Abstract
Abstract. Impacts of low-latitude, explosive volcanic eruptions on climate and the carbon cycle are quantified by forcing a comprehensive, fully coupled carbon cycle-climate model with pulse-like stratospheric aerosol optical depth changes. The model represents the radiative and dynamical response of the climate system to volcanic eruptions and simulates a decrease of global and regional atmospheric surface temperature, regionally distinct changes in precipitation, a positive phase of the North Atlantic Oscillation, and a decrease in atmospheric CO2 after volcanic eruptions. The volcanic-induced cooling reduces overturning rates in tropical soils, which dominates over reduced litter input due to soil moisture decrease, resulting in higher land carbon inventories for several decades. The perturbation in the ocean carbon inventory changes sign from an initial weak carbon sink to a carbon source. Positive carbon and negative temperature anomalies in subsurface waters last up to several decades. The multi-decadal decrease in atmospheric CO2 yields a small additional radiative forcing that amplifies the cooling and perturbs the Earth System on longer time scales than the atmospheric residence time of volcanic aerosols. In addition, century-scale global warming simulations with and without volcanic eruptions over the historical period show that the ocean integrates volcanic radiative cooling and responds for different physical and biogeochemical parameters such as steric sea level or dissolved oxygen. Results from a suite of sensitivity simulations with different magnitudes of stratospheric aerosol optical depth changes and from global warming simulations show that the carbon cycle-climate sensitivity γ, expressed as change in atmospheric CO2 per unit change in global mean surface temperature, depends on the magnitude and temporal evolution of the perturbation, and time scale of interest. On decadal time scales, modeled γ is several times larger for a Pinatubo-like eruption than for the industrial period and for a high emission, 21st century scenario.
Highlights
Variability on a wide range of time scales is present in the atmospheric CO2 record from ice core and direct atmospheric samples
It remains unclear whether the reconstructed changes in the fractions of anthropogenic carbon emissions absorbed by the ocean and land and in the fraction remaining in the atmosphere herald a decrease in the relative sink strength of the ocean and the land biosphere in response to long-term climate change and nonlinearities in the carbonate chemistry of ocean waters
Like the Pin.10x case, there is still a significant reduction of temperature after a decade compared to the control simulation
Summary
Variability on a wide range of time scales is present in the atmospheric CO2 record from ice core and direct atmospheric samples. Different studies that investigate recent trends in the airborne fraction of anthropogenic emissions arrive at disparate conclusions on the feedback question even though analyzing the same data (Gloor et al, 2010; Sarmiento et al, 2010; Knorr, 2009; Le Quereet al., 2009; Canadell et al, 2007, and other studies) It remains unclear whether the reconstructed changes in the fractions of anthropogenic carbon emissions absorbed by the ocean and land and in the fraction remaining in the atmosphere herald a decrease in the relative sink strength of the ocean and the land biosphere in response to long-term climate change and nonlinearities in the carbonate chemistry of ocean waters.
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