Cities are not only getting warmer, they are also getting brighter. This study shows that artificial light at night plays a major role in shaping when plants grow in cities. Using satellite data from 428 cities across the Northern Hemisphere, we found that nighttime light can extend the growing season more strongly than temperature, mainly by delaying when plants stop growing in the fall.

This matters because longer growing seasons affect how cities function. Changes in plant timing influence carbon uptake, water use, and urban climate, and can also shape pollen exposure and human health. As urban areas continue to expand, light pollution becomes an important but often overlooked driver of environmental change. The results highlight a gap in how we think about urban impacts on ecosystems. Temperature has long been the focus, but this work shows that light is also a key control on ecosystem dynamics. Accounting for artificial light will improve how we model and manage urban environments under ongoing environmental change.

Wang, L., Meng, L., Richardson, A., Hölker, F., Li, H., Mao, J., Longcore, T., Xia, J., She D. (2025). Artificial light at night outweighs temperature in lengthening urban growing seasons. Nature Cities, 1-12. 

Plants do more than respond to climate. They actively shape it. As leaves emerge, mature, and eventually fall, vegetation changes how energy and water move between the land and the atmosphere. These seasonal transitions influence temperature through processes such as shading, reflectivity, and evapotranspiration, yet their net effect has been difficult to pin down. 

In this study, we combined satellite observations and ground data across forests in the Northern Hemisphere to track how vegetation affects land surface temperature through the growing season. We found that the presence of leaves generally cools the land surface, and that this cooling effect is stronger than warming across most stages of the season. In many regions, this cooling becomes even more pronounced under warmer climate conditions. 

These findings matter because they refine how we understand climate–ecosystem interactions. They highlight the importance of incorporating phenology into climate models and land management strategies. Accounting for when plants grow, not just where they are, can improve predictions of future climate and inform efforts such as afforestation, ecosystem management, and climate adaptation.

Li, Y., Meng, L., Richardson, A.D., Lee, X., Menzel, A., Mao, J., Diehl, J.L., Wang, A. (2025). Cooling outweighs warming across phenological transitions in the Northern Hemisphere. Proceedings of the National Academy of Sciences of the United States of America, 122(37), e2501844122.