Built on Facts

Earth Hour

I have a Fermi problem for you. By the very nature of a Fermi problem, a precise answer is impossible, we’re merely looking for a justified order-of-magnitude estimate. Here goes:

During last week’s Earth Hour event, what amount of CO2 was not released that otherwise would have been? What is that number in terms of percentage reduction compared to the total worldwide CO2 release during an equivalent time period not during Earth Hour?

Now I’m not knocking the idea. I like to see people avoid trashing the biosphere too badly. Doubly so when it’s possible to shave some money off of the electric bill. I have almost precisely the same set of environmental opinions as Mike Rowe. The Earth is incredibly, unbelievably amazing. So are the staggering wonders of human technological achievement and mastery over many of the forces of nature. They can conflict, but there’s no reason they have to. Those guys Mike meets who turn landfill methane into energy (or any of a hundred other things) do more than any celebrity benefit concert can even think about doing to actually keep the environment on an even keel.

But I’m lapsing into preacher mode here and that’s boring. The Fermi problem was not rhetorical, I’d actually be very interested in a figure. Wikipedia has some local data as a starting point for estimates.

Extra credit: how many coal power plants would have to be replaced by nuclear plants to achieve earth-hour level reductions in emissions rates permanently?


  1. #1 Russell
    March 31, 2009

    My guess would be “zero.” It will be interesting to see if the power companies report any statistically significant deviation from demand during that time.

  2. #2 Brian
    March 31, 2009

    I would concur. It would depend on the average ratio of incandescent bulbs to CFL, and the average amount of heating. In the NE and NW, I would a functionally 0% change, possibly a thousandth of a percent or less.

    At someplace like Vegas, where a lot of the lights on the strip were dimmed, you might see a 1-5% reduction during that time, at best.

    That’s about as Fermi as I’m going to get.

  3. #3 Scott Belyea
    March 31, 2009

    Worldwide? No idea.

    But as one more data point, the drop in demand in Toronto and area was reported to have been in excess of 15%.

  4. #4 Ville Lindholm
    March 31, 2009

    In Helsinki the figure quoted in the papers was on the order of a few megawatts, so it’s probably in the gigawatt range worldwide. (Helsinki wasn’t very active in Earth Hour either.)

  5. #5 Stephen
    March 31, 2009

    The figure given for the Netherlands was a reduction of 50 MW, or about 8W per household. That’s not going to save many polar bears.

  6. #6 MRW
    March 31, 2009

    Complications to be considered:
    1) Some used batteries (for example, there were web sites that recommended blogging earth hour on your laptop) to replace outlet power. That would hide some of the energy usage/carbon production and might even increase overall energy usage for a device over what would have been with it plugged into the wall.
    2) Candles are not carbon-neutral.

  7. #7 Joshua Zelinsky
    March 31, 2009

    This is going to be difficult to estimate without a better idea of how many people participated. There are two distinct approaches to this problem:

    1) Empirical, using some of the data from locations that gave actual estimates of how much was saved and extrapolate from there. The primary problem with this method is that places that had many people doing this are much more likely to report on it than areas that did not. This could lead to overestimating.

    2) Estimate how many people did it and estimate how much energy a person would save. If we do this we should keep in mind that individuals who do this are more likely to be people who are already somewhat more efficient than people who don’t (more likely to have already switched away from incandescent bulbs for example).

    I’m going to go with the first type of estimate since it is easier to do and since Stephen gave us a starting estimate to work with. Assuming that the Netherlands are roughly representative and restricting ourselves to developed nations, the Netherlands have a pop of about 20 million, the developed world has a pop of about 4 billion. So assuming the rate overall was about the same that gives us around 10,000 MW or about 10 GW. This may be an overestimate since the Netherlands is already more environmentally conscious than much of the rest of the world. On the other hand, they are also more efficient to start with so that’s a reason that this is an underestimate. Between 1 and 15 GW is probably a safe estimate.

  8. #8 Michael F. Martin
    March 31, 2009

    10 billion people in developed world (where “Earth Hour” is publicized)

    1 in 10 are reached by publicity of Earth Hour

    1 in 10 of those remember to act on publicity by turning off lights

    100 watt-hours saved by each of those persons during Earth Hour

    = 100 Megawatt-hours saved

    or about 0.1 % of the total electricity generated in the U.S. that hour


    These things are good for raising awareness, but not a practical solution to energy savings.

