(Disclaimer: This transcript is auto-generated and may contain mistakes.)

And the equation on CO2 is actually a very straightforward one. If you sum up the CO2 that gets emitted, that leads to a temperature increase. And that temperature increase leads to some very negative effects. The effects on the weather, perhaps worse, the indirect effects in that the natural ecosystems can't adjust to these rapid changes, and so you get ecosystem collapses. Now the exact amount of how you map from a certain increase in CO2 to what temperature will be and where the positive feedbacks are, there's some uncertainty there, but not very much. And there's certainly uncertainty about how bad those effects will be, but they will be extremely bad. I asked the top scientists on this several times, do we really have to get down to near zero? Can't we just cut it in half or a quarter? And the answer is that until we get near to zero, the temperature will continue to rise. And so that's a big challenge. It's very different than saying, you know, we're a 12 foot high truck trying to get under a 10 foot bridge and we can just sort of squeeze under. This is something that has to get to zero. Now we put out a lot of carbon dioxide every year, over 26 billion tons. For each American, it's about 20 tons. For people in poor countries, it's less than one ton. It's an average of about five tons for everyone on the planet. And somehow we have to make changes that will bring that down to zero. It's been constantly going up. It's only various economic changes that have even flattened it at all. So we have to go from rapidly rising to falling and falling all the way to zero. This equation has four factors, a little bit of multiplication. So you've got a thing on the left, CO2, that you want to get to zero. And that's going to be based on the number of people, the services each person's using on average, the energy on average for each service, and the CO2 being put out per unit of energy. So let's look at each one of these and see how we can get this down to zero. Only one of these numbers is going to have to get pretty near to zero. That's back from high school algebra. But let's take a look. First we've got population. The world today has 6.8 billion people. That's headed up to about 9 billion. Now if we do a really great job on new vaccines, health care, reproductive health services, we could lower that by perhaps 10 or 15%. But there we see an increase of about 1.3. So we're going to see an increase in the number of new vaccines, new vaccines, new vaccines, health care, reproductive health services. We could lower that by perhaps 10 or 15%.