Is hydroelectricity contributing to climate change?

Hydroelectric power stations as a source of greenhouse gases (GHGs)? Really? Well, nothing about climate change is easy or straightforward, so it shouldn't really surprise us.

Methane is a potent GHG (an estimated 80 tonnes more potent than carbon dioxide, although much shorter-lived in the atmosphere). About 40% of it comes from oil and gas production, and 32% comes from agriculture (principally cow burps). But it turns out that a not insignificant amount of methane is created by hydroelectricity power generation - some 3 million tonnes of the 51 billion tonnes of GHGs emitted by people each year, or about 6%. So, a lot less than fossil fuels or even cows, but perhaps more than you might have thought.

The reason? There is a lot of carbon-rich organic matter captured in tropical swamps, peat bogs and waterlogged soils, but also in the sediment of (particularly tropical) freshwater. Waste-water treatment plants and rice paddies are other (man-made) water sources that store up potentially polluting organic matter. 

Whether naturally-occurring or man-made, this organic matter is decomposed by microbes, releasing methane. When it is agitated, this methane is released into the air, much like shaking up a soda bottle. So, when reservoir water is churned up in a hydroelectricity plant, this is exactly what happens.

Now, in the scheme of things, this is still a relatively minor source of GHGs, and hydro is still a good, relatively non-polluting source of power. But we should recognize that hardly anything we do is completely pollution-free. There are schemes afoot to capture and use the methane produced by hydroelectricity plants (methane is the primary component of natural gas, and a good power source in itself). These schemes are still in their infancy, but are showing promise. It certainly seems a lot more practical than capturing cow burps!