The main greenhouse gases are methane and carbon dioxide. Methane comes mainly from the anaerobic decomposition of animal wastes in agriculture. In brief, this needs to be contained where possible, cleaned to separate sulfur, and burned as fuel. This converts one methane into one carbon dioxide, but carbon dioxide has a less serious greenhouse effect, so this will cause a net improvement. Carbon dioxide is formed by burning carbon.
Carbon is the major element in wood, coal, petroleum, natural gas, etc.
To decrease CO2 production, we must decrease the combustion of these materials. Generally, we believe carbon dioxide is someone else's fault, and we don't need to do anything different. But we really are the major culprits in carbon dioxide pollution. A tank of gasoline in an automobile contains about 120 pounds of carbon. In the internal combustion engine, this is combined with 320 pounds of oxygen, to form 440 pounds of carbon dioxide.