WE now have a pretty good idea who will be on the ballot in November: Hillary Clinton, almost surely (after the South Carolina blowout, prediction markets give her a 96 per cent probability of securing her party's nomination), and Donald Trump, with high likelihood (currently 80 per cent probability on the markets). But even if there's a stunning upset in what's left of the primaries, we already know very well what will be at stake - namely, the fate of the planet.

Why do I say this?

Obviously, the partisan divide on environmental policy has been growing ever wider. Just eight years ago, the GOP-nominated John McCain, whose platform included a call for a "cap-and-trade" system - that is, a system that restricts emissions, but allows pollution permits to be bought and sold - to limit greenhouse gases. Since then, however, denial of climate science and opposition to anything that might avert catastrophe have become essential pillars of the Republican identity. So the choice in 2016 is starker than ever before.