This is something I didn’t know about. I knew that when they build a dam, they cut down the trees on the land that will be underwater. But there are still lots of carbon in the soil.
p.69
<< Hydropower has a lot going for it — it’s relatively cheap — but it also has some big downsides. Making a reservoir displaces local communities and wildlife. When you cover land with water, if there’s a lot of carbon in the soil, the carbon eventually turns into methane and escapes into the atmosphere—which is why studies show that depending on where it’s built, a dam can actually be a worse emitter than coal for 50 to 100 years before it makes up for all the methane it’s responsible for*. In addition, the amount of electricity you can generate from a dam depends on the season, because you’re relying on rain-fed streams and rivers. And, of course, hydropower is immobile. You have to build the dams where the rivers are.
* These calculations are drawn from a life cycle assessment of dams. Life cycle assessment is an interesting field that involves documenting all the greenhouse gases that a given product is responsible for, from the time it’s produced until the end of its life. These assessments are a useful way to analyze the climate impact of various technologies, but they’re pretty complicated, so in this book I will focus on direct emissions, which are easier to explain and generally lead to the same conclusions anyway. >>