  9. #9 MRW
    March 31, 2009

    Regarding my earlier comment…

    The Earth Hour website actually prominently recommended taking pictures & videos and live blogging & tweeting during the hour. All of those use energy.

    From the Christian Science Monitor
    It looks like a candle produces carbon at about the same rate as a compact fluorescent lamp. If you use more than one candle per lamp that you turned off, you’re actually producing more carbon than if you’d just left the light on.

  10. #10 CCPhysicist
    March 31, 2009

    I know it wasn’t much, because I didn’t see any news stories about the collapse of the electrical grid due to a sudden massive drop in demand and a failure of standard “load shedding” mechanisms to handle the problem – like when a broken transmission line leads to a cascading failure.

    You can’t just turn off a power plant when everyone pulls the main breaker at the same time.

  11. #11 Uncle Al
    March 31, 2009

    More than a million illegal Mexicans flood north over the California border each year. How many compact fluorescent lamps should Californians buy to offset that energy-using increment, annually and cumulatively? One hour of light abstinence is Bristol Palin bushwa.

  12. #12 Chris
    March 31, 2009

    You missed the point if you light candles to replace the lights. As I understood it, it’s much more just an effort to make people aware of things they could turn off without impacting their lives. Ideally they’ll carry this forward.

    The real payback occurs over time. Replacing light bulbs with CFL is nice, but imagine replacing half of the computers with ones built on top of laptop guts. That can cut power usage dramatically, as seen by replacing heavy power supplies (300+ W) with warts. Those systems are good enough for all of the tasks needed by most people. (MS Office, surfing, email, youtube, hulu.) Remembering to turn off copiers and laser printers.

    Of course all it takes is one widescreen plasma TV to make all of the other changes moot. 🙁

    P.S., and sometimes you learn that you really do need the ‘waste’ light. I leave a CFL light on in another room at night. I tried other things but the combination of a large black dog and a large dog the same color as the carpet has proven that anything less tends to result in problems when the older dog routinely needs to go out at 3 AM.

  13. #13 humorix
    March 31, 2009

    In 1948, Citroen throws the car 2 cv. With a central lighthouse (1!) with glow-worms to light !(in french)
    It is THE car of tomorrow!

  14. #14 Charlie
    March 31, 2009

    Uncle Al, “Bristol Palin bushwa” sounds nasty! I don’t want any.

    We turned everything off and took a nap during earth hour.

  15. #15 rob
    March 31, 2009

    10^10 people in the world, 1/10 of which turn off one 100 W bulb for 1 hr:

    3600 s x 10^10 x 100 W = 3.6e14 Joules not expended.

    During coal combustion, say each 10 eV of energy released creates 1 CO2 molecule.

    3.6e14 Joule x 6e18 eV/Joule x 1 CO2/10 eV = 2e32 molecules of CO2.

    2e32 molecules x 1 mole/6e23 molecules = 3.6e8 moles

    CO2 is 44 grams per mole, so

    3.6e8 moles x 0.044 kg/mole = 1.6e7 kg of CO2.

    so about 16,000 tonnes of CO2 was not emitted.

    27,245,758,000 tonnes of CO2 is produced worldwide in a year (from wikipedia).

    2.7e10 / 365 days /24 hour = 3e6 tonnes per day.

    1.6e4/3e6 = 0.005

    this is a recuction of about 1/2 percent versus a normal hour of energy consumption.

  16. #16 Uncle Al
    March 31, 2009

    10^10 people in the world, 1/10 of which turn off one 100 W bulb for 1 hr: No more than 7 billion people overall, perhaps 4 billion of whom might have lightbulbs.

    Tabulated heats of combustion for coals range from 2.4-3.2×10^7 J/kg. The all-purpose heat of combustion rule: 5 eV for every molecule of O2 used. This gives 4×10^7 J/kg for pure carbon oxidized to CO2, and is consistent.

    Let’s conservatively rescale your 0.005% to 0.0005% (at least 1/3 the world was asleep anyway). “This is a reduction of about 1/20 of 1 percent versus a normal hour of energy consumption worldwide.” It is piffle, bupkis; Enviro-whinerism. 99.9995% is 100%.

  17. #17 MRW
    March 31, 2009

    “at least 1/3 the world was asleep anyway”
    Really? At 8:30 local time? Seems like an overestimate.

    On the other hand, the 100W/bulb seems like an order of magnitude overestimate. Those likely to participate are also likely to have compact fluorescent lamps, I would think.

