Warming-induced increase in aerosol number concentration likely to moderate climate change

• Published in: Nature geoscience Vol. 6; no. 6; pp. 438 - 442
• Main Authors: Paasonen, Pauli, Asmi, Ari, Petäjä, Tuukka, Kajos, Maija K., Äijälä, Mikko, Junninen, Heikki, Holst, Thomas, Abbatt, Jonathan P. D., Arneth, Almut, Birmili, Wolfram, van der Gon, Hugo Denier, Hamed, Amar, Hoffer, András, Laakso, Lauri, Laaksonen, Ari, Richard Leaitch, W., Plass-Dülmer, Christian, Pryor, Sara C., Räisänen, Petri, Swietlicki, Erik, Wiedensohler, Alfred, Worsnop, Douglas R., Kerminen, Veli-Matti, Kulmala, Markku
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2013; Nature Publishing Group
• Subjects: 704/106; 704/106/35; Aerosols; Air pollution; Air quality; Anthropogenic factors; Atmosphere; Biosphere; Black carbon; Boundary layer; Boundary layers; Climate; Climate change; Climate effects; Climate system; Clouds; Condensation nuclei; Earth and Related Environmental Sciences; Earth Sciences; Earth System Sciences; Emissions; Fysik; Geochemistry; Geology; Geophysics/Geodesy; Geovetenskap och relaterad miljövetenskap; Greenhouse gases; letter; Natural Sciences; Naturgeografi; Naturvetenskap; Physical Geography; Physical Sciences; Precursors; Solar radiation; Subatomic Physics; Subatomär fysik; Vapour emission; Europe
• ISSN: 1752-0894; 1752-0908; 1752-0908
• DOI: 10.1038/ngeo1800

Atmospheric aerosol particles can significantly influence the climate system. Analyses of observations and observation-based modelling data reveal that biogenic aerosol emissions soar in response to warming, exerting a cooling effect in a negative feedback loop. Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei 1 , 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 gases 1 . In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect 5 , 6 , 7 . Natural aerosols, too, might affect future warming 2 , 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.