It is estimated that the world’s 50 largest cities together emit the equivalent of 2,600 megatons of CO2 per year, surpassed only nationally by China, the United States and India.

A man protects himself from pollution in Beijing, ChinaCARLOS GARCA RAWLINSREUTERS

A total of 25 megacities (23 of them in China) are responsible for 52% of urban CO2 emissions, according to a study published in Frontiers in Sustainable Cities and directed by Professor Shaoquing Chen, from Guanzhou Sun Yat-sen University. Based on data from 167 cities in 53 countries, the report reveals the extremely high contribution of overcrowded Chinese cities, although per capita emissions remain higher in Europe, North America and Australia.

“Day by day, more than 50% of the world’s population lives in cities, which are at the same time responsible for 70% of emissions “, emphasizes Shaoquing Chen.” Cities therefore have a great responsibility for the decarbonization of the economy, but the methods used so far are highly variable and make it very difficult to evaluate mitigation progress in space and time “, he points out.

Handan, Shanghai and Suzhou top the list of emissions caused by megacities, with Beijing in fifth place, Wuhan in eighth place and Hong Kong in 23. The only cities outside of China in the top 25 are Moscow (which makes the seventh) and Tokyo (number 17). It is estimated that the world’s 50 largest cities together emit the equivalent of 2,600 megatons of CO2 per year, surpassed only nationally by China, the United States and India.

The Frontiers in Sustainable Cities report highlights the substantial reductions in emissions per capita in cities such as Oslo, Houston, Seattle and Bogota, in contrast to the increase in Johannesburg, Rio de Janeiro or Curitiba, considered until now the most sustainable city in Brazil. . The study includes Spanish cities, but neither Madrid nor Barcelona appear on the “black list” of the 50 largest radio stations, where they are New York (number 26), Frankfurt (33), London (43) or Mexico City (49 ).

It is estimated that 60% of emissions come from the generation of energy for residential, commercial and industrial use, and around 30% is attributable to road transport, while emissions from rail, aviation or navigation are lower at 15%. The proportion varies remarkably by country: the high contribution of Chinese megacities is mainly explained by the existence of more than a thousand coal-fired power plants throughout the country.

A total of 113 of the 167 cities studied have set clear targets for reducing emissions, and 40 have the goal of carbon neutrality on the horizon. However, the study concludes that the objectives are completely insufficient to meet the objectives of the Paris Agreement and avoid an increase in temperatures of more than 1.5 degrees.

“Cities must set more ambitious emission reduction targets and put in place more effective strategies to measure and achieve mitigation,” says Professor Chen. “The first step has to be the identification of key sectors, including urban waste management, which until now has not been sufficiently taken into account. We also need inventories of greenhouse gas emissions with a common methodology for all cities. And finally you have to raise the bar, move towards absolute mitigation targets and reach global carbon neutrality by 2050. “

The Sun Yat-sen University report does not go into evaluating the role that megacities of more than 10 million inhabitants, which could reach 50 worldwide in 2030. The C40 group of cities for climate – promoted by the former mayor of New York Michael Bloomberg– has recently presented the report Climate Action in Megacities 2.0, with a global call to action in areas such as the circular economy, renaturation or mobility, such as the implementation of systems such as the Bus Rapid Transit (BTA) that is spreading through South American cities.

NASA has also put its grain of sand with the launch of the Megacities Carbon Project, led by scientists Riley Duren and Charles Miller. The objective is to develop homologous emission monitoring systems in the great cities of the world: Los Angeles and Paris will be the experimentation laboratories in a first phase, which will later be extended to South America and Asia.

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