So for the past 12 years, I've been obsessed with this idea that climate change is an information issue that computers will help us fight. I went from data science to climate policy research, from tech to public service, in pursuit of better data to avoid the wasted energy, resources, opportunities that lead to runaway carbon emissions. Until one day, running in the streets with a friend, it hit me: the same cars, factories, power plants whose emissions are wrecking our climate over time also release harmful, local pollutants that threaten our health right here and right now. All this time I'd focused on the long-term environmental risk when I should have been up in arms about the immediate health impact of pollutants in the air. Air pollution is a burning public health crisis. It kills seven million people every year, it costs five trillion dollars to the world economy and, worst, it robs us of our most precious gift, the years in our lives: six months of life expectancy in my hometown of Paris and up to three, four, five years in parts of India and China. And in the US, more people die from car exhaust than from car accidents. So how do we protect ourselves from pollution? The reason it's difficult is an information gap. We simply lack the data to understand our exposure. And that's because the way we monitor air quality today is designed not to help people breathe but to help governments govern. Most major cities operate networks of air-quality monitoring stations like this one in London, to decide when to cut traffic or when to shut down factories. And these machines are like the computers from the '60s that filled entire rooms. They're incredibly precise but incredibly large, heavy, costly -- so much that you can only deploy just a few of them, and they cannot move. So to governments, air pollution looks like this. But for the rest of us, air quality looks like this. It changes all the time: hour by hour, street by street, up to eight times within a single city block. And even more from indoor to outdoor. So unless you happen to be walking right next to one of those stations, they just cannot tell you what you breathe. So what would environmental protection look like if it was designed for the age of the smartphone? So for the past three years, my team and I have been building a technology that helps you know what you breathe and fits in your hand. Flow is a personal air-quality tracker that you can wear with you on a backpack, a bike, a stroller. It's packed with miniature sensors that monitor the most important pollutants in the air around you, like nitrogen oxides, the exhaust gas from cars, or particulate matter that gets into your bloodstream and creates strokes and heart issues. Or volatile organic compounds, the thousands of chemicals in everyday products that we end up breathing. And that makes this data actionable and helps you understand what you're breathing by telling you where and when you've been exposed to poor air quality, and that way you can make informed decisions to take action against pollution. You can change the products you use at home, you can find the best route to cycle to work, you can run when pollution is not peaking and you can find the best park to bring your children out. Over time you build better habits to decrease your exposure to pollution, and by tracking air quality around them, cyclists, commuters, parents will also contribute to mapping air quality in their city. So we're building more than a device, but a community. And last summer, we sent early prototypes of our technology to 100 volunteers in London, and together they mapped air quality across 1,000 miles of sidewalk and 20 percent of all of central London. So our goal now is to scale this work around the world, to crowdsource data so we can map air quality on every street, to build an unprecedented database so scientists can research pollution, and to empower citizens, civic leaders, policy makers to support clean-air policies for change. Because this can and must change. Remember cigarettes in bars? It took decades of lung cancer research and second-hand smoking studies, but eventually, we reached a tipping point and we passed smoking-ban laws. We must reach the same tipping point for air quality and I believe we will. In the past couple years alone, governments have fined carmakers record amounts for cheating on emission standards. Cities have passed congestion charges or built bike lanes -- like Paris that turned this highway, right next to my home, in the middle of the city, into a waterfront park. And now mayors around the world are thinking of banning diesel outright by 2025, 2030, 2035. But how much faster could we go, how many lives could we save? Technology alone will not solve climate change, nor will it make air pollution disappear overnight. But it can make the quality of our air much more transparent, and if we can empower people to take action to improve their own health, then together we can act to bring an end to our pollution. Thank you very much. (Applause)