PLENTY of people say it, and the rest of us probably think it as we browse the energy-efficient light bulbs, unplug our TV or leave the car and walk to the shops instead. What's the point in cutting our personal carbon footprint when more than a billion Chinese and most of the rest of the planet are jacking up their emissions as if there were no tomorrow?
It's a fair question. After all, the atmosphere doesn't distinguish between a tonne of Chinese carbon dioxide and a tonne emitted by the west. As the rest of the world carries on regardless, are the paltry savings from recycling your beer cans or insulating your roof anything more than a drop in the ocean?
If you just stopped trying, would the planet notice? In this special investigation, we crunch the numbers to find out whether going green is worth all the bother.
First though, the big picture. Every year human activities add about 30 billion tonnes of CO2 to the atmosphere, largely through burning fossil fuels but also through destroying natural carbon sinks, such as forests. Half of this CO2 is absorbed by the remaining forests, soils and oceans, but the rest accumulates in the atmosphere.
Since pre-industrial times, the concentration of CO2 in the air has risen by a little over one-third, from 270 parts per million to 380 ppm - or from 2.2 trillion tonnes to almost 3 trillion. Most scientists think it would be unsafe to let CO2 concentrations rise beyond 450 ppm - an additional 500 billion tonnes. That level would be reached by around 2040 if emissions continue at today's rates. But as developing countries industrialise, global emissions are unlikely to stay the same. Last year, China hiked its emissions by 8 per cent, or around 450 million tonnes - an increase almost as great as the UK's entire annual carbon footprint. Emissions of other large developing countries like India, Brazil and Mexico are increasing at a similar pace.
Against this remorseless rise of CO2 from the developing world, can the individual actions of a few concerned westerners really make any difference? To answer this we first need to work out what our personal emissions are. That means including items omitted from the UN statistics - particularly international air travel - and the carbon footprint of goods made in foreign countries but imported for our use. When these are taken into account, the CO2 footprint of the average western European amounts to some 12 tonnes. For Americans and Australians, the figure is almost twice that, mainly because they drive more, in cars with bigger engines.
In general, just under half of the emissions for which each of us is responsible come from things over which we have personal control, such as how much we drive and fly and how we heat and power our homes. Of the rest, about 25 per cent of the total arises indirectly through powering our workplaces, about 10 per cent comes from maintaining public infrastructure and government, and about 20 per cent is emitted during the production of the things we buy, including food. We can still influence some of these indirect emissions through what we buy - or we could if we had access to the right kind of information - but by and large it makes sense to concentrate on the emissions we can control directly.
So how much can we realistically save and, more to the point, will it be worth it in terms of global emissions? Chris Goodall, author of How to Live a Low Carbon Life, believes so. He reckons it is possible to cut individual emissions by around 75 per cent without seriously altering our lifestyles. For a western European, that means slashing personal emissions from about 12 tonnes of CO2 to just 3 tonnes.
So how do we do it? Like charity, reducing your emissions begins at home (see Diagram). Of course, individual emissions will vary a fair bit, depending on the size of your house, how many people live in it, and how carbon-conscious you are. But a typical western home, with a total power throughput of about 20,000 kilowatt-hours per year, might generate emissions of around 5 tonnes. For each individual in the typical household this would average 2.3 tonnes, of which 1.2 tonnes is from heating the house, 0.4 tonnes from heating water and cooking, and 0.7 tonnes from general use of electricity for lighting and appliances.
Many people are surprised at the importance of heating to most homes' carbon footprint, and clearly there are big hits to be made here. You can cut heating-related emissions by 40 per cent or more by replacing an inefficient old-style boiler with a condensing model, by improving house insulation, and by turning down the thermostat by 2 °C in winter. But the biggest gain here can be from installing a wood-burning stove in your living room. These are attractive features and heat the house using a renewable fuel. Such a stove could cut household emissions by 2 tonnes of CO2 per year or 0.9 tonnes per inhabitant, on average.
You can halve the emissions for heating water and cooking by cutting out baths, taking short showers (no power-showers please - they are as bad as baths) and by using a microwave or pressure cooker. You can also halve electricity bills. The big four energy guzzlers in most households are refrigerators, tumble dryers, computers and lighting. Of these, the tumble dryer is the worst offender. Using it for 1 hour less per week could cut a household's annual emissions by 0.07 tonnes, and cutting it out entirely will double that saving. A computer left switched on through waking hours but turned off at night will be responsible for up to 0.4 tonnes of CO2 in a year. Switching to a laptop, which is more energy-efficient, could save you 0.2 tonnes.
