The major culprits are big nations

When researchers looked at cities in Asia, Latin America, and Africa, they found low
emissions per person across the board. "This paper reminds us that it is the world's wealthiest cities and their wealthiest inhabitants that cause unsustainable levels of greenhouse gas emissions, not cities in general," said editor David Satterthwaite, a senior fellow at the International Institute for Environment and Development.

Most cities in Africa, Asia, and Latin America have low emissions per person. The challenge for them is to keep these emissions low even as their wealth grows.

Researchers examined data from 100 cities in 33 nations for clues about which were the biggest polluters and why, according to the report in the peer-reviewed journal Environment and Urbanization.

While cities across the world were to blame for around 71 percent of the world's
greenhouse-gas emissions, urban dwellers who can use public transportation rather than drive helped to lower per capita emissions in some cities.

For instance, the sprawling western U.S. city of Denver's per capita emissions were nearly double those in New York City, home to 8 million inhabitants and a heavily used subway system. This is mainly attributable to New York's greater density and much lower reliance on the automobile for commuting.

Time for thought.