Monday, September 7, 2015

Global warming: how much heat, exactly?

It is often difficult to visualize what we are doing to our planet. But a simple calculation shows that the greenhouse effect generated by fossil fuels can be seen as the equivalent of turning on more than a hundred 1 kW electric heaters for each human being on the earth. And we can't turn them off!

If you look at the way climatologists describe global warming, you'll see that they use a lot the term "forcing"; that is, the additional effect of human activities to the natural heating from sunlight. Not all forcings increase temperatures, some tend to reduce it; for instance, atmospheric particulate. The overall result is called "imbalance" or "net forcing." You can think of a forcing in terms of someone trying to budge a person who doesn't want to move. If the person pushing is stronger, the net resulting force will cause the person being pushed to move. In the case of climate, the warming forcings are stronger than the cooling forcings, and the net result is a rise in temperature.

As we keep emitting CO2 and other gases in the atmosphere, the greenhouse forcing increases, as you see in the figure below (Hansen 2011).

In this figure, forcings are measured in terms of W/m2 (watts per square meter), as it is generally done in climate science. Unfortunately, it is a kind of unit that doesn't convey a feeling of the magnitude of what we are doing to our planet. A few watts per square meter are approximately equivalent to a single Christmas light, and that doesn't look worrisome. But, if you take into account the effect on the whole planet (510 million km2), then the overall forcing is gigantic. From Hansen's figure, you can calculate something like 1500 TW (terawatts, or trillions of watts) for the greenhouse gas forcing and around 500 TW for the net forcing. These numbers vary depending on which factors are considered; for instance, Zhang and Caldeira, (2015) consider the effect of CO2, alone, and calculate a forcing of 1.57 W/m2, that is about 800 TW. (For more data, see also Steve Easterbrook and Dana Nuccitelli et al.).

In any case, we are talking about huge numbers, at least hundreds of TW. For comparison, think that the total primary energy generated by burning fossil fuels is "just" about 15 TW, and practically all of it is eventually turned into heat. So, the indirect greenhouse warming effect is 1-2 orders of magnitude larger. We may also compare with the total solar irradiation that arrives to the earth's surface, around 90,000 TW (Szargut 2003). The effect of the sun is much larger than the human forcing, but not so much larger that the latter can be considered negligible. So, it is not surprising that human activities are causing a detectable warming of the whole planet.

Note also that we have been discussing just the effect of the current forcing. But, whereas the heat from burning fossil fuels is rapidly dissipated, CO2 remains in the atmosphere for a long time, tens of thousands of years and even more (Archer 2005). And this CO2 will keep warming the earth for a total effect that Zhang and Caldeira (2015) estimate as about 100,000 times larger than the direct thermal effect of the combustion that created it.

At this point, we can try to visualize these values by comparing them to something familiar. As an order of magnitude, let's take the number calculated from Zhang and Caldeira's paper, that is a forcing of 800 TW resulting from CO2 alone. That would correspond to 800 billion electric heaters of 1 kW each, all turned on together.

Considering that there are more than seven billion people on the earth, we may think that the CO2 forcing, alone, is equivalent to each one of us turning on a hundred electric heaters of one kW each. The net forcing - the actual heat being added to the atmosphere - is smaller, but the overall picture doesn't change: we can visualize it as corresponding to 250-400 billion heaters, about 50 per person. And, if we want to make the number of heaters proportional to energy consumption, people living in the rich West would be associated with many more. Imagine each home in your neighborhood stacking hundreds of electric heaters in their front yard, all turned on at full power, and you have some idea of what we are doing to our planet.

So, we have turned the heat on, and now we discover that there is no way to turn it off. (At least not as easily as you can turn off an electric heater). The best we can do, for the time being, is to avoid adding too many heaters to the ones already on. Even that seems to be extremely difficult, but we can at least try.

h/t Steve Easterbrook, Dana Nuccitelli, John Cook, Ben, Michael Tobis, John Abraham, and others. Note also that there are other attempts to visualize the total amount of heat generated by human forcing, for instance, in terms of "four Hiroshima bombs detonated per second" Spectacular, but probably less intuitive than electric heaters.



Archer, David (2005) Fate of fossil fuel CO 2 in geologic time  Journal of Geophysical Research vol. 110 (C9) p. C09S05

Hansen, J., M. Sato, P. Kharecha, and K. von Schuckmann, 2011: Earth's energy imbalance and implications. Atmos. Chem. Phys., 11, 13421-13449, doi:10.5194/acp-11-13421-2011.

Szargut, Jan T. 2003. “Anthropogenic and Natural Exergy Losses (exergy Balance of the Earth’s Surface and Atmosphere).” Energy 28 (11): 1047–54. doi:10.1016/S0360-5442(03)00089-6.

Zhang, Xiaochun,  Caldeira, Ken, (2015) Time scales and ratios of climate forcing due to thermal versus carbon dioxide emissions from fossil fuels,  Geophys. Res. Lett, 42, 11,  1944-8007


  1. Note that if we stop generating CO2 we will also stop generating aerosols, which will add an immediate 1 w/m2 step change increase in forcing and about a 50% increase in the rate of warming. I'm not saying we shouldn't reduce our CO2 emissions, but if we do we should be prepared for even faster warming in the short run.

    1. James Hansen used the term 'Faustian bargain' for this effect in a review paper 25 years ago in Nature . I still have my hard copy: Hansen & Lacis; Nature: 346, 23 August, 1990, 713 - 719

      He concluded, after outlining the imperative of higher priority government policies, and using as he put it the mid-American vernacular; "Otherwise we risk the danger of finding ourselves up the proverbial creek without a paddle". I think he covered most of the points we needed to know.

