The world is doing its best to try and work together to reduce its carbon footprint, and a rise in the use of renewable energy generation is certainly one way in which to achieve this. In what is a nothing less than a profoundly irritating revelation, a new study in the journal BioScience has confirmed that one of these supposedly clean sources of renewable energy – hydroelectric dams – actually unleashes a vast amount of greenhouse gases every single year.
Specifically, they release methane from their enormous reservoirs over time. This foul gas is a powerful heat-trapping compound that, although shorter lived that carbon dioxide, is 28 to 36 times more potent in terms of global warming. Aggravatingly, this team's calculations suggest that the world’s hydroelectric dams release the equivalent of 907 million tonnes (1 billion tons) of carbon dioxide on annual basis.
This is 1.3 percent of the world’s man-made greenhouse gas emissions, which may not sound like a lot on its own, but it’s extremely disappointing that an otherwise clean energy source turns out to be an underappreciated source of climate-changing gases. When comparing this value to the output of entire nations, however, it really stands out as something quite shocking.
Hydroelectric dams emit more greenhouse gases than Germany, Indonesia or Canada. They emit over twice as much as the UK, and three times as much as France. China, the world’s largest carbon emitter, releases 9.7 billion tonnes (10.7 billion tons) of carbon dioxide per year. This means that hydroelectric dams emit about a tenth of this.
“We had a sense that methane might be pretty important but we were surprised that it was as important as it was,” lead author Bridget Deemer, a research associate at Washington State University, said in a statement. “It’s contributing right around 80 percent of the total global warming impact of all those gasses from reservoirs. It’s a pretty important piece of the budget.”
The top 12 carbon emitters in the world, as of 2014, measured in megatonnes (million tonnes) of carbon dioxide per year. Hydroelectric dams alone would in sixth place if they were a separate nation. Global Carbon Atlas
Methane is often found to be degassing from watery or icy reservoirs, and it is a major concern for climatologists. Although it rapidly decays in the atmosphere, the short sharp boost it gives to atmospheric warming means that it could set off a feedback cycle.
A quick rise in temperature will warm the world’s oceans and cryosphere, which – due to a quirk of chemistry – will allow more methane and carbon dioxide to escape. This will again warm the world, and so on and so forth.
Hydroelectric dam reservoirs tend to contain more methane than many natural sources, however, as they contain a plethora of concentrated organic matter that decomposes into various greenhouse gases. Upstream rivers also continually refill them with nitrogen and phosphorous that further exacerbate greenhouse gas production.
Although this finding is bad news, it’s important to know if the world is to proceed towards a low-carbon future. As many reports are already highlighting, the Paris agreement is a good start but not enough to prevent us from breaching that all-important (but somewhat symbolic) 2°C (3.6°F) warming limit. This finding highlights just how much more aggressive we need to be in terms of cutting carbon emissions.
Nevertheless, hydroelectric dams’ carbon footprint pales in comparison to fossil fuel-fired plants'. Ideally, a near-future energy revolution would ditch these harbingers of climate change and would instead focus on all renewables and nuclear power. They will still have a carbon footprint, of course, but it would be magnitudes lower than the one the world currently has today.
It’s unlikely hydroelectric dams will ever become the primary renewable energy source anyway. After all, you need a network of mountains and rivers for these to work – not something that every nation on Earth possesses.
The famous Hoover Dam. Andrew Zarivny/Shutterstock
