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Climate change: Just 25 mega-cities emit 52 per cent of the world’s urban greenhouse gases

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Just over half of the world’s urban greenhouse gas emissions come from just 25 mega-cities — 23 of which are located in China — a study has reported.

The cities that emit the most greenhouse gases included Handan, Suzhou, Dalian, Beijing and Tianjin in China — but also Tokyo, Japan, and Moscow, Russia.

Researchers from the Sun Yat-sen University in China recorded, for the first time, the greenhouse emission levels of 167 cities located across the globe. 

Even though cities only cover some two per cent of the Earth’s total surface area, they are major contributors to the climate crisis, the team explained.

Moreover, they said, current urban greenhouse gas mitigation efforts are not enough to meet global targets to limit the extent of climate change by the century’s end. 

In 2015, 170 countries committed to the Paris Agreement, which set forth the goal to limit average global temperature increases to within 2.7°F (1.5°C). 

However, research by the United Nations has found that unless we take more drastic action, we are on track for a more than 5.4°F (3°C) increase by 2100.

Just over half of the world's urban greenhouse gas emissions come from just 25 mega-cities, with Shanghai (pictured, Tokyo and Moscow topping the list, a study has found

Just over half of the world’s urban greenhouse gas emissions come from just 25 mega-cities, with Shanghai (pictured, Tokyo and Moscow topping the list, a study has found

THE WORST EMITTERS

In their study, Dr Chen and colleagues looked at greenhouse gas emissions from 167 cities across 53 countries.

The worst 30 cities for total emissions were as follows (with figures in megatonnes of CO₂ equivalent):

  1. Handan, China (199.71)
  2. Shanghai, China (187.93)
  3. Suzhou, China (151.79)
  4. Dalian, China (142.51)
  5. Beijing, China (132.58)
  6. Tianjin, China (125.89)
  7. Moscow, Russia (112.53)
  8. Wuhan, China (110.86) 
  9. Qingdao, China (93.56)
  10. Chongqing, China (80.58)
  11. Wuxi, China (76.88)
  12. Urumqi, China (75.32) 
  13. Guangzhou, China (71.03)
  14. Huizhou, China (68.74)
  15. Shijiazhuang, China (67.80)
  16. Zhengzhou, China (66.16)
  17. Tokyo, Japan (66.08) 
  18. Shengyang, China (64.10)
  19. Kaohsiung, China (63.64)
  20. Kunming, China (62.96)
  21. Shenzhen, China (62.91)
  22. Hangzhou, China (61.41)
  23. Hong Kong, China (55.90)
  24. Yinchuan, China (55.49)
  25. Chengdu , China (54.49)
  26. New York City, US (51.31)
  27. Manilla, Philippines (49.47)
  28. Bangkok, Thailand (49.22)
  29. Dubai, UAE (48.26)
  30. Seoul, Korea (48.06)

‘Nowadays, more than 50 per cent of the global population resides in cities,’ said paper author and urban environmental management researcher Shaoqing Chen of the Sun Yat-sen University in Guangzhou.

‘Cities are reported to be responsible for more than 70 per cent 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.’ 

In their study, Dr Chen and colleagues first conducted sector-level greenhouse gas emissions inventories of 167 cities from 53 different countries across the globe.

Each city was chosen for its representativeness in terms of urban size and regional distribution, the team explained.

Next, they assessed how each city’s efforts to reduce their carbon footprint had been performing by comparing changes in emission levels from 2012–2016 with their stated short-, mid- and long-term carbon mitigation goals.

The team found that cities with high greenhouse gas emission levels could be found in both developed and developing countries, but noted that megacities like Shanghai and Tokyo) were particularly significant emitters. 

In addition, cities in Europe, the US and Australia tended to put out more emissions than the majority of urban centres in developing countries.

China — classified by the UN as a developing country — had several cities that matched the per capita emissions levels of developing countries, largely thanks to how the latter often outsource high-carbon production chains to China.

Of the 42 cities with available longitudinal data, the team found that emissions decreased for 30 locations between 2012 and 2016, with the largest per capita reductions seen in Oslo, Houston, Seattle, and Bogotá.

In contract, the largest increases in per capita emissions over the study period were seen in Rio de Janeiro, Curitiba, Johannesburg, and Venice. 

According to the team, 113 of the 167 cities studied set targets for reducing their levels of greenhouse emissions, with 40 having carbon neutrality goals, but the findings show that we are a long way off meeting Paris Agreement targets.

Researchers from the Sun Yat-sen University in China recorded, for the first time, the greenhouse emission levels of 167 cities located across the globe. Pictured: the skyline of Tokyo, one of the most significant greenhouse gas emitters identified in the new study

Researchers from the Sun Yat-sen University in China recorded, for the first time, the greenhouse emission levels of 167 cities located across the globe. Pictured: the skyline of Tokyo, one of the most significant greenhouse gas emitters identified in the new study

‘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,’ said Dr Chen.

The two main sources of greenhouse gas emissions, the team found, came from so-called stationary energy the transportation sector.

Stationary energy emissions, including those from electricity and fuel consumption by residential, commercial, industrial and institutional buildings contributed 60–80 per cent of emissions in European and North American cities.

Road-based transportation accounted for more than 30 per cent of greenhouse gas emissions in one third of the cities, while less than 15 per cent of total emissions were traced back to railways, waterways and aviation. 

Current urban greenhouse gas mitigation efforts are not enough to meet global targets to limit the extent of climate change by the century's end, the researchers warned. Pictured: night begins to fall on Moscow, one the largest greenhouse gas emitting cities identified in the study

Current urban greenhouse gas mitigation efforts are not enough to meet global targets to limit the extent of climate change by the century’s end, the researchers warned. Pictured: night begins to fall on Moscow, one the largest greenhouse gas emitting cities identified in the study

Based on their data, the team have proposed three policy recommendations. 

First, Dr Chen said, ‘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.’

Next, he added, urban greenhouse gas reductions policies need to be monitored with methodologically consistent emissions inventories.

Finally, Dr Chen explained, ‘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.

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

The full findings of the study were published in the journal Frontiers in Sustainable Cities.

THE PARIS AGREEMENT: A GLOBAL ACCORD TO LIMIT TEMPERATURE RISES THROUGH CARBON EMISSION REDUCTION TARGETS

The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change.

It hopes to hold the increase in the global average temperature to below 2°C (3.6ºF) ‘and to pursue efforts to limit the temperature increase to 1.5°C (2.7°F)’.

It seems the more ambitious goal of restricting global warming to 1.5°C (2.7°F) may be more important than ever, according to previous research which claims 25 per cent of the world could see a significant increase in drier conditions.

In June 2017, President Trump announced his intention for the US, the second largest producer of greenhouse gases in the world, to withdraw from the agreement.  

The Paris Agreement on Climate Change has four main goals with regards to reducing emissions:

1)  A long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels

2) To aim to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change

3) Goverments agreed on the need for global emissions to peak as soon as possible, recognising that this will take longer for developing countries

4) To undertake rapid reductions thereafter in accordance with the best available science

Source: European Commission 

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