Trajectory sensitivity of the transient climate response to cumulative carbon emissions

AbstractThe transient climate response to cumulative carbon emissions (TCRE) is a key metric in estimating the remaining carbon budget for given temperature targets. However, the TCRE has a small scenario dependence that can be non-negligible for stringent temperature targets. To investigate the parametric correlations and scenario dependence of the TCRE, the present study uses a 512-member ensemble of an Earth system model of intermediate complexity (EMIC) perturbing 11 physical and biogeochemical parameters under scenarios with steady increases of 0.25%, 0.5%, 1%, 2%, or 4% per annum (ppa) in the atmospheric CO2 concentration (pCO2), or an initial increase of 1% followed by an annual decrease of 1% thereafter. Although a small difference of 5% (on average) in the TCRE is observed between the 1-ppa and 0.5-ppa scenarios, a significant scenario dependence is found for the other scenarios, with a tendency toward large values in gradual or decline-after-a-peak scenarios and small values in rapidly increasing scenarios. For all scenarios, correlation analysis indicates a remarkably large correlation between the equilibrium climate sensitivity (ECS) and the relative change in the TCRE, which is attributed to the longer response time of the high ECS model. However, the correlations of the ECS with the TCRE and its scenario dependence for scenarios with large pCO2 increase rates are slightly smaller, and those of biogeochemical parameters such as plant respiration and the overall pCO2–carbon cycle feedback are larger, than in scenarios with gradual increases. The ratio of the TCREs under the overshooting (i.e., 1-ppa decrease after a 1-ppa increase) and 1-ppa increase only scenarios had a clear positive relation with zero-emission commitments. Considering the scenario dependence of the TCRE, the remaining carbon budget for the 1.5 °C target could be reduced by 17 or 22% (before and after considering the unrepresented Earth system feedback) for the most extreme case (i.e., the 67th percentile when using the 0.25-ppa scenario as compared to the 1-ppa increase scenario). A single ensemble EMIC is also used to indicate that, at least for high ECS (high percentile) cases, the scenario dependence of the TCRE should be considered when estimating the remaining carbon budget.

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Large ensemble assessment of how the global surface warming response to cumulative carbon differs for negative and positive carbon emissions

10.5194/egusphere-egu21-12718 ◽

2021 ◽

Author(s):

Negar Vakilifard ◽

Katherine Turner ◽

Ric Williams ◽

Philip Holden ◽

Neil Edwards ◽

...

Keyword(s):

Carbon Emissions ◽

Radiative Forcing ◽

Climate Model ◽

Climate Feedback ◽

Climate Response ◽

Ocean Heat Uptake ◽

Transient Climate Response ◽

Surface Warming ◽

Radiative Processes ◽

Negative Emission

The controls of the effective transient climate response (TCRE), defined in terms of the dependence of surface warming since the pre-industrial to the cumulative carbon emission, is explained in terms of climate model experiments for a scenario including positive emissions and then negative emission over a period of 400 years. We employ a pre-calibrated ensemble of GENIE, grid-enabled integrated Earth system model, consisting of 86 members to determine the process of controlling TCRE in both CO2 emissions and drawdown phases. Our results are based on the GENIE simulations with historical forcing from AD 850 including land use change, and the future forcing defined by CO2 emissions and a non-CO2 radiative forcing timeseries. We present the results for the point-source carbon capture and storage (CCS) scenario as a negative emission scenario, following the medium representative concentration pathway (RCP4.5), assuming that the rate of emission drawdown is 2 PgC/yr CO2 for the duration of 100 years. The climate response differs between the periods of positive and negative carbon emissions with a greater ensemble spread during the negative carbon emissions. The controls of the spread in ensemble responses are explained in terms of a combination of thermal processes (involving ocean heat uptake and physical climate feedback), radiative processes (saturation in radiative forcing from CO2 and non-CO2 contributions) and carbon dependences (involving terrestrial and ocean carbon uptake).&#160;&#160;

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Assessing the implications of human land-use change for the transient climate response to cumulative carbon emissions

Environmental Research Letters ◽

10.1088/1748-9326/11/3/035001 ◽

2016 ◽

Vol 11 (3) ◽

pp. 035001 ◽

Cited By ~ 15

Author(s):

C T Simmons ◽

H D Matthews

Keyword(s):

Land Use ◽

Land Use Change ◽

Carbon Emissions ◽

Climate Response ◽

Transient Climate Response ◽

Human Land Use

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Increase of uncertainty in transient climate response to cumulative carbon emissions after stabilization of atmospheric CO 2 concentration

Environmental Research Letters ◽

10.1088/1748-9326/10/12/125018 ◽

2015 ◽

Vol 10 (12) ◽

pp. 125018 ◽

Cited By ~ 8

Author(s):

Kaoru Tachiiri ◽

Tomohiro Hajima ◽

Michio Kawamiya

Keyword(s):

Carbon Emissions ◽

Climate Response ◽

Transient Climate Response

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Increase of the transient climate response to cumulative carbon emissions with decreasing CO 2 concentration scenarios

Environmental Research Letters ◽

10.1088/1748-9326/ab57d3 ◽

2019 ◽

Vol 14 (12) ◽

pp. 124067 ◽

Cited By ~ 3

Author(s):

K Tachiiri ◽

T Hajima ◽

M Kawamiya

Keyword(s):

Carbon Emissions ◽

Climate Response ◽

Transient Climate Response

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Controls of the Transient Climate Response to Emissions: effects of physical feedbacks, heat uptake and saturation of radiative forcing

10.5194/egusphere-egu2020-8433 ◽

2020 ◽

Author(s):

