Archive for the 'environment' Category

Why I gave up beef


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:


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.

Colouring Doubt’s Flag


Judith Curry is keen to frame doubt in the form of an italian flag. Specifically with reference to this statement from IPCC WG1 Summary for Policy Makers:

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

Curry’s flag interpretation of this statement is that we could colour the flag 5% white (uncommitted belief), 67% green (anthropogenic forcing), 28% red (natural variability). A minor quibble: the opposite of “due to increase in anthropogenic GHG” is not “natural variability” as that excludes other anthropogenic activies such as sulphate emissions and secondary effects like ozone increases due to Montreal protocol. Anyway, her flag would look like this (if she drew it):

Does that seem right, can we be almost certain that there is only 5% wiggle room for doubt? Also, if I say that 70% of the variation is anthropogenic that doesn’t mean the rest (or almost all the rest) is natural, it just means I don’t know. I interpret the IPCC statement as meaning that there are a wide range of supportable beliefs about the anthropogenic cause of 20th century warming, but 95% (ish) of those will have more than 50% of the flag coloured green. Amongst the population of possible flags is this one:

Note that this flag already represents quite an extreme position with respect to the IPCC statement, because whilst it’s compatible with the IPCC statement, only 5% of the flags have a smaller green area than this. Here’s a more median position:

How can we represent the range of beliefs that are compatible with the IPCC statement. Like this?

Screw the planet!


The earth is getting warmer. Ecosystems are changing. Food webs around the world are upset. We are in the middle of mass extinction.

For years the green lobby have been complaining about this, finally over the last decade their voice can be heard as global warming becomes a political talking point. We can save the Earth.

Screw that! The greens are getting way too much political capital out of global warming. Sending your money to Friends of the Earth, World Wildlife Fund for Nature, the RSPB, and so on, will not solve global warming. They are not in the game.

The planet is not under threat. Our life on this planet is under threat. Runaway global warming will be bad. For any metazoan. Everything larger than than a hyrax will be wiped out. But life will go on, the Earth will be claimed once more by the Archaea and it will be business as usual really. Nature’s brief experimental dalliance with multi-cellular life will have ended. She will conclude that “further research is necessary”.

So the debate around global warming is not about saving the Earth, it is about saving our way of life on the Earth. And let’s get this straight, once we’ve “solved” global warming, we’ll have put a nuclear power plant on every (100 Km or so of) coastline, we’ll have replaced inefficient sheep pastures with huge plantations of biofuel crops, we’ll have peppered the entire countryside with wind turbines, and glazed vast deserts with solar PV farms.

We will not have saved the polar bear, the poison arrow tree frogs. All those bromeliads teetering on the brink of their fragile hilltop ecosystems in the South American rain forest? All gone. It will be our fault, collectively. And it will be sad. But solving global warming and saving your favourite obscure cute species are not the same problem.

Carbon into Trees


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?

Windy isn’t it?


Damn hippies think we can just sprinkle a few wind mills around, and because Europe has “huge wind resources” we’ll be okay.

This silly web article claims that europe’s wind energy potential is “huge”, and “equivalent to almost 20 times energy demand in 2020”.


YA RLY, according to the European Environment Agency’s report, Europe’s onshore and offshore wind energy potential.


YA RLY: It’s hard to miss this sentence from the executive summary: “Europe’s raw wind energy potential is huge. … it may be equivalent to almost 20 times energy demand in 2020”.

“energy demand”, that’s the problem. Their assumed energy demand is between 3537 TWh and 4078 TWh. (By the way, notice that the EEA cover their backs with a “may” when they use the lower demand figure to get the “20 times” headline-grabbing numbers, but the web article referencing somehow manages to drop the “may”). So, Europe has 271e6 people (according to Google); that’s 15.3 kWh per person per day. Oops. They must have meant…

Electricity demand.


The electricity demand, in Europe, in nothing like our energy demand. In the UK we travel around by burning oil, and we heat our houses and food by burning gas. That hugely swamps our electricity usage.

Energy and Electricity are not the same thing.

Double twats for the people who ignorantly repeated them. Of course the European Environment Agency know the difference. There are two occurrences of the phrase “energy demand” in the document; 7 occurrences of “electricity demand”. Both the “energy demand” phrases related to the “20 times” sentence. One is in it, the other is in the footnote of the table of data on the same page as the “20 times” sentence. Before I did the textual analysis (by which I mean I used the PDF search feature; it’s abysmal, but it’s what I have available) I put the use of “energy demand” down to sloppy practice. Now I think it’s mischievously deliberate. I think they used “energy demand” in that “20 times” sentence in the executive summary because they knew people would make a headline of it.

I have to say that apart from this headline grabbing glitch, the report is well worth reading. Map 6.1 is particularly interesting (apologies for the pixelly rendering, partly their fault, partly mine, but mostly the fault of STOOPID PDFs):
Cost of wind in europe

Basically the British Isles is the only place in Europe (not quite, but nearly so) with cheap on-shore wind. And we’re full of NIMBYs.

Screw Hydro!


The Archimedean screw. A venerable machine for lifting water. You can run it in reverse to generate power. How much?

