Fraction of natural area as main predictor of net CO 2 emissions from cities

Cities account for most anthropogenic greenhouse‐gas emissions, CO 2 being most important. We evaluate the net urban contribution to CO 2 emissions by performing a meta‐analysis of all available 14 annual CO 2 budget studies. The studies are based on direct flux measurements using the eddy‐covariance technique which excludes all strong point sources. We show that the fraction of natural area is the strongest predictor of urban CO 2 budgets, and this fraction can be used as a robust proxy for net urban CO 2 emissions. Up‐scaling, based on that proxy and satellite mapping of the fraction of natural area, identifies urban hotspots of CO 2 emissions; and extraction of 56 individual cities corroborates their inventory‐based estimates. Furthermore, cities are estimated as carbon‐neutral when the natural fraction is about 80%. This fresh view on the importance of cities in climate change treats cities as urban ecosystems: incorporating natural areas like vegetation.