Im going to talk today about energy and climate. And that might seem a bit surprising because my full-time work at the foundation is mostly about vaccines and seeds,about the things that we need to invent and deliver to help the poorest two billion live better lives. But energy and climate are extremely important to these people,in fact,more important than anyone else on the planet. The climate getting worse means that many years that many years,their crops wont grow . There will be too much rain,not enough rain,things will change in ways that their fragile environment simply cant support. And that leads to starvation,it leads to uncertainty,it leads to unrest. So, the price of energy is very important to them. In fact, if you could pick just one thing to lower th- e price of, to reduce poverty, by far you would pick energy. Now ,the price of energy has become down over time. Really advanced civilization is based on advances in energy.The coal revolution fueled the Industrial Revolution, and,even in 1990s weve seen a very rapid decline in the price of electricity, and thats why we have refrigerators,air-conditioning, we can make modern materials and do so many things. And so ,were in a wonderful situation with electricity in the rich world. But, as we make it cheaper-and lets go for making it twice as cheap-we need to meet a new constrain,and that constrain has to do with CO2. CO2 is warning the planet, 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 nature ecosystems cant adjust to these rapid changes, and so you get ecosystem collapses.Now, the exact amount of how you map from a certain increase of CO2 to what temperature will be and where the positive feedback are, theres some uncertainty there,but not very much. And theres 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? Cant 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 thats a big challenge. Its very different than saying “Were a twelve-foot-high truck trying to get under a ten-foot bridge, and we can just sort of squeeze under.” This is something that has to get to zero. Now,we put out of a lot of carbon dioxide every year, over 26 billion tons. For each American, its about 20 tons; for people in poor countries,its less than one ton. Its 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. Its been constantly going up. Its only various economic changes that have been flattened it at all, so we have to go from rapid rising to falling, and falling all the way to zero. This equation has four factors, a little bit of multiplication: So, youre got a thing on the left,CO2,that you want to get to zero,and thats going to be based on the number of people,the services each persons using on average,the energy on average for each service, and the CO2 being put out per unit of energy. So ,lets look at each one of these and see how we get this down to zero. Probably, one of this number is going to have to get pretty near to zero. Now thats back from high school algebra,but lets take a look. First, weve got population. The world today has 6.8 billion people. Thats headed up to about nine 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 percent, but there we see an increase of about 1.3. The second factor is the services we use. This encompass everything: the foot we eat, clothing, TV,heating. These are very good things:getting rid of poverty means providing these services to almost everyone on the planet. And its a great thing for this number to go up. In the rich world,perhaps the top one billion,we probably could cut back and use less,but every year, this numer, on average,is going to go up,and so, over all,that will more than double,the services delivered per person. Here we have a very basic service: Do you have lighting in your house to be able to read your homework? And, in fact,these kids dont,so theyre going out and reading their school work under the street lamps. Now, efficiency,E,the energy for each service,here finally we have some good news. We have something thats not going up. Through various inventions and new ways of doing lighting through different types of car,different ways of building-there are a lot of services where you can bring the energy for that service down quite substantially. There are other services like how we make fertilizer,or how we do air transport,where the rooms fo