 A climate agreement can reduce the risk from climate change by cutting greenhouse gas emissions, but in my opinion the capacity for that to be really significant is really quite limited. We collectively as a society should be looking at other options to reduce risk from climate change. One set of ideas that has received increasing attention is called climate engineering. What this is, it's a group of proposals to intentionally intervene and modify natural planetary systems in order to reduce risk from climate change. There's two categories and perhaps I can give an example in each to help you see what I'm talking about. One thing we might be able to do is to encourage the earth to pull out carbon dioxide, which is the most important greenhouse gas from the air. That gas stays there for a long time on its own. Perhaps we could build machines of some type that pull carbon dioxide out of the air on a large scale and store it somewhere, perhaps underground, perhaps at the bottom of the ocean. Another approach we could take is to alter the planet or parts of the planet in such a way to make it just slightly more reflective. This would bounce off just enough of the sunlight in order to counterbalance the warming effect of climate change, the global warming. One way we could do this is to spray a fine mist into the upper atmosphere, higher than where airplanes fly. This would effectively make the sky just a touch hazy and like a hazy day is a little bit cooler, this could cool the planet by just enough to counterbalance this warming effect. The particular use of the second method of sunlight blocking is that it's fast. Part of the challenge of climate change is that if it turns out to be really bad then it's going to be too late to cut our emissions. The damage is already done, the carbon dioxide is already in the air and the earth is going to keep warming up. If that turns out to be the case, it might be very useful to have the knowledge of how to reflect some sunlight as something of a tool in case of emergency. Thus, a desire to research this does not imply that we should necessarily do it. It has a high value just as a capacity. And that's what some researchers are thinking about. They think it's probably about time to move beyond what's been done thus far, which is computer modeling as to how this would work and maybe work a little bit outdoors and see how these fine particles might behave in the upper atmosphere and whether they could in fact cool the planet. There's a few risks that scientists think this may have. The leading risk is that both climate change and climate engineering would affect both temperature changes and rainfall patterns. They would do so differently and these changes would be different around the world. So a big question would be what's the net effect when you put the two things together? We're going to end up with places that are still a little bit warm and still a little bit cool and maybe too wet and maybe too dry. So would it be worth it? Would the net effect be worth it? The evidence thus far is that it would. Europe has been a world leader in cutting greenhouse gas emissions. It's really embraced this as a cause that the EU is behind. And to that extent this idea of climate engineering, particularly blocking sunlight, continental Europeans in particular are a bit nervous about this. The other places that have been considering this and been doing research such as England and America have been in my opinion somewhat warmer to the idea. No one is enthusiastic about it to be clear. It's something of a sign of desperation and concern about climate change and about the limited ability and likelihood of greenhouse gas cuts to really do what needs to be done.