Nature: The price of European Union (EU) allowances for carbon dioxide emissions has reached an all-time low, hit by falling oil and gas prices, and expectations that economic recession will lead to reduced energy demand. Under the EU’s mandatory emission trading system — set up in 2005 and still by far the largest such scheme in the world — power plants and other CO2-intensive industries can buy emission allowances that allow them to exceed their government-allocated CO2 caps. In 2008, the …