  2. The implications of the climate impacts of negative forcings shown on the chart are startling to this layman. In about 1992 the combination of human generated aerosols and a single volcanic event were sufficient to more than overcome all the effects of greenhouse gasses. I now understand how geoengineers like Bill Gates believe that they can control global warming as if it were yet another machine. Purposely producing a volume of aerosols equivalent to that of the volcanic event is not inconceivable. What is less credible is that the complexity of the planet''s geophysics can be understood and modeled adequately so that the impact of geoengineering forcings could achieve the desired results.

    In the real world that is not how humans behave. Take for instance the development history of nuclear energy. When we say nuclear energy we inevitably have in mind the solid fuel light water reactors that are the universal standard. A grossly expensive engineering nightmare, moderated by water at extreme pressures that will flash into hydrogen explosion instantly upon system failure requiring continual active systems to prevent runaway meltdown, fueled by zirconium clad fuel rods that are sourced from a single monopoly supplier, uses only 5% of the potential energy in the fuel and produces large volumes of highly radioactive long-lived waste. But that radioactive waste is exactly why civilian nuclear power was developed because the waste product could be made into the 7,000 plutonium bombs that a MAD country coveted.

    The blueprint for a different type of nuclear energy was proposed by the same individual scientist at the same time. The liquid sodium thorium reactor produces a fraction of the radioactive waste and most of that with a short half life, requires no active safety systems and passively shuts down automatically with no radioactive release, potentially could be manufactured by the hundreds on an assembly line, and uses a common fuel source with thousands of years availability. But its waste isotopes are unsuitable for bomb making.

    There are hundreds of dangerous light water reactors around the world, and not a single LFTR in operation. Why? Because humans fight wars against the other tribe--always have-- and progress is not about developing an energy system that could safely supply energy for everyone, but rather about developing a more deadly weapon to destroy the other tribe. Short of figuring out a way to weaponize geoengineering I can't see it being funded. And that is probably for the best!

  3. I think such presentations do more harm than good. For those who already understand the situation, they're unnecessary. For those who don't, just like the "four Hiroshimas per second," such people will say "50 one kilowatt heaters each for me, my spouse, and each of my two kids? I'd notice that instantly. It's obviously b.s." So, if you're going to use these, you need to be ready to explain how they're not noticing the four Hiroshimas per second or the 200 one kilowatt heaters in their locale.

    1. You may well be right. If people stick their heads in the sand, they won't notice anything, ever and will react to the next heat wave by saying "Mars is warming, too." Unfortunately, however, if we take this position, there is nothing ever that we will be able to do to carry the message. So, I think that we should at least try. Facing the idea of the electric heaters, some people will just shrug and click away. But some may gain a better understanding of the magnitude of the global warming effect.

    2. if they say its a silly idea because they would notice such heat, then there is a very simple answer. yes, their 50 heaters each would be very obvious if all in one place. but heat does not stay in one place. in reality their 50 heaters are spaced out all over the world, in the places where there arnt many people to see them. they will be over the open fields, the amazon, the pacific. out of sight, out of mind.

    3. I tend to support Rob's critical attitude. I even see such comparisons (atomic bombs, electric heaters . . .) as counterproductive, because they try to capitalize just on big numbers, in a kind of shock and awe tactics, that have no relation to physical relevant mechanisms.
      It is a characteristic feature of global warming, that the forcing power density is relatively faint in comparison to the total power flow - and that has, IMO, to be communicated. Even if a certain percentage won't get it. May be together with the information, that the ice ages have been triggered by much fainter forcings, i.e. the Milankovitch cycles.
      I plead for another focus: thinking together. In the media, not to speak about advertizing, topics as economy are still treated as if there is no such thing as global warming and the necessity of a structural change - only look at the outcry about Chinese stock exchange.

    4. I am sorry, dlen, but I think that "relatively faint" is a vague term that just doesn't convey much information. The point of a forcing is whether it detectably affects the system or not. And the forcing associated to greenhouse gases today is strong enough that it definitely affects the climate system.

      Quantifying the effects of the forcing is a matter of modeling, but in terms of communication I think an effort should be made to communicate the fact that this forcing is strong enough to cause a lot of damage to people. Then, how to do it is debatable, but we fight against a common attitude that sees human beings too small and weak to have any effect on the planet. Saying that the forcing is "faint" we just play into the hands of those who use this argument for denying climate science.

      And most people will continue to think that the vagaries of the Chinese stock exchange are more important than the ongoing destruction of the ecosystem.

  4. It's amazing to me the large amount of climate change denial that there is! Even if some scientists have a problem agreeing with the charts that are out there, all one has to do is observe the everyday happenings of the weather! Here in NYC, the drought has been taking its toll on the trees and grasses-as they are already beginning to change into fall colors in early September! There will be a few days of rain starting today, thankfully, so maybe that will help things a bit around here!

  5. Not only do you have to turn off your 50 heaters you have to forcefully turn off the 500 heaters 10 other people are using. They will not thank you for it.

  6. Hey Ugo, I think that most of those heaters are in the oceans where people can't see them :) ?

  7. Great metaphor!

    Also interesting to see it from the point of view of human metabolism :
    If you approximate 100W per human, then each of us lives with a thousand of "phantom people" heating up the atmosphere.
    I've heard that in rich countries we have (on average) about 200 "energy slaves" doing our bidding. Your number of 15TW gives an average of 20 "energy slaves" per human on Earth, so we're back to the factor of about 50 between what we use and the CO2 forcing...
    (and I hear methane, mostly from releases due to warming itself, is quickly catching up to CO2 these days in terms of causing the most warming...)



Ugo Bardi is a member of the Club of Rome and the author of "Extracted: how the quest for mineral resources is plundering the Planet" (Chelsea Green 2014)