When we think about global warming at all, the arguments tend to be ideological, theological and economic.

The models that have been constructed agree that when, as has been predicted, the level of carbon dioxide or its equivalent in other greenhouse gases doubles from pre-Industrial Revolution concentrations, the global average temperature will increase, and that the increase will be 1.5 to 4.5 degrees Celsius or 3 to 8 degrees Fahrenheit... In Dallas, for instance, a doubled level of carbon dioxide and other gases like methane, would increase the number of days a year with temperatures above 100 degrees from 19 to 78 each year.

The Old Testament contains in many places, but especially in the book of Job, one of the most far-reaching defenses ever written of wilderness, of nature free from the hand of man. The argument gets at the heart of what the loss of nature will mean to us....God seems to be insisting that we are not the center of the universe, that he is quite happy if it rains where there are no people - that God is quite happy with places where there are no people, a radical departure from our most ingrained notions.

Where people aren't as deeply reliant on fossil fuel as in the United States, it's far easier for them to imagine change on this scale. When you go to Europe, they're much more ready. They use half the amount of energy per capita that we use. They can imagine using less than that. They see the benefits. They're ready to go.

In the States we've had by far the largest demonstrations in the last few years. The largest civil disobedience actions about anything in US history in the last 30 years have all been centred around the climate.

We also have to engage - and I think this is important - in national politics because there is no way to address questions of this scale in the short time that we have to address them without engaging in real political change.

Permafrost in the soil [is melting], in the boreal and arctic areas in the world, and, probably even more alarming in the last six or eight months, the data on what is happening to the ice shelves in Greenland and the west Antarctic has begun to cause people to radically reassess the earlier conviction that those ice shelves were stable on a kind of century-long time scale.