The world’s nations would need to cut their greenhouse gas emissions by a lot. And even that wouldn’t stop all global warming.
For example, let’s say we wanted to limit global warming to below 2°C. To do that, the IPCC has calculated that annual greenhouse gas emissions would need to drop at least 40 to 70 percent by midcentury.
Emissions would then have to keep falling until humans were hardly emitting any extra greenhouse gases by the end of the century. We’d also likely need to pull some carbon dioxide out of the atmosphere. The blue line below shows the path emissions would have to take to for a better-than-even chance of staying below 2°C:
By contrast, if emissions fall less sharply (the yellow line) or keep growing indefinitely (the red line), then the world would likely be on track for more warming — 3°C or 4°C or more.
Cutting emissions that sharply is a daunting task. Right now, the world gets 87 percent of its primary energy from fossil fuels: oil, gas, and coal. By contrast, just 13 percent of the world’s primary energy is “low-carbon”: a little bit of wind and solar power, some nuclear power plants, a bunch of hydroelectric dams. That’s one reason why global emissions keep rising each year.
To stay below 2°C, that would all need to change radically. By 2050, the IPCC notes, the world would need to triple or even quadruple the share of clean energy it uses — and keep scaling it up thereafter. Second, we’d have to get dramatically more efficient at using energy in our homes, buildings, and cars. And stop cutting down forests. And reduce emissions from agriculture and from industrial processes like cement manufacturing.
The IPCC also notes that this task becomes even more difficult the longer we put it off, because carbon dioxide and other greenhouse gases will keep piling up in the atmosphere in the meantime, and the cuts necessary to stay below the 2°C limit become more severe.
For more on this, see: Here’s what the world would look like if we took global warming seriously.