The global warming deniers persist in this air of unreality. After all, the entire north polar icecap, which has been there for most of the last 3 million years, is disappearing before our eyes. Forty percent is already gone. The rest is expected to go completely within the next decade. What do they think is causing this?

The science linking the increased frequency and severity of extreme weather to the climate crisis has matured tremendously in the last couple of years.

What's at risk [in 100 years] if we do not take action, truly is the survival of civilization as we know it... Literally that is the case. We have seen global warming so far of just a little bit less than one degree Celsius and look at what's happened. Superstorm Sandy. Boulder Colorado. All these fires. Hurricane Irene one year before.

There are many who would much prefer that the word 'climate' never be mentioned and that the issue be eliminated from our national conversation.

I would distinguish between Donald Trump and the United States of America. Although he is president, he does not speak for the country on the climate change, and that was vividly illustrated in the aftermath of his speech pulling the US out of the Paris Agreement. Almost immediately, not only did the rest of the world double down on its commitments, but also here in this country, governors, mayors, business leaders, they said, we're still in the Paris Agreement, and they're doubling down. A lot of cities have now made a decision to go 100% renewable energy.

Our world faces a true planetary emergency. I know the phrase sounds shrill, and I know it's a challenge to the moral imagination.

When you look at what has happened over the last few decades the natural fluctuations point in the opposite direction of what has actually occurred. When they run the models and plug in the man-made pollution, the correspondence is exact. Beyond that, the scale of natural fluctuations has now been far exceeded by the impact of man-made global warming.