Ann: Hazer Achieves First Hydrogen and Graphite at CDP, page-61

biogas and natural gas are similar in composition, both being mainly a mix of CH4 and CO2 but depending on the source in varying proportions. The big difference is that natural gas is a fossil fuel so when used adds CO2 to the atmosphere. A second problem arises because there are lots of methane fugitive emissions from extraction, transfer and transportation. By contrast biogas is carbon already in the system, not adding to it. Flaring the methane or burning it in an engine to create electricity simply converts it to CO2, a less harmful greenhouse gas than CO2. This is why it's important to make the distinction between natural gas and biogas and why pyrolysis of biogas is carbon negative, effectively removing carbon from the atmosphere as solid carbon rather than returning it as CO2.