Switching to energy-efficient light bulbs is another smart move, saving 0.25 tonnes for a household with 25 bulbs. A digital TV set-top box on standby uses enough energy to emit 0.06 tonnes of CO2 in a year (roughly the total emissions of an average citizen of Burundi), so you can save most of that by unplugging every time you switch off the TV, and maybe half if you switch off only at night. And think about all the other kit you leave on standby. Get rigorous about unplugging every time and a typical household can save another 0.1 tonnes. It is small compared to some other savings, but significant nonetheless.
A final option is to buy into green electricity tariffs. Read the small print, though, because some companies are simply asking you to subsidise what they are already obliged to do by law. In the best schemes, however, you will be helping to ensure that more wind turbines and other green sources of electricity are built. The annual carbon savings from these greener energy sources could be as much as 0.8 tonnes of CO2 per person.
In the UK, road transport accounts for nearly one-sixth of a typical citizen's emissions, or about 1.8 tonnes per head. In the US, at 5.6 tonnes per head, it makes up more than one-quarter of a rather larger total. The average car there, carrying an average of 1.2 people, emits 556 grams of CO2 for every person-kilometre. A typical British car, also carrying 1.2 people, emits less than half this, at 180 grams of CO2 for every person-kilometre travelled. There are numerous ways of getting these figures down. The average American driver could save a whopping 2.5 tonnes per year by changing to a gasoline-electric hybrid car. In the UK the gains would be lower, but still significant, at 0.8 tonnes. Buying a smaller, more efficient car running on diesel or liquified petroleum gas could cut emissions by 0.4 tonnes per car per year. Turning off car air conditioning can save 0.1 tonnes, while driving moderately and at the most fuel-efficient speeds will enable some drivers to cut emissions by 0.2 tonnes a year.
Another idea is to delay buying a new car. A typical car takes between 3 and 5 tonnes of CO2 to manufacture. That is twice what it typically emits in a year. So even if the new model would be more fuel-efficient, it is probably better to put off buying it.
The bottom line, of course, is that we should all drive less. Getting rid of the car would be best, but is rarely practical. Sadly, cutting out short journeys to the shops does little to cut emissions. For most people it will be less than 0.1 tonnes, though cutting out a daily short journey might double that saving.
Taking public transport to work makes a much more useful contribution. With every 1500 kilometres of commuting, you save 0.5 tonnes of CO2. Public transport is generally a greener option, but there are exceptions.
Trains, for example, are quite variable. In the UK, the average emissions are 40 grams per passenger-kilometre (g/p-km) but, depending on the engine, the source of power and the journey, the figure varies from more than 70 g/p-km down to 27 g/p-km. So going by train is usually better, but a small, fuel-efficient car with four passengers may be more carbon-efficient than taking one of the less efficient trains. Be warned, too, that taking a sleeper train from, say, London to Edinburgh or Paris to Venice may not always be greener than flying. Sleeper cars carry fewer passengers than regular carriages, and that could push the carbon footprint of the typical sleeper passenger above that of someone flying the same route at a typical CO2 emission rate for short-haul flights of 150 g/p-km.
For longer journeys, coaches such as Greyhound in the US or National Express in the UK could be just the ticket. In the UK, this would save about 140 grams per kilometre for each passenger who would otherwise have made the journey by car - the difference between the 180 g/p-km from driving a typically laden car and the 40 g/p-km on a typical coach ride - while in the US you could save 516 g/p-km. Over a 200-km drive that amounts to nearly 30 kg per trip in the UK and over 100 kg in the US.
Truth about flying
If you fly more than once a year, cutting back on those journeys will be the best single thing you could do to cut your emissions. Cut out that long return flight from Europe to Miami, or the US to Rome, and you have saved 2.5 tonnes of CO2 - which is probably more than you emit from your car all year. The simple truth is that frequent fliers have carbon footprints tens of times bigger than the rest of us.
