A new study published in the journal Frontiers in Sustainable Cities presents the first global balance sheet of greenhouse gasses (GHGs) emitted by major cities around the world.
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The aim was to research and monitor the effectiveness of historical GHG reduction policies implemented by 167 globally distributed cities that are at different developmental stages.
While only covering 2% of the Earth's surface, cities are big contributors to the climate crisis.
But current urban GHG mitigation targets are not sufficient to achieve global climate change targets by the end of this century.
"Nowadays, more than 50% of the global population resides in cities. Cities are reported to be responsible for more than 70% of GHG emissions, and they share a big responsibility for the decarbonization of the global economy. Current inventory methods used by cities vary globally, making it hard to assess and compare the progress of emission mitigation over time and space," says co-author Dr. Shaoqing Chen, of Sun Yat-sen University, China.
The results showed that both developed and developing countries have cities with high total GHG emissions, but that megacities in Asia (such as Shanghai in China and Tokyo in Japan) were especially important emitters.
The inventory of per capita emissions showed that cities in Europe, the U.S., and Australia had significantly higher emissions than most cities in developing countries. China, classified here as a developing country, also had several cities where per capita emissions matched those of developed countries. It is important to note that many developed countries outsource high carbon production chains to China, which increases export-related emissions for the latter.
The researchers also identified some of the most important sources of greenhouse gas emissions. "Breaking down the emissions by sector can inform us what actions should be prioritized to reduce emissions from buildings, transportation, industrial processes and other sources," says Chen. ■