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CO2 is warm in the planet.

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And the equation on CO2 is actually a very straightforward one.

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If you sum up the CO2 that gets emitted, that leads to a temperature increase.

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And that temperature increase leads to some very negative effects.

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The effects on the weather perhaps worse the indirect effects in that the natural ecosystems

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can't adjust to these rapid changes.

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And so you get ecosystem collapses.

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Now the exact amount of how you map from a certain increase in CO2 to what temperature will be

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and where the positive feedbacks are.

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There's some uncertainty there, but not very much.

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And there's certainly uncertainty about how bad those effects will be, but they will be extremely bad.

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I asked the top scientists in several times.

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Do we really have to get down to near zero?

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Can't we just cut it in half or a quarter?

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And the answer is that until we get near to zero, the temperature will continue to rise.

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And so that's a big challenge.

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It's very different than saying we're a 12 foot high truck trying to get under a 10 foot bridge.

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And we can just sort of squeeze under.

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This is something that has to get to zero.

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Now we put out a lot of carbon dioxide every year over 26 billion tons.

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For each American, it's about 20 tons.

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For people in poor countries, it's less than one ton.

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It's an average about five tons for everyone on the planet.

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And somehow we have to make changes that will bring that down to zero.

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It's been constantly going up.

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It's only very a economic changes that have even flattened it at all.

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So we have to go from rapidly rising to falling and falling all the way to zero.

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This equation has four factors, a little bit of multiplication.

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So you've got a thing on the left, CO2 that you want to get to zero.

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And that's going to be based on the number of people.

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The services, each person's using on average.

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The energy on average for each service.

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And the CO2 being put out per unit of energy.

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So let's look at each one of these and see how we can get this down to zero.

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Probably one of these numbers is going to have to get pretty near to zero.

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That's back from a high school algebra.

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But let's take a look.

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First we've got population.

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The world today has 6.8 billion people.

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That's headed up to about 9 billion.

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Now if we do a really great job on new vaccines, health care, reproductive health services,

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we could lower that by perhaps 10 or 15%.

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But there we see an increase of about 1.3.