A new study published this week in Journal of Climate strengthens previous results on the effect of rising atmospheric CO2 concentration on the future CO2 uptake by the oceans. Unlike earlier work in this field, based on global models, this article is based on a comparative study on the regional impacts of climate change. It compares model results from four key European laboratories, including France, Germany, Norway, and Switzerland. The Bjerknes Centre for Climate Research has contributed with the Norwegian model results. The study splits the world oceans into four regions and demonstrates which areas that will be most crucial for future uptake: The Arctic, the North Atlantic, the Tropics, the South Atlantic, and the Southern Ocean.
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| photo: Eirik Kolstad |
The climate models used in this experiment are so-called earth system models, which in addition to the simulation of physical processes also include biogeochemical interactions. The simulated climate change by the models causes a reduction of oceanic CO2 uptake by the end of this century by 41.5 Giga-tons carbon, which is equivalent with approximately five years of present annual CO2 emissions.
The Atlantic Ocean becoming less efficient
While the ocean in total will remain a net sink for human-produced CO2, there are big regional changes in how uptake rates by the ocean will develop in the future. Until now, the North Atlantic has been the most efficient sink for atmospheric CO2 per square meter. The model results show that the North Atlantic region is particularly sensitive to freshwater supply changes (from melting of mountain glaciers and Greenland ice sheet) and may experience a considerable decrease in uptake strengths.
The Southern Ocean: key region for future uptake
The Southern Ocean around Antarctica has been confirmed to probably develop into a key region for CO2 uptake in the decades to come. The four different models give qualitatively a broadly consistent picture, but – due to the different representation of physical, biological, and chemical processes – show a quantitative spread in their results for regional air-sea fluxes. This spread is an indication of our current limitations to predict even more accurately regional CO2 sink strengths changes. Improving networks of oceanic and atmospheric carbon observations will contribute to reducing these uncertainties in the years to come.