 Mae gwaith yw yw'r holl bwysig o'r hyfrannu lluniaeth argyndoedd. Mae hyn yn armaodol yn rhain oes, a mae'n rhain. Mae'n ei wneud ar hynny o'r holl bwysig o'r holl bwysig o'r 60 miliwn ffyrd o'r hynny yw fel yw rhan. Mae'n meddwl o'r hyfforddd arbennigol. Mae'n meddwl i'r hyfforddd argynniadau i'r hefyd. Mae'n meddwl i'r hefyd yn hawddiaeth yn y stryd. Mae'r holl bwysig i'r hefyd. If it rains very hard the streams only rise a little bit and then go down and although they're growing fast this tremendous turnover the water flowing out of a rain forest is as pure as the water falling in the rain so how do they do it in a hectare of forest, a lot of water which then either evaporates or drops slowly to the ground it's absorbed by the leaf litter and so on. This on the other hand is a large city. Environment ecosystems like that have been around for less than 100 years. 1900 there were no cities with more than 10 million people. 2050 there were one city in New York now there are about 30. But we already know that they're not sustainable. For example there are no surfaces to absorb the water. It rains and the water runs off into the low lying areas. The drains are too small or more likely the drains are blocked then you get flooding. So what we do we cure the symptoms. To prevent the flooding we build bigger drains or we straighten out the river or we build a culvert. And that causes problems itself. Flood surge is downstream, too much sediment, banks eroding, heavy metal pollution and so on. And of course it's extremely ugly. Or take another example buildings absorb solar radiation. They consume huge amounts of energy. The concrete holds the heat. Cities get hot. As you can see this is the case of Paris. But a tropical city can be 7 degrees warmer than the surrounding areas. It's not climate change, that's the urban heat island effect. So the solution, air conditioning. Leacwyn you described this as the great invention of the 20th century. But the problem is it creates more problems. You walk past all of those air conditioners it's unbearable. And of course the city is getting warmer. So what do we need? More air conditioning. So how do you make a city resilient? The answer is that you treat it as a system and you understand how all of the processes interact together. And that's exactly what my colleagues at Future Cities Laboratory are doing to try and improve air cooling. They're trying to understand all of the factors which affect air temperature. Because then they can make very focused changes. Not just cooling lots of unnecessary air. And if they do that the benefits are enormous. You have the amount of electricity you need to cool. And even better you need less ducting. You can get three floors in the space of two. Think of the savings. So can we take that kind of thinking and apply it to the city as a whole? Now my opinion is that we have to. Because fixing symptoms simply causes more problems. And we can start by doing simple things. Replacing some of the processes we've taken away. What about? More trees? Or green roofs? Or permeable pavements? These are simple things. Many cities are doing them. But mostly they're doing them for aesthetic reasons. Because they make the city more livable. They don't really know how these are improving the environment in terms of its performance and its resilience. But there have been some studies investigating that. And again the results are surprising. A green roof can reduce the cooling costs in a hot climate by 50%. A green roof, or lots of green roofs, can reduce the storm overflows by 25%. Someone calculated in the San Francisco Bay Area all of the trees produced value of about $5 billion a year. So if you have that information, you put it together with the normal information for constructing buildings and planning. Here's an expert system developed by one of my colleagues to incorporate that ecological information. Then you can use it. And my vision of a sustainable city, a resilient city, is it's a bit more, a bit like a natural ecosystem, which regulates its environment through its structure and all sorts of internal feedbacks. And a city like that will be healthier, safer, more livable and more resilient.