Thursday, 31 May 2012

How green is my charcoal barbecue?

The barbecue season has started. In my book I looked at cooking on the hob and in the oven but I didn't think of barbecues. You might think that using charcoal on your barbecue is carbon neutral because charcoal is made from wood which is renewable fuel. This is not entirely true because of greenhouse gas emissions (a) during manufacture of the charcoal and (b) in transport.  So how does cooking on the barbie compare with, say, under a grill in the kitchen?


My friend Neil is a barbecue expert and he says he uses about 1.2 kg charcoal to cook for 2-4 people. This is close to the minimum viable size.

Burning 1.2kg charcoal produces around 3.1 kg CO2. That is assuming the charcoal is 70% carbon, which is a reasonable quality [1], and that it is burnt cleanly. 3.1 kg CO2 is the equivalent in greenhouse gas emissions of about 6 kWh of electricity or 17 kWh of natural gas. To put that into perspective, the grill mode on my oven says it generates 3.2 kW heat so burning the charcoal for one barbecue produces the same CO2 emissions as about 5 hours of gas grill.

However, that doesn't matter because all the carbon in your charcoal came from trees and you did use FSC charcoal (didn't you?) so the trees are being replaced. Phew.

However, to make charcoal you have to heat the wood to burn off impurities and break down the wood structure and this process generates all sorts of gas products, one of them being methane which is a very potent greenhouse gas.  Methane is produced because the wood is being heated with insufficient oxygen to burn it. Charcoal production is a delicate balance between enough oxygen to burn and generate the heat needed to break down the wood but not enough to burn it completely. Partial combustion products like methane are inevitable and traditional charcoal production in a closed kiln ultimately vent it into to the air. There is another method called the retort method in which heat is applied to the charcoal oven from outside. Then the gas emissions, including the methane which is a useful fuel, are collected and burnt to help heat the oven; the whole process is relatively clean and efficient. However, the equipment for this is more expensive. There are good descriptions of the kiln method and the retort method here. 

A very large proportion of the charcoal we use is imported from places like Brazil and East Africa where it is made almost exclusively using the closed kiln method. We produce about 5000 tonnes of charcoal in the UK (2010)  [2] but we use more like 60,000 tonnes [3] so 92% is imported. Producing 1 kg of charcoal in a typical kiln in Kenya produces methane equivalent to 200-400g CO2 [4]. Also, bringing the charcoal back to the UK by ship is 11000 km by container ship which adds another 150 g CO2e [5]. The lorry journeys from the producer to the port, and in the UK to wholesaler and then retail warehouse and then retail outlet can easily add another 1000km which is another 90g even in an efficient container lorry. If you make a special trip to the shop to buy the supermarket, a 3 mile round trip would be another 750g of CO2 but if you buy a 6 kg bag this will do you for 5 barbecues. All told then we have at least 545g worth of CO2 equivalents per kg of charcoal or 625 g per barbecue session, as shown in the table below.

GHG emissions (in CO2 equivalents) from typical barbecue charcoal,  imported from Kenya


g CO2e per kg charcoalg CO2e per 1.2 kg barbecue session
Charcoal production200-400 *240-480
Ship Kenya to UK (11000 km)150180
Lorry here there and everywhere (500-1000 km)45-9055-110
5km (3m) by car to buy 6kg charcoal from supplier, typical new car 2009 [5].125150
Total545-790625-920
* This figure is based on the 100 year GWP for methane -  the 20 year figure would be 10 times higher because methane impact is intense but relatively short term.

If you were burning natural gas instead, 625g worth would be 3.4 kWh or an hour of my gas grill. That is probably twice as long as it would take to grill a piece of chicken and maybe 4 times as long as to cook a steak if you like it rare. This means your barbecue, even with FSC produced charcoal, probably generates at least twice the emissions that you would have generated with fossil fuels under a gas grill.  For large parties, you won't need so much charcoal per person so the emissions overall could be just about the same as using the gas grill.

