The Earth's climate system is very complex, so nobody can say absolutely, without question, this is going to happen in five, 10, 50 years time.

The capacity of human beings to take actions have truly global consequences is a new thing. This is a big challenge, and it requires some real effort to open up dialogue.

There may not be a magic pill. There may well be certain players -- nations, states, companies -- that address the issue in different ways.