Ric Williams ◽

Paulo Ceppi ◽

Anna Katavouta

Keyword(s):

Carbon Emissions ◽

Radiative Forcing ◽

Carbon Emission ◽

Atmospheric Co2 ◽

Climate Response ◽

Climate Feedbacks ◽

Ocean Heat Uptake ◽

Transient Climate Response ◽

Surface Warming ◽

Heat Uptake

The surface warming response to carbon emissions, defines a climate metric, the Transient Climate Response to cumulative carbon Emissions (TCRE), which is important in estimating how much carbon may be emitted to avoid dangerous climate. The TCRE is diagnosed from a suite of 9 CMIP6 Earth system models following an annual 1% rise in atmospheric CO2 over 140 years.&#160;&#160; The TCRE&#160;&#160; is nearly constant in time during emissions for these climate models, but its value&#160;&#160; differs between individual models. The near constancy of this climate metric is due to a strengthening in the surface warming per unit radiative forcing, involving a weakening in both the climate feedback parameter and&#160;&#160; fraction of radiative forcing warming the ocean interior, which are compensated by a weakening in the radiative forcing per unit carbon emission from the radiative forcing saturating with increasing atmospheric CO2. Inter-model differences in the TCRE are mainly controlled by the&#160;&#160; surface warming response to radiative forcing with large inter-model differences in physical climate feedbacks dominating over smaller, partly compensating differences in ocean heat uptake. Inter-model differences in the radiative forcing per unit carbon emission&#160;&#160; provide smaller inter-model differences in the TCRE, which are mainly due to differences in the ratio of the radiative forcing and change in atmospheric CO2 rather than from differences in the airborne fraction.&#160;&#160;&#160;&#160; Hence, providing tighter constraints in the climate projections for the TCRE during emissions requires improving estimates of the physical climate feedbacks,&#160;&#160; the rate of ocean&#160;&#160; heat uptake, and how the radiative forcing saturates with atmospheric CO2.

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The Effect of Ocean Ventilation on the Transient Climate Response to Emissions

Journal of Climate ◽

10.1175/jcli-d-18-0829.1 ◽

2019 ◽

Vol 32 (16) ◽

pp. 5085-5105 ◽

Cited By ~ 5

Author(s):

Anna Katavouta ◽

Richard G. Williams ◽

Philip Goodwin

Keyword(s):

Southern Ocean ◽

Time Scales ◽

Mixed Layer ◽

Carbon Emissions ◽

Deep Ocean ◽

Climate Response ◽

Transient Climate Response ◽

Surface Warming ◽

Ocean Ventilation ◽

Meridional Overturning

Abstract The surface warming response to carbon emissions is affected by how the ocean sequesters excess heat and carbon supplied to the climate system. This ocean uptake involves the ventilation mechanism, where heat and carbon are taken up by the mixed layer and transferred to the thermocline and deep ocean. The effect of ocean ventilation on the surface warming response to carbon emissions is explored using simplified conceptual models of the atmosphere and ocean with and without explicit representation of the meridional overturning. Sensitivity experiments are conducted to investigate the effects of (i) mixed layer thickness, (ii) rate of ventilation of the ocean interior, (iii) strength of the meridional overturning, and (iv) extent of subduction in the Southern Ocean. Our diagnostics focus on a climate metric, the transient climate response to carbon emissions (TCRE), defined by the ratio of surface warming to the cumulative carbon emissions, which may be expressed in terms of separate thermal and carbon contributions. The variability in the thermal contribution due to changes in ocean ventilation dominates the variability in the TCRE on time scales from years to centuries, while that of the carbon contribution dominates on time scales from centuries to millennia. These ventilated controls are primarily from changes in the mixed layer thickness on decadal time scales, and in the rate of ventilated transfer from the mixed layer to the thermocline and deep ocean on centennial and millennial time scales, which is itself affected by the strength of the meridional overturning and extent of subduction in the Southern Ocean.

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Quantifying non-CO2 contributions to remaining carbon budgets

npj Climate and Atmospheric Science ◽

10.1038/s41612-021-00203-9 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Stuart Jenkins ◽

Michelle Cain ◽

Pierre Friedlingstein ◽

Nathan Gillett ◽

Tristram Walsh ◽

...

Keyword(s):

Global Warming ◽

Confidence Interval ◽

Carbon Emissions ◽

Radiative Forcing ◽

Two Dimensional ◽

Climate Response ◽

Carbon Budgets ◽

Special Report ◽

Transient Climate Response ◽

The Impact

AbstractThe IPCC Special Report on 1.5 °C concluded that anthropogenic global warming is determined by cumulative anthropogenic CO2 emissions and the non-CO2 radiative forcing level in the decades prior to peak warming. We quantify this using CO2-forcing-equivalent (CO2-fe) emissions. We produce an observationally constrained estimate of the Transient Climate Response to cumulative carbon Emissions (TCRE), giving a 90% confidence interval of 0.26–0.78 °C/TtCO2, implying a remaining total CO2-fe budget from 2020 to 1.5 °C of 350–1040 GtCO2-fe, where non-CO2 forcing changes take up 50 to 300 GtCO2-fe. Using a central non-CO2 forcing estimate, the remaining CO2 budgets are 640, 545, 455 GtCO2 for a 33, 50 or 66% chance of limiting warming to 1.5 °C. We discuss the impact of GMST revisions and the contribution of non-CO2 mitigation to remaining budgets, determining that reporting budgets in CO2-fe for alternative definitions of GMST, displaying CO2 and non-CO2 contributions using a two-dimensional presentation, offers the most transparent approach.

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