burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations in the air. land use change (mainly deforestation in the tropics) accounts for about a quarter of total anthropogenic GHG emissions.[30] livestock enteric fermentation and manure management,[31] paddy rice farming, land use and wetland changes, man-made lakes,[32] pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane. use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes. agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N 2O) concentrations.