The most effective ways to cut down your emissions are to reduce your intake of meat (especially beef, which can cut out about a metric ton of CO2eq per year), to reduce the amount you travel (driving half as much would cut out two metric tons of CO2eq per year and forgoing a round-trip flight between London and New York would eliminate a metric ton of CO2eq), and to use less electricity and gas in the home (especially by installing loft insulation, which would save a metric ton of CO2eq for a detached house).
