This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: With Hong Kong recently recording record-breaking high temperatures, extreme weather has once again raised public awareness of global warming and emission-reduction measures. A large-scale international study led by The Hong Kong University of Science and Technology (HKUST) has revealed that intercity collaboration on emission reduction can improve overall sustainability performance by more than 10%.
This comprehensive analysis covers 4,116 cities and spans 11 years of data, shedding new light on regional and global strategies for achieving the United Nations Sustainable Development Goals (SDGs). Lu Mengqian, a professor in the Department of Civil and Environmental Engineering at HKUST, the research, titled "Spatiotemporal changes in inter-city sustainability impacts linked to emission challenges worldwide," has been published in the journal Nature Communications. Lu noted that conventional environmental governance typically views urban emission reduction as a purely local issue.
Cities often pursue industrial upgrading, energy transition or environmental policies to cut emissions, reaping only local benefits. However, the impact of atmospheric pollutants and greenhouse gas emissions transcends borders. The scientific community's long-standing inability to systematically understand the spatiotemporal heterogeneity of these intercity interactions has hindered the formulation of globally coordinated emission-reduction strategies.
To fill this research gap, the team employed an innovative spatial econometric model. The assessment covered intercity interactions among emission-related SDG indicators across 4,116 cities in 103 countries, including Hong Kong, Paris and Los Angeles, between 2010 and 2020. These cities accounted for more than 90% of global gross domestic product (GDP) during this period.
Pollutant and greenhouse gas data were sourced from a range of satellite products. The findings further illuminate a significant ripple effect: The vast majority of cities (93.51%) are demonstrably influenced by the emission-related SDG indicators of others. Specifically, a 10% improvement in particulate matter pollution indicators (PM2.5 and PM10, under SDG 11.6—reducing the adverse per capita environmental impact of cities, including by paying special attention to air quality), gaseous pollutants (SO2 and NOX, under SDG 12.4—achieving the environmentally sound management of chemicals and all wastes throughout their life cycle), and greenhouse gases (CO2 and CH4, under SDG 13.2—integrating climate change measures into national policies, strategies and planning to reduce greenhouse gas emissions) in other cities can lead to an average improvement of 0.2% to 0.45% in the focal city's corresponding SDG performance.
However, an intercity interaction may be either positive, known as a synergistic effect, or negative, known as a trade-off effect. For example, Hong Kong benefited from intercity synergistic effects in advancing SDG 13.2 (CO2 emissions) in 2020, possibly attributable to industrial upgrading by its neighbors in the Greater Bay Area. Copenhagen's performance on SDG 13.2 (CO2 emissions) also was positively correlated with that of its connected cities.
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