A new study has determined that Denver, US, released the largest amount of greenhouse gases (GHG) and Barcelona, Spain, the smallest amount this year.
The study documented how differences in climate, population density and other factors affect GHG emissions in global cities.
Scientist Christopher Kennedy and colleagues note in the new study that some cities are developing strategies to reduce releases of GHG, which include carbon dioxide, methane, and other gases that can contribute to global warming through the greenhouse effect.
Not enough information was previously available on why emissions vary considerably among different cities.
The researchers asked, "How and why do emissions differ between cities?"
To help answer those questions, the scientists analyzed those variations and how climate, power generation, transportation, waste processing, and other factors contributed to the differences.
Denver had the highest overall GHG emissions, with levels two to five times higher than other cities.
Its high levels were due partly to its high use of electricity, heating and industrial fuels, and ground transportation, according to the scientists.
Los Angeles was second on the list, followed by Toronto and Cape Town (tied for third), Bangkok, New York City, London, Prague, Geneva, and Barcelona.