Methane. A greenhouse gas emitted by natural sources such as wetlands, but is also emitted from industry, agriculture and waste management activities. These include human activities such as leakage from natural gas production and the raising of livestock. Globally, over 60 per cent of total CH4 emissions come from human activities. Since methane is much more effective than carbon dioxide in traping heat in the atmosphere, both types of GHG emissions need to be addressed in order to effectively reduce the impacts of climate change.