Carbon-free energy is simply something we have to do. The time for talk is past. If we turn around net carbon emissions by 2020 rather than 2040, we get another 2° of fever rather than 3° - and that's a big difference.

Since Serengeti-scale savanna scenes are only one or two million years old, our earliest after-the-apes ancestors didn't move into this scene so much as they evolved with it, as the slower climate changes and uplift produced more grass and less forest.

You can always spot the pioneers by the arrows in their backs.

Our CO2 mixes with everyone else's within a year, then hangs around for centuries like a shroud.

Carrying on as usual carries enormous risks, condemning today's students to a world of constant insecurity and frequent catastrophes.

Anyone who would tackle our current addiction to fossil fuels is going to have to maneuver around denial.

Even if we stop the growth, we'd still be adding a constant amount of fossil carbon to the atmosphere each year.