Nathaniel Keohane:

Well, I think, if we're going to tackle this problem well, we need two things. One is that sense of urgency that we just were talking about that I think is increasing with the evidence of our eyes and the reports and so on.

But the other is a sense that there are solutions out there, that we have what it takes, if we put our minds to it, if we put the resources to it, to address this problem.

And, there, I think we're really seeing some bright spots. I will just give you a couple of examples. If you look at renewable energy, like wind and solar, the costs of that energy are plummeting. In some places in the United States, wind and solar are cheaper than existing coal as an means of generating electricity, so cheaper to run than current coal plants.

You have a big electric utility in the Mountain West, Xcel Energy, that's agreed to cut its emissions 80 percent by 2030 and 100 percent by 2050.

You look internationally, China, even though its emissions are still creeping up, is likely to peak its emissions and start on a downward path in the middle of the next decade, which is five years ahead of its own commitment.

So there are tailwinds, the economic drivers on renewable power, on renewable energy, clean technology, that are blowing in our direction. And I think that's what gives me some optimism that we have the solutions we need, if we can match them to that sense of urgency we should all have.