Just a few days ago, Earth crossed a most important and very scary threshold, with scientists declaring that levels of atmospheric CO2 have legitimately exceeded 400 parts per million, and there’s slight hope of them ever returning them to harmless levels. And currently, things are looking even worse, because a new discovery has identified a completely new source of greenhouse gas discharges that we hadn’t even considered, and it is responsible for more atmospheric CO2 and methane than the whole nation of Canada.
Just to put that into perspective, we are talking about something that’s been emitting approximately 1 giga-ton (1 billion tons) of carbon dioxide a year, and 1.3% of all greenhouse gases made by humans, into our atmosphere this whole time, and we had no knowledge. So if you believed the circumstances was bad before, it just got a whole lot poorer. And wait till you hear what this recently discovered source of greenhouse gases is: the dams and reservoirs used to produce 'clean' hydroelectric power and water crops in some 1 million facilities around the globe.
What’s most worrying is that enormous 79% of the gas generated by these reservoirs is methane, which has up to 36 times the global warming possibility of carbon dioxide, a capacity that takes into account a gas's ability to absorb energy, and how long it stops in the atmosphere. Carbon dioxide and nitrous oxide were found to structure the remaining 17% and 4% of the reservoir emissions, respectively.
The finding was made by an international team of scientists, who just finished the largest study of reservoir greenhouse gas discharges to date. They analyzed more than 200 earlier studies on potential emissions from 267 dams and reservoirs around the globe, which have a combined surface area of nearly 30,000 square miles (77,699 square km). When all the data was organized, they found that these facilities were significantly worse for the environment than anyone had estimated.
Bridget Deemer, from Washington State University, one of the team member told Chris Mooney at The Washington Post, "There’s been quite an explosion in research into efforts to guess emissions from reservoirs. So we synthesized all known estimates from reservoirs worldwide, for hydro-power and other purposes, like flood control and irrigation. And we found that the estimates of methane discharges per area of reservoirs are about 25% higher than previously thought, which we believe is significant given the global boom in dam structure, which is now underway."
As Deemer points out, it is not just hydroelectric facilities that are contributing to these huge, unaccounted for expenses of greenhouse gases; it’s all artificial dams and reservoirs. So principally, if we have consciously flooded areas of land to produce energy, water our crops, or complete flood control, we are funding to the accelerated warming of the planet. As the team describes, human-made reservoirs tend to flood massive areas that contain massive totals of organic life, such as grass and leaf matter, all in one go.
As this carbon-rich material is overpowered in water, it very quickly runs out of oxygen, and this gives growth to populations of microbes that breathe CO2 and makes methane as a byproduct. Many of these dams are also fed by rivers, which carry in them a whole lot of new carbon-based matter, which means the cycle can last long after the original stuff has decomposed away.
Natural bodies of water, on the other hand, like ponds, lakes, rivers, or wetlands, have developed far more increasingly, and are much less likely to run out of oxygen like dams and reservoirs. One of the team members, John Harrison from Washington State, told The Washington Post, "If oxygen is present, then methane gets transformed back to CO2. If oxygen is not present, it can get emitted back to the atmosphere as methane."
So does that mean hydroelectric power is no longer a sustainable option?
Not essentially, the scientists say, but pressure that we need to be far more informed about the possibly harmful side-effects of huge facilities like dams and reservoirs, which basically change huge amounts of land very quickly, and take that into explanation when we are figuring out how far we need to go to 'decarbonize' the global economy.
Harrison said, "We are trying to deliver policymakers and the public with a broader picture of the consequences of damming a river."
The study has been accepted for publication in upcoming week's edition of BioScience.