In the past few years, the scientific community has achieved a near-consensus that our energy profligate lifestyles are contributing to a process that threatens future life on earth. As Robin Stott describes [1] the Global Commons Institute has put forward the only realistic framework to prevent this. Based on principles of precaution and equity, the policy of contraction and convergence is already commanding impressive national and international support [2].

Given that scientists have calculated that the capacity of the planet to absorb greenhouse gases without serious destabilisation of the climate is finite, could anyone reasonably support the proposition that the contraction should converge towards an unequal distribution? If that capacity is therefore divided by the world’s population, each person’s fair annual allocation of carbon dioxide emissions cannot be greater than about 1 tonne. At present, the UK’s average emissions are about 10 tonnes, two and a half times the current world average.

How big is your carbon footprint?
The figures below are based on data from How We Can Save the Planet [3]. If any of the questions below do not apply to you, move to the next question.

How many kilowatt hours (kWh) are shown on your four quarterlyelectricity bills combined?

  In the home

1. How many kilowatt hours (kWh) are shown on your four quarterlyelectricity bills combined?
   
2. Divide your total by 2 and then divide again by the number of people (adults and children) usually living in your home
   Put your answer here ______kg
3. How manykilowatt hours are shown on your four quarterly gas bills combined?
   Divide your total by 5 and then divide again by the number of people usually living in your home
   Put your answer here ______kg
4. Howmany litres of heating oil do you buy each year?
   Multiply your total by 3 and then divide by the number of people usually living in your home
   Put your answer here ______kgFor travel
   Private transport
   Fuel consumption does not rise very much when passengers are carried. So estimate your annual mileage only if you were the driver of a car or rider of a motorbike, scooter, or moped.
5. Abouthow many miles do you typically drive a car (or van) each year? A good source is the milometer reading since your vehicle was acquired divided by the years (and parts of a year) that you have driven it. With an older vehicle, see the mileage shown on your last two MoT certificates.
   Divide your total by 3 if your car (or van) runs on petrol
   Divide your total by 4 if your car (or van) runs on diesel
   Put your answer here ______kg
6. Abouthow many miles do you typically ride a motorbike, scooter, or moped each year?
   Divide your total by 6 if you ride a motorbike
   Divide your total by 8 if you ride a scooter or moped
   Put your answer here ______kg
7. About how many miles do you typically walk andcycle each year? As these forms of travel are emissions free, your answer will be 0 kg
   Public transport
   The average number of passengers carried in peak and off-peak times has been used to determine emissions per person mile. Think about the number and length of your train, bus and coach journeys, especially the longer ones, including getting home.
8. About how many milesdo you typically travel by rail each year?
   Divide your total by 8 for underground or metro journeys
   Divide your total by 6 for intercity train journeys
   Divide your total by 4 for other train journeys
   Put your answer here ______kg
9. About how manymiles do you typically travel by bus each year?
   Divide your total by 7 for London buses
   Divide your total by 4 for buses outside London
   Put your answer here ______kg
10. About how manymiles do you travel by coach each year?
    Divide your total by 8 for coaches
    Put your answer here ______kg
    Air travel
11. Abouthow many miles did you fly last year?
    For example, a round flight from London to New York is about 7000 miles and from Manchester to Athens about 3000 miles.
    Divide your total by 3 for flying
    Put your answer here ______kg
    Now add up your 10 answers to determine your total annual emissions.
    Put your total here ______kg
    Divide by 1000 to turn kg into tonnes
    Put your total here ___tonnes

Average UK emissions for personal use is about 5 tonnes. This figure must be reduced to about 0.5 tonnes to stop contributing to climate change.

Clearly, it would be wholly impractical for us as individuals or for the economy to cope with an immediate reduction to the 1 tonne allowance, although it must be achieved as soon as possible. A year-on-year reduction will be needed. But given due warning of each future annual allowance, people can make changes to their home, transport arrangements, and general lifestyle at the least cost and in the way that suits them best (box). By including all personal transport and household energy use in the allowance, a large proportion of total emissions will be covered. Units of the allowance will be surrendered when gas and electricity bills are paid, petrol is purchased, and air tickets bought. The contribution made by the business, industry, commerce, and public sectors which produce our goods and services can be included at a later date within a wider allowance system.

Trading allowances
A key feature of the proposal is buying and selling [4]. Those who lead less energy intensive lives and who invest in energy efficiency and renewable energy are unlikely to use all their allowance. They will then not only be spending less on fuel but will also add to their income by selling their surplus units. The process will be a far more effective driver towards minimising the impact of climate change than attempting to encourage individuals to adopt green practices.

Carbon allowances will act as a parallel currency to real money as well as creating an ecologically virtuous circle. Individuals with low energy use—and therefore low emissions—will have a surplus to sell, while those maintaining high energy use will have to buy this surplus. But the cost of doing so will rise steadily in line with the reduction of the allowance because price will be determined by the availability of the surplus set against the demand for it. In effect, a conserver gains principle will complement the conventional polluter pays principle [5].

Where does the prime responsibility for the adoption of such a radical but essential transformation of society lie? Of course, only government can ensure that individuals are obliged to exercise their responsibilities in this way. Without action, we will be knowingly handing over a dying planet to the next generation.

Competing interests: None declared.

References

1. Stott R. Healthy response to climate change. BMJ 2006;332: 1385-7.
2. Meyer A. Contraction and convergence: the global solution to climate change. Dartington: Green Books, 2000.
3. Hillman M, Fawcett T. How we can save the planet. London: Penguin, 2004.
4. Starkey R, Anderson K. Domestic tradable quotas. A policy instrument for reducing greenhouse gas emissions from energy use. Tyndall Centre technical report No 39, December 2005 http://www.tyndall.ac.uk/sites/default/files/t3_22.pdf
5. Carley M, Christie I, Hillman M. Towards the next environment white paper. Policy Studies 1991;12: 36-51.

Originally published in the British Medical Journal  Vol.332: 1387-1388, 10 June 2006.