October 2009

Dear Mr. Levitt,

The problem of global warming is so big that solving it will require creative thinking from many disciplines. Economists have much to contribute to this effort, particularly with regard to the question of how various means of putting a price on carbon emissions may alter human behavior. Some of the lines of thinking in your first book, Freakonomics, could well have had a bearing on this issue, if brought to bear on the carbon emissions problem. I have very much enjoyed and benefited from the growing collaborations between Geosciences and the Economics department here at the University of Chicago, and had hoped someday to have the pleasure of making your acquaintance. It is more in disappointment than anger that I am writing to you now.

I am addressing this to you rather than your journalist-coauthor because one has become all too accustomed to tendentious screeds from media personalities (think Glenn Beck) with a reckless disregard for the truth. However, if it has come to pass that we can’t expect the William B. Ogden Distinguished Service Professor (and Clark Medalist to boot) at a top-rated department of a respected university to think clearly and honestly with numbers, we are indeed in a sad way.

By now there have been many detailed dissections of everything that is wrong with the treatment of climate in Superfreakonomics , but what has been lost amidst all that extensive discussion is how really simple it would have been to get this stuff right. The problem wasn’t necessarily that you talked to the wrong experts or talked to too few of them. The problem was that you failed to do the most elementary thinking needed to see if what they were saying (or what you thought they were saying) in fact made any sense. If you were stupid, it wouldn’t be so bad to have messed up such elementary reasoning, but I don’t by any means think you are stupid. That makes the failure to do the thinking all the more disappointing. I will take Nathan Myhrvold’s claim about solar cells, which you quoted prominently in your book, as an example.

As quoted by you, Mr. Myhrvold claimed, in effect, that it was pointless to try to solve global warming by building solar cells, because they are black and absorb all the solar energy that hits them, but convert only some 12% to electricity while radiating the rest as heat, warming the planet. Now, maybe you were dazzled by Mr Myhrvold’s brilliance, but don’t we try to teach our students to think for themselves? Let’s go through the arithmetic step by step and see how it comes out. It’s not hard.

Let’s do the thought experiment of building a solar array to generate the entire world’s present electricity consumption, and see what the extra absorption of sunlight by the array does to climate. First we need to find the electricity consumption. Just do a Google search on “World electricity consumption” and here you are:


Now, that’s the total electric energy consumed during the year, and you can turn that into the rate of energy consumption (measured in Watts, just like the world was one big light bulb) by dividing kilowatt hours by the number of hours in a year, and multiplying by 1000 to convert kilowatts into watts. The answer is two trillion Watts, in round numbers. How much area of solar cells do you need to generate this? On average, about 200 Watts falls on each square meter of Earth’s surface, but you might preferentially put your cells in sunnier, clearer places, so let’s call it 250 Watts per square meter. With a 15% efficiency, which is middling for present technology the area you need is

2 trillion Watts/(.15 X 250. Watts per square meter)

or 53,333 square kilometers. That’s a square 231 kilometers on a side, or about the size of a single cell of a typical general circulation model grid box. If we put it on the globe, it looks like this:


So already you should be beginning to suspect that this is a pretty trivial part of the Earth’s surface, and maybe unlikely to have much of an effect on the overall absorbed sunlight. In fact, it’s only 0.01% of the Earth’s surface. The numbers I used to do this calculation can all be found in Wikipedia, or even in a good paperbound World Almanac.

But we should go further, and look at the actual amount of extra solar energy absorbed. As many reviewers of Superfreakonomics have noted, solar cells aren’t actually black, but that’s not the main issue. For the sake of argument, let’s just assume they absorb all the sunlight that falls on them. In my business, we call that “zero albedo” (i.e. zero reflectivity). As many commentators also noted, the albedo of real solar cells is no lower than materials like roofs that they are often placed on, so that solar cells don’t necessarily increase absorbed solar energy at all. Let’s ignore that, though. After all, you might want to put your solar cells in the desert, and you might try to cool the planet by painting your roof white. The albedo of desert sand can also be found easily by doing a Google search on “Albedo Sahara Desert,” for example. Here’s what you get:


So, let’s say that sand has a 50% albedo. That means that each square meter of black solar cell absorbs an extra 125 Watts that otherwise would have been reflected by the sand (i.e. 50% of the 250 Watts per square meter of sunlight). Multiplying by the area of solar cell, we get 6.66 trillion Watts.

