Joint Seminar: Variability in oceanic oxygen and anthropogenic trends in the ocean: Ensemble simulations with the NCAR global coupled carbon cycle-climate model

A major challenge in climate research is the uncertainty associated with the high level of natural variability in the coupled carbon cycle-climate system. It is still ambitious to identify a current anthropogenic trend in the marine carbon cycle. Understanding and quantifying mechanisms of the carbon cycle-climate system variability is therefore crucial for interpreting observed changes in the context of natural and anthropogenic changes.

First, the impact of natural variability on the detection of anthropogenic trends in oceanic oxygen is investigated. A six-member ensemble simulation the NCAR CSM1.4-carbon model was performed over the period 1820 to 2100. The results show that simulated anthropogenically forced O2 decrease is partly compensated by volcanic eruptions, which cause considerable interannual to decadal variability. Oxygen variability in the North Atlantic is associated with changes in the North Atlantic Oscillation index. The future part of the global warming simulations shows that the oceanic O2 inventory is projected to significantly decrease over the next century. The large interannual to decadal variations in oceanic oxygen and the limited data availability make the detection of human-induced O2 changes still challenging.

In a second part, reversible ind irreversible impacts of anthropogenic carbon and greenhouse gas emissions on human timescales are investigated with the NCAR model. Emissions commitment scenarios with zero emissions after 2100 and 2000 are run up to the year 2500. Carbon emissions of the 21st century show irreversible impacts on centennial to millennial timescales in most regions, whereas regional perturbations in temperature and precipitation by historical emissions and by non-CO2 agents are largely reversible within centuries. System time lags and physical-biogeochemical coupling often cause largest impacts to accrue after emissions have been stopped. The volume of supersaturated water providing habitat to calcifying organisms is reduced from preindustrial 40% to 25% in 2100 and to 10% in 2300.




15:15 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Thomas L. Frölicher, ETH Zurich


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