Archive for the 'carbon footprint' Category

Why I gave up beef

2014-08-15

or “peer reviewed article changed behaviour”, or “this one crazy trick will reduce your land use by 66%!”.

Land use of animal calories

I had known for a while that eating meat was resource intensive, and beef was particularly bad (mostly from MacKay’s Sustainable Energy Without the Hot Air), and over the last couple of years I have been trying to reduce my meat intake. Sometimes I claimed I was “mostly vegetarian” (with some success, a friend had known me for a few weeks before realising, as I chewed my bacon one lunchtime, that I wasn’t vegetarian). Recently a friend gave up beef, and as I said at the time it was probably a better environmental commitment than my “mostly vegetarian”. But it wasn’t until I saw the numbers crunched in Eshel et al 2014 that I decided to eliminate beef.

It is no longer reasonable to entertain doubt as to the environmental impact of beef.

The graph I show above is for land use per megacalorie. I had to redraw it from Eshel et al 2014 figure 2 because… Well, why don’t you see:

esheletal2014figure2

In order to fit each graph into its tiny rectangle the long bars have been truncated and the extra long bit that has been removed has been replaced with a tiny number giving the coordinate that should have been plotted. For beef land use it’s 147 m²·yr (compared to poultry which is 4). So where the graph should show a spike that’s 40 times bigger, instead it shows one that’s 4 or 5 times. And this is their headline figure. The whole point of the article is to show how much more resource intensive beef is. Are the PNAS page charges really so high that they have to cram all the graphs into one corner?

I’ve just shown the land use figure, but Eshel et al 2014 have analyses for water, greenhouse gasses, and reactive nitrogen. Tiny little arrows give numbers for potato, wheat, and rice (which are on the whole a lot smaller, except the rice’s use of water). You can explore the Supplementary Information too, including the spreadsheet they used.

Obviously peer review is not perfect (it is merely evidence that a couple of reviewers ran out of reasons to delay its publication), and there are caveats. This studies only US beef. What about Europe? What about ostriches? What about food miles? But I think you would be foolish to think that these other matters would affect the central conclusion: eating beef uses a lot of resources.

Carbon into Trees

2009-11-25

The BBC report that the Forestry Commission want to afforest 4% of the UK. And thereby get us 10% of the way towards our 80% emissions reduction target. Their wording is slightly odd, but see paragraph 12:

It is hoped the latest plan would absorb 10% of the UK’s target of slashing its emissions of greenhouse gases by 80% by 2050.

Alarm bells ringing. 1 million hectares (4% of the UK land) can sequester 8% (10% of an 80% emissions reduction) of the UK’s current CO2 emissions? No. My earlier article on coppicing willow suggests that an optimistic estimate for sequestration is 18 tonnes CO2 per hectare. So with 4% of the UK land, we could sequester 18 million tonnes, or about 3% of our (600 million tonnes of) emissions. I think my 3% figure is a really top end estimate. It’s not like willow grows particularly well in this country (but it is one of the best crops for sequestration) and with 4% of the UK covered, we may have to afforest some sub-optimal sites; short rotation coppicing is also different from growing mature forest, but I have a hard time believing that growing mature forest pulls down more carbon (yeah yeah, soil, nitrogen).

So where do the Forestry Commission get 8% from? I have no idea. And as usual the clueless journalists at the BBC fail to use the power of hyperlinking (welcome to the 1990’s) and they don’t have a link to the Forestry Commission research. Or even their press release (I suppose that would let everyone know they copied their homework).

Oh wait, here’s the first paragraph of the Forestry Commision press release: (ewgh Lotus Notes)

If an extra four per cent of the United Kingdom’s land were planted with new woodland over the next 40 years, it could be locking up ten per cent of the nation’s predicted greenhouse gas emissions by the 2050s.

Oh. So they mean 10% of our 2050 emissions. Which, as you know, are going to be 80% less than our current emissions. So 10% of 20% of our current emissions. Or 2%. Yeah, I buy that (just about, but at least it’s biologically plausible).

So the BBC mangled the press release. Does the BBC version seem very unclear to anyone else?

Food Chain Emissions

2009-07-13

Friends of the Earth have sent our household a postcard. It says «The meat and dairy industry produces more climate-changing emissions than all the planes, cars and lorries on the planet.» They don’t quote a study, or any other source. Just a bold assertion which, on the face it, seems implausible. Even if you eat a gargantuan 250 g of meat a day (in other words, the typical US diet; Europeans eat about half that), does that really compare to all that driving round? It also seems a little bit mean to exclude trains and ships on the “transport” side. Is the balance between transport and food really so close that those 2 modes make all the difference? In the UK, rail and water account for about 4% of the total transport energy budget, so I would hope that the question isn’t so close that adding them back in tips the scales the other way. For one thing, any reasonable quantification of errors is bound to swamp that.

I think the FoE statement is false, here’s my homework.

