Denmark will tax livestock farmers for the greenhouse gases emitted by their cows, sheep and pigs from 2030, the first country in the world to do so as it targets a major source of methane emissions, one of the most potent gases contributing to global warming. The aim is to reach a 2030 target of cutting greenhouse gas emissions by 70% from 1990 levels. Although carbon dioxide typically gets more attention for its role in climate change, scientists say methane traps about 87 times more heat on a 20-year timescale. In recent months, farmers across Europe have protested against environmental measures and regulations that they say are driving them to bankruptcy.