New Mills, where the Sett meets the Goyt, has a community owned Archimedean screw. From their blog the energy generated for each month is:

September: 11108 kWh
October: 25356 kWh
November: 24232 kWh
December: 29513 kWh
January: 19512 kWh
February: 9185 kWh
March: 20330 kWh
April: 3091 kWh
May: 4436 kWh
June: 1389 kWh

Somewhat arbitrarily, but giving them some benefit of the doubt, I’ll replace September’s figure with October’s (perhaps the low September output was mostly teething troubles), and for the missing July and August figures I’ll use May’s.

So the total is: 25356 + 25356 + 24232 + 29513 + 19512 + 9185 + 20330 + 3091 + 4436 + 1389 + 4436 + 4436 = 171272 kWh per year.

or 19.6 kW. This is considerably lower than the 31 kW quoted by one of their investors.

Nice rule of thumb I discovered whilst writing the post: 1 kWh per year is 0.1 W.

The people who built it give it a plate rating of 63 kW (it’s capacity, or maximum power output). So it’s load factor is a little less than 1/3 at 0.31. They also quote a flow rate of 2860 l/s with a drop of 3m. Neglecting the water’s kinetic contribution (which I’m not sure is reasonable), the water has a power of about 86 kW (2860 litres of water is about 28600 Newtons, dropping 3m every second). So the extractive efficiency is about 73%. Quite impressive. I wonder if it can really be that high? Perhaps at high flow rates the kinetic energy is a more useful contribution.

The seasonal nature of the power is clear from the graph:

(the empty bars are missing data, not zero generation)

Basically, you only get power in winter, when it rains. The rest of the load factor gets eaten away by maintenance (oiling, fishing, that sort of thing), high water flow (!) and HSE requests (which I take to mean noise complaints).

David MacKay, in his book “Sustainable Energy – without the hot air” has a cute chapter about hydro. He analyses the total energy of the rain falling on our land and concludes that we can only ever produce about 1.5 kWh per person per day from hydro. After that there’s not much to say, and the chapter is correspondingly short. His figures for actual UK production (page 56) suggest a load factor of 0.29 for large scale hydro, and 0.16 for small scale hydro. So Torrs Hydro is doing atypically well (or I’ve been overly generous in filling the data).

The thing that surprises me is that the Archimedean screw produces a solution that is comparable, in load factor and efficiency, to large scale hydro.

[edited in 2014-07 to remove/change broken links]

Food Chain Emissions


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”, :

“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:

«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!


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


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.

Putting the Heat on Wheat


Wherein I play with the lovely Google Charts API and expose my total incompetence in statistics, economics, agriculture, and geography. And quite possibly other things too.

So I was reading the Open Knowledge Foundation blog and came across this article featuring US wheat production, which points to this dataset of wheaty goodness. My recent work on Clear Climate Code had made me already aware of the availability of GISTEMP’s summary data products.

So it occurred to me that this could be used to answer the question “when the weather is warmer, does more wheat grow?”.

So the wheat data is US wheat production, including yields in bushels/acre, sigh. GISTEMP even do a dataset that shows the temperature anomaly for the US. I think this is incredibly parochial, but it happens to be just what I want.

So the wheat yield (volume of wheat per harvested unit area) has a general upward trend. At least from the mid 1930’s or so. Because I’m only interested in the local variation I have detrended the wheat data:

My hypothesis is that any deviation of the temperature from the long term average will lower wheat yields. I think this because I would expect that over the thousands of years of selection humans will have cultivated a variety of wheat that is optimised to grow at the average temperatures and it will do less well when temperatures deviate.

So what do we see? Here’s wheat yields and temperatures together:

Well, there’s no obvious correlation to eyeball. Scattergram:

(which is almost just changing ‘cht=lc’ to ‘cht=s’ in the above chart URL)

Bit of a blurry mess. If anything a slight negative trend, which would mean that colder temperatures gave a higher wheat yield. And indeed Pearson’s correlation is about -0.3 (assuming my calculations are correct) indicating a weak negative correlation.

There are problems. One problem is that I have no p-value. That’s partly because I haven’t read that far on the Wikipedia page (I’m not using some fancy stats package for my analysis; everything is hand-coded in Python), and partly because I have a degrees of freedom problem. Temperature is autocorrelated, so whilst I have 128 samples, that’s fewer than 128 degrees of freedom, so the standard assumption of independent variables is incorrect.

The other problem is that it looks like the detrending might have introduced a bit of an alarming feature into the wheat anomalies. There’s a gentle hump from 1866 to about 1940 and a similar one from about 1940 to 2000. This is almost certainly because I’ve used a cubic polynomial to fit to the data to detrend it. It looks like a two-leg linear fit would be better (with a kink around 1942), but I haven’t found how to do that. I have a sneaking suspicion I have some FORTRAN code lying around here to do it, but I’m too scared to look.

Final tiny problem almost too small to be worth mentioning: the wheat data is for the entire US, whereas the temperature data is for the contiguous 48. I’m guessing that Alaska and Hawaii make so little wheat contribution that it doesn’t matter.

In any case it doesn’t really look like fixing these problems would ever indicate a strong positive trend between temperature anomalies and wheat yields. So we can reject the notion that warmer weather means higher wheat yields. Of course warmer weather might mean we can grow more of something else (possibly just a different variety of wheat); it also might mean that the available belt of land for growing wheat is larger (but this is unlikely since it probably means the available belt of land for growing wheat has moved North).