2 Comments »Posted on Monday 15 June 2009 at 9:40 pm by Jacob Aron
In Climate Change & Environment


It is an undeniable fact that if we are to successfully hold back climate change, people are going to have to make some adjustments to their lifestyles. We simply can’t afford to continue using energy at the current rate, and carbon emissions must be cut. You already know this of course, in fact you are probably sick of hearing it. Therein lies the problem.

Change your ways, we are told. Don’t leave the bathroom light on. Be sure to put out the recycling. And have you considered installing solar panels? There is a constant niggling feeling that we must all do something to fight climate change, but no real idea if our actions have any impact. Surely, people say, there’s nothing that I can do?

New research published in last week’s Nature could have the answer. Scientists from Canada and the UK lead by Damon Matthews, a professor in Geography, Planning and the Environment at Concordia University, have come up with a way of quantifying a person’s individual impact on the climate. It works by simplifying the complex web of interactions involved in climate change in to a single number: the global temperature increase per tonne of carbon emitted.

Matthews and colleagues calculated this figure, known as the carbon-climate response (CCR), by running computer simulations and examining historical climate data.. Although other climate factors can vary significantly, the CCR appears to remain constant even over a period of 1,000 years. Depending on the model used, they estimate that releasing one trillion tonnes of carbon in to the atmosphere will raise the Earth’s temperature by between 1 and 2.1 °C. To put it another way, for every tonne of carbon you emit in your day-to-day activities, the planet will warm by 0.0000000000015 °C, or 1.5 x 10-12 °C. This is a tiny amount, but it is easy to see how emissions add up.

This 2000 US Department of Energy report gives an average value of around 1.35 pounds of carbon dioxide released for every kilowatt hour of electricity used. We can convert this to pure carbon by multiplying by 12/44, a fraction which takes into account the relative atomic masses of carbon and oxygen. Converting again from pounds to tonnes gives a figure of around 0.00017 tonnes of carbon per kilowatt hour.

From this I calculate that leaving a 100W bulb switched on for a year releases around 0.15 tonnes of carbon in to the atmosphere, resulting in a temperature increase of 2.25 × 10-13. Again, this is a very small amount, but consider how many light fixtures there are in the entire UK when you include all households, offices, shops, schools, hospitals…the list goes on. Estimating the country’s population at 61 million, with 3 light bulbs per person (a number I have admittedly pulled out of thin air, but one that seems reasonable) that works out at a temperature increase of 0.00005 °C. Now we’re talking slightly bigger numbers, especially when you consider this is just lighting, and just the UK.

The crux of the matter is that if we are to avoid catastrophic climate change, switching your lights off really does make a difference. Yes, the effects of these behaviour changes are small, but if everyone does them this new research shows that the effect on the climate can be significant. When you’re next told, for the nth time, to reduce your carbon footprint, remember that doing your bit really does matter.

Matthews, H., Gillett, N., Stott, P., & Zickfeld, K. (2009). The proportionality of global warming to cumulative carbon emissions Nature, 459 (7248), 829-832 DOI: 10.1038/nature08047

  1. 2 Comments

  2. Gets more complicated though, when trying to equate the different GHGs with their different atmospheric residency times.

    By Tom Rees on Monday 15 June, 2009 at 10:03 pm

  3. Cambridge University physicist David MacKay uses the 40W light bulb as a reference for helping people to think clearly about what really makes a difference. Here he is in a short video http://www.800.cam.ac.uk/page/122/cambridge-ideas-how-many-lightbulbs.htm and you can download his entire book ‘Sustainable Energy – Without the hot air’ for free at http://www.withouthotair.com (I haven’t read it yet but it’s on my list).

    By Sam Wong on Monday 15 June, 2009 at 10:50 pm

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