In an interview on Science and Climate Change

Your next book is Factor Four: Doubling Wealth, Halving Resource Use by Ernst von Weizsacker, Amory B Lovins and L Hunter Lovins.

This is an inspirational book written quite some years back. It was really saying that we don’t have to go back to living in stone caves and wearing hair shirts in order to sort this problem. If we use our intelligence we could achieve this factor four, which is expressed as doubling wealth and halving resources. And that is quite an appealing message.

Amory Lovins was one of the best known environmentalists and at the time most of them were saying that we must do less of this and less of that. But he was saying that if we use technology intelligently we don’t have to be poor again. We could still maintain the lifestyle to which we all aspire.

And do you think that is just wishful thinking?

There is some wishful thinking in the book I am sure. But it is possible. The main problem is the carbon dioxide issue is a lot bigger than a factor of four. I have a lecture that I give on climate change which suggests that it is a factor of 40, which is a derivation from the title of this book. What I mean by that is that we need to reduce carbon dioxide emissions by about 75 per cent by the end of the century or maybe a bit sooner.

At the same time the world’s population is probably going to double which makes it worse. And the developing world is liable to use more energy rather than less. If the bulk of the developing world only comes up to the level of Europe (let alone North America) that is another factor of five.

So I multiply four by two, then by five, and come up with 40 as the amount by which we have to reduce the amount of carbon we use to produce one unit of GDP. So factor four gets us some of the way but not all of it.