Assuming we muster the political and popular will, here are a few ways we can reduce greenhouse-gas emissions.
1. We could use less energy (either by becoming more energy-efficient or by conserving).
2. We could switch to cleaner sources of energy.
3. We could also reduce emissions from deforestation and agriculture.
The goal is to avoid a global temperature increase of more than 2 degrees Celsius. This will necessitate reducing worldwide emissions 40 to 70 percent by mid-century.
The International Energy Agency has argued that such a cut would require $24 trillion in clean energy investments between now and 2020 (and more thereafter).
That would include:
Each year, on average, 15 power plants and industrial facilities would have to be fitted with technology to capture carbon emissions and store it underground rather than emit it into the atmosphere. (This technology, known as CCS, is still in its infancy.)
On average, 32 new nuclear plants and 17,500 wind turbines would need to be built each year to provide carbon-free electricity.
The world would need to make its transportation sector much more efficient between now and 2020. That means lighter vehicles, putting 20 million electric cars on the road, and more efficient airplanes.
Buildings and factories would also need to become dramatically more efficient at using energy.