It seems an easy choice - sacrifice the tree for a human life - until one learns that three trees must be destroyed for each patient treated. Suddenly we must confront some tough questions. How important are the medical needs of future generations?

A leapord never changes his stripes.

We need to put a price on carbon. This needs to be a priority for all of us in how we vote.

When people flirt with despair about the future, they are less likely to take the actions necessary to safeguard it, focusing instead on the short-term.

We're putting 70 million tonnes of pollution into the atmosphere every day, trapping an enormous amount of extra heat from the sun inside the earth's atmosphere. It's threatening to push the planet past a tipping point beyond which climate change would be difficult to stop

There's a law of physics: For every action there's an equal and opposite reaction. And sometimes that shows up in politics and society. And I think that the reaction to President Trump's decision on the Paris Agreement has been much stronger than I had even hoped for. And the determination being expressed by so many people in state governments, city governments, in the business community, the investor community, is really heartening to me.

The warnings about global warming have been extremely clear for a long time. We are facing a global climate crisis. It is deepening. We are entering a period of consequences.