That 6.66 trillion Watts is the “waste heat” that is a byproduct of generating electricity by using solar cells. All means of generating electricity involve waste heat, and fossil fuels are not an exception. A typical coal-fired power plant only is around 33% efficient, so you would need to release 6 trillion Watts of heat to burn the coal to make our 2 trillion Watts of electricity. That makes the waste heat of solar cells vs. coal basically a wash, and we could stop right there, but let’s continue our exercise in thinking with numbers anyway.

Wherever it comes from, waste heat is not usually taken into account in global climate calculations for the simple reason that it is utterly trivial in comparison to the heat trapped by the carbon dioxide that is released when you burn fossil fuels to supply energy. For example, that 6 trillion Watts of waste heat from coal burning would amount to only 0.012 Watts per square meter of the Earth’s surface. Without even thinking very hard, you can realize that this is a tiny number compared to the heat-trapping effect of CO2. As a general point of reference, the extra heat trapped by CO2 at the point where you’ve burned enough coal to double the atmospheric CO2 concentration is about 4 Watts per square meter of the Earth’s surface — over 300 times the effect of the waste heat.

The “4 Watts per square meter” statistic gives us an easy point of reference because it is available from any number of easily accessible sources, such as the IPCC Technical Summary or David Archer’s basic textbook that came out of our “Global Warming for Poets” core course. Another simple way to grasp the insignificance of the waste heat effect is to turn it into a temperature change using the standard climate sensitivity of 1 degree C of warming for each 2 Watts per square meter of heat added to the energy budget of the planet (this sensitivity factor also being readily available from sources like the ones I just pointed out). That gives us a warming of 0.006 degrees C for the waste heat from coal burning, and much less for the incremental heat from switching to solar cells. It doesn’t take a lot of thinking to realize that this is a trivial number compared to the magnitude of warming expected from a doubling of CO2.

With just a little more calculation, it’s possible to do a more precise and informative comparison. For coal-fired generation,each kilowatt-hour produced results in emissions of about a quarter kilogram of carbon into the atmosphere in the form of carbon dioxide. For our 16.83 trillion kilowatt-hours of electricity produced each year, we then would emit 4.2 trillion kilograms of carbon, i.e. 4.2 gigatonnes each year. Unlike energy, carbon dioxide accumulates in the atmosphere, and builds up year after year. It is only slowly removed by absorption into the ocean, over hundreds to thousands of years. After a hundred years, 420 gigatonnes will have been emitted, and if half that remains in the atmosphere (remember, rough estimates suffice to make the point here) the atmospheric stock of CO2 carbon will increase by 210 gigatonnes, or 30% of the pre-industrial atmospheric stock of about 700 gigatonnes of carbon. To get the heat trapped by CO2 from that amount of increase, we need to reach all the way back into middle-school math and use the awesome tool of logarithms; the number is

(4 Watts per square meter) X log2(1.3)

or 1.5 Watts per square meter. In other words, by the time a hundred years have passed, the heat trapped each year from the CO2 emitted by using coal instead of solar energy to produce electricity is 125 times the effect of the fossil fuel waste heat. And remember that the incremental waste heat from switching to solar cells is even smaller than the fossil fuel waste heat. What’s more, because each passing year sees more CO2 accumulate in the atmosphere, the heat trapping by CO2 continues to go up, while the effect of the waste heat from the fossil fuels or solar cells needed to produce a given amount of electricity stays fixed. Another way of putting it is that the climate effect from the waste heat produced by any kind of power plant is a one-off thing that you incur when you build the plant, whereas the warming effect of the CO2 produced by fossil fuel plants continues to accumulate year after year. The warming effect of the CO2 is a legacy that will continue for many centuries after the coal has run out and the ruins of the power plant are moldering away.