David MacKay stacks up the UK’s energy consumption (Sustainable Energy – Without the Hot Air, Chapter 18, page 103), he has (per person): car 40 kWh/d, plane 30 kWh/d, food 15 kWh/d. So with 70 kWh/d (82 if we add the other transport modes) on the side of transport, and 15 kWh/d on the side of food then it does indeed seem implausible that food chain emissions would be higher. Note that we have all food production on one side, I can’t be bothered separating out meat from the rest, clearly meat forms the bulk of the energy consumption anyway. But wait…

As well as emissions related to the energy required to maintain the animals, they produce carbon-dioxide and methane all by themselves. In other words the food industry has emissions not related to its energy inputs (even if all the energy was produced sustainably, there would still be emissions). Non-energy related emissions show a weakness in David MacKay’s book; he neglects them completely. That’s okay, because his focus is Sustainable Energy, but be aware that it’s not the whole picture. Food, concrete, deforestation all have non-energy emissions. For animals I think we can neglect the CO2 emissions because the carbon originally came from the atmosphere anyway (respiration forms part of a close carbon cycle). Methane however is not negligible.

I reckon 1 kg of lamb produced between 60 g and 180 g of methane when it was walking about in the Peak District. That’s equivalent to about 2.4 kg of CO2. Let’s say I eat 100g of lamb a day. That’s (methane emissions equivalent to) emissions of 240g CO2, or about 1kWh of diesel. That’s roughly 0.1 litres; if you fill up 40 litres (about the size of my small car’s tank) every two weeks then that’s 3 litres a day. How often do you fill up? From a personal perspective, It looks like food-related methane emissions are not even close (to transport emissions).

Okay. So much for the ovine. What about the bovine, porcine, and, er, chickens? Well, I’m no veterinarian so this will take a lot of piecemeal research. Bugger that, lets go to a (competent?) summary: The UK’s Fourth National
Communication under the United Nations Framework Convention On Climate Change
. In 2004 UK agriculture (note: not just meat and dairy) emitted 13.8 MtC (megatonnes of carbon equivalent); transport emitted 37.4 MtC. Just what are these Friends of the Earth smoking that makes them think they can claim “The meat and dairy industry produces more climate-changing emissions than all the planes, cars and lorries on the planet” when it is so out of line with the UNFCCC GHG inventory. Is the UK really so atypical?

I suspect that what’s really happening is that the FoE are doing some clever accounting. There’s probably a little bit of double accounting (example, counting transport of feed on both sides), and I suspect some land use change. Perhaps they include chopping down ancient forest to grow soya beans for animal feed as an emission on the food change? I just don’t know, because they don’t show their homework. But I have a couple of points to make anyway. The first is that it’s not at all clear that the beef industry is too blame. If there was less demand for beef (and hence soya beans to feed the cows), then I think it’s likely that the same companies would have chopped down the same forest to grow something else. Miscanthus perhaps. The second is that while this land use change will be an emission (the UNFCCC recognises land use and land use change as a carbon source / sink), this emission occurs only once. Once the forest is cleared to grow soya, there will be no land use change emissions. So the emissions from the single land use change should be amortised over all future soya bean seasons. I think.

So FoE, how do you make the sums add up?

Appendix for the pedantic

«250g of meat a day … the typical US diet»

A quote from USDA Agriculture Factbook 2001-2002, Chapter 2, “Profiling Food Consumption in America”, http://www.usda.gov/factbook/chapter2.htm :

“In 2000, total meat consumption … reached 195 pounds … per person”. That’s 242 g per person per day (2000 was a leap year).

«rail and water account for about 4% of the total transport energy budget»

Department for Transport, TSGB Chapter 3: http://www.dft.gov.uk/pgr/statistics/datatablespublications/energyenvironment/

«1kg of lamb produced between 60g and 180g of methane»:

One 60 kg ewe produces about 20 litres methane a day (see below). Boned and trimmed meat is about 2/3 of the animal’s weight, so 0.5 litres / kg (boned). Lamb is generally defined as less than 12 month’s old or less than 18 month’s old for export. 360 days × 0.5 litres = 180 litres. × (the density of methane gas) 0.717 g/l = 129 g. 60 g to 180 g gives a range around this (to account for younger and older lambs, for one thing).

«one 60 kg ewe produces about 20 litres methane a day»

See Proceedings of the Nutrition Society, Volume 41, page 9A, meeting of 1981-07-17, “Methane production in lambs fed high- and low-roughage diets”. It depends on their diet: about 23 litres for high roughage; about 9 litres for low roughage. Two things: 1) when did you last see sheep being fed lucerne hay? 2) using 20 litres per day favours the FoE case anyway.

«equivalent to about 2.4 kg of CO2»

In terms of greenhouse gas warming potential, per kilo, methane is 20 times more potent than CO2. So 120 g methane equivalent to 2.4 kg CO2.

Four candles!

2009-03-31

A hilarious blunder in my previous article about candles has me out by a factor of 10 on the calorific value of candles. In that article I said wax has about the same calorific value as butter, 3 kJ/g. It turns out that the calorific value of butter is about 30 kJ/g. Oopsie.

