Archive for the 'environment' Category

My PyCon UK talks


My «Embedded Programming with Python» talk was the first Saturday morning slot, and really it was about manipulating hex-files and ‘scope dumps with Python:

Slides as PDF, 2.5e6 octets.

On Sunday Nick B gave a presentation of Clear Climate Code. I didn’t do much during the presentation; I was the OmniGraffle monkey. Here’s the presentation at the Clear Climate Code site.

BBC: remove errors bars for better headline


In this article from the BBC Richard Black claims “This year appears set to be the coolest globally this century”. There is no basis for this claim, and moreover the very notion of picking warmest and coolest years amounts to bickering about global warming.

Black appears to be making this claim on the basis of looking at column 2 of the HadCRUT data. Here’s a graph, freshly minted from the Google Chart API:

The data is taken from HadCRUT, here’s a relevant extract:

2000  0.238  0.249  0.227  0.333  0.144  0.238  0.233  0.334  0.143  0.334  0.143
2001  0.400  0.411  0.388  0.495  0.304  0.400  0.394  0.495  0.304  0.495  0.303
2002  0.455  0.466  0.445  0.553  0.358  0.455  0.450  0.553  0.358  0.553  0.357
2003  0.457  0.468  0.447  0.556  0.359  0.457  0.452  0.556  0.358  0.556  0.358
2004  0.432  0.444  0.421  0.530  0.335  0.432  0.426  0.530  0.334  0.530  0.334
2005  0.479  0.490  0.469  0.580  0.378  0.479  0.473  0.581  0.378  0.581  0.378
2006  0.422  0.432  0.412  0.517  0.327  0.422  0.416  0.518  0.326  0.518  0.326
2007  0.404  0.414  0.394  0.501  0.307  0.404  0.398  0.502  0.307  0.502  0.307
2008  0.281  0.292  0.270  0.428  0.134  0.281  0.275  0.429  0.134  0.429  0.134

The format of the data is described here, by Hadley.

In the graph the red line is the best estimate, the pink lines shows the combined 95% uncertainty from all sources. You can get more, or possibly just different, graphs from Hadley.

The first thing to notice is that Black’s claim is false if you include the year 2000. Okay so technically I know that “this century” starts in XX01 but I also know we all celebrated the beginning of the millennium in 2000 and we accepted then that although 2001 was technically the beginning of the millennium (and hence the century) it was much hipper to celebrate 2000. So that deserves a mention at least.

But really my gripe is about not observing the error bars. The uncertainty in the data is such that the error bars all overlap! The data does not support the claim that 2008 is warmer than 2005 for example; if we take as our null hypothesis that these two years are the same temperature then we cannot reject it with any confidence. The same is true about any other pair of years (except possibly for 2005 versus 2000; we might be able to claim that 2005 was warmer than 2000).

Neglecting 2000, as Black obviously does, the data are consistent with a constant anomaly of +0.4°C. That’s just an example, many other temperature series would be consistent with the data, including ones which make 2005 the coolest year.

And that’s the problem with trying to “rank” years. The uncertainties in the data are all so large compared to the yearly changes that it’s totally meaningless to talk about the warmest year or the coolest year. We just don’t know.

Of course, if Richard Black had thought about the uncertainties in the data then he would’ve had to say “latest HadCRUT data shows 2008 about as warm as any other year this century”, and that’s not a very controversial thing to say. All this dramatic concentration on the yearly, monthly, daily ups and downs of global temperatures, greenhouse gas levels, what-have-you is nonsense. It’s just talking about the weather while the planet burns.

DEFRA promotes bovine TB in herds


Farming Link is a magazine published by DEFRA. I assume it is sent to all DEFRA registered farmers (in the UK in order to receive money under the Single Payment Scheme you must be the registered owner of entitled land; DEFRA probably uses this list or something similar).

August’s edition is hot off the press and contains an article that introduces the gamma interferon test (for bovine tuberculosis). This article correctly identifies the major benefit of the gamma interferon test, namely higher sensitivity compared to the skin test. Sensitivity is the proportion of infections that are identified as positive according to the test. So the gamma interferon test correctly identifies more infections than the skin test. The appendices of Specificity Trial of the BOVIGAM® IFN-Gamma Test in GB Cattle give a sampling of figures for sensitivity: around 77% for skin test; around 88% for gamma interferon.

Currently in some situations it is up to the farmer whether a herd should be tested using the more sensitive gamma interferon test or the traditional skin test. Carl Padgett, president of the British Cattle Veterinary Association, is quoted as saying “If you have a herd with a brand new infection, you want to get rid of that infection as quickly as possible before it spills over to neighbouring farms or into the local wildlife population. So you want to take out as many animals as possible that might be infected rather than keeping them in the herd”. Sounds like jolly good advice to me.

But then the article goes on to say that in some herds with recurrent TB problems “the [gamma interferon] test may pick out more infected cattle than the standard skin test”. Well yeah, it’s more sensitive, that’s what it’s supposed to do. The articles says that in these circumstances the gamma interferon “might not be in the farmer’s interests”. In other words DEFRA is saying that because the skin test leaves more infected animals in the herd it could be better for the farmer; the farmer will have to replace fewer heifers (expense) and therefore should opt for skin test. In any case I don’t really buy the expense argument. Animals that test positive are compensated for at the market rates, isn’t there an equivalence between money and heifers? Isn’t this what economics is about?

What is DEFRA’s agenda here? Reducing bovine TB, or minimising the number of positive animals it has to purchase?

Brake with your left foot


The driving manual has one recommended procedure where you should brake using your left foot:

After fording you should keep your right foot on the accelerator (to avoid stalling) and test your brakes with your left foot.

Needless to say, do this gently and after informing other people in the car that you are about to test your brakes using your left foot.

Secrets of Reducing Your Carbon Footprint


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.

Behold the colour purple


I walked into my garden today (actually yesterday; there’s a sort of timewarp blog effect) to find it had been invaded by a load of coloured… things.

On my wall:

A thing on my wall.



Several things lurking under the table:

Small purple flowers.

A penta-thing:

Blue flower with 5-fold symmetry.



Very ominous looking things. Are they spawning vessels for more things?

Some things.