Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1383-1401, 2017
http://www.biogeosciences.net/14/1383/2017/
doi:10.5194/bg-14-1383-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
20 Mar 2017
Drivers of multi-century trends in the atmospheric CO2 mean annual cycle in a prognostic ESM
Jessica Liptak1, Gretchen Keppel-Aleks1, and Keith Lindsay2 1Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
2Climate and Global Dynamics, National Center for Atmospheric Research, Boulder, CO, USA
Abstract. The amplitude of the mean annual cycle of atmospheric CO2 is a diagnostic of seasonal surface–atmosphere carbon exchange. Atmospheric observations show that this quantity has increased over most of the Northern Hemisphere (NH) extratropics during the last 3 decades, likely from a combination of enhanced atmospheric CO2, climate change, and anthropogenic land use change. Accurate climate prediction requires accounting for long-term interactions between the environment and carbon cycling; thus, analysis of the evolution of the mean annual cycle in a fully prognostic Earth system model may provide insight into the multi-decadal influence of environmental change on the carbon cycle.

We analyzed the evolution of the mean annual cycle in atmospheric CO2 simulated by the Community Earth System Model (CESM) from 1950 to 2300 under three scenarios designed to separate the effects of climate change, atmospheric CO2 fertilization, and land use change. The NH CO2 seasonal amplitude increase in the CESM mainly reflected enhanced primary productivity during the growing season due to climate change and the combined effects of CO2 fertilization and nitrogen deposition over the mid- and high latitudes. However, the simulations revealed shifts in key climate drivers of the atmospheric CO2 seasonality that were not apparent before 2100. CO2 fertilization and nitrogen deposition in boreal and temperate ecosystems were the largest contributors to mean annual cycle amplification over the midlatitudes for the duration of the simulation (1950–2300). Climate change from boreal ecosystems was the main driver of Arctic CO2 annual cycle amplification between 1950 and 2100, but CO2 fertilization had a stronger effect on the Arctic CO2 annual cycle amplitude during 2100–2300. Prior to 2100, the NH CO2 annual cycle amplitude increased in conjunction with an increase in the NH land carbon sink. However, these trends decoupled after 2100, underscoring that an increasing atmospheric CO2 annual cycle amplitude does not necessarily imply a strengthened terrestrial carbon sink.


Citation: Liptak, J., Keppel-Aleks, G., and Lindsay, K.: Drivers of multi-century trends in the atmospheric CO2 mean annual cycle in a prognostic ESM, Biogeosciences, 14, 1383-1401, doi:10.5194/bg-14-1383-2017, 2017.
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We analyzed the evolution of the atmospheric CO2 mean annual cycle simulated during 1950–2300 under three scenarios designed to separate the effects of climate change, CO2 fertilization, and land use change. CO2 fertilization in boreal and temperate ecosystems drove mean annual cycle amplification over the NH midlatitudes during 1950–2300. Boreal and Arctic climate change drove high-latitude amplification before 2200, after which CO2 fertilization contributed nearly equally to amplification.
We analyzed the evolution of the atmospheric CO2 mean annual cycle simulated during 1950–2300...
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