52% of emissions from major urban areas come from just 25 big cities
Around 56 percent of the world's population currently live in cities, a figure that is expected to increase in coming decades. It follows that these urban areas account for a large amount of the world's greenhouse has emissions, and a new study designed to gauge the scale of this pollution has concluded that around half come from just 25 cities, with so-called megacities in China and Japan proving to be particularly potent emitters.
“Nowadays, more than 50 percent of the global population resides in cities," says co-author Dr Shaoqing Chen, of Sun Yat-sen University. "Cities are reported to be responsible for more than 70 percent of greenhouse gas 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."
Chen and his co-authors sought to tackle this issue by piecing together a sample of 167 locations made up of predominantly core cities, larger urban zones and metropolitan areas of 53 different countries. More cities were selected from heavily emitting countries like China, the US, India and in Europe to offer a truer representation of distribution of emissions across the globe, with the authors also distinguishing between developed and developing countries based on UN classification.
The result is a sector-by-sector greenhouse gas emission inventory for those 167 cities between 2012 and 2016, representing what the authors say is the first global balance sheet for greenhouse gas emissions for the world's major cities. This revealed that just 25 megacities were responsible for 52 percent of total emissions from the 167 cities studied, most of which are situated in Asia, such as Handan, Shanghai and Suzhou in China and Tokyo in Japan, along with European cities in Moscow and Istanbul.
Most cities in developed countries such as Australia, the US and those in Europe had significantly higher per capita emissions than cities in developing countries, with the exception of China, which was classed as a developing county but featured several cities with similar per capita emissions. The two main sources of emissions were transportation and stationary energy, which encompasses fuel combustion and electricity use in residential, industrial and commercial buildings.
The authors say the research highlights the need for consistent greenhouse gas emission inventories across the globe, which will ultimately make it easier to track the effectiveness of emissions reduction policies in different locations. Ultimately, much more drastic measures are needed to meet the targets outlined in the Paris Agreement and limit average global temperature increase to 1.5 °C (2.7 °F) above pre-industrial levels. The researchers say the type of framework adopted here can make it easier to highlight areas in need of most improvement.
“Key emitting sectors should be identified and targeted for more effective mitigation strategies," says Chen. "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 research was published in the journal Frontiers in Sustainable Cities.