Mountaintop removal mining exposes rock that _______ heavy metals and other toxic chemicals into the environment.
Hydraulic fracturing consumes precious water resources, has the potential to pollute groundwater, and can even cause _______.
Nuclear power doesn't directly emit greenhouse gases, but it does leave behind dangerous nuclear _______.
Alternative energy sources of wind power and solar thermal power don't burn fossil fuels, but both affect _______ populations.
The total carbon emissions from alternative energy sources are much _______ than the carbon emitted from fossil fuel plants, making them a good alternative to generating electricity.

Respond to the following based on your reading.

How do hydroelectric dams emit greenhouse gases like methane without burning any fossil fuels?