That means one modest candle burns at 75 W (not 7.5) and four candles burns at a whopping 300 W! So if you lit any candles then you were probably emitting more carbon than the “business as usual” scenario of having a couple of lights on.

This more or less confirms my prejudices that Earth Hour was a pointless and futile gesture so you could be seen to do something, without actually having to bother to go carbon free.

Light a Candle

2009-03-30

When you switched off for Earth Hour and lit a candle, did you stop to think whether you were emitting more or less carbon than before? The answer turns out to depend on how many lights you switched off and how many candles you lit.

A 27g candle provides 3 hours of light. Calorific value of wax is the same as butter, right? About 3kJ/g. So burning a candle uses source fuel (wax) at the rate of 7.5W. Four candles, 30W. About the same as 1 10W CFL bulb (assuming electricity is generated from fossil fuels with about 30% efficiency). [edit 2009-03-31: massive blunder: not 3 kJ/g but 30 kJ/g, making four candles equal 10 CFL bulbs. See later correction article]

So if you switched off your dining room light and lit 4 candles for dinner, you were carbon neutral [edit: no, it’s all wrong, see later correction article]. 4 candles is a pretty romantic light level, way way less than your 10W CFL will give.

Only slightly relevant observation: candles can be made sustainably, at least in principle, from beeswax, soy, and tallow. But if you think that lighting your house with organic soy candles is somehow promoting a sustainable lifestyle, you’re way off base.

Secrets of Reducing Your Carbon Footprint

2007-04-23

Can we grow willow and bury it?

This carbon footprint article from The Independent reckons that the average Briton’s carbon footprint is 10.92 tons of CO2.

This article about phytoremediation in Sweden suggests short rotatation coppicing gives a yield of about 6-12 tonnes of oven-dried willow per hectare per year. Similar yields in England are suggested by the survey results that I got Ian Tubby of the Forestry Commission’s Biomass Energy Centre to e-mail me. Optomistic rule of thumb: 10 tonnes of willow per hectare per year.

Willow is about 50% carbon. So from one hectare we can sequester 3-6 tons of carbon.

That seems like a long way off the 10.92 tons of CO2 that we’re each responsible for producing. But hold onto your apples and oranges there. A little bit of chemistry reveals that 1 ton of carbon is equivalent to 3.67 tons of CO2. That’s because carbon has atomic weight 12, but CO2 has molecular weight 44 (12+16+16), so every 44 tons of CO2 has only 12 tons of carbon in it.

So our 10.92 tons of CO2 per year is only 2.98 tons of carbon. Which we can easily offset with 0.6 hectares of willow or so. Of course to actually offset the carbon we need to bury the willow. In a hole in the ground. Like maybe a coal mine. (And how do we replace the P, N, and K that I’ve just buried?)

Of course as well as sequestering carbon to offset my footprint I could displace carbon. Instead of burning coal (geological carbon) I could burn willow. This leaflet from some random consultants suggests that 0.7 hectare of willow is sufficient to heat a 3 bedroom house.

Anyone know the average number of KWh per year it takes to heat a house in the UK? It’s surprisingly hard to find the answer in anything approaching an SI unit. This so obviously transient page (referenced on 2007-04-20) links to dataset ST341114 from the Office of National Statistics. That gives a 2001 figure of 1210 for space heating and 450 for water heating. Per household. The units? Why, kilograms of oil equivalent of course (haven’t these guys heard of SI?). Which Wikipedia suggests is a bit of a variable quantity; 1 kilogram of oil equivalent could be 42, 41.868, or perhaps 41.85 MJ. Really I only need a rough guide. Call it 42. That’s 69.72 GJ per jear.

Plausibility check: I burn about 1.2 tonnes of anthracite a year, plus some electricity to heat water in the summer. Anthracite has calorific value of 36 MJ kg-1 so that’s 43.2 GJ plus the electricity. So we’re in the right ball park. An even cruder check would be that 1.2 tonnes of coal is surely about the same amount of heat as 1.2 tonnes of crude. This time I’m thankful that the ONS uses silly non-SI units.

Seasoned wood has a calorific value of 16 MJ kg-1. The average household will need 69.72/16 = 4358 Kg of seasoned willow. About 0.5 hectare then (and a 5-year lead time (3 for growing up to the first harvest, 2 for seasoning), eek!). So the random consultants are in the same ball park with 0.7 hectare. There are 2.4 people per household so we only need 0.2 or 0.3 of a hectare per person to displace the carbon we were using for heating (which, according the The Independent article, is .40 tonnes). The lower calorific value of willow (compared to anthracite or crude) means we need to grow more willow, but we end up burying less.

So by swallowing a few assumptions, I personally could make myself carbon neutral with less than a hectare of willow. Unfortunately the UK has only 24 million hectares of land (and no, we’re not going to be growing willow on all of it). What are the rest of you going to do?

Still, it was a nice thought experiment.