Thanks to abundant cheap flights, Britons are the world's worst offenders on this score, with average emissions equivalent to 1.6 tonnes of CO2 per person - more than double the rate for the average American. Cheap flights are booming in China and India too, but the annual carbon footprint for travel for average citizens in those two countries is still only around one-tenth of those in Europe and North America.
Of the things we buy, food makes up about another 2 tonnes of CO2 per head. Concerned consumers often make an effort to cut their carbon footprint from food by buying locally, which reduces their "food miles". This makes some sense. A quarter of the trucks on our roads are carrying food and raw materials for the food industry. Yet many of the biggest energy inputs (and hence carbon outputs) of our food come from growing and processing food, rather than transporting it. Manufacturing fertiliser, heating greenhouses and food processing are major energy guzzlers, so buying locally is by no means automatically the greenest option. Trucking in tomatoes from sunny Spain often uses less energy than heating a greenhouse in the UK, for instance.
As a rule of thumb, meat and dairy products have high carbon footprints because of the energy needed to grow the feed for the animals. Going vegetarian could halve your carbon footprint from food to 1 tonne per year, but only if you cut back on dairy products too. If you can't go without meat and milk, you could instead halve your food footprint by going organic, largely because of the saving in fertiliser. A diet made up exclusively of locally grown, non-processed and non-packaged food can strip another 0.7 tonnes from your food-based carbon footprint, bringing an impressive total saving of 1.7 tonnes per person.
Drinks packaging matters too. Smelting aluminium is one of the most energy-intensive industries in the world, and making one beer or soda can emits 170 grams of CO2. That's the same as running your TV for 3 hours. The average person gets through 120 cans in a year, which adds up to 0.2 tonnes of CO2. So always recycle your cans and, for preference, buy draught beer or bottles instead. Glass's carbon footprint is rather less than aluminium's.
By making these small changes, the average western European can cut nearly 8 tonnes from their personal carbon footprint, taking their personal emissions down to around 2 tonnes. Multiply that by enough people and the impact could be significant. Take the UK, for example. If just one-third of the UK population did the same it would save 160 million tonnes of CO2, or more than a quarter of the nation's emissions.
Yet again, given the scale of the increases in China, India and South America, is all this effort really worth it? The answer is an unequivocal yes. Emissions reductions are a bit like taxes: you may not like them, and your individual contribution may seem too measly to matter, but multiply that by several million and you can start to move mountains.
Scaled up to global level, these cuts become highly significant. If 100 million people in richer nations cut their CO2 emissions by 10 tonnes per year, on average, that would save a billion tonnes of CO2 emissions a year, or around 5 per cent of the current global total. That won't solve the problem on its own, but it would create space for China and India to grow their economies and their carbon emissions for another year. Then we would need to add another 100 million people for the next year. And so on and so on, until new low-carbon technologies become cheap enough for developing countries like China and India to adopt them without undermining their economic development.
The global community would prefer not to allow the developing world to continue increasing their emissions indefinitely. Next month, diplomats and politicians will gather in Bali, Indonesia, to discuss what to do when the Kyoto protocol expires in 2012. Many will demand limits on the growing emissions of developing countries, including China and Indonesia, which was recently revealed to have the world's third-highest emissions - when the carbon sinks it has lost to the logging of rainforests and the draining of tropical peat swamps is taken into account.
Negotiating limits for China will not be easy. It may be about even with the US as the top emitter of CO2, but divide its output by its total population and the figures look rather different. The typical Chinese citizen is responsible for less than one-quarter of the emissions of the typical American: 4.8 tonnes compared to 20 tonnes. Individual Indians and Africans have emissions averaging 1 tonne or less (see Diagram).
With this in mind, a growing number of politicians are suggesting a fairer approach to cutting carbon, based not on national emissions but on setting tradeable individual carbon quotas (see "What's your quota?").
Ultimately, we will need to bring global emissions down low enough to match nature's ability to absorb them, which may be as low as 10 to 20 per cent of today's global emissions. But if a significant number of people change their ways and demand greener products, that will send a big signal to the market, encouraging the supply of green energy, low-carbon products, organic food and so on.
So while it may be tempting to think that only governments can act on the scale necessary to make real change by rationing carbon and setting tax regimes to provide the necessary carrots and sticks for development, there is no escaping the fact that individuals can make a difference by acting just a little bit greener. The big picture seems daunting but it can be done. And we have to start somewhere. So don't give up.