Transient Earth system responses to cumulative carbon dioxide emissions: linearities, uncertainties, and probabilities in an observation-constrained model ensemble
Information on the relationship between cumulative fossil CO<sub>2</sub> emissions and multiple climate targets is essential to design emission mitigation and climate adaptation strategies. In this study, the transient response of a climate or environmental variable per trillion tonnes o...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-02-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/1071/2016/bg-13-1071-2016.pdf |
| Summary: | Information on the relationship between cumulative fossil CO<sub>2</sub>
emissions and multiple climate targets is essential to design
emission mitigation and climate adaptation strategies. In this
study, the transient response of a climate or environmental variable
per trillion tonnes of CO<sub>2</sub> emissions, termed TRE, is
quantified for a set of impact-relevant climate variables and from a large set of multi-forcing scenarios extended to
year 2300 towards stabilization. An ∼ 1000-member ensemble of
the Bern3D-LPJ carbon–climate model is applied and model outcomes are
constrained by 26 physical and biogeochemical observational data
sets in a Bayesian, Monte Carlo-type framework. Uncertainties in TRE
estimates include both scenario uncertainty and model response uncertainty. Cumulative fossil
emissions of 1000 Gt C result in a global mean surface air
temperature change of 1.9 °C (68 % confidence
interval (c.i.): 1.3 to 2.7 °C), a decrease in
surface ocean pH of 0.19 (0.18 to 0.22), and a steric sea level
rise of 20 cm (13 to 27 cm until 2300). Linearity between
cumulative emissions and transient response is high for pH and
reasonably high for surface air and sea surface temperatures, but
less pronounced for changes in Atlantic meridional overturning,
Southern Ocean and tropical surface water saturation with respect to
biogenic structures of calcium carbonate, and carbon stocks in
soils. The constrained model ensemble is also applied to determine the
response to a pulse-like emission and in idealized CO<sub>2</sub>-only simulations.
The transient climate response is constrained,
primarily by long-term ocean heat observations, to
1.7 °C (68 % c.i.: 1.3 to
2.2 °C) and the equilibrium climate sensitivity to
2.9 °C (2.0 to 4.2 °C). This is
consistent with results by CMIP5 models but inconsistent with
recent studies that relied on short-term air temperature data
affected by natural climate variability. |
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| ISSN: | 1726-4170 1726-4189 |