Nonlinearities in patterns of long‐term ocean warming

Rugenstein, Maria; Sedláčék, Jan; Knutti, Reto

doi:10.1002/2016gl068041

Cited by 29 publications

(26 citation statements)

References 73 publications

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“…Assuming a 5 to 7 m contribution from the Greenland ice sheet (Koenig et al, 2015) and 0.5 to 1 m from thermal expansion of the oceans (assuming 1 to 3 • C ocean warming) (Rugen- (Miller et al, 2012;Rovere et al, 2014;Winnick and Caves, 2015). However, by considering likely air-ocean temperature relationships (Rugenstein et al, 2016), as well as empirical records of an absent WAIS and a retreated EAIS at this time Cook et al, 2013), we are able to identify two scenarios as most plausible. Figure 6a and b illustrate the modelled Antarctic ice-sheet geometry that arises under constant forcing with the Pliocene climate, modified to incorporate a +2 • C air temperature bias and a 0 or 1 • C bias in the ocean (see "Methods").…”

Section: Resultsmentioning

confidence: 97%

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

et al. 2017

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Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offlinecoupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of icesheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO 2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

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Section: Resultsmentioning

confidence: 97%

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

et al. 2017

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“…1e and f) were found by Rugenstein et al (2016) based on EMIC simulations over 10 000 years with ECBILT-CLIO, which features a dynamic, quasi-geostrophic atmosphere. Schmittner et al (2008) also found similar AMOC and Indo-Pacific MOC characteristics for their EMIC UVic 2.7, which includes an atmospheric energy balance model with fixed wind fields similar to the Bern3D model, over a 2000-year simulation.…”

Section: Uncertainties In O 2 Projectionsmentioning

confidence: 83%

Hazards of decreasing marine oxygen: the near-term and millennial-scale benefits of meeting the Paris climate targets

Battaglia

Joos

2018

Earth Syst. Dynam.

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Abstract. Ocean deoxygenation is recognized as key ecosystem stressor of the future ocean and associated climate-related ocean risks are relevant for current policy decisions. In particular, benefits of reaching the ambitious 1.5 • C warming target mentioned by the Paris Agreement compared to higher temperature targets are of high interest. Here, we model oceanic oxygen, warming and their compound hazard in terms of metabolic conditions on multi-millennial timescales for a range of equilibrium temperature targets. Scenarios where radiative forcing is stabilized by 2300 are used in ensemble simulations with the Bern3D Earth System Model of Intermediate Complexity. Transiently, the global mean ocean oxygen concentration decreases by a few percent under low forcing and by 40 % under high forcing. Deoxygenation peaks about a thousand years after stabilization of radiative forcing and new steady-state conditions are established after AD 8000 in our model. Hypoxic waters expand over the next millennium and recovery is slow and remains incomplete under high forcing. Largest transient decreases in oxygen are projected for the deep sea. Distinct and near-linear relationships between the equilibrium temperature response and marine O 2 loss emerge. These point to the effectiveness of the Paris climate target in reducing marine hazards and risks. Mitigation measures are projected to reduce peak decreases in oceanic oxygen inventory by 4.4 % • C −1 of avoided equilibrium warming. In the upper ocean, the decline of a metabolic index, quantified by the ratio of O 2 supply to an organism's O 2 demand, is reduced by 6.2 % • C −1 of avoided equilibrium warming. Definitions of peak hypoxia demonstrate strong sensitivity to additional warming. Volumes of water with less than 50 mmol O 2 m −3 , for instance, increase between 36 % and 76 % • C −1 of equilibrium temperature response. Our results show that millennial-scale responses should be considered in assessments of ocean deoxygenation and associated climate-related ocean risks. Peak hazards occur long after stabilization of radiative forcing and new steady-state conditions establish after AD 8000.

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“…The RTCS is positive everywhere in the observational data sets (Figure ), except for an area in the North Atlantic where deep water forms, but given that the trend is not significant, it is likely to be a transient phenomenon (see Rugenstein et al, , for a discussion of nonlinearities in ocean warming).…”

Section: Rtcsmentioning

confidence: 98%

Regional Climate Sensitivity‐ and Historical‐Based Projections to 2100

Hébert

Lovejoy

2018

Geophysical Research Letters

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Reliable climate projections at the regional scale are needed in order to evaluate climate change impacts and inform policy. We develop an alternative method for projections based on the transient climate sensitivity (TCS), which relies on a linear relationship between the forced temperature response and the strongly increasing anthropogenic forcing. The TCS is evaluated at the regional scale (5° by 5°), and projections are made accordingly to 2100 using the high and low Representative Concentration Pathways emission scenarios. We find that there are large spatial discrepancies between the regional TCS from 5 historical data sets and 32 global climate model (GCM) historical runs and furthermore that the global mean GCM TCS is about 15% too high. Given that the GCM Representative Concentration Pathway scenario runs are mostly linear with respect to their (inadequate) TCS, we conclude that historical methods of regional projection are better suited given that they are directly calibrated on the real world (historical) climate.

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Nonlinearities in patterns of long‐term ocean warming

Cited by 29 publications

References 73 publications

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Hazards of decreasing marine oxygen: the near-term and millennial-scale benefits of meeting the Paris climate targets

Regional Climate Sensitivity‐ and Historical‐Based Projections to 2100

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Nonlinearities in patterns of long‐term ocean warming

Cited by 29 publications

References 73 publications

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Hazards of decreasing marine oxygen: the near-term and millennial-scale benefits of meeting the Paris climate targets

Regional Climate Sensitivity‐ and Historical‐Based Projections to 2100

Contact Info

Product

Resources

About

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma