Causes of Higher Climate Sensitivity in CMIP6 Models

Geophysical Research Letters, Journal Year: 2020, Volume and Issue: 47(1)

Published: Jan. 3, 2020

Abstract Equilibrium climate sensitivity, the global surface temperature response to CO doubling, has been persistently uncertain. Recent consensus places it likely within 1.5–4.5 K. Global models (GCMs), which attempt represent all relevant physical processes, provide most direct means of estimating sensitivity via quadrupling experiments. Here we show that closely related effective increased substantially in Coupled Model Intercomparison Project phase 6 (CMIP6), with values spanning 1.8–5.6 K across 27 GCMs and exceeding 4.5 10 them. This (statistically insignificant) increase is primarily due stronger positive cloud feedbacks from decreasing extratropical low coverage albedo. Both these are tied representation clouds CMIP6 lead weaker responses cover water content unforced variations temperature. Establishing plausibility higher imperative given their implied societal ramifications.

Language: Английский

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Presentation and Evaluation of the IPSL‐CM6A‐LR Climate Model

Journal of Advances in Modeling Earth Systems, Journal Year: 2020, Volume and Issue: 12(7)

Published: May 28, 2020

Abstract This study presents the global climate model IPSL‐CM6A‐LR developed at Institut Pierre‐Simon Laplace (IPSL) to natural variability and response anthropogenic forcings as part of sixth phase Coupled Model Intercomparison Project (CMIP6). article describes different components, their coupling, simulated in comparison previous versions. We focus here on representation physical along with main characteristics carbon cycle. The model's climatology, assessed from a range metrics (related particular radiation, temperature, precipitation, wind), is strongly improved Although they are reduced, number known biases shortcomings (e.g., double Intertropical Convergence Zone [ITCZ], frequency midlatitude wintertime blockings, El Niño–Southern Oscillation [ENSO] dynamics) persist. equilibrium sensitivity transient have both increased IPSL‐CM5A‐LR used CMIP5. A large ensemble more than 30 members for historical period (1850–2018) smaller emissions scenarios (until 2100 2300) also presented discussed.

Language: Английский

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UKESM1: Description and Evaluation of the U.K. Earth System Model

Journal of Advances in Modeling Earth Systems, Journal Year: 2019, Volume and Issue: 11(12), P. 4513 - 4558

Published: Oct. 31, 2019

We document the development of first version U.K. Earth System Model UKESM1. The model represents a major advance on its predecessor HadGEM2-ES, with enhancements to all component models and new feedback mechanisms. These include core physical well-resolved stratosphere; terrestrial biogeochemistry coupled carbon nitrogen cycles enhanced land management; tropospheric-stratospheric chemistry allowing holistic simulation radiative forcing from ozone, methane, nitrous oxide; two-moment, five-species, modal aerosol; ocean two-way coupling cycle atmospheric aerosols. complexity between ocean, land, atmosphere climate biogeochemical in UKESM1 is unprecedented for an system model. describe detail process by which was developed tuned achieve acceptable performance key quantities discuss challenges involved mitigating biases complex connections components. Overall, performs well, stable pre-industrial state good agreement observations latter period historical simulations. However, global mean surface temperature exhibits stronger-than-observed cooling 1950 1970, followed rapid warming 1980 2014. Metrics idealized simulations show high sensitivity relative previous generations models: Equilibrium 5.4 K, transient response ranges 2.68 2.85 cumulative emissions 2.49 2.66 K TtC−1.

Language: Английский

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An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence

Reviews of Geophysics, Journal Year: 2020, Volume and Issue: 58(4)

Published: July 22, 2020

We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective S. This includes feedback process understanding, the historical record, and paleoclimate record. An S value lower than 2 K is difficult reconcile with any three lines evidence. The amount cooling during Last Glacial Maximum provides strong against values greater 4.5 K. Other in combination also show that this relatively unlikely. use a Bayesian approach produce probability density function (PDF) for given all evidence, including tests robustness difficult-to-quantify uncertainties different priors. 66% range 2.6–3.9 our Baseline calculation remains within 2.3–4.5 under tests; corresponding 5–95% ranges are 2.3–4.7 K, bounded 2.0–5.7 (although such high-confidence should be regarded more cautiously). indicates stronger constraint on reported past assessments, lifting low end range. narrowing occurs because agree judged largely independent confidence understanding processes combining identify promising avenues further S, particular using comprehensive models address limitations traditional forcing-feedback paradigm interpreting changes.

Language: Английский

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Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models

Science Advances, Journal Year: 2020, Volume and Issue: 6(26)

Published: June 24, 2020

A historical context is provided for interpreting the equilibrium climate sensitivity (ECS) and transient response (TCR).

Language: Английский

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Confronting the Challenge of Modeling Cloud and Precipitation Microphysics

Journal of Advances in Modeling Earth Systems, Journal Year: 2020, Volume and Issue: 12(8)

Published: May 11, 2020

In the atmosphere, microphysics refers to microscale processes that affect cloud and precipitation particles is a key linkage among various components of Earth's atmospheric water energy cycles. The representation microphysical in models continues pose major challenge leading uncertainty numerical weather forecasts climate simulations. this paper, problem treating divided into two parts: (i) how represent population particles, given impossibility simulating all individually within cloud, (ii) uncertainties process rates owing fundamental gaps knowledge physics. recently developed Lagrangian particle-based method advocated as way address several conceptual practical challenges representing particle populations using traditional bulk bin parameterization schemes. For addressing critical physics knowledