Well-established theories collapse under the weight of new facts and observations which cannot be explained, and then accumulate to the point where the once useful theory is clearly obsolete.

The presidency is more than a popularity contest.

We ought to approach this challenge [of global warming] with a sense of profound joy and gratitude: that we are the generation about which, a thousand years from now, philharmonic orchestras and poets and singers will celebrate by saying, they were the ones that found it within themselves to solve this crisis and lay the basis for a bright and optimistic human future.

We face a climate crisis now that is the most serious challenge our civilization has ever confronted. And the greatest country in the world [America] has to remain a part of this unprecedented global agreement to deal with it.

We're still putting 110 million tons of man-made global pollution into the air every single day as if the sky is an open sewer. More than 90% of the extra heat energy is going into the oceans, and that's why superstorm Sandy was so much more destructive, that's why the ice is melting more rapidly, that's why the water cycle is being disrupted and we get a lot more water vapor coming from the oceans into the sky, and that's why we get these enormous downpours and big floods. They happen all the time. Every night on the TV news is like a nature hike through the Book of Revelation.

You have to rip your opponent's lungs out and then move on.

The signs that the world is spinning out of kilter are increasingly difficult to misinterpret. The question is how to convince enough people to join a critical mass of urgent opinion, in the U.S. and the rest of the world.