Remember that the problem is bigger than the car you drive or the types of lightbulbs in city hall. We need a fundamental shift away from dirty fossil fuels that spew carbon pollution. To make that happen, we need to put pressure on our leaders to take the bold actions necessary to move us off dirty sources of energy.

It's an important point, and every little bit helps not least because those who make those kinds of changes are more likely to make their voices heard as citizens. But the ultimate solutions are going to come through policies.

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.

In physics there's the old law for every action there's a equal amount of reaction. Sometimes that's true in politics. If somebody's out there making nonsensical statements, but wielding power behind them a lot of people say, "Well, I need to react to that." Another reason for the increased prominence of the climate-change issue is the Paris Agreement itself. It's not a small thing when just about every nation in the entire world comes together and makes an historic agreement like this. It's a big deal. And the old cliché "The train is leaving the station" kind of applies.

I don't have the illusion that there's any position or role in the world with as much potential for bringing about change as that of president of the United States.

The cumulative amount of man-made global pollution that's in the atmosphere now traps as much extra heat energy every day as would be released by 400,000 Hiroshima-class atomic bombs exploding every day. It's a big planet, but that's an awful lot of energy.

The entire North Polar ice cap is disappearing before our very eyes. It's been the size of the continental United States for the last 3 million years and now 40 percent is gone and the rest of it is going.