Just 25 mega-cities emit 52% of world's urban greenhouse gas

While covering just 2 per cent of the Earth's surface, cities are big contributors to the climate crisis

The top 25 cities accounts for 52 per cent of the total urban greenhouse gas (GHG) emissions and cities in Europe, Australia and the US have significantly higher per capita emissions than cities in developing countries, new research covering 167 cities globally has revealed.

While covering just 2 per cent 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 per cent of the global population resides in cities. Cities are reported to be responsible for more than 70 per cent of GHG emissions, and they share a big responsibility for the decarbonisation of the global economy," said Shaoqing Chen from Sun Yat-sen University, China, in a paper published in the journal Frontiers in Sustainable Cities.

"Current inventory methods used by cities vary globally, making it hard to assess and compare the progress of emission mitigation over time and space," Chen added.

The findings showed that stationary energy and transportation were the two main sources of emissions.

"Of the 42 cities that had time-series traceable data, 30 decreased the annual GHG emissions over the study period. Though in several cities, there was an increase in emissions," the study noted.

The cities were chosen from 53 countries (in North and South America, Europe, Asia, Africa, and Oceania) and were selected based on representativeness in urban sizes and regional distribution.

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.

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 pointed out.

In 2015, 170 countries worldwide adopted the Paris Agreement, with the goal limiting the average global temperature increase to 1.5-degree Celsius.

Following the agreement, many countries and cities proposed targets for greenhouse gas mitigation.

However, the UNEP Emissions Gap Report 2020 showed that, without drastic and strict actions to mitigate the climate crisis, we are still heading for a temperature increase of more than 3-degree Celsius by the end of the 21st century.

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

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