Some dam reservoirs emit more greenhouse gases than thermal alternatives

Based on recent research gathered from Canada, Brazil, French Guiana, and Finland, the Commission found considerable variation in emissions of greenhouse gases (GHGs) between lakes in different climates. The study is aimed to help countries more accurately assess their greenhouse gas emissions reductions strategies and the global warming impacts of development choices.

Preliminary findings of the study are that reservoirs in boreal climates, such as in Canada and Scandinavia, emit very low levels of greenhouse gases. In Brazil, however, of ten dams studied, emissions varied from levels similar to those in boreal climates, to emissions reaching the ranges of thermal energy plants. The flooded biomass alone does not explain gas emissions, says the WCD. Carbon flows into the reservoir from the entire basin upstream, and other development and resource management activities in the basin can change future carbon inputs to the reservoir. Further research is necessary to improve the little-understood cycling of GHGs within reservoirs, says the WCD.

“In short, the World Commission on Dams found that while dams may produce net greenhouse gas emissions, that fact alone cannot be removed from the context of place, scale, time or how that dam compares to the other options available in any given country,” said Jamie Skinner, Senior Advisor in the WCD secretariat. “Further, the science on this issue is still young, and additional research is needed before any proposed new hydro projects could be definitively classed as ‘cleaner’ in terms of GHGs than their thermal equivalents and therefore eligible for carbon credits.”

According to Commission Chair, Professor Kader Asmal, the discovery that a dam reservoir emits greenhouse gases is not, by itself, sufficient to determine its ultimate contribution to global warming. “What should matter to governments and the international community concerned about climate change and GHGs is the critical net change that their decisions will bring, and whether the project selected to meet energy needs will in fact emit less than other alternatives considered.”

But even that explanation unlocks only part of the global GHG emissions puzzle, according to the WCD. Each reservoir’s emissions will vary widely, depending on geography, altitude, latitude, temperature, size, depth, depth of turbine intakes, dam operations, and construction procedures.

“The Commission recommends that governments, energy developers, and Climate Convention authorities will need to establish the baseline level of emissions produced by a given river basin before a dam is introduced, and then compare the net change with emissions and warming impacts of other irrigation, energy and water supply options,” said Asmal. “The final choice may be ‘not so clean’, ‘cleaner’, or ‘cleanest’ in terms of GHG emission.”