 So, I grew up three miles from the wall to Czechoslovakia and East Germany, a wall that I thought to be impermeable, which was a surprise when you wake up as a child and all of a sudden your backyard is full of black snow. My parents explained to me that this black particulate matter came from power plants on the other side of this wall. On a spring day in 1986, we woke up one morning and weren't allowed to go outside because the rain was radioactive. This was due to the fact that a reactor had exploded almost exactly a thousand miles away. At that point, I became really interested in studying how you can solve global problems. As an undergrad, when you don't know what you're doing yet, I walked into a lecture by famous economist John Kenneth Galbraith, who's also an alum of Berkeley and one of the leading thinkers in the United States, and he explained to me that you can affect physical change in the world through resetting something invisible, incentives. So, the most powerful incentives that we set as a society are prices. Today, I want to talk to you briefly about a price you've never heard of and a price that I think is the most important number in global change research, the social cost of carbon. The social cost of carbon is an estimate of the damage in dollar terms that one ton of CO2 emitted in the atmosphere does on the entire globe. One ton of CO2 is roughly what you emit driving your Camry from San Francisco to Chicago. This number is not a dollar figure that anybody ever pays. It's a number that governments should use in order to evaluate the benefits and costs from new regulations that affect greenhouse gas emissions. Now, we're looking at a global scale in all sectors. So, these damages include effects on the electricity system. Think of, on a hot day, you're going to turn on your air conditioner. Everybody does that. The electricity system is stressed. This includes effects on human conflict. There's very convincing empirical evidence that extreme heat leads to increased incidence of human conflict at all scales. This includes impacts on the agricultural system. Agriculture only contributes 2% to global GDP, however, it contributes 100% of the calories we eat. So, the impacts of climate change on agriculture are clearly of incredible importance. Now the Obama administration put together an effort to arrive at an initial estimate of what the social cost of carbon should be in federal rulemaking. They arrived at a number of $42 per ton of CO2. Now this is, as I said, an initial estimate. What we are going to do, going forward, is address the things that aren't in that number. A recent report commissioned by the White House, which I was a part of, identified a number of significant additional research avenues that need to be pursued urgently in order to update this number and really calculate the damage from each ton of CO2 that we emit. So what is it going to take? It is going to take an interdisciplinary team of all stars. It's going to take people with crystal balls that can tell us what a future society looks like over the next 100 or 200 years. It is going to take climate modelers that build climate models that work very well in this very specific context. But maybe most importantly what this is going to require is a Herculean effort in order to really understand what the damages on different sectors are. Some sectors we understand very well, other sectors we don't understand very well. So I think for example of impacts on labor productivity. I think of monetizing the impacts of extreme heat on school attendance and how well our kids do on exams. So there are a number of these effects that are not in the current number that are certainly important. Now going forward what I wish we can do here is fill in the missing piece of the pie. Is it $42? Is it $100? But what we need to learn is what is the true number here in order to come up with the one number, the one number that rules them all, the one number that every government across the globe should use. We don't need an effort by every single government. We literally need just one number. And that number is something we need to work on over the next 5 to 10 years. Thank you very much.