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Atmospheric Sciences & Global Change Division
Research Highlights

May 2009

Lead in Clouds: A Bad News/Good News Scenario

Everyday activities pump lead into the atmosphere and may affect climate change, according to a recent article in Nature Geoscience.

Lead in Clouds
Lead shows as black dots in a scanning electron image of ice-crystal residual particles from clouds collected in the Swiss Alps. Lead from human activities may influence climate through cloud formation. Enlarge Image.

Results: By sampling clouds and making their own, an international research team has shown for the first time that lead from human activities is changing the properties of clouds and, therefore, the way the sun's energy affects the atmosphere. The results from the study led by Pacific Northwest National Laboratory's Dr. Dan Cziczo suggest a bad news-good news scenario. The lead causes clouds to form at warmer temperatures and with less water, which could change rainfall patterns and reduce snowpack. On the other hand, lead-laden clouds send more heat from the earth back into space, cooling the world slightly and possibly lessening global warming by greenhouse gases. The research appears in Nature Geoscience, a new journal in the prestigious Nature publishing series.

Why it matters: Knowing more about the effects of atmospheric lead is important for understanding the total picture of climate change. It is generally accepted that the addition of greenhouse gases such as carbon dioxide to the atmosphere have contributed to global warming. Less understood—and more difficult to measure—is the influence of aerosol particles from human sources, particularly the use of coal and other fossil fuels.

Airborne particles in the form of naturally occurring dusts and human-produced aerosols can serve as ice nuclei, sites around which water vapor condenses into clouds. The clouds affect the "global radiative balance" by reflecting solar energy or trapping terrestrial radiation. This creates a warming or cooling effect, depending on cloud properties such as altitude and thickness.

Methods: Scientists have known since the 1940s that seeding with silver and lead iodide can produce artificial ice nuclei in cirrus clouds. These are the high streaky clouds that cover much of the earth and have significant impact on climate.

The current research project sought to determine how lead from daily human activities affects formation of ice nuclei. The researchers used mass spectrometry to analyze the ice crystals in natural and artificial clouds. The results showed lead in about half of the particles that nucleate clouds.

To investigate what this might mean for the earth's climate, the researchers simulated the global climate with lead-free particles, as well as with 10 and 100 percent of the particles containing lead. They found that lead "supercharges" the clouds, causing them to form at higher temperatures and with less water vapor. Because lead affects the distribution and density of cirrus clouds, the presence of lead may affect where and when precipitation occurs.

What's next: The interactions between lead, water vapor, and temperature are extremely complex. Future work will look at the type of lead and the quantity needed to affect clouds and precipitation, as well as the atmospheric distribution of the metal dust.

Acknowledgments: PNNL is transforming the nation's ability to predict climate change and its impacts. This research was supported by the Atmospheric Composition Change: A European Network, ETH Zurich, the German Research Foundation, and Pacific Northwest National Laboratory directed research funding as part of the Aerosol Climate Initiative.

Research Team: Cziczo led the research team, which included Olaf Stetzer, Ulrike Lohmann, Stephan Weinbruch, and Stephane J. Gallavardin from ETH Zurich; Annette Worringen and Martin Ebert from the Technical University Darmstadt; Michael  Kamphus, Joachim Curtius, and Stephan Borrmann from Johannes Gutenberg University of Mainz; Karl D. Froyd from the National Oceanic and Atmospheric Administration; Stephan Mertes from Leibniz-Institute for Tropospheric Research; Ottmar Möhler from the Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe. The research team thanks P. J. DeMott, D. M. Murphy, and D. S. Thomson for their assistance with measurements. They also acknowledge the participants of the INSPECT and CLACE field studies, the support of the High Altitude Research Foundation Gornergrat and Jungfraujoch, and the experimental group at the Aerosol Interactions and Dynamics in the Atmosphere cloud chamber of Forschungszentrum Karlsruhe.

Citation: Daniel J. Cziczo, Olaf Stetzer, Annette Worringen, Martin Ebert, Stephan Weinbruch, Michael Kamphus, Stephane J. Gallavardin, Joachim Curtius, Stephan Borrmann, Karl D. Froyd, Stephan Mertes, Ottmar Möhler, and Ulrike Lohmann. April 2009. "Inadvertent Climate Modification Due to Anthropogenic Lead." Nature Geoscience, 2:333-336. DOI: 10.1038/NGEO499.


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