    These 1 lightbulb per person calculations seem to leave out the effect of businesses/landmarks turning off the lights – are those significant effects?

    Chris – Yes, you’ve probably missed the point if you burn candles to replace electric light, but I think a lot of people missed that point.

  18. #18 nanoAl
    April 1, 2009

    Well, last time, Canada averaged a 9% drop, and the province of BC saved about 125 MegaWatts(with about 3 million people). BC has a really high hippie population (cliche-wise anyway). Canada also has a really high standard of living, and a proportionally high per capita uptake in the social media used to to promote these activities. We also use a lot more power per capita than most other nations. perhaps the two balance eachother out. only one city saw an increase in power use (Calgary, of course). 9% is probably a really high number, so maybe 4 or 5 for other developed nations and a lot less for the third world.

    Result: a modest reduction amongst developed countries and a blip on the world stage. I’ll play statistics and crunch some numbers during the day tomorrow (thats a lie).

  19. #19 Dunc
    April 1, 2009

    You missed the point if you light candles to replace the lights.

    Considering that the Earth Hour website actually recommended having a candlelit dinner party, I think they missed the point too…

  20. #20 Lu F.
    April 1, 2009

    I think that people are missing the fact that my burning candles have never caused acid rain problems from my next door neighbors.

    And yes, Earth hour was nothing but an awareness campaign, so “enviro-whinerism-whiners” should probably get over themselves. If this stunt helps persuade government officials to start better funding scientist addressing this issue, then it was a total success. Like Matt said, it’s going to be a technological advancement that will save us (if we do indeed get saved). I’ve seen a few lecturers that have said the task it near impossible (http://blog.longnow.org/2009/01/19/saul-griffith-climate-change-recalculated/), but I’m still holding out a bit of hope for the scientific community.

  21. #21 rob
    April 1, 2009

    there is another fermi problem over at xkcd.

  22. #22 Michael F. Martin
    April 1, 2009

    Nice to see that the two people who answered the question posed agreed to within an order of magnitude!

  23. #23 rob
    April 1, 2009

    …or like an order of pi squared…

  24. #24 Alex Deam
    April 7, 2009

    My estimate: 0%.

    If everyone turned off their lights for an hour, then surely the C02 still gets released? The fossil fuels are still being burnt at the power plant, the difference is that the energy from them will not be used for an hour. So the CO2 is still emitted, even if I turn my lights off.

  25. #25 JM
    April 9, 2009

    Another data point.

    Australian capital city power companies reported reductions both this year and last year of about 10%

  26. #26 Anonymous
    April 9, 2009

    “Nice to see that the two people who answered the question posed agreed to within an order of magnitude!”

    Perhaps, but it would be better if they had also started from similar assumptions:

    #8 “10 billion people in developed world …” No there are only 1 billion people in the developed world

    # “10^10 people in the world … 1/10 who participate” This one’s better.

    But the main problem is piling up spurious factors of 1/10 in a chain to come to an equally spurious and uncertain number.”

    How about doing it in one step

    #15 “27,245,758,000 tonnes of CO2 is produced worldwide in a year (from wikipedia).”

    First order assumption – it’s all from coal for power (not bad, most of it is), round to 30 billion tonnes of CO2.

    First order assumption – 1/2 of that is in the developed world “Earth Day” area

    First order assumption – 1/2 of that is for power at night

    so 7.5 billion tonnes per year spread over 8 hours per night, 365 days.

    =20 million tonnes per day or about 3 million tonnes for 1 hour

    Check it: 3 million tones x 24 hours x 365 days ~ 27 billion tonnes. Looks good.

    About .01% of annual output. 0.01% x 8 hours x 365 days = 30% of annual output devoted to light, appliances etc in the developed world. Still good.

    Check it again. 365 days = 2920 hours of nightime. 1 hour is about .03% of that, we assumed 1/2 x 1/2 = 0.25 therefore 0.03/4 ~ 0.01 looks in the right ballpark.

    Check it against data points (10-15%) reduction. 1 hour out of 8 is approx 12% and most power at night is for light, so still looking good.

    I put my money on about 3 million tonnes.

    Although, I’m on the side of those who point out the educative value. I was celebrating a friends birthday in an expensive restaurant at the time and we weren’t really affected. They warned us to order before 7:45 so they could get our main meals out before they switched off the oven and the candlelit atmosphere added greatly.

    So yes, we can be more careful in our power usage.

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