Footprints

Climate march, greenhouse effect

The People’s Climate March, London, 21st September 2014

A couple of weeks ago, People’s Climate marches were held in cities across the world. Held immediately before the UN climate summit, thousands rallied to emphasise the fact that we all need to work to lower our carbon dioxide emissions before it is too late. It is often said that we can “do our bit” by boiling only enough water to make the amount of tea/coffee that we want. So the question is, how much carbon dioxide is emitted as a result of preparing my morning cafetiere? And a related question, will it really make a difference if I boil the kettle efficiently?

A small cafetiere holds, roughly, 500ml of water. We need to increase the temperature of the water by approximately 80 C (from room temperature around 20 C to boiling point) in order to make the coffee. It is a property of water that, to raise its temperature by 1 C, we need to supply 4.186 Joules of (heat) energy per gramme (ml) of water (ref). To boil the amount needed for a cafetiere therefore takes 167 440 Joules of energy. (In practise it will take more than this owing to the efficiency, or inefficiency, of the kettle but this gives us a “ball-park” figure and a lower estimate).

How to turn this “energy” into a carbon footprint? Perhaps the simplest estimate would be to use the CO2 emissions guide for different electricity generation methods (link). The amount of CO2 emitted during electricity generation depends on the way that the electricity is generated. A wind farm is clearly going to produce far less CO2 than a coal fired power station. However, as a lot of electricity is still generated by burning fuels, let’s calculate the CO2 emissions for a ‘dirty’ fossil fuel such as (hard) coal and a ‘cleaner’ fossil fuel such as natural gas. According to estimates, (link) hard coal emits 115 kg of CO2 per GJ (ie. per 1 000 000 000 Joules) of energy produced. Natural gas emits 63 kg/GJ. This means that for one cafetiere (167 kJ), 19g of CO2 is emitted if your kettle is powered by a coal burning power station, or 11g (if your electricity supplier largely relies on natural gas).

chemex, coffeeBut what do these figures mean in terms of our carbon footprint? In the UK in 2010, 7900 kg of CO2 was emitted per person, according to the World Bank (link). This means that one cafetiere is the equivalent of 0.1% of an individual’s footprint for one day. This does not seem much but let’s phrase it differently. According to the British Coffee Association, 70 million cups of coffee per day are consumed in the UK and approximately 2 billion per day world wide. For the sake of simplicity in our calculations, let us assume (not unreasonably I think) that one cafetiere is the equivalent of two cups. Then, if we take the worst case (electricity generation from hard coal), each day there are 665 metric tons of CO2 produced in the UK from people enjoying their coffees (19g x 35 million cafetiere equivalents). Worldwide this equates to 19 000 tons of CO2 per day. If each person was boiling twice the amount of water that they needed for their coffee, more CO2 would be emitted each day due to our coffee making than the total annual CO2 emissions of the country of Lesotho (2010 figures, ref).

Something to think about while enjoying a coffee.

2 Responses to Footprints
  1. I guess as well as figuring the emissions of boiling the water, there’s also the emissions from growing the beans (not even sure of the sign for that), transporting the coffee from half way around the world, roasting the beans, and distributing the coffee aroudn the UK. Not completely obvious even if the water boiling is the biggest component in there….. needs more research 🙂 Hmmmm, and the energy costs of making the cafetiere in the first place…. hopefully one doesn’t break them so often that that is neglible.

  2. beanthinking says:

    True, breaking the cafetiere would be bad and not only in terms of it’s energy costs!

    You are right of course that there are far more energy costs involved in a cup of coffee than just boiling the kettle. Unfortunately, we have no control over most of these if we want to carry on drinking coffee. The question is, if we boil the water efficiently, can we help to reduce energy costs slightly? I think that the answer seems to be yes.

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