Authors' response to a review by David Archer of ``Amplification of global warming through pH-dependence of DMS-production simulated with a fully coupled Earth system model '' by Schwinger et al.

2017 ◽  
Author(s):  
Jörg Schwinger
Keyword(s):  
Global Warming ◽  
Ph Dependence ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Fully Coupled

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

2017 ◽  
Vol 14 (15) ◽  
pp. 3633-3648 ◽  
Author(s):  
Jörg Schwinger ◽  
Jerry Tjiputra ◽  
Nadine Goris ◽  
Katharina D. Six ◽  
Alf Kirkevåg ◽  
...  
Keyword(s):  
Global Warming ◽  
Ocean Acidification ◽  
Dimethyl Sulfide ◽  
Ph Dependence ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Radiative Fluxes ◽  
Global Average ◽  
Fully Coupled

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 0.30 K (0.47 K) towards the end of the 22nd century when DMS emissions are reduced by 7.3 Tg S yr−1 or 31 % (11.5 Tg S yr−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. 041 K per 1 Tg S yr−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 0.56 K (0.89 K) 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.

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

2017 ◽  
Author(s):  
Jörg Schwinger ◽  
Jerry Tjiputra ◽  
Nadine Goris ◽  
Katharina Six ◽  
Alf Kirkevåg ◽  
...  
Keyword(s):  
Global Warming ◽  
Ocean Acidification ◽  
Dimethyl Sulfide ◽  
Ph Dependence ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Radiative Fluxes ◽  
Global Average ◽  
Fully Coupled

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 off-line model set-up. Assuming a medium (strong) sensitivity of DMS-production to pH, we find an additional transient global warming of 0.30 K (0.47 K) towards the end of the 22nd century when DMS-emission are reduced by 7.3 Tg S yr−1 or 31 % (11.5 Tg S yr−1 or 48 %). The main mechanism behind the additional warming is a reduction of cloud albedo, but a change in short-wave 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 −0.041 K per 1 Tg S yr−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 0.56 K (0.89 K) 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.

scholarly journals Understanding why the volume of suboxic waters does not increase over centuries of global warming in an Earth System Model

2012 ◽  
Vol 9 (3) ◽  
pp. 1159-1172 ◽  
Author(s):  
A. Gnanadesikan ◽  
J. P. Dunne ◽  
J. John
Keyword(s):  
Global Warming ◽  
Dissolved Oxygen ◽  
Lateral Diffusion ◽  
Earth System Model ◽  
System Model ◽  
Oxygen Solubility ◽  
Earth System ◽  
Eddy Transport ◽  
Term Analysis ◽  
The Tropical Pacific

Abstract. Global warming is expected to reduce oxygen solubility and vertical exchange in the ocean, changes which would be expected to result in an increase in the volume of hypoxic waters. A simulation made with a full Earth System model with dynamical atmosphere, ocean, sea ice and biogeochemical cycling (the Geophysical Fluid Dynamics Laboratory's Earth System Model 2.1) shows that this holds true if the condition for hypoxia is set relatively high. However, the volume of the most hypoxic (i.e., suboxic) waters does not increase under global warming, as these waters actually become more oxygenated. We show that the rise in dissolved oxygen in the tropical Pacific is associated with a drop in ventilation time. A term-by-term analysis within the least oxygenated waters shows an increased supply of dissolved oxygen due to lateral diffusion compensating an increase in remineralization within these highly hypoxic waters. This lateral diffusive flux is the result of an increase of ventilation along the Chilean coast, as a drying of the region under global warming opens up a region of wintertime convection in our model. The results highlight the potential sensitivity of suboxic waters to changes in subtropical ventilation as well as the importance of constraining lateral eddy transport of dissolved oxygen in such waters.

Sea-state dependency of air-sea fluxes for high winds in ECMWF Earth System Model

2020 ◽  
Author(s):  
Jean Bidlot
Keyword(s):  
Drag Coefficient ◽  
Tropical Cyclones ◽  
Coupled System ◽  
Wave Model ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Sea State ◽  
Medium Range ◽  
Fully Coupled

<p>The global analyses and medium range forecasts from the European Centre for Medium range Weather Forecasts rely on a state-of-the-art Numerical Weather Prediction (NWP) system. To best represent the air-sea exchanges, it is tightly coupled to an ocean wave model.  As part of ECMWF approach to Earth System Model, it is also coupled to a global ocean model for all its forecasting systems from the medium range up to the seasonal time scale.</p><p>Because the feedback from and to the ocean can be significant, it is only in the fully coupled system that parameterisation for air-sea processes should be revisited. For instance, it is now accepted that the drag coefficient should generally attained maximum values for storm winds but should level or even decrease for very strong winds, namely in tropical cyclones or intense mid-latitude wind storms.</p><p>A modification of the wind input source was tested, whereby the Charnock coefficient estimated by the wave model and therefore the drag coefficient sharply reduce for large winds (> 30 m/s). As a consequence, ECMWF tendency to under predict strong tropical cyclones was sharply alleviated, in better agreement with observational evidence. This change is now planned for operational implementation with the next model cycle (CY47R1, June 2020).</p><p>Experimental evidences also point to a sea state/wind dependency of the heat and moisture fluxes.  Following an extension of the wind wave generation theory, a sea state dependent parameterisation for the roughness length scales for heat and humidity has been tested. Again, a proper assessment of the different parameterisations warrants the fully coupled system. Experimentations so far indicate the benefit of such change. Ongoing work aims at future operational implementation.</p>

scholarly journals Implementation of methane cycling for deep time, global warming simulations with the DCESS Earth System Model (Version 1.2)

2017 ◽  
Author(s):  
Gary Shaffer ◽  
Esteban Fernández Villanueva ◽  
Roberto Rondanelli ◽  
Jens Olaf Pepke Pedersen ◽  
Steffen Malskær Olsen ◽  
...  
Keyword(s):  
Global Warming ◽  
Time Scales ◽  
Sediment Cores ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Deep Time ◽  
Methane Cycling ◽  
Model Version ◽  
Ocean Atmosphere

Abstract. Geological records reveal a number of ancient, large and rapid negative excursions of carbon-13 isotope. Such excursions can only be explained by massive injections of depleted carbon to the Earth System over a short duration. These injections may have forced strong global warming events, sometimes accompanied by mass extinctions, for example the Triassic-Jurassic and End-Permian extinctions, 201 and 252 million years ago. In many cases evidence points to methane as the dominant form of injected carbon, whether as thermogenic methane, formed by magma intrusions through overlying carbon-rich sediment, or from warming-induced dissociation of methane hydrate, a solid compound of methane and water found in ocean sediments. As a consequence of the ubiquity and importance of methane in major Earth events, Earth System models should include a comprehensive treatment of methane cycling but such a treatment has often been lacking. Here we implement methane cycling in the Danish Center for Earth System Science (DCESS) model, a simplified but well-tested Earth System Model of Intermediate Complexity. We use a generic methane input function that allows variation of input type, size, time scale and ocean-atmosphere partition. To be able to treat such massive inputs more correctly, we extend the model to deal with ocean suboxic/anoxic conditions and with radiative forcing and methane lifetimes appropriate for high atmospheric methane concentrations. With this new model version, we carried out an extensive set of simulations for methane inputs of various sizes, time scales and ocean-atmosphere partitions to probe model behaviour. We find that larger methane inputs over shorter time scales with more methane dissolving in the ocean lead to ever-increasing ocean anoxia with consequences for ocean life and global carbon cycling. Greater methane input directly to the atmosphere leads to more warming and, for example, greater carbon dioxide release from land soils. Analysis of synthetic sediment cores from the simulations provides guidelines for the interpretation of real sediment cores spanning the warming events. With this improved DCESS model version and paleo-reconstructions, we are now better armed to gauge the amounts, types, time scales and locations of methane injections driving specific, observed deep time, global warming events.

Can ocean deoxygenation accelerate global warming via enhanced marine N2O production?

2020 ◽  
Author(s):  
Angela Landolfi ◽  
Wolfgang Koeve
Keyword(s):  
Global Warming ◽  
Ocean Circulation ◽  
Positive Feedback ◽  
Emission Scenario ◽  
Earth System Model ◽  
System Model ◽  
Metabolic Rates ◽  
Earth System ◽  
N2o Production ◽  
Ocean Deoxygenation

<p>Ocean warming is projected to cause marine deoxygenation, reduce solubility, affect ocean circulation and enhance metabolic rates over this century. These changes, affecting oceanic N<sub>2</sub>O production and emissions, have been suggested to potentially rise atmospheric N<sub>2</sub>O concentrations and increase the positive feedback to anthropogenic climate change.However, current global model projections all suggest a decline in marine N<sub>2</sub>O emissions under global warming but the processes leading to this decline are poorly constrained. Here, using an Earth system model of intermediate complexity, we disentangle the contribution of ocean deoxygenation and the direct and indirect warming effects on oceanic N<sub>2</sub>O production and emissions changes under RCP8.5 emission scenario. We find that ocean deoxygenation and warming-reduced N<sub>2</sub>O solubility do in fact increase oceanic N<sub>2</sub>O emissions, however this increase is overcompensated by ocean circulation slow-down and reduced export production, suggesting a neglectable N<sub>2</sub>O-emssion feedback to climate on centennial timescales.</p>

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