Note that you don’t actually have to wait a hundred years to see the benefit of switching to solar cells. The same arithmetic shows that even at the end of the very first year of operation, the CO2 emissions prevented by the solar array would have trapped 0.017 Watts per square meter if released into the atmosphere. So, at the end of the first year you already come out ahead even if you neglect the waste heat that would have been emitted by burning fossil fuels instead.

So, the bottom line here is that the heat-trapping effect of CO2 is the 800-pound gorilla in climate change. In comparison, waste heat is a trivial contribution to global warming whether the waste heat comes from solar cells or from fossil fuels. Moreover, the incremental waste heat from switching from coal to solar is an even more trivial number, even if you allow for some improvement in the efficiency of coal-fired power plants and ignore any possible improvements in the efficiency of solar cells. So: trivial,trivial trivial. Simple, isn’t it?

By the way, the issue of whether waste heat is an important factor in global warming is one of the questions most commonly asked by students who are first learning about energy budgets and climate change. So, there are no shortage of places where you can learn about this sort of thing. For example, a simple Google search on the words “Global Warming Waste Heat” turns up several pages of accurate references explaining the issue in elementary terms for beginners. Including this article from Wikipedia:


A more substantive (though in the end almost equally trivial) issue is the carbon emitted in the course of manufacturing solar cells, but that is not the matter at hand here. The point here is that really simple arithmetic, which you could not be bothered to do, would have been enough to tell you that the claim that the blackness of solar cells makes solar energy pointless is complete and utter nonsense. I don’t think you would have accepted such laziness and sloppiness in a term paper from one of your students, so why do you accept it from yourself? What does the failure to do such basic thinking with numbers say about the extent to which anything you write can be trusted? How do you think it reflects on the profession of economics when a member of that profession — somebody who that profession seems to esteem highly — publicly and noisily shows that he cannot be bothered to do simple arithmetic and elementary background reading? Not even for a subject of such paramount importance as global warming.

And it’s not as if the “black solar cell” gaffe was the only bit of academic malpractice in your book: among other things, the presentation of aerosol geoengineering as a harmless and cheap quick fix for global warming ignored a great deal of accessible and readily available material on the severe risks involved, as Gavin noted in his recent post. The fault here is not that you dared to advocate geoengineering as a solution. There is a broad spectrum of opinion among scientists about the amount of aerosol geoengineering research that is justified, but very few scientists think of it as anything but a desperate last-ditch attempt, or at best a strategy to be used in extreme moderation as part of a basket of strategies dominated by emissions reductions. You owed it to your readers to present a fair picture of the consequences of geoengineering, but chose not to do so.

May I suggest that if you should happen to need some friendly help next time you take on the topic of climate change, or would like to have a chat about why aerosol geoengineering might not be a cure-all, or just need a critical but informed opponent to bounce ideas off of, you don’t have to go very far. For example…


But given the way Superfreakonomics mangled Ken Caldeira’s rather nuanced views on geoengineering, let’s keep it off the record, eh?

Your colleague,

Raymond T. Pierrehumbert
Louis Block Professor in the Geophysical Sciences
The University of Chicago

807 Responses to “An open letter to Steve Levitt”

  1. 1
    jyyh says:

    Lol, the route avoids administration building and the chemistry labs.

    [Response: Yeah, I noticed that. I just went with the walking route Google Maps picked out. Google doesn’t know about where you can walk through campus, evidently. And also tends not to take shortcuts routed through buildings. –raypierre]

  2. 2
    Steve Missal says:

    I actually laughed out loud at this. Too good. Dr. Levitt had best skedaddle to an ethics class, along with a sizable portion of his quasi-denialist peers, and try to remember what integrity was. Or is. It’s one thing to play loose and fancy with facts in the sale of a used car. It’s quite another to fiddle with facts when the fate of a planet is on the line.

  3. 3

    It’s always great when really important things can be demonstrated with
    simple arithmetic. Wonderful post!

  4. 4
    Hank Roberts says:

    Hm, carefully picked the long-way-’round route to avoid any risk he’d accidentally get to that circle and just keep going ’round and ’round, eh?
    But seriously, I hope the fellow listens to you, and then counts to ten.
    Several times. “You may very well be right” is one of the smartest responses I know of to this kind of lecture, when anyone cares enough to give it.

