Public Release: 

Future health of Earth's atmosphere, how to make it snow

National Center for Atmospheric Research/University Corporation for Atmospheric Research

BOULDER--The challenge of anticipating potential harm to Earth's atmosphere and the science of making snow will be addressed by two scientists from the National Center for Atmospheric Research (NCAR) at the annual meeting of the American Association for the Advancement of Science in Denver, February 13-18.


Tom Wigley will discuss the future of the Earth's atmosphere over the next several centuries. He will focus on the extent to which greenhouse gases can build up in the atmosphere before they reach a level that might cause dangerous interference in the climate system. His talk is part of the symposium "Greenhouse Effects in Planetary Atmospheres."

Earth's atmosphere is facing extraordinary changes because of the high levels of carbon dioxide and other greenhouse gases emitted by human activities. Concerns that emissions of carbon dioxide and other greenhouse gases will profoundly alter Earth's climate over time make climate change a vital matter for both policy makers and scientists.


Charles Knight will talk about the formation of atmospheric and artificial snow as part of the symposium "The Science of Snow and Skiing." He will focus on nucleation, which is the process by which an ice crystal begins to form in liquid water. Nucleation is important for snow that is produced both artificially at ski resorts and naturally in the atmosphere, so researchers have spent considerable time studying how it occurs. Knight will look at how water can cool below the freezing point, why nucleation is needed for the formation of snow, and how nuclei work in principle. The formation of artificial snow includes an interesting aspect: it is often aided by ice nuclei that are produced by culturing a certain type of bacteria, which is processed into a powder and added to the water entering the snow guns. Knight will talk about the discovery of these bacteria and the ongoing efforts to figure out what is causing the nucleation. Parts of the puzzle are known, but not the whole story.



Charles Knight has developed 40 years of expertise in NCAR on hail, ice, and snow. His primary research areas include formation of precipitation in clouds and the structure of snowflakes. Knight has been interested in ice crystals since he studied sea ice on the ice islands of the Arctic Ocean as a researcher for the University of Washington. He holds a Ph.D. in geology from the University of Chicago.

Tom Wigley is one of the world's foremost experts on climate change. He has participated in each of the reviews of the climate change problem by the Intergovernmental Panel on Climate Change. A mathematical physicist with a doctorate from the University of Adelaide in Australia, he has published articles on diverse aspects of climatology, including climate modeling, the detection of human influences on climate, climate impacts on agriculture and water resources, and carbon cycle modeling. For more complete biographical information on Wigley, see

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