New scientific data supports the belief that methane emissions from big hydroelectric dams outweigh the benefits.
In many rocky regions low on vegetation and population, such as in Iceland and other northern mountainous regions, the production of electricity from hydropower is clearly a net gain in the battle against climate change.
In Asia, Africa and South America, however, masses of methane are produced from dams by the drowning of tropical forests in them. As long ago as 2007, researchers at Brazil’s National Institute for Space Research calculated that the world’s largest dams emitted 104 million tonnes of methane annually and were responsible for 4 percent of the human contribution to climate change.
Since methane has an impact 84 times higher over 20 years than the same quantity of carbon dioxide, this is a serious short-term threat to pushing the planet towards the danger threshold of increasing temperatures by 2°C (3.6°F).
Despite the warnings that big dams in the tropics might be adding to climate change, governments go on building them — while often claiming that large dams equal clean energy.
The new research shows that the methane discharges are probably even worse than current calculations.
In an attempt to find out exactly what the perils and benefits of big dams in the tropics can be, a French team from the National Center for Scientific Research has been studying the Nam Theun 2 reservoir in Laos — the largest in Southeast Asia — prior to its filling, in May 2008, right up to the present to calculate the total methane emissions.
Methane is produced by bacteria feeding on the plant material drowned when the dam is filled. This is added to by more organic matter that is washed into it by rivers and rains.