James Lovelock developed the concept of Gaia, that the earth has a self-regulatory system composed of all lifeforms, the atmosphere, the oceans and geo-physical process that maintains the earth within a very narrow range suitable for earth's lifeforms.

As with all negative feedback systems, push them to their regulatory limit and they will flip into another state.

That is the danger we now face.

James Lovelock made himself highly unpopular when he said the only solution was nuclear power.

Also read:

Sustainable Energy by David Mackay