  5. 5
    Richard Pauli says:

    Thanks. Given the importance of the issue, your tone was very civil.

    Should you have included instructions on how to read the map?

  6. 6

    Thank you, professor Pierrehumbert. I would add that the present temperature of the Universe is 2.7 degrees Kelvin [2.7 degrees above absolute zero Centigrade or 270 Centigrade below zero]. This gives the Earth a very cold resevoir in which to dump excess heat forever. And the Universe as a whole is cooling off. The temperature of the Earth is regulated by greenhouse gasses.
    The problem is, how to get your letter above the same or greater publicity and distribution as your opponent got.

  7. 7
    Jonathan says:

    What an embarrassing predicament for Prof. Levitt! To be flayed in such a precise and devastating manner. I (sadly) agree with Prof. Pierrehumbert’s public reproach; the offense is too flagrant. I have read Freakonomics, but not Superfreakonomics. I felt Freakonomics was shallow in treatment of topics in which I have no background. Prof. Pierrehumbert’s analysis in a field of which I do have a background leads me to question anything that has been written by Dr. Levitt! How sad. I enjoy Real Climate and thank the authors for their articles, analysis and explanations. I thank the participants, too, for lively conversation if not communication. Cheers. JG

  8. 8
    pt says:

    I wouldn’t reference Wikipedia. Its not peer-reviewed.

  9. 9
    Steve Bloom says:

    Arguably, it gets worse: On the Diane Rehm show a couple of days ago Levitt addressed the ocean acidification problem by claiming that all we would need to do is dump a bunch of base into the oceans.

    [Response: That’s another arithmetic assignment then. How much Drano do you have to dump into the ocean? What fraction of the world’s shipping is that? How much CO2 do you emit schlepping that around? What does it add to the costs of geoengineering? What if you do it with limestone instead of Drano? –raypierre]

    [Response: Given the bulk required, you could only use limestone. The white cliffs of dover would do nicely. Roughly 20 Gt CaCO3 every year is required to neutralise 2 Gt C (at current rates). (according to the Royal Soc report (p45)). – gavin]

  10. 10
    ubrew12 says:

    Now perhaps we know how most American economists missed the greatest housing bubble/ derivatives superbubble ever unleashed on the American public.

  11. 11
    BJ_Chippindale says:

    That was definitely worth more than the price of admission!



  12. 12
    Canada Guy says:

    Well, there’s nothing wrong with looking for simple, cheap, and easy fixes, there are some to find, but not many. Of course, geoengineering isn’t going to provide any of that, as this site and others have well documented.

    But we already have some easy, simple fixes that don’t require lifestyle changes or even sacrifice. Number one, at Copenhagen, if they do nothing else, they should sign an international agreement to ban the mass production and sale of plastic water bottles. I wrote an article about this today:

    This is low-hanging fruit. The biggest sacrifice anyone might endure is going back to what they used to do 10 or so years ago. Yet this would produce substantial savings of energy and resources and would result in a real global reduction in carbon emissions.

    This wouldn’t be close to enough, of course, but this is the easy stuff. We also need changes to transporation infrastructure and industry on a global scale (and especially in the US.) That will be more difficult. But if we can’t even do the easy stuff, how do we expect to tackle the hard stuff?

  13. 13
    Joëlle LEROY says:

    Merci beaucoup pour votre article. Je le transmets autour de moi dès à présent.

    Thank you so much for your contribution. I’ll transfer it to my english speaking relatives and friends right away.

  14. 14
    Ian says:

    As always, nice thorough work! It’s a pleasure to read, and unfortunate it’s even necessary…

  15. 15
    L says:

    It surprises me when serious academicians do not do the arithmetic properly and that includes scientists. The thing to do the arithmetic for is the mining of Li or whatever new tech for batteries and the Cd/Si/Ga/As/In/Se etc for the panels. Also their safe disposal..the energy requirement for their disposal after the 20 years or whatever of use, their pollution of ground/water etc . It is these that must be weighed in the balance before embracing total solarisation of the power segment. However, my layman vote is still for solar power.

