 Many impacts we're already seeing today, we're already seeing warming temperatures shifting rainfall patterns, changes in the intensity and frequency of extreme events. But by the time we get to 2 degrees Celsius, we also expect to see very noticeable impacts in terms of the frequency and severity of wildfires, particularly in the western U.S., in terms of the average yield that we get from many of our major food crops, in terms of the amount of snowpack left in the mountains that supplies most of the west with its water, and in terms of the things that we're already seeing today, the frequency of heat waves, heavy rainfall events or droughts, the geographic extent of invasive pests like kudzu and red fire ants, also the geographic extent of potentially endangered species. In the short run, the true economic costs of not limiting emissions of greenhouse gases are related fundamentally to the opportunities that the economy misses to take into account the future as it will unfold. The future involves changing climate, climate risks, climate damages, and frankly climate policy that will make carbon and fossil fuel more expensive. Investments that are made without anticipating that will lock in antiquated structures, antiquated technologies. They'll create competitive disincentives for American businesses globally. People's Republic of China is now considering a cap and trade on carbon to be implemented in around 2014 to reduce carbon emissions to 1990 levels in 20 or 30 years. They will be developing their own technologies and their own ways of reducing carbon emissions, and frankly we won't compete unless we set up similar incentives in this country. Well the most important non-CO2 gases are methane, which is the same as natural gas, and it leaks out from a lot of places, sometimes from utilities or gas lines or things. And it has a lifetime in the atmosphere of 10 years, but it turns out per molecule to be 20 to 100 times roughly as important as a molecule of CO2. And so it's very important to get at and go after. Other ones are tropospheric ozone, which is sort of caused by air pollution, and so that's another one you naturally want to go after to try and get down. Another one is black carbon, just that black soot that comes off from diesel vehicles or from inefficient burning and biomass, and that absorbs extra solar radiation, and so by absorbing that extra solar radiation it basically makes things warmer, and then the greenhouse gases amplify that. And CO2 determines a lot about our long-term climate change, and these short-lived species, methane and black carbon, determine what's going to happen over the next few decades. And if you want to make a difference and slow the rate of warming over the next few decades, you have to pay attention to the short-lived gases.