Earth hour, candles and carbon dioxide

I wrote this last year, and it turned out to be a very, very popular blog post. Since Joanna asked about it, I thought I’d repost this – and take the opportunity to double check the figures at the same time.

There’s one thing in particular that bothers me about Earth Hour – these people who turn off the electric lights and then go and light up candles, and think that they’re helping do something about anthropogenic forcing of climate change.

The widespread practice of misguided eco-Luddites turning off their lights for Earth Hour and burning candles as a source of light is grossly misguided and actually contributes to increased carbon dioxide emissions.

Perhaps they might say that it’s symbolic – but if your symbol has ten times more greenhouse gas emissions than the alternative non-symbol, I reckon you should go find a more environmentally friendly symbol.

Yes, I know candles are nice and romantic – but you’re taking paraffin wax, in the form of a candle, and burning it, very inefficiently, at a low temperature. This stuff is pure hydrocarbon – it’s a heavy alkane fraction distilled straight off crude oil. This stuff is getting so scarce that nations are prepared to go to war just to secure it, remember?

A candle flame burns at a relatively low temperature – so it’s a thermodynamically very inefficient source of energy – and most of the energy released in a candle is wasted as heat, anyway.

Even if 80% of your electricity comes from coal and fossil fuel fired power stations, as it does in Australia, burning candles is very polluting and certainly very greenhouse gas and carbon dioxide emissions intensive, even more so than electric lighting.

If you need to do something that requires light – then leave an electric light on – just one, or the minimum number that you need. I usually find that it’s absolutely fine to have one electric light on at a time. It’s far more efficient, less carbon dioxide emissions intensive and better for the environment – not to mention much safer than using hazardous candles.

If you want the romance of a candle, try looking for candles that you are certain are made from pure “carbon neutral” beeswax or tallow – not from crude oil in the form of paraffin wax. I agree, they are romantic. Just be careful; don’t want to burn the house down now, do we?

Using electricity for lighting is far more efficient and environmentally sound than the primitive technologies, burning fossil fuels dirtily, at ambient pressure and relatively low temperatures, that came before electrification.

The use of electricity, and the use of electric lighting, is part of our way of life, in a developed, technological first-world society – I, for one, am not prepared to give that up, not the least because we don’t have to.

Light bulbs don’t produce greenhouse gases – burning fossil fuels to generate electricity does.

Let’s focus our efforts on moving away from fossil fuel based electricity generation, and expanding the use of non-greenhouse gas intensive hydroelectricity, nuclear energy, and wind energy, to solve our problems with anthropogenic greenhouse gas emissions.

Earth Hour should be about doing everything that you can to reasonably, sensibly limit your demand for electricity – and we can do this every hour of every day, of course. It makes sense for everyone – after all, you pay for the electricity.

Instead of spending your Earth Hour bearing with an uncomfortable, dark lifestyle, use that hour to think about the things that we can all do every day to limit electricity consumption, that we will actually bother to do every day, that are compatible with the fact that, yes, in our developed first-world society, we actually use electricity, and we work after the sun goes down. Think about the things that are compatible with our sensible lifestyles in the developed world, and do them, and
it works out better for everybody!

Now; the ostensibly interesting bit. Stand back.

Now, let’s consider just how much, quantitatively, this use of candles during Earth Hour is responsible for increased emissions of greenhouse gases.

Postulate I: A typical candle produces about 13 lumens of visible light, from a total power output of about 40 W, most of which is heat.
Postulate II: A 40 W electric incandescent light bulb consumes 40 W of electric power, and produces approximately 500 lumens of visible light output.
Postulate III: The overwhelming majority of candles are made from petroleum, in the form of paraffin wax. Paraffin wax has a heat of combustion of approximately 42 kJ/g, and can be assumed to consist, chemically, entirely of pentacosane – \mathrm{C_{25}H_{52}}.
Postulate IV: The average greenhouse gas emissions intensity for electric power generation in Australia is about 1000 g \mathrm{CO_{2e}}/kWh, and electricity is transmitted with transmission losses of about 7%.

\mathrm{C_{25}H_{52}(g)\ +\ 38\ O_{2}(g)\ \to 26\ H_{2}O(g)\ +\ 25\ CO_{2}(g)}

\mathrm{M(C_{25}H_{52})} = 352.68 g/mol;

\mathrm{M(CO_{2})} = 44.0 g/mol.

Thus, we know the emission of carbon dioxide from burning candles:

\mathrm{\frac{40\ W/candle\ \cdot\ 25\ mol/mol\ \cdot\ 44\ g/mol\ \cdot\ 3600\ s/h}{4.2\ \times\ 10^{4}\ J/g\ \cdot\ 352.68\ g/mol}\ =\ 10.69\ gCO_{2e}} – per candle per hour.

And the rate of carbon dioxide emissions from the electricity generation corresponding to the use of 13 lumens worth of lighting – the equivalent of one candle – for one hour:

\mathrm{\frac{13\ lumens/candle\ \times\ 1000 g/kWh\ \times\ 107\%\ \times\ 40\ W\ \times\ 10^{-3}\ kW/W}{500\ lumens}\ =\ 1.11\ gCO_{2e}} – per candle-equivalent of electric light per hour.

Ooh yeah. Did I ever mention that WordPress has built-in LaTeX? <3

Therefore, for every candle that is burned to replace electric lighting during Earth Hour, the greenhouse gas emissions over the course of the one hour are are just under ten times that than the electricity generation for the light bulb; emissions are increased by 9.6 g of carbon dioxide.
If the light output from a 40 W light bulb was to be completely replaced by candles, this will lead to the emission of an extra 295 grams of carbon dioxide per over simply using the electric lights – if the equivalent of one thousand 40 W bulbs are replaced by candles, that’s an extra 295 kilograms of \mathrm{CO_{2}} emitted.

In places where a greater proportion of the electricity supply is generated by nuclear energy or hydroelectricity, this increase in greenhouse gas emissions is even larger.


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