  16. 16
    L says:

    One more thing, what about never wearing dark clothes. Increase your reflectiveness by only wearing white clothes… maybe we can cook up numbers to prove that if everyone wore only white clothes, we can reverse global warming! The population is growing afterall!

  17. 17

    So what the map tells us is that economics is a lot closer to theology than climatology is ;-)

    I thoroughly enjoyed this post. Substance, style, education value, gentle humour… this is the way to do it.

  18. 18
    Chris says:

    #16 Despite the close proximity of the economics and theology, I suspect not even God knows how the global economy operates….

  19. 19
    Mark says:

    “Also their safe disposal..the energy requirement for their disposal after the 20 years or whatever of use, their pollution of ground/water etc”

    Why throw these valuable materials away?

    Why not recycle them.

  20. 20
    Donald Oats says:

    Very vivid and clear. Personally, I prefer to see these sorts of arguments raised when objecting to the rather baseless claims made by the well-known denierati. For people without much scientific background, I think they would especially appreciate the picture of the world with the little black rectangle on it – it makes the whole argument you are putting forward resonate, and hopefully sways the still skeptical to at least follow your argument through to the end.

    At the end of the day it is the simple comparisons of scale, energy, cost, and emissions that will convince people that attempting to reverse CO2 emissions growth rate is not catastrophic to the economies; indeed, a rapid transition will involve employment opportunities that were lost in the recent global finanical crisis.

    Well done.

  21. 21
    CM says:

    Steve Levitt: thanks for provoking Ray Pierrehumbert into posting again.

  22. 22
    Iain Inglis says:

    When reading Myhrvold’s original comment I did wonder whether the efficiency was relevant, since the 15% will end up behind the fridge. The efficiency does, of course, matter when calculating the coal-generated electricity substituted and the CO2 therefore saved.

  23. 23
    jyyh says:

    If all humans wore whites and laid down in Saudi-Arabia would it make a difference? Should try to get back to work.

  24. 24
    Mark says:

    Donald, the problem is getting that small black square in the public eye.

    Fox won’t show it.

    The BBC would have to have “balance” and post both the black square and any unrebutted mumblings of how that black square is all wrong from the denialists.

    Sky won’t show it.

    ABC won’t.


    What you can do is get that black square mentioned as often as possible and maybe it will get picked up when it becomes well known enough to be unignorable.

  25. 25
    ML says:

    Dear Realclimate,

    It is with immense relief that I read the above, clear and logically stated argument that puts this issues into very easily understandable perspective. Thank you so much. I just hope Steve Levitt can read this and offer a reply. Realclimate does the world a real valuable service. Thank you.

  26. 26
    Tony Rogers says:


    An interesting post. I hope that the following is sufficiently on-topic because I would welcome your opinion of my arithmatic.

    One number from your post caught my eye as it related to a calculation I had done myself; that of 0.012 Watts per square meter of waste heat from electricity production. I made a calculation for total fossil fuel production (and therefore released energy) and obtained a figure of 0.026 Watts per square meter for the year 2000. This seems reasonable given your figure.

    My interest was to compare the possible effect of waste heat on the temeperature of urban areas. To do this I made some (wild!?) assumptions that 50% of the world population lived in urban areas but 90% of waste heat was released in urban areas (power stations, industry and residential vs residential/low tech in rural areas). I used world population and a an estimate of urban population density to calculate an estimate for the area of the earth’s surface that was “urban”.

    Using this method I obtained figures for waste heat in urban areas of 7.7 W/m^2 in 1900 and 20.6 W/m^ in 2000. These seemed like fairly significant numbers to me.

    Would you expect such changes in waste heat to have a significant effect on the instrumental record of urban temperature records? Are the adjustments made to urban temperature records sufficient to account for such a large release of waste heat? It makes me wonder whether urban temperature records are of much use.

  27. 27
    tharanga says:

    Given that the emissions due to manufacturing solar cells figured pretty heavily into the assertion in Superfreakonomics, it’s perhaps worth more than just a passing mention. Perhaps somebody (need not be this author) should write a follow-up on that.

