1. Natural Gas and Oil Production: This is the largest source of human-caused methane emissions. Methane leaks from wells, pipelines, processing plants, and other infrastructure during the extraction, production, processing, and transportation of natural gas and oil.

2. Livestock: Livestock, particularly cattle, are a significant source of methane. They produce methane as a byproduct of their digestive process.

3. Waste Management: The decomposition of organic waste in landfills and wastewater treatment plants releases methane. This occurs as bacteria break down the waste in the absence of oxygen.