Understanding The Other Climate Change Agent

24
Sep
2014

When it comes to studying climate change, most of the focus is on greenhouse gases that absorb radiation and warm temperatures at the Earth’s surface. But despite capturing the majority of the blame, greenhouse gases are not the sole contributor to global warming. Aerosols, the small particles once blamed for depleting the planet’s protective ozone layer, are also known to influence the Earth’s climate, though they are sometimes excluded from computer simulations due to their short lifespan and complex effects.
 
In her talk at the Computation Institute on September 18, Yan Feng, an assistant computational atmospheric scientist in the Environmental Science Division at Argonne National Laboratory, made the case for new efforts to understand how aerosols factor into climate change. Her research, some of it conducted with CI Senior Fellow V. Rao Kotamarthi, looks at whether aerosols compound or buffer the warming effect of greenhouse gases, how aerosols interact with clouds and other atmospheric systems, and how best to include these effects in state-of-the-art climate models used at Argonne and elsewhere.
 
A central issue to studying aerosols is that the term describes a wide range of different particles, most of which come from natural sources such as wildfires and volcanoes. Only 10 percent of aerosols are released into the atmosphere by human activities, including industrial activity and transportation, but studies have shown for decades that some of these human-generated aerosols -- such as “black carbon” from soot and smoke -- are dangerous to air quality and public health. Less well known are the effects of these particles upon climate, in part because of a mixed effect: some aerosols trap radiation and contribute to warming, while others scatter radiation and have a cooling effect.
 
In fact, the overall effect when all aerosols are taken into account actually reduces the warming caused by greenhouse gases, Feng said, referencing her 2008 paper with Veerabhadran Ramanathan at the Scripps Institution of Oceanography. Other projections of future climate change if carbon emissions are reduced find that the warming already in progress will reach a higher peak before abating if aerosols are also curbed. The results suggest that better computer modeling of aerosol effects on climate are needed to determine the best mitigation policies for the future.

aerosol-curve.jpg
(From Schnellnhuber, 2008; Future temperature projections with (A) and without (B) current levels of aerosols.)
 
“We need to better understand aerosols, because their effect is comparable to greenhouse gases, and that will affect our decision-making going forward,” Feng said.
 
In her current research, Feng uses the high-performance resources at the Argonne Leadership Computing Facility to model aerosol effects on climate and the hydrological cycle in areas such as California and South Asia. The models, which simulate the atmosphere in three dimensions and combine physics and chemistry, require massive power and generate equally impressive amounts of data -- a recent 10-year simulation of the western United States used 4 million core hours of compute time and generated 11.5 terabytes of data per year. But the additional detail provides new insight on the role of lesser-known aerosols, such as brown carbon, which a 2013 paper found contributes to as much as 20 percent of the radiative forcing effect of aerosols on climate.
 
For more on Feng’s aerosols research, view her complete talk using Adobe Connect.
 
(Image: Portrait of Global Aerosols/William Putman, NASA/Goddard. From Wikimedia Commons.

This portrait of global aerosols was produced by a GEOS-5 simulation at a 10-kilometer resolution. Dust (red) is lifted from the surface, sea salt (blue) swirls inside cyclones, smoke (green) rises from fires, and sulfate particles (white) stream from volcanoes and fossil fuel emissions. High-resolution global atmospheric modeling run on the Discover supercomputer at the NASA Center for Climate Simulation at Goddard Space Flight Center, Greenbelt, Md., provides a unique tool to study the role of weather in Earth's climate system. The Goddard Earth Observing System Model, Version 5 (GEOS-5) is capable of simulating worldwide weather at resolutions of 10 to 3.5 kilometers (km).)

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