New modeling strategy could improve understanding of complex multi-sector interactions with the Earth system and provide a powerful risk assessment tool
The Science
To assess long-range risks to food, water, energy and other critical natural resources, decision-makers must rely on Earth-system models capable of producing reliable projections of regional and global environmental changes spanning decades. A key component of such models is the representation of atmospheric chemistry. Atmospheric simulations utilizing state-of-the-art complex chemical mechanisms promise the most accurate simulations of atmospheric chemistry, but their size, complexity and computational requirements tend to limit such simulations to short time periods and a small number of scenarios to account for uncertainty. Now a team of researchers led by the MIT Joint Program on the Science and Policy of Global Change has devised a strategy to incorporate simplified chemical mechanisms in atmospheric simulations that can match the results produced by more complex mechanisms for most regions and time periods.
The Impact
If implemented in a three-dimensional Earth-system model, the new MIT modeling strategy could enable scientists and decision-makers to perform low-cost, rapid atmospheric chemistry simulations that cover long time periods under a wide range of scenarios. This new capability could both improve scientists’ understanding of complex multi-sector interactions with the Earth system and provide a powerful risk assessment tool.
Summary
Study researchers conducted three 25-year simulations of tropospheric ozone chemistry using chemical mechanisms of different levels of complexity within the CESM CAM-chem framework, and compared their results to observations. They investigated conditions under which these simplified mechanisms matched the output of the most complex mechanism, as well as when they diverge. The researchers showed that, for most regions and time periods, differences in simulated ozone chemistry between these three mechanisms is smaller than the model-observation differences themselves. They then explored how the concurrent utilization of chemical mechanisms of different complexities can further our understanding of atmospheric chemistry at various scales. The study found that scientists could streamline atmospheric chemistry investigations by developing simulations that include both complex and simplified chemical mechanisms. In such simulations, complex mechanisms would provide a more complete representation of complex atmospheric chemistry, and simple mechanisms would efficiently simulate longer time periods to better understand the roles of meteorological variability. Simplified mechanisms could also enable scientists to run a much larger number of scenarios to explore different sources of uncertainty in atmospheric simulations.
BER PM Contact
Bob Vallario
PI Contact
Noelle Selin (selin@mit.edu)
Associate professor, MIT Institute for Data, Systems and Society/MIT Department of Earth, Atmospheric and Planetary Sciences
Faculty affiliate, MIT Joint Program on the Science and Policy of Global Change
Funding
The study was funded by the U.S. Department of Energy (DOE) Office of Science under the grant DE-FG02-94ER61937 and other government, industry and foundation sponsors of the MIT Joint Program.
Publication
Brown-Steiner, B., N.E. Selin, R. Prinn, S., L. Emmons, J. Lamarque and P. Cameron-Smith (2018): Evaluating simplified chemical mechanisms within present-day simulations of the Community Earth System Model version 1.2 with CAM4 (CESM1.2 CAM-chem): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast chemistry. Geoscientific Model Development, online first (doi: 10.5194/gmd-2018-16).
Image: Ozone and other air pollutants are common in urban areas in late afternoon. (Credit: UCAR)
