What's the true environmental impact of the things we do and buy? In a new book, MIKE BERNERS-LEEhas calculated the carbon footprints of various human activities and natural phenomena, from the consumption of a tomato to the eruption of a volcano – with some surprising results
A pint of tap water
0.14g carbon dioxide equivalent (CO2e) one pint
14kg CO2e: a year’s tap water for typical person
A year’s supply for one person is the same as a 20-mile drive in an average car. That includes drinking, washing, cleaning — the lot.
Unlike the bottled alternative, which has around 1,000 times the impact, cold tap water is not a major carbon concern for most people. Indeed, the provision and disposal of household water accounts for less than half a per cent of our carbon footprint, though climate change looks set to cause serious water stress in some parts of the world.
Interestingly, if our pint of tap water is poured down the drain, its footprint leaps almost fourfold to just over half a gram because it is more carbon intensive to treat waste water than to supply the water in the first place. If the eventual fate of the drink is to be flushed down the loo (along with another 6 litres of water), that takes the total to 4g CO2e.
A paper carrier bag
12 g CO2e: recycled and lightweight
80 g CO2e: an elaborate bag from mainly virgin paper as supplied by many clothing retailers
A common misconception is that paper bags must be environmentally preferable to plastic. Wrong. The paper industry is highly energy intensive. Printed virgin paper typically produces between 2.5 and 3kg CO2e per kilo of paper manufactured. This is comparable to the emissions required to produce 1kg of polypropylene plastic bags.
However, paper bags have to be much heavier, so overall the paper bag ends up having a bigger footprint.
Recycled paper is roughly half as energy intensive to produce as virgin paper. But even a lightweight recycled paper bag produces slightly more greenhouse gas emissions than a typical plastic carrier.
Ironing a shirt
14g CO2e: a quick, expert skim on a slightly damp shirt
25g CO2e: an average ironing effort
70g CO2e: a thoroughly crumpled shirt ironed by unskilled hands.
Ironing five shirts every week is about the same as a 10-mile drive once a year in an average car
For ironing that simply has to be done, the best green step is to have the clothes slightly damp and use the ironing process itself to finish off the drying. That saves both time and carbon. Even more effective is simply using the iron less often. A few people allegedly enjoy this activity, almost as a hobby. If ironing is how you get your kicks, it works out at about 400g CO2e per hour. That’s about five times worse than watching the average TV but dramatically better than going for a drive.
A nappy
89g CO2e: reusable, line-dried, washed at 60°C, passed on to a second child
145g CO2e: disposable
280g CO2e: reusable, tumble-dried and washed at 90°C
At 550 kg per child for two-and-a-half years in disposable nappies, that is the equivalent of nearly 2,500 large cappuccinos.
Most parents will be relieved to hear that there is usually no carbon advantage to be had from reusable nappies. On average, they come out slightly worse, at 570kg per child compared with 550kg for disposables. And if you wash them very hot and tumble-dry them, reusables can be the worst option of all. However, if you put your mind to it you can make reusables the lowest carbon option.
To do this, pass them on from child to child (so that the emissions embedded in the cotton are spread out more), wash them at a lower temperature (60°C), dry them on the line, and wash them in large loads. For a disposable nappy, most of the footprint comes from its production.
But about 15 per cent arises from the methane emitted as its contents rot down in landfill. But try to keep all of this in perspective: if you take just one family holiday by plane you will undo the carbon savings of perfect nappy practice many times over.
A banana
80g CO2e each, or 480g per kilo
Bananas are a great food for anyone who cares about their carbon footprint. For just 80g of carbon, you get a whole lot of nutrition: 140 calories as well as stacks of vitamin C, vitamin B6, potassium and dietary fibre.
Overall, they are a fantastic component of the low-carbon diet. There are three main reasons that bananas have such low carbon footprints compared with the nourishment they provide: they are grown in natural sunlight — no hot-housing required; they keep well, so although they are often grown thousands of miles from the end consumer, they are transported by boats (about 1 per cent as bad as flying); and there is hardly any packaging – if any – because they provide their own.
But there are environmental issues: monoculture has been criticised for degrading the land and requiring the liberal use of pesticide and fungicide, and there are still parts of the world in which forests are being cleared for banana plantations.
1 kg of tomatoes
0.4kg CO2e: organic loose tomatoes, traditional variety, grown locally in July
9.1kg CO2e: average
50kg CO2e: organic ‘on the vine’ cherry tomatoes, grown here in March
For the same impact as just 1kg of the most energy-intensive tomatoes, a 16-stone man could eat his own body weight in oranges.
Tomatoes, at their worst, are among the highest carbon foods. But at their best, tomatoes are perfectly fine.
At the low end of the scale, a high-yield classic variety is grown in the summer with no artificial heat. The middle and high figures are based on a detailed but controversial study by Cranfield University. The middle figure is averaged across all varieties and times of year. Classic loose tomatoes, the ones that our parents were brought up on, cause only just over half the carbon, at 5.6kg CO2e per kilo, whereas “specialist” varieties (defined here as cherry, plum, cocktail, beef and others) come in at almost 30kg CO2e per kilo because the yield is so much lower per hectare, so they need more heat per kilogram.
