Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei1,2,3,4. Apart from black carbon aerosol, aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases1. In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect5,6,7. Natural aerosols, too, might affect future warming2,3,8,9. Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid- and high-latitude environments. We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. This natural growth mechanism produces roughly 50% of particles at the size of cloud condensation nuclei across Europe. We conclude that biosphere–atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality.
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This work was funded by European Research Council (ATMNUCLE, 227463), Academy of Finland (Center of Excellence Program project 1118615; projects 11750, 127210, 132640 and 139656), European Commission sixth Framework program (EUCAARI, contract no 036833-2; EUSAAR, contract no 026140), European Commission seventh Framework program (ACTRIS, contract no 262254; PEGASOS, contract no 265148), Maj and Tor Nessling Foundation (projects 2010143, 2011200, 2012443 and 2013325) and the Otto A. Malm foundation. For providing data, we acknowledge the Physical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado (for the boundary layer height data acquired from their web site at http://www.esrl.noaa.gov/psd/), the Hungarian Meteorological Service, Gerald Spindler, Pasi P. Aalto and Harald Flentje. We thank Ville Vakkari for help in quality assurance of Botsalano data and students and staff of North-West University (Mafikeng Campus), RSA, for weekly maintenance. The various measurements were supported by the German Federal Ministry for the Environment (FE 370343200), Environment Canada, NSERC, CFCAS-CAFC, the National Science Foundation (#0544745 and supplement, and 1102309), the Swedish Research Council (projects 2007-3745, 2007-4619 and 2010-4683) and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas, project 2009-615).
About this article
Nature Climate Change (2018)