In the eyes of advertisers, all that is necessary for a product to be ‘green’ is for there to be another product out there that is worse according to some environmental measure. As such, a gigantic pickup truck might be ‘green’ as long as it is a hybrid, or it has recycled plastic in the interior. This use of the word strips it of meaning and turns it into nothing more than a vague label designed to help sell things to people who try to be ethically conscious.

I think it is possible to use the word ‘green’ in a much more rigorous and meaningful way. Specifically, it can be used to refer to technologies, products, and undertakings that are fundamentally sustainable: those that can be made use of forever. As such, a ‘green’ fishery would be one where the catch rate could be sustained indefinitely; a ‘green’ forestry project would be one where trees were cut at the same rate as others matured; and so on.

These sorts of ‘green’ technologies will often require a melange of old and new, in their approaches. For instance, one of the best ways to encourage the emergence of green fisheries is to restrict the use of modern gear. If fishers could only operate using wooden sailing ships (with modern safety gear), a lot of the pressure would be removed from the world’s marine ecosystems, and then would have a better chance of being able to endure the constant demands of humanity. Similarly, green agricultural will probably involve some ancient techniques that preceded the mechanization and artificial fertilizer that have accompanied the explosion of fossil fuels into human life. At the same time, green systems on a planet of seven billion will need to incorporate innovative technologies: innovative mechanisms for turning wind and sunlight into power, new means of transmitting and using that energy efficiently, and perhaps eventually exotic technologies like space-based solar power or nuclear fusion.

By this standard of ‘green’ there aren’t many green things on Earth at the moment. That said, it is true by definition that the future of humanity depends on ‘greening’ in this sense. We need to find a way to live within the bounds of the physical world, both in terms of the resources we consume and the wastes that we produce. A green world is one in which human beings will be able to survive and flourish indefinitely.