The Greener Sex

Women win:

As with the European study, the most significant difference between the genders came in the transport category: Single men's driving habits have a carbon footprint of 13 metric tons of CO2e, compared with women's 9.4 tons.

After that, the most important differences, from a greenhouse gas perspective, were that single women spent more on home utilities and health care, and single men spent more on alcohol, tobacco, and education.