Hello, how is everyone feeling? (Cheers) Are you ready to solve climate change? (Cheers) Good. Do you know what a pettawat hour is? Yeah, it's a unit of energy like kilowatt hour or megawatt hour. I've been a climate activist since age 11 and I studied engineering, and so I was familiar with those terms. Kilowatt, megawatt, even gigawatt and terawatt. But I had never heard of a petawatt hour until I wrote a book on climate change solutions. That's because it's so big. But that's the scale I want to talk about. A petawatt hour is a trillion kilowatt hours. And today the world generates about 25 trillion kilowatt hours of electricity each year. Most of that is from fossil-fuel power plants, and the dominant mindset is that we have to change the current electricity system by replacing those fossil-fuel plants with clean generation by 2050. Well, over one third of our electricity generation is already clean, mostly from hydro and nuclear, along with wind and solar, and clean generation is growing. Projections based on current policies around the world show that we are on track to have about 25 petawatt hours of clean electricity generation in 2050. That's two and a half times today's amount of clean generation and equal to today's total generation. So this is great. We can replace all our fossil fuel plants, have a clean version of today's world, walk away, we've solved climate change. Thank you very much. Oh, but I did forget one tiny little detail. We actually need five times that much. To be clear, we need and we're on track to have two and a half times today's amount of clean generation to switch to a clean version of our current electricity system. But changing the current system isn't enough. We need five times that, all of it clean, or 12 times today's clean electricity production, to actually avoid the worst impacts of climate change. Can I repeat that? To avoid the worst impacts of climate change, we have to multiply today's clean electricity production by 12 times. There are four main reasons we need that much. First, let’s keep in mind scientists’ goalpost for addressing climate change: achieving net-negative emissions globally by around 2050. Most of us know that to do so, we'll have to electrify a whole range of vehicles, heating systems and some industrial processes. Electric equipment is more efficient than fuel-based equipment. So electrification actually lowers total global energy demand, but it increases electricity generation needed. In our current energy world, electrifying 60 percent, which is ambitious, would add enough demand that we would need roughly 40 petawatt hours of total electricity generation by 2050. Second, it's not OK to simply replace today's world with a clean version. In today's world, over 700 million people don't have access to electricity. Billions more have access only to small amounts or to unreliable supply that often cuts out. Energy demand in rich industrialized countries will grow more slowly over the next few decades with increased efficiency. But energy demand in developing countries will continue to grow dramatically, especially if we can make electricity cheaper. This is good. Energy access is lifting people out of poverty, driving access to education, commerce, health care and lower birth rates. Both for moral and practical reasons, those of us in richer countries need to realize that addressing climate change will necessarily center on a massive expansion of energy access in developing countries. So electricity generation will have to grow even more and get cheaper to accommodate global economic development. Based on projections of global development by 2050, generation needed rises to 60 petawatt hours per year. The third reason is a bit more debatable, but it needs to be talked about more in public discourse. It has to do with the fact that not everything can be electrified by 2050. Long-range airplanes, for instance, are still going to need the energy density of a liquid fuel. Similar for some industrial processes. Now, many models waive this issue away with two overoptimistic assumptions: that all those factories continue burning fossil fuels but use carbon capture, which costs extra and will only happen where governments mandate it, and that all those long-range vehicles use sustainable biofuel, which is only sustainable if every supplying country, and its local governments, fully enforces strict standards for biomass to avoid deforestation and other impacts that could increase emissions from agriculture. Some amount of carbon capture at factories and sustainable bioenergy will absolutely be part of the picture. But I’ve been in politics, and I am sure that we should plan for imperfect policy. And that means we need to plan for building even more electricity generation. We can use this additional generation to synthesize fuels that are truly carbon neutral or entirely carbon free: hydrogen, ammonia, synthetic jet fuel and others. This is a much rougher estimate, but to be confident of minimizing climate change impacts, we should aim to push our line up to around 90 petawatt hours per year. Finally, the fourth reason is that we need not only net-zero but net-negative emissions in 2050. There will be some non-energy emissions that remain, especially from agriculture. And we'll have to pull CO2 from the atmosphere to make up for those. But we also need to use all our possible carbon-removal methods at their maximum capacity to remove more CO2 each year, getting as far as possible into net-negative emissions, drawing down levels of greenhouse gases in the atmosphere to eventually restore a stable climate. One of the carbon-removal methods we’ll have to use is direct air-capture: arrays of fans filtering CO2 from the air. And doing enough of this to restore safe temperatures within decades, not centuries, will require yet more electricity generation. Again, the exact amount depends on quite how ambitious we're able to be. But for a comfortable rate of carbon removal, we would need perhaps 120 petawatt hours per year total. So roughly five times today's total global electricity system, 12 times today's clean electricity production, and that can actually achieve net-negative emissions globally. And there's a bonus reason to consider. Because clean electricity is going to power so much of the rest of the transition: electrification, global development, synthesized fuels and sequestration, to achieve net-negative emissions by 2050, we should really build as much as possible of that new electricity generation at the beginning of the transition, starting now. This will make sure that clean electricity is abundant and cheap soon enough to still leave time for all of the other transitions that rely on it to fully roll out by 2050. And when we talk about abundant and cheap electricity, we're talking about eliminating poverty faster, powering access to water desalination, strengthening medical supply chains, so much more. Decarbonizing and scaling electricity generation will also be the biggest global development project ever. So if we want to avoid the worst of climate change, we need to discard that dominant mindset about merely replacing fossil fuel generation. My point is, that misses the scale. Our project is not changing the current global electricity system. Our project is building a new global electricity system. Political action that tinkers around within the current system will never get us where we need to be by 2050. Arguments over which sources of clean electricity we should use are unhelpful. We need all of them: hydro, solar, wind, nuclear, advanced nuclear, advanced geothermal, mandates for carbon capture on remaining fossil plants. If you look at the potential rates of addition for each of these, you'll see we need everything as much as possible and we may still fall short. It's not changing the electricity system. It's building a new electricity system. One five times bigger than today's total system and 100 percent clean. As fellow youth activists often say, the project is much more comparable to the World War II-era manufacturing boom than anything the world has done since. Building new things that we've barely ever built before, in massive amounts, to create a new system entirely. In fact, this mindset goes beyond electricity-generation itself. Many people are wary of ambitious climate action because they see the project as changing the familiar current world. That's not it. Addressing climate change means building a new world. A world in which energy is healthier, doesn't pollute the air we breathe and where it's cheaper and everyone globally has access to it. A world with higher incomes, longer and better lives, greater equality. A better world. Thank you, and let's make it happen. (Applause)