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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 15
Biogeosciences, 14, 3633-3648, 2017
https://doi.org/10.5194/bg-14-3633-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Progress in quantifying ocean biogeochemistry – in honour...

Biogeosciences, 14, 3633-3648, 2017
https://doi.org/10.5194/bg-14-3633-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Aug 2017

Research article | 04 Aug 2017

Amplification of global warming through pH dependence of DMS production simulated with a fully coupled Earth system model

Jörg Schwinger1, Jerry Tjiputra1, Nadine Goris1, Katharina D. Six2, Alf Kirkevåg3, Øyvind Seland3, Christoph Heinze4,1, and Tatiana Ilyina2 Jörg Schwinger et al.
  • 1Uni Research Climate, Bjerknes Centre for Climate Research, Bergen, Norway
  • 2Max Planck Institute for Meteorology, Hamburg, Germany
  • 3Norwegian Meteorological Institute, Oslo, Norway
  • 4Geophysical Institute, University of Bergen, Bjerknes Centre for Climate Research, Bergen, Norway

Abstract. We estimate the additional transient surface warming ΔTs caused by a potential reduction of marine dimethyl sulfide (DMS) production due to ocean acidification under the high-emission scenario RCP8.5 until the year 2200. Since we use a fully coupled Earth system model, our results include a range of feedbacks, such as the response of marine DMS production to the additional changes in temperature and sea ice cover. Our results are broadly consistent with the findings of a previous study that employed an offline model set-up. Assuming a medium (strong) sensitivity of DMS production to pH, we find an additional transient global warming of 0.30K (0.47K) towards the end of the 22nd century when DMS emissions are reduced by 7.3TgSyr−1 or 31% (11.5TgSyr−1 or 48%). The main mechanism behind the additional warming is a reduction of cloud albedo, but a change in shortwave radiative fluxes under clear-sky conditions due to reduced sulfate aerosol load also contributes significantly. We find an approximately linear relationship between reduction of DMS emissions and changes in top of the atmosphere radiative fluxes as well as changes in surface temperature for the range of DMS emissions considered here. For example, global average Ts changes by −0. 041K per 1TgSyr−1 change in sea–air DMS fluxes. The additional warming in our model has a pronounced asymmetry between northern and southern high latitudes. It is largest over the Antarctic continent, where the additional temperature increase of 0.56K (0.89K) is almost twice the global average. We find that feedbacks are small on the global scale due to opposing regional contributions. The most pronounced feedback is found for the Southern Ocean, where we estimate that the additional climate change enhances sea–air DMS fluxes by about 9% (15%), which counteracts the reduction due to ocean acidification.

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Transient global warming under the high emission scenario RCP8.5 is amplified by up to 6 % if a pH dependency of marine DMS production is assumed. Importantly, this additional warming is not spatially homogeneous but shows a pronounced north–south gradient. Over the Antarctic continent, the additional warming is almost twice the global average. In the Southern Ocean we find a small DMS–climate feedback that counteracts the original reduction of DMS production due to ocean acidification.
Transient global warming under the high emission scenario RCP8.5 is amplified by up to 6 % if a...
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