Perhaps Cranfield’s most unsettling finding was that when heat from fossil fuels is required, organic is the highest carbon option, again because the yield was thought to be lower. At the high-carbon end, therefore, with a staggering 50kg of greenhouse gas per kilogram, are out-of-season organic cherry tomatoes sold “on the vine”.
So, tomato lovers concerned about climate change would do well to stick to the season (July to October here) and to favour classic varieties, sold loose. In the winter, it makes carbon sense to stick to tinned tomatoes, but if you do want to buy fresh tomatoes outside the local growing season, it is almost certainly preferable to buy them from Spain or another warmer place rather than versions produced locally in heated greenhouses.
Being cremated
80 kg CO2e
That’s less than one ten-thousandth of your life’s carbon footprint.
My advice would be to treat yourself on this one occasion to whichever method takes your fancy. This is the one time when it is too late to start worrying about your carbon footprint. And anyway, you have already done the most carbon-friendly thing possible.
The average cremation uses 285 kilowatt hours of gas and 15 kilowatt hours of electricity; on top of the carbon, cremation sends significant amounts of mercury into the atmosphere. Burial sounds like a more climate-friendly solution, but there is an argument that the carbon cost of burial turns out 10 per cent higher once you take account of cemetery maintenance for the next 50 years. If what you most want to do is send a final eco-message to the world, the best answer is to be dressed in easy-to-rot clothing and put in a wicker coffin.
Having a child
100 tonnes CO2e: a carbon-conscious child
373 tonnes CO2e: average
2,000 tonnes CO2e: high-impact offspring
So if you have two typical children, that’s 746 tonnes over their lifetimes.
Unless you will ever contemplate lighting a bushfire, the decision to reproduce is probably the biggest carbon choice you will ever make. The more of us there are, the greater the pressure on the world’s resources.
I’m not saying you shouldn’t have children just that, according to my sums, one of the consequences will be a few thousand tonnes of carbon emissions.
The average lifetime footprint of 373 tonnes CO2e is based on your child’s living to 79 years. I have assumed that during that time he or she will lead a typical lifestyle in carbon terms and make average demands on public services, and that his/her average carbon footprint will decrease by 3.9 per cent each year as national carbon emissions are reduced.
At the high end of the scale are children who, even after you have done your best to encourage sustainability values, then go on to lead high-carbon lives. At the low end of the scale are children who grow up with carbon priorities embedded in their lifestyle and are serious about reducing emissions.
All scenarios assume that the child is living in the developed world (the numbers would be much lower in developing countries).
A volcano
1 million tonnes CO2e: Mount Etna in a quiet year
42 million tonnes CO2e: Mount Pinatubo, Philippines, 1991
If you have been a victim of the rumour persistent in some circles that volcanic emissions dwarf those of human activity, now is the time to be liberated.
All the world’s volcanoes together produce a total of about 300 million tonnes CO2e per year. This is well under 1 per cent of the annual emissions from mankind’s activities.
Nonetheless, as the figures above show, each active volcano does have a massive footprint, with a major eruption causing tens of millions of tonnes CO2e. But these numbers are misleading because, alongside their warming effect, volcanic emissions also cause a cooling effect.
The ash and sulphur dioxide that they throw up into the stratosphere reflect sunlight away from the earth. Overall, the Mount Pinatubo eruption of 1991 is thought to have resulted in a net planetary cooling of 0.5°C the following year. Over time the cooling effect fades faster than the greenhouse effect of the carbon, so the question of whether the warming effect or the cooling effect is greater is not clear cut.
The World Cup
2.8 million tonnes CO2e: the 2010 South Africa World Cup
That’s 6,000 space shuttle fights, three quiet years for Mount Etna, or 20 cheeseburgers for every man, woman and child in the UK.
The headline footprint figure here comes from a study of the 2010 South Africa World Cup and includes players and their entourages travelling around, the construction of the sites, energy used at the stadiums, accommodation, and fans travelling.
An estimated 1.2 million spectators will see matches live, so that would be at a massive carbon cost of 2.3 tonnes per viewing. Luckily for the carbon credentials of the World Cup, each of the 64 matches will be viewed on the television by an estimated 93 million people worldwide.
At two hours per match, including intervals, extra times, penalty nailbiters and the bit where they swap shirts at the end, that adds up to a massive 12 billion fan-hours of top-quality entertainment.
If these numbers are correct, the World Cup comes in at 230g CO2e per fan-hour of entertainment, though of course the viewers’ footprints are boosted by their own televisions. The worst scenario is that you are watching alone on a 42-inch plasma screen, in which case your TV makes up about half of the footprint of your viewing experience. Even if you watched 24 hours a day, 7 days a week for a whole year (that’s a whole year alone without sleep in front of the plasma TV in permanent World Cup ecstasy) you’d only clock up a 4-tonne footprint.
By comparison, a Premiership match, at 820 tonnes, comes out at a tiny 45g per viewer-hour (excluding all the televisions), with over nine-tenths of the entertainment being exported around the world.
Even better is a kick-around in your local park or street. This is virtually emissions-free, making it one of the best carbon bargains.
How Bad are Bananas? The carbon footprint of everythingby Mike Berners-Lee is published by Profile Books, £8.99
