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Megacities account for half the world's urban greenhouse gas emissions

Though a new study classified China and its cities as developing, the nation's largest cities emit as much greenhouse gas as the largest cities in more developed parts of the world, including Europe and North America. File Photo by Stephen Shave/UPI
Though a new study classified China and its cities as "developing," the nation's largest cities emit as much greenhouse gas as the largest cities in more developed parts of the world, including Europe and North America. File Photo by Stephen Shave/UPI | License Photo

July 12 (UPI) -- Scientists have produced the first global balance sheet of greenhouse gasses emitted by the world's biggest cities.

The new balance sheet, published Monday in the journal Frontiers in Sustainable Cities, can help policy makers identify the worst polluters, as well as gauge the efficacy of emissions reduction policies.

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According to authors of the latest audit, despite the outsized carbon footprint of the world's largest cities, current mitigation efforts are -- at their current pace -- unlikely to meet global climate change targets set by the Paris Agreement.

"Nowadays, more than 50 percent of the global population resides in cities. Cities are reported to be responsible for more than 70 precent of greenhouse gas emissions, and they share a big responsibility for the decarbonization of the global economy," co-author Shaoqing Chen said in a press release.

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"Current inventory methods used by cities vary globally, making it hard to assess and compare the progress of emission mitigation over time and space," said Chen, a climate scientist at Sun Yat-sen University in China.

For the study, researchers surveyed greenhouse gas emissions data for 167 major cities -- metropolises from across the globe and at different different developmental stages.

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The analysis showed the biggest 25 cities were responsible for 52 percent of urban greenhouse gas emissions.

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Researchers found stationary energy and transportation were the two biggest sources of greenhouse gas emissions, and that major cities in Australia, Europe and North America emit greater amounts of per capita greenhouse gas than developing cities.

Of the 42 cities for which accurate time-stamped greenhouse gas data was available, 30 cities decreased their greenhouse gas emissions between 2012 and 2016.

A majority of the cities in the survey have set greenhouse gas emission reduction targets, and 40 have targeted carbon neutrality.

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In addition to major cities in Australia, Europe and North America, researchers found megacities in Asia, such as Shanghai and Tokyo, were especially problematic polluters.

The data also showed that several of China's biggest cities, though classified as developing, emit as much greenhouse gas as the biggest cities in Europe and North America.

Though a majority of the world's major cities are making some effort to reduce emissions, the latest research suggests such efforts must be strengthened if the world is to avoid catastrophic warming.

"Key emitting sectors should be identified and targeted for more effective mitigation strategies," Chen said. "For example, the differences in the roles that stationary energy use, transportation, household energy use, and waste treatments play for cities should be assessed."

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Researchers said they hope the newly published balance sheet will help regulators and policy makers in cities around the world hold themselves and each other accountable, and to make adjustments in order to further reduce emissions.

"Cities should set more ambitious and easily-traceable mitigation goals. At a certain stage, carbon intensity is a useful indicator showing the decarbonization of the economy and provides better flexibility for cities of fast economic growth and increase in emission," Chen said.

"But in the long run, switching from intensity mitigation targets to absolute mitigation targets is essential to achieve global carbon neutrality by 2050," Chen said.

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