Atmospheric Chemistry, Carbon Cycle, and Climate (AC4) is a newly formed program that combines the previously existing Atmospheric Composition and Climate (ACC) and Global Carbon Cycle (GCC) programs within Climate Program Office. Recognizing the many connections linking research into greenhouse gases, aerosols, and climate, NOAA’s Earth Systems Science (ESS) Division integrated its previous efforts in these areas to stimulate a more holistic approach to studies of atmospheric chemistry and carbon cycle as they relate to climate.
In Fiscal Year 2013, AC4 is concentrating on three focus areas:
1. Observational constraints on emissions of greenhouse gases
Accurate estimates of greenhouse gas and aerosol precursor emissions are at the core of climate forcing calculations. Both anthropogenic and natural emission estimates, however, remain very uncertain. Terrestrial emission estimates, particularly of biogenic aerosol precursors and of agricultural ammonia, nitrous oxide, and methane, represent a gap in knowledge, and they would benefit from additional observations and from analysis of recent and future NOAA field measurements (e.g., CalNex, SENEX). Emissions from megacities and other metropolitan areas, both in the U.S. and abroad, are projected to grow in coming decades, and their estimates require targeted measurements (such as CalNex and INFLUX) and analysis of multi-species and/or isotopic data sets. Recent increases in emissions from oil and gas extraction are only beginning to be measured, and additional observations and analysis are needed to confirm uncertain inventory estimates for this source sector.
2. Improvements to CarbonTracker
Policy makers, industry, scientists, and the public need accurate carbon dioxide flux information to make informed decisions related to atmospheric greenhouse gas levels. NOAA/ESRL/GMD’s CarbonTracker, a system that produces quantitative estimates of atmospheric carbon uptake and release for North America and the rest of the world that are consistent with observed patterns of CO2 in the atmosphere, is designed to supply that information. The new release of CarbonTracker ("CT2011") uses multiple models to explicitly estimate the influence of first-guess fluxes on the final result. CarbonTracker is intended to be a tool for the community, and feedback and collaboration from anyone interested are welcome.
3. Improved understanding of nitrogen cycle
Human activities have vastly perturbed the nitrogen cycle, which has resulted in emissions and deposition of climate-relevant atmospheric constituents. While N2O is a major greenhouse gas and ozone-depleting substance, other nitrogen containing species contribute to ozone production and aerosol formation, with a resulting mix of uncertain positive and negative radiative forcing. Extensive measurements have been made of various nitrogen-containing species (e.g., SOS99, CalNex, NACHTT), including aerosols and aerosol precursors.
AC4 Highlights
Reducing Uncertainties about CO2 Exchange in the Terrestrial Biosphere
AC4-funded scientists used the Princeton-NOAA Geophysical Fluid Dynamics Laboratory global land model to examine how interactions between land use changes, atmospheric nitrogen deposition, and climatic conditions govern terrestrial ecosystems’ responses to CO2 in the atmosphere. The project brought together a group of experimental, theoretical, and modeling scientists with the goal of improving simulations of terrestrial carbon
exchange.
The team conducted their study in the forests of Barro Colorado Island in collaboration with the Smithsonian Tropical Research Institute in Panama. These forests represent an ideal model system for lowland tropical forecasts. By applying the longest and most complete record of forest growth and watershed nutrient dynamics available worldwide to this system, the team was able to better understand the influence of climate change and land disturbance on the nitrogen cycle. This project’s findings demonstrate that feedbacks between the carbon and the nitrogen cycles and interactions with land may constrain carbon uptake in terrestrial ecosystems.