Halting climate change requires a change more fundamental than a series of lifestyle choices.
On the face of it, the threat which climate change poses to the environment - and even to the possibility of human life of this planet - has nothing to do with the class struggle.
In January the US energy secretary claimed that the private sector will deal with the problem because it affects them as much as anyone else: "The people who run companies do have children, they do have grandchildren, they do live and breathe in this world."
But the major factor determining the behaviour of giant corporations is not the personal inclinations of their directors. The corporations are part of a competitive system, in which each has to keep its costs to a minimum if it is to stay in business. That is why firms and national governments retreat from measures needed to stop climate change.
George Monbiot has used his Guardian columns to show why their answers - like carbon trading, growing crops to produce biodiesel, storing liquid carbon dioxide underground, and above all nuclear energy - are either ineffective or contain dangers of their own.
But then, in a very depressing column early in December, he asked whether there were measures which could compensate for the big reduction in the use of coal and oil that that are necessary to limit climate change. His conclusion was that there would be "an energy gap". The only way to avoid catastrophe, he wrote, was to "change our way of life" and use much less.
For many people influenced by environmental movements that means we all have to make sacrifices. Only a hairshirt existence can save the planet.
But for most people this is not an option. For example, they use energy-consuming transport not by choice, but because their work is some distance from home. The structure of existing society determines what the individual does, not the other way round. And vast amounts of energy are not used by individuals at all, but by corporations driven by profit.
There may be a small, dedicated minority of people prepared to slash their living standards, but there is no way to win the great majority to this programme - think of the billions across the world who already live below the breadline. Imposing massive cuts in the living standards of millions of people is inconceivable outside of a highly repressive, near-totalitarian dictatorship - and this approach does not even point to a mechanism for bringing this dictatorship about. It lacks what is sometimes called "agency".
Fortunately, there is a different view of what it means to "change our way of life".
It starts from seeing existing society as a class society. We do not all use equal amounts of energy. In general, the rich use much more than the poor. They have the biggest houses to heat, bigger cars, and so on. And that is not all. Existing society is also extremely wasteful. It lights up prestige office blocks, it transports foods thousands of miles just to make a bit of extra profit, it maintains vast war machines, it wastes resources on advertising, and most of all it wastes resources on building rival production and distribution facilities.
A class approach can massively reduce the amount of energy used in two ways. The first is by challenging the massive amounts of energy consumed by the luxury lifestyles of the rich. The second is by fighting to provide the mass of people with ways of keeping warm - and of travelling - that are better than those at present but no more expensive, and that use much less energy.
A crash programme to insulate everyone's home would be an obvious measure, and it would also be popular. So would free installation of wind generators and solar panels for millions of homes. Comfortable, cheap and frequent public transport is the way to stop people using cars.
But it is not just a question of raising such demands in the abstract. As climate change takes effect, and certain vital resources run short, there will be an intensification of social tensions. A Pentagon report warned the US government two years ago that the result could be a proliferation of wars and civil wars.
When past societies faced catastrophe because of their destructive effect on the environment - the Mayas of southern Mexico and Guatemala, or the inhabitants of Easter Island, for instance - bitter struggles erupted, with the lower classes rising in revolt against the upper classes they blamed for their plight.
But such struggles will do nothing to halt climate change if they are simply an attempt to obtain a bigger share of resources that are in decline. The outcome could then be what Marx called "the mutual destruction of the contending classes". That is why the input of socialists is so important. There is a political battle to win the exploited classes to fight to protect their living standards on a programme that can save the whole of humanity from the destructive effects of climate change.
Chris Harman is the editor of International Socialism journal (www.isj.org.uk)