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?

When it comes to climate, we can all make a big difference.

Adopting a central organizing principle means embarking on an all-out effort to use every policy and program, every law and institution, to halt the destruction of the environment.

I think the ethical standards established in this White House have been the highest in the history of the White House.

If the only tool we use to analyse what's valuable is a price tag, then those things that don't have price tags begin to look like they have no value.

You know the old saying: you win some, you lose some... and then there's that little-known third category.

The ten hottest years in the atmospheric record, going back only 160 years, have been in the last eleven years.