Until recently all future climate projections using models did not include external forcing such as volcanic eruption. Yet, studies have shown that this forcing plays an important role and influences past climate variability over years to decadal time scales.
At the Bjerknes Center for Climate Research, Jerry Tjiputra and Odd Helge Otterå published a new study in Earth System Dynamics, which used a sophisticated Earth system model to investigate the potential effect of volcanic eruption (or injection of sulphur aerosols into the stratosphere) on future climate change.
In addition to the business-as-usual carbon emissions, they introduced volcanic eruptions varying in frequencies and magnitudes to a series of future climate simulations. In one of the cases where the large volcanic eruptions were included every five-years frequency, the model simulates a persistent cooler climate through the end of the 21st century.
This cooling is mainly attributed by the eruption-released sulphur aerosols, which stays in the lower stratosphere for a few years and reduces the short wave radiation reaching the Earth’s surface.
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| Figure1. Expected mean regional temperature change by end of the 21st century relative to present-day for simulation (above) without and (under) with large and frequent episodic large volcanic eruptions equivalent to Mt. Pinatubo. |
The largest climate cooling occurs over land in the high latitude northern hemisphere. It leads to longer soil carbon turnover rate and increased carbon sequestration through plant photosynthesis. As a result, the volcanic eruptions also improve the terrestrial biosphere carbon uptake.
This increase in global carbon uptake reduces the fraction of anthropogenic carbon remaining in the atmosphere, hence further reducing the anthropogenic climate change effect.
Despite some positive impacts of the volcanic eruptions, the study emphasizes that the future concentration of anthropogenic carbon in the atmosphere remains the dominant driver for long-term climate variability. There are also other remaining issues associated with the high CO2 world that is not significantly affected by volcanic eruptions, for example the ocean acidification.