Question of the Week

How do you measure carbon dioxide emissions?

Sun, 10th Jan 2010

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Jenny Boyd asked:

How do countries measure their carbon dioxide emissions?


We put this to Gregg Marland at the Environmental Sciences division, Oakridge National Laboratory in the US:

Gregg -  Actually, I think there’s a misconception that CO2 emissions are measured.  What you try to do is to measure how much fuel is burned and if you know how much carbon is in the fuel, you can calculate how much CO2 must be produced, and very seldom is that, in fact, measured.  Although there are some large power plants in which they actually put measurement devices in the smoke stack and can measure the amount of CO2 that comes out, that is unusual.  Smokestacks from a wartime production plant, World War II.The Intergovernmental Panel on Climate Change has published a five-volume set of guidelines that all the countries now use, as part of the UN Framework Convention on climate change, for estimating emissions on all greenhouse gases and it does produce uniformity across countries.  The error margin depends on the country and on the greenhouse gas.  I think the interest is partly in carbon dioxide emitted from energy systems, and in that case, it really depends on how much a country invests in collecting energy statistics.  For countries like those in the EU or the US or Japan, my guess is that the error margin is something in the order of plus or minus 5%.  For those discharging smaller quantities of CO2, the error bars, I think can be as high as 20 to 25% and there are some very large countries – in China, we’ve actually published the estimate that they are maybe as large as 15 or 20%.


Diana -   And Gregg also said that a major problem countries face in adding up their CO2 emissions is where to charge them if the fuel is bought in one country, but burned in another.  So, if you board a plane in the UK bound for the USA and the fuel has been bought in the UK, but it’s expended over the Atlantic, whom do you charge the CO2 to?  At the moment, the international convention is to charge the CO2 to no one and they estimate about 3.1% of global emissions don't appear in international accounts.  And that’s on the order of a billion tons of CO2.


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For most I would hazard that they measure how much oil, gas and other fossil fuel they import or consume, and assume it is solid carbon mass for the most case.

Or they do a ginormous thumb suck, based on other similar populations and incomes.

SeanB, Thu, 24th Dec 2009

good question. I said contentiously and recently on Facebook that I would lower carbon dioxide emissions (not me personally, of course) even if I felt that global warming didn't exist. I found that this did have some widespread support, even from die-hard climate change deniers. Interestingly, in Nature this week, there was a paper on the rate of climate change, implying that some features of climate change are being accepted as 'scientific fact', a bit of a taboo in science. Will keep you posted. By the way, my remark was supposed to be a parody of a remark made elsewhere about a completely different subject....... belated xmas or advance happy new year according to your preferences.  best wishes Shibs, Sun, 27th Dec 2009

I know that companies in the UK measure the energy or fuel they consume and use conversion factors published by Defra to calculate the CO2equivalent emissions:  So for example they calculate electricity consumed in a year (in kWh) and convert to CO2 by using the relevant factor.

I assume the government uses some sort of proxy measure ... and I'm not sure how accurate it can be.  Not sure if other countries have different approaches. zed, Mon, 28th Dec 2009

Indeed, we know how much "energy" we consume each year in terms of fuels and electricity - not least because people pay tax on that and so reasonable records exist. This energy consumption - in any forum (petrol, gas, electricity etc) - can be considered in terms of "carbon equivalents" - the amount of carbon / carbon dioxide that must have been liberated when that fuel / energy source is utilised. On this basis, I think this is how the estimated national and per-capita outputs are calculated.

So, to answer the original question, I think that the carbon calculations are very rough and ready on a person by person basis, but reasonably accurate when considered on the level of a whole country or indeed the whole world.

Chris chris, Mon, 4th Jan 2010

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