Wednesday, 11 May 2011

Does saving energy reduce your carbon emissions? - avoiding the rebound effect

In a pub enjoying a beer
The trouble with saving energy is that it also saves us money and that means we have more money to spend which we can do in different ways, generating varying amount of carbon emissions,  maybe more than we saved in the first place; this is the rebound effect. So I have been looking at how we spend our leisure and at the general rate of carbon emissions per unit money spend for various activities such as reading a book, watching TV or going to the pub.

The simplest case is probably going down to the pub and having a drink. The cost of a pint varies between say £3.50 and £4.20. The associated greenhouse emissions for cask ale or lager could be 300-500g CO2e/pt (1). Hence the ghg emissions per unit cost are around 0.9-1.2 g CO2e/p.

On the other hand, if you buy bottled beer from the supermarket to drink at home, then the beer will be cheaper and have more carbon emissions (because the heavy bottles add to the transport emissions) so you generate correspondingly more greenhouse gases for your pennies.

Drinking in a pub is better than reading a book from this perspective. A typical paperback novel costing £7 has embodied carbon emissions of about 2.5kg (4) so about 4 g CO2e/p. Splashing out on a steak dinner would be even worse: an 8oz steak costing about £3 in the supermarket is associated with upwards of 4.5 kg CO2e so 15 g CO2e/p (5).

If you save money for these activities by using your car less, then you will be saving around 18g CO2e/p (based on 150p/litre and 2672 g 2elitre (2)) and if you are using less electricity then that is even better – around 45g CO2e/p saved (based on 12p/unit) – at least with the current power stations. (Hopefully this figure will go down as we get more and more renewable and low-carbon electricity. ) Even a return flight to New York (£400 and around 930kg CO2e(3)  so 23g CO2e/p) has lower carbon emissions for the cost. If you reduce your energy use by turning lights off you can spend the money you save on almost anything else without getting a rebound effect.

However, if you decide to cut back on your drinking, and spend the money on steak dinners or a new TV, then you will hit the rebound effect. For just under the cost of a pint you can get an 8oz steak with 9-15 times the carbon emissions and if you saved up to buy a new TV that would be around 4 times the emissions from the beer. 

Penceg CO2eg CO2e/p
Electricity 1kWh1254545
Plane trip to New York4000092960023
Diesel 1 litre150267218
250g steak300450015
Buy TV250001000004.0
Pint imported beer in pub4205001.2
Pint local beer in pub3503000.9

Another way of looking at leisure activities is how much greenhouse gases we emit per hour. Looked at this way, watching TV is usually very low in carbon emissions, despite the electricity use. Drinking in the pub can easily be ten times worse – depending on the sort of TV and how many fast you drink. I will look at this next time.

(1) How Bad are Bananas, Mike Berners-Lee
(2) 2672 g CO2e/litre diesel from 2010 Guidelines to DEFRA/DECC’s GHG Conversion Factors For Company Reporting DEFRA 2010
(3) 83g/passenger km from the same source.
(4) What Penguin are doing to help reduce a books carbon footprint Penguin 2007
(5) derived from Environmental Impacts of Food Productionand Consumption Final report to DEFRA December 2006 Manchester Business School 2006  – as with all food related figures this figure is more uncertain than most.

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