In:
Earth System Dynamics, Copernicus GmbH, Vol. 13, No. 2 ( 2022-05-16), p. 885-909
Abstract:
Abstract. Future climate projections from Earth system models
(ESMs) typically focus on the timescale of this century. We use a set of
five ESMs and one Earth system model of intermediate complexity (EMIC) to
explore the dynamics of the Earth's climate and carbon cycles under
contrasting emissions trajectories beyond this century to the year 2300.
The trajectories include a very-high-emissions, unmitigated fossil-fuel-driven scenario, as well as a mitigation scenario that diverges from the
first scenario after 2040 and features an “overshoot”, followed by a
decrease in atmospheric CO2 concentrations by means of large
net negative CO2 emissions. In both scenarios and for all models
considered here, the terrestrial system switches from being a net sink to
either a neutral state or a net source of carbon, though for different
reasons and centered in different geographic regions, depending on both the
model and the scenario. The ocean carbon system remains a sink, albeit
weakened by carbon cycle feedbacks, in all models under the high-emissions
scenario and switches from sink to source in the overshoot scenario. The
global mean temperature anomaly is generally proportional to cumulative
carbon emissions, with a deviation from proportionality in the overshoot
scenario that is governed by the zero emissions commitment. Additionally,
23rd century warming continues after the cessation of carbon emissions in
several models in the high-emissions scenario and in one model in the
overshoot scenario. While ocean carbon cycle responses qualitatively agree
in both globally integrated and zonal mean dynamics in both scenarios, the
land models qualitatively disagree in zonal mean dynamics, in the relative
roles of vegetation and soil in driving C fluxes, in the response of the
sink to CO2, and in the timing of the sink–source transition,
particularly in the high-emissions scenario. The lack of agreement among
land models on the mechanisms and geographic patterns of carbon cycle
feedbacks, alongside the potential for lagged physical climate dynamics to
cause warming long after CO2 concentrations have stabilized, points to
the possibility of surprises in the climate system beyond the 21st century
time horizon, even under relatively mitigated global warming scenarios,
which should be taken into consideration when setting global climate policy.
Type of Medium:
Online Resource
ISSN:
2190-4987
DOI:
10.5194/esd-13-885-2022
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2578793-7
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