If you want a barbecue with less carbon emissions, use UK produced charcoal, as local as you can find, and don't make a special car trip to buy it: combine with some other shopping, use public transport or cycle. UK producers are helping to manage our woodland sustainably too, using traditional techniques such as coppicing. However, even in the UK many charcoal producers use the closed kiln method for charcoal production. The websites I have found all show production using kilns.  Bioregional (who supply charcoal to B&Q) have a network of local producers and they say 'We are aware of the methane emissions from traditional kilns and have worked over the years with our producers to encourage the use of retorts whenever possible, as well as investing time and money into research for even cleaner technologies.' If your charcoal was made in a kiln you still have at least 240g CO2e or so emissions per barbecue, not counting any for transport. That is equivalent to 25 minutes of my gas grill.

Which brings us to the carbon emissions in the meat. That will be another 540g for chicken or 1800g for beef per 100g portion [6] - but you would have eaten that anyway.

[1] FAO Simple technologies for charcoal making chapter 10 Using charcoal efficiently
[2] Forestry Commission, 2010, UK Wood Production and Trade
[3] Guardian, 2008, Tread lightly: Buy British barbecue charcoal
[4] Bailis, R., 2009, Modeling climate change mitigation from alternative methods of charcoal production in Kenya, Biomass and Energy (33) 1491-1502
[5] Emission factors for a container ship from  DEFRA via my book
[6] from Manchester Business School, 2006, Environmental Impacts of Food Production and Consumption, final report to DEFRA via  my book

8 comments:

  1. For a Charcoal barbecue it is considered green only if it is less consuming and more output is given

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  2. Hi there. Could you please share with me how you calculated the ghg emissions. Thanks.
    Arthur

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    1. The emissions from making the barbecue come from reference 4. The transport emissions come from my book which got them from DEFRA's GHG emissions factors. They are now here http://www.ukconversionfactorscarbonsmart.co.uk/

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  3. yes I agree to the previous comment, because less burning smoke would give lesser environmental hazard if you are using meat smokers


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  4. This comment has been removed by a blog administrator.

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  5. If you are going to cook food it is going to use energy and unless you are using purely nuclear energy as that source (and even that isnt carbon free) then you are going to have a carbon footprint. As mentioned, what you eat also has a bearing, so locally produced grass fed cattle, or outdoor free range poultry, slaughtered and sold locally has less of a footprint. So when you buy your low grade beak and eyeball sausages from a supermarket for 99p or 8 burgers for 2 quid, you certainly arent getting quality and are probably getting ingredients from many sources, if you are lucky, from within the EU.
    Check your list of ingredients, if you dont know what it is, question it. Its probably preservatives, to keep it looking better for longer.

    So a supposed healthy lifestyle for self and the planet in being a vegan or vegetarian, if you did it properly, then yes, but next time you are in the supermarket or your supposed health food store, look at the list of ingredients on the vegan "cheese" block. Now tell me that this product is not processed to death and carries less carbon than an equivalent block of cheese made from milk from real cow juice. And is better for you?
    Same for locally produced charcoal.

    A raw fruit and vegetable diet with stuff grown in your back garden is probably the most sustainable and low carbon way to live.

    What we are doing in producing carbon isnt something new, its just that there are so many people living in an unsustainable way. Roll back even 50 years and most food was produced and sold locally, supermarkets were in their infancy, go back 100 years and yes we had grocery stores then but stocked with local produce, people made charcoal as a necessity because it burned longer and hotter than wood without the smoke, just CO to worry about indoors then. Go back 200 years, 1820 when we had the first shopping parades and consumerism was gathering pace, driven by commercialism.
    Go back 300 years, high fashion and the gap between rich and poor was so wide, if you were at the bottom, you would never be able to make your way. Now what we have is much more level. There is still a gap between haves and have nots, poverty still exists as does exploitation.
    So to sum up, a charcoal grill may produce slightly more CO2 than a domestic oven. But it doesnt bring people together in the same way, it doesnt taste the same and isnt as much fun.

    Improved BBQ and grill design also now sees pellet models, insulated ceramic grills, grills that run for 24hrs on one load of charcoal for example.
    Do we need to calibrate on this one?

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  6. 1.2kg of charcoal for preparing a meal for 2-4 is way too much charcoal. As a regular user, with my Aussie Walkabout charcoal griller, I could easily feed 10 adults with 1.2kg. With Pakistani Anghati style I wouldn't be suprised if I could triple that, though I have only used it 4-5 times for 6 adults. It is a lot shallower and the food rests very close to the charcoal. Usually make 1/2 chicken/person or about 300g/person of beef/mutton/goat.

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  7. If you're really that concerned, don't have a BBQ - it's all relative.

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