Hydropower is often thought of as climate-friendly because dams don’t burn fossil fuels to produce electricity, however scientific studies indicate that the warming impact of tropical reservoirs can be much higher than even the dirtiest fossil-fuel power plants.
Reservoirs produce significant amounts of methane, carbon dioxide, and nitrous oxide when organic matter rots and decays. According to the most detailed estimate available, done by Ivan Lima and colleagues from Brazil’s National Institute for Space Research (INPE), large dams (taller than 15 meters) are the largest single anthropogenic source of methane, being responsible for 23% of all methane emissions due to human activities. This implies that dam methane emissions are responsible for at least 4% of the total warming impact of human activities. The thermal, chemical and biological conditions in tropical reservoirs, like the ones planned for Sarawak, have higher methane emissions than those from reservoirs elsewhere.
Land Clearing, Construction, and Deforestation
Other dam-related greenhouse gas emissions include the fossil fuels and building materials used during dam construction; land clearing for reservoirs and resettlement sites, transmission lines and access roads; and the expansion of irrigated agriculture. Globally, loss of forests contributes as much as 30 percent of global greenhouse-gas emissions each year–rivaling emissions from the global transportation sector. Trees capture carbon dioxide by taking it into their cells through photosynthesis and storing the carbon in their bodies. When trees are burned, harvested, or otherwise die, they release their carbon back into the atmosphere. The SCORE dams would result in the loss of 2425 square kilometers of rainforest, not including the land that would be cleared for resettlement sites. The Bakun Dam reservoir alone is the size of Singapore. The massive loss of forest would release huge amounts of carbon into the atmosphere.
Learn more about dam emissions from the International Rivers Dirty Hydro Fact Sheet.
Take a closer look at tree cover in Malaysia through Global Forest Watch.
Learn more about the Bornean rainforest on Mongabay’s Borneo page .