A new study has revealed the under-appreciation that exists for the role dams play in climate change; how the reservoirs behind them can cause surges of greenhouse gases as the water levels go up and down. In a study of the water column at such a reservoir, marine scientists found an astonishing 20-fold increase in methane emissions as water levels were drawn down. Bubbles coming out of the mud and sediment at the bottom were chock full of this potent greenhouse gas.