A study released earlier this week has found that just 25 cities — nearly all of them in China — have accounted for more than half of the climate-warming gases emitted by a sample of 167 urban hubs around the world, with emissions from cities in the richest parts of the world still generally higher than those from urban centres in developing countries.

Published in the open access journal Frontiers in Sustainable Cities, the study compares greenhouse gas emissions reported by 167 cities in 53 countries, and found that 23 Chinese cities, including Shanghai and Beijing, along with Moscow and Tokyo account for 52 percent of the total.

Only 30 of the 42 cities where progress was tracked in the study had shown a reduction. Most of them were in the United States and Europe.

Average global temperatures have already risen by more than 1 degree Celsius compared to the pre-industrial baseline and are still on track to exceed the 1.5-2 degree limit set by the Paris Agreement.

The researchers were quick to point out that some data may be skewed, with some cities reporting numbers from as far back as 2005. A lack of consistency in how cities report emissions can also make comparisons difficult.

A report from 2018 that was published within the Environmental Research Letters journal, contained a larger research quantity to the recent study, analysing 13,000 cities. It found that 100 cities containing 11 percent of the world's population drove 18 percent of its carbon footprint.

Yale University Professor Karen Seto, who co-authored the 2018 paper, says that the new research is still of importance, saying that it "contributes to the growing literature and our understanding of urban emissions," in an interview with Reuters.

The new analysis is the first to look at the emissions reduction targets of megacities and their processes of cutting back. Sixty-eight of the cities, mostly in developed nations, had set absolute emissions reduction targets.

The study confirms scientists' pre-conceptions that whereas in China, cities with high per capita emissions are generally major manufacturing hubs, those in developed nations with the highest per capita rates tend to have strong levels of consumption.

Ontario Tech University Professor and former World Bank adviser on sustainable and climate change Dan Hoornweg, says that while more developed economies in Europe and elsewhere can now grow without increasing emissions, the world is moving at different speeds.

"They generated a tonne of emissions on the way to get there and China is in that stage now. We know India is getting there at some point and the last big push in all of this will be Africa," he says.

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