  28. 28
    Mark says:

    “Would you expect such changes in waste heat to have a significant effect on the instrumental record of urban temperature records? Are the adjustments made to urban temperature records sufficient to account for such a large release of waste heat?”

    Oh dear.

    We have another surfacestations acolyte here.

    Look at the NOAA use of the 72 “good or excellent” stations that Watts noted in the same analysis of temperature trends and you’ll see that whatever correction is made to those other “UHI affected” stations is good enough to make the unaffected stations read the same trend.

    If the corrections made were not enough, then there would be a difference when you include the corrected records of these sites.

  29. 29
    Foobear says:

    I just finished the book yesterday, and was expecting Real Climate to get its collective panties in a bunch over Super Freakonomics. The most important point in the book – that 1) it is difficult-to-impossible to actually implement the kinds of hippie changes people like Al Gore advocate (nearly every zero-carbon advocate is a horrible hypocrite on the matter) and 2) There can be approaches that will solve the problem without plunging the world into a permanent economic depression, which is more unethical than emitting CO2 into the atmosphere.

    Also, his points on the anti-scientific claims that a lot of Al Gore clones make (“CO2 is a poison!” “Our lifestyle is unsustainable!”) are all perfectly valid.

    Hell, if we really want to stop global warming, all we really have to do is get our coal plants to start belching tons of particulate matter into the air again. Of course, acid rain will start making a comeback, but you can’t have it all, right?

    [Response: If Levitt is unable or unwilling to do basic energy accounting when thinking about solar cells,why do you trust him to get the economic arguments right? I certainly don’t. His claims about economic catastrophe from carbon mitigation are just economic alarmism. –raypierre]

  30. 30
    yomismo says:

    The changes of Mr. Levitt replying to this are even lower than the effect of waste heat on global warming.

    But hey, let us not allow science to get on the way of selling books

  31. 31
    Mark says:

    Ah, foobear is panty-bunching.

  32. 32
    Thomas Huld says:

    Another little back-of-the-envelope calculation, just for fun.

    This summer the arctic sea ice area was about 1.0 million km2 less than the average for 1979-2000, ( which is 17 times more than the PV area calculated by Ray.

    Assuming albedo=0.45 for ice and 0.1 for water gives the same difference as between sand (0.45) and PV modules (0.1, actually) (

    The average irradiance at 80deg.N 20deg. W is about 83W/m2 (see, which is about one-third that used by Ray.

    The net result is that the contribution to the heating of the earth from missing sea ice is about 6 times greater than using PV to generate 100% of our electricity.

  33. 33
    Fubar says:

    When you have no argument to make…invoke Al Gore’s name as often as possible. It’s the Godwin’s law equivalent for climate change.

  34. 34
    Stephen Pranulis says:

    Gee, foobear, haven’t you ever read “How to Win Friends and Influence People”? BTW, CO2 is a poison for air breathing animals last I checked, and it has an LD50 (is lethal to 50percent of the population) of about 100,000 ppm and starts causing various problems well below that level. And its great to hear from you that our current lifestyle is sustainable. What, by the way, is our current lifestyle? And for how long? Cheers.

  35. 35
    BCC says:

    It’s not like there’s no easily accessible research on this topic:

    Nemet, G.F. (2009). “Net radiative forcing from widespread deployment of photovoltaics.” Environmental Science & Technology 43(6): 2173–2178.

    Surprise! Albedo impacts are generally very small.

  36. 36
    Todd Albert says:

    You’ve done it again! I can’t help and chuckle, but it is also so sad that people are walking around believing the garbage that they read in these books — which seem a last ditch effort to thwart the science — and what is touted in the media.

  37. 37
    Marcus says:

    Great post – small, picky point: “250 Watts per square meter of sunlight”: Technically, you’re probably placing your solar cells at the equator, so 1000 W/m2 divided by pi = about 320 W/m2 of sunlight for your solar cell, right? (eg, rather than the average solar for the planet which is 1370/4*0.7 = 240)

  38. 38
    Polarbear says:

    Foobear: Who claims “CO2 is a poison”? A google search on the claim brought 65 hits, all of them from somebody claiming that someone else has claimed it. The “Al Gore clone” claiming CO2 is a poison is a mythical creature, as rare as the yeti…

  39. 39

    I emailed this to Dr. Levitt’s university email address, which I’m sure the author also did. Interesting to see if he replies. Thanks again, RealClimate! Keep up the great work!

