A large but transient carbon sink from urbanization and rural depopulation in China

China has pledged to achieve carbon neutrality by 2060 but policies favouring urbanization could slow down progress. This study tests the hypothesis that urbanization and carbon neutrality are not mutually exclusive and that sustainably managed urbanization could increase carbon sequestration, especially in rural areas. China has experienced unprecedented urbanization and associated rural depopulation during recent decades alongside a massive increase in the total population. By using satellite and demographical datasets, we here test the hypothesis that urbanization and carbon neutrality are not mutually exclusive and that sustainably managed urbanization may even be an integral part of the pathway to reduce atmospheric CO2. We show that, although urban expansion caused an initial aboveground carbon loss of -0.02 PgC during 2002-2010, urban greening compensates these original losses with an overall balance of +0.03 PgC in urban areas during 2002-2019. We further show that a maximum increase in aboveground carbon stocks was observed at intermediate distances to rural settlements (2-4 km), reflecting the decreased pressure on natural resources. Consequently, rural areas experiencing depopulation (-14 million people yr(-1)) coincided with an extensive aboveground carbon sink of 0.28 +/- 0.05 PgC yr(-1) during 2002-2019, while at the same time only a slight decline in cropland areas (4%) was observed. However, tree cover growth saturation limits the carbon removal capacity of forests and only a decrease in CO2 emissions from fossil fuel burning will make the aim of carbon neutrality achievable.

Automated summary

This study tests the hypothesis that urbanization and carbon neutrality are not mutually exclusive, and that sustainably managed urbanization could increase carbon sequestration. The results show that urban greening compensates for initial carbon losses caused by urban expansion, and rural areas experiencing depopulation coincide with extensive aboveground carbon sinks. However, the capacity for carbon removal by forests is limited, and reducing CO2 emissions from fossil fuel burning is necessary to achieve carbon neutrality.