Turns out overcoming global warming is way more than merely reducing our energy consumption and burning less fossil fuels. What we thought was clean energy – hydropower – may end up being a source of greenhouse gas (methane) in the atmosphere.
Reservoirs are a classic instance of how major human alteration’s to the Earth’s landscape can have unexpected effects. Flooding large areas of Earth can set off new chemical processes as tiny microorganisms break down organic matter in the water, sometimes doing so in the absence of oxygen — a process that leads to methane as a byproduct. One reason this happens is that the flooded areas initially contain lots of organic life in the form of trees and grasses.
The impact of agriculture (farming) nearby also excerabates matters:
Meanwhile, as nutrients like nitrogen and phosphorus flow into reservoirs from rivers — being poured in by human agriculture and waste streams — these can further drive algal growth in reservoirs, giving microorganisms even more material to break down. The study finds that for these reasons, reservoirs emit more methane than “natural lakes, ponds, rivers, or wetlands.”
“If oxygen is around, then methane gets converted back to CO2,” said John Harrison, another of the study’s authors, and also a researcher at Washington State. “If oxygen isn’t present, it can get emitted back to the atmosphere as methane.”And flooded areas, he said, are more likely to be depleted of oxygen.
Similarly, our asian food staple of rice also contributes to greenhouse gas emissions.
A similar process occurs in rice paddies, which are also a major source of methane emissions.
So what now? Stop consuming rice and abandon all reservoirs? No…
…reservoirs may be emitting just shy of a gigaton, or billion tons, of annual carbon dioxide equivalents. That would mean they contributed 1.3 percent of the global total.
Just as there are unavoidable contributions to ghg emissions – hydropower is most likely still cleaner than fossil fuels, and rice will still remain a staple food for many Asians, we can focus out attention on avoidable sources of greenhouse gases. These include the excessive usage of electricity, overuse of motor vehicles instead of public transport or other means of transportation, etc.