  40. 40
    jr says:

    @37 you get more W/m^2 at the surface in the tropics than you do at the equator.

  41. 41
    robert says:

    Re: #15… I suspect Levitt did indeed do his basic artithemtic properly. Let’s see, that’s 3 million copies, selling at an average of $20 per…

  42. 42
    Lucas says:

    Levitt also ignored the possibility of recovering the waste heat (i.e., solar co-generation) for hot water and air heating applications.
    So he flunked the basic math of waste heat and global warming and he also treated WH as a worthless product.

  43. 43
    Thomas Huld says:

    Marcus @37: Your last formula giving G=240W/m2 is the radiation absorbed by the earth. But some of does not reach the ground (absorption in the atmosphere). The average irradiance at the ground is around 198W/m2.

    The radiation is not necessarily highest at the equator. Have a look at our site: .

    If you try a place in the desert, say 27.4degs.N 13.5degs.E (Libyan desert) you get average yearly G=252W/m2 (annual average daily irradiation divided by 24 hours). It’s not the absolute highest value (eastern Chad is nearly 300W/m2), but it’s a location where large-scale solar energy plants could supply the European market.

  44. 44
    Rando says:

    I’m curious about this statement….”All means of generating electricity involve waste heat” and how this applies to hydro-electric power generation.

    [Response: Good point. The ‘waste’ heat in hydro is actually the same as you would have had anyway as the rivers ran to the sea, so this is not contributing. Wind power as well is probably close to ‘waste heat’ neutral. – gavin]

  45. 45
    A Siegel says:

    Thank you very much for this quite thoughtful and well-done examination of this element of deception and shallowness in the book. Both appreciated and learned from it.

    Sadly, Superfreakonomics is now getting 593,000 google hits. This tremendous open letter has 2400. That is a gap worth filling.

    By the way, re ‘geoengineering’, they could have tried to make an argument that ‘we don’t see emissions being driven down fast enough, therefore we should be working on geoengineering as part of the solution sets’. That sort of reasoned discussion, however, wouldn’t have been such a book seller and made them heros in the anti-science syndrome suffering community.

    As long as I’m on the subject of geoengineering, seems that a question is what are core principles that should govern examination and prioritization of geoengineering options (after, of course, energy efficiency, clean energy, and other steps to reduce emission levels). As postulated here, it seems that ‘win-win-win’ techniques are the most valuable to pursue. For example, cool roofing makes sense for energy efficiency, urban heat island, comfort levels, and financial reasons — and a very large global cool roofing program could help lower global temperatures. A significant biochar/agrochar program globally could contribute to enrichment of soil & increased agricultural productivity while sequestering significant amounts of carbon. Etc … Note that Levitt/Dubner failed to lay out such principles to guide any potential investments in / pursuit of geoengineering paths.

  46. 46
    Mark says:

    “For example, cool roofing makes sense for energy efficiency, urban heat island, comfort levels, and financial reasons — and a very large global cool roofing program could help lower global temperatures.”

    Yup, a great idea. Not so great painting the roads etc or even the pavements (which in the UK would quickly become dog-doo-brown and pavement-pizza-orange in no time anyway).

    But still people complain “But it gets really COLD here! I want as much warming of the roof!”. And then complaining that it’s not the same when you point out that their roof is generally covered with snow which tends to be white anyway and is, in any case, a good insulator.

    All it needs is roofing tiles to be made white.

  47. 47
    steve levitt says:


    I enjoyed your intentional misreading of my chapter
    on global warming! I think it has really contributed
    to moving towards a solution to these important problems.

    Myrhvold’s *main* point was about the energy required
    to produce the solar cells, not the radiated heat.
    He has expanded on it here:

    His view is simply that solar panels are not a
    *short-run* solution to cooling the planet. I doubt
    you could disagree with that, given the arguments
    you make in your own blog post.

    So he, and we, thought it made sense to explore
    some solutions that DO cool the earth in the short-run.

    That doesn’t mean you don’t work on long run solutions
    as well.

    I’m not sure why that is blasphemy.

    Steve Levitt

    [Response: Steve, glad to see you’re reading this. Something I have found rather bizarre about your responses to the criticisms of your climate chapter is the way you continually try to change history about what you actually wrote, which is plainly there for anybody to see. I found it so unbelievable that you included the “black solar cell” meme when I first heard it that I actually went over to Borders and stood there and intentionally read (not misread) the chapter to see if it was true. Anybody reading what you wrote would never, ever guess that the waste heat effect was so trivial unless they already knew the subject from some other source. And as for the “short term vs. long term” issue, here’s something to chew on: if you instantaneously built a solar array big enough to meet the entire world electricity demand, you would only have to wait something under a year before the avoided CO2 radiative forcing paid back the waste heat effect. The payback time for recouping the carbon cost of manufacturing solar cells is somewhat longer, but still substantially less than the lifetime of the solar cells — and coming down as technology improves. So, there is really no sensible construction I can put on your statement.

    Now regarding geoengineering, your “global warming quiz” in the NYT Freak blog had the main danger of geoengineering laid out right in front of you, but you failed to see it. Namely, you see the rapid recovery time after Pinatubo as evidence that geoengineering is harmless because you can reverse it any time. However, the bigger implication of that fact is that if you rely on geoengineering to allow the economy to burn up all the coal and raise the atmospheric CO2 to high levels, then if you ever have to stop, you are hit with the full effects of maybe a century or more of global warming practically all at once. What’s more, you don’t even get to know how much it will warm after stopping until you actually stop. That’s because of the uncertainty of predictions of climate sensitivity. Even if we take a long time to bring down emissions, at least we’ll know what state the planet is in because the warming can be monitored as we go along and work towards zero emissions. The Atlantic Monthly writer, who interviewed both me and Ken pretty extensively, did a good job of bringing that sort of thing out. –raypierre]

  48. 48
    Marcus says:

    Re: 43: Thomas, thanks for the additional information. My original calculation, using 1000 W/m2, was meant to take into account the atmospheric absorption… but obviously, I missed some other correcting factor. Does your number include cloudiness? I guess that would make a difference for equator vs. tropics…

  49. 49
    Susann says:

    I read Freakonomics but I won’t be reading Superfreak. I will be posting about that black square and emailing it to all my contacts though, because I can bet this errant thinking will be hauled out as evidence by both denialists and just plain misinformed readers. It needs to be countered.

  50. 50

    Well done Ray! I was writing a piece on this myself (and had just emailed Gavin for advise on reasonable albedo change –> CO2-eq conversions), but it would probably be superfluous now.

    That said, there does seem to be some lingering misconceptions in the general public about the role of different “stock” and “flow” forcings. For example, the whole effort to paint roofs white touted by Chu and his LBNL colleagues comes with some impressive numbers, but albedo-related mitigation is less important than GHG mitigation right now simply because it would be just as easy to paint those roofs white in 2050 as today, which we cannot easily remove the forcing from CO2 emitted in the interim. Indeed, given the turnover rates of housing stock and the fact that the economic impacts of climate change grow exponentially with forcing, it might be possible to model the relative benefits now and later of “flow” mitigation (e.g. albedo changes) and GHG “stock” mitigation.

    [Response: The issues of green roofs vs. white roofs is pretty fascinating. I looked into this closely when I was on Mayor Daley’s climate task force. Part of the advantage of green roofs is that they have a pretty high albedo but don’t require much maintenance to stay that way in a city, which is an advantage over white roofs. On the other hand, their biggest cooling effect comes from evaporation, and that just takes energy out of the building and puts it into the atmosphere, so it’s a wash so far as the planet goes. But, for either green roofs or white roofs, the big climate impact comes from the reductions in air conditioning needed, which reduces the CO2 emitted. –raypierre]