dramatically different thing. if we had acted decades ago, we could have brought our carbon emissions down fairly gently. we could have sort of gradually move d away from fossil fuels. now to avoid a catastrophic warming of the planet of more than 3 degrees fahrenheit, we have to bring the emissions down by a factor of 50% within the next ten years. that's going to require a monumental effort on our part. there's some signs of progress. the united states has made a very bold pledge to spring its car -- bring its carbon emissions down by that amount in the next ten years. the united states is leading again on this issue, and that's making a real difference. but there's still a gap between what countries are promising and the policies that they have in place, what we call an implementation gap. we're still building new fossil fuel infrastructure. when the conservative international energy agency has told us that if we are to avert