Big cities are not always biggest polluters

Big cities like New York, London and Shanghai send less pollution into the atmosphere per capita than places like Denver and Rotterdam, said a study released on January 25. 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 Urbanisation.
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 transport rather than drive helped to lower per capita emissions in some cities. For instance, the sprawling western US city of Denver's per capita emissions were nearly double those in New York City, home to eight million inhabitants and a gritty, heavily used subway system.
"This is mainly attributable to New York's greater density and much lower reliance on the automobile for commuting," said the study. Even Denver's per capita emissions, at 21.5 tonnes of carbon dioxide equivalent (tCO2e), were sharply higher than Shanghai at 11.2 tCO2e, Paris (5.2) and Athens (10.4). Chinese cities stood out from the rest of the world because their average emissions were far higher - for instance with Beijing emitting 10.1 tonnes of carbon dioxide equivalent - than the country as a whole, which emits 3.4 tCO2e.
"This reflects the high reliance on fossil fuels for electricity production, a significant industrial base within many cities and a relatively poor and large rural population," said the study.
Looking at greenhouse gas emissions per GDP, researchers found that "citizens of Tokyo are 5.6 times more efficient than Canadians."
The port city of Rotterdam in the Netherlands got a particularly bad rap because of its links to shipping and heavy industry. "Rotterdam's per capita value of 29.8 tCO2e versus 12.67 tCO2e for the Netherlands reflects the large impact of the city's port in attracting industry, as well as fuelling of ships," said the study.
"This is similar to cities with busy airports and highlights the need to view the city-based GHG emissions cautiously and holistically." Other trends included the tendency for cities in cold climates to have higher emissions, and for poor and middle income countries to have lower emissions per capita than wealthy countries.