Impacts of atmospheric chemistry on the biosphere: feedbacks on water and carbon cycles
FY2006 activities
TIIMES Theme:
BGS
Compiled by Peter Hess - ACD - TIIMES
Research Team : Peter Hess- ACD & TIIMES, Louisa Emmons-ACD & TIIMES, Gabriele Pfister-ACD, Elisabeth Holland-ACD & TIIMES, Jean-François Lamarque-ACD,
Phil Rasch-CGD, Peter Thornton-CGD & TIIMES
Collaborators: Colette Heald-NOAA, Jim Randerson-UCI |
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A comparison between net change in radiative flux (W/m2) at the top of the atmosphere between 2004, a high fire year in Alaska, and 2000, a low fire year. The simulated results are on the left, measured results from space using CERES (Clouds and the Earth Radiant Energy System) data are on the right. The simulations suggest that about half the simulated cooling over Alaska is due to aerosols. Figure courtesy of Gabriele Pfister. |
Atmospheric chemical species and the biosphere interact in a number of complex ways. The bio-atmospheric nitrogen cycle has important impacts on the terrestrial biosphere and carbon uptake. Evidence suggests that increased future nitrogen deposition could increase NPP by alleviating N limitation of carbon uptake. Ozone generation, produced by the same chemical cycles that generate oxidized N deposition, negatively impacts terrestrial carbon uptake and may change the partitioning of latent and sensible heat exchange by damaging plant stomatal uptake. In many locations future concentrations of ozone and nitrogen deposition are expected to greatly increase.
As a first step to examine the impact of atmospheric chemistry on the biosphere we have recently completed the first step in development and integration of Chemistry in the Atmospheric Model (CAM). This model has been developed so as to simulate chemistry online using CAM generated winds or offline using winds from the National Centers for Environmental Prediction (NCEP). The model includes chemistry from the latest version of the Model of Ozone and Related Tracers (MOZART), but with improved wet deposition of aerosols from CAM. The model also includes a full suite of aerosols, including ammonia nitrate necessary for evaluation of the ammonia cycle. Updates in the aerosols and microphysics are currently being developed through the Climate-Chemistry and Atmospheric working groups of the CCSM which allows for a significant improvement in wet-deposition and representation of aerosols. Coupling with the land model is proceeding through collaborations with Colette Heald and others. We are currently participating in the Hemispheric Transport on Air Assessment (HTAP), established by the UNECE Convention on Long Range Trans-boundary Air Pollution (LRTAP).
This model has recently been used to investigate the effect of Boreal Fires on Climate. The years 2003 and 2004 were record fire years for Siberia and Alaska, respectively, with evidence from the Alaska fire that substantial peat was burned. With increased warmth in the Arctic one might expect the incidence of fires to increase in a future climate, releasing substantial amounts of carbon dioxide. We have used the chemistry model in CAM to evaluate the impact of species emitted from high-latitude fires (see Figure 1). In collaboration with Jim Randerson (UCI), a new study shows that these impacts are rather small, especially in the long-term (Randerson et al., 2006, The Impact of Boreal Fire on Climate Warming, accepted to Science). This study suggests that changes in surface albedo associated with high latitude fires leads to a net cooling effect. |
