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I've made slides for a colloquium talk I'm giving Wednesday 17 April 2013 at the Perimeter Institute:
I'm pretty happy with them but I'd love comments. I believe the talk will be videotaped, so I'll only announce it to the world (on the blog, and G+) when that video is available.
Preparing this talk made me oddly optimistic. In 2011 I gave a talk saying solar power needed to grow by a factor of 120 to reduce carbon emissions by one gigatonne per year. I updated that information and now it only needs to grow by a factor of 30. That's still a lot, but it's pretty rapid progress. Something similar but less dramatic happened when I updated the information on wind power. Of course it gets harder to grow by larger factors from a bigger starting-point.
Another thing that made me happy is that it's easier to list things physicists can do than mathematicians.