Hazards of decreasing marine oxygen: the near-term and millennial-scale benefits of meeting the Paris climate targets
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Published:2018-06-13
Issue:2
Volume:9
Page:797-816
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ISSN:2190-4987
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Container-title:Earth System Dynamics
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language:en
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Short-container-title:Earth Syst. Dynam.
Author:
Battaglia GiannaORCID, Joos FortunatORCID
Abstract
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 O2 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 O2 supply to an organism's O2 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 O2 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.
Publisher
Copernicus GmbH
Subject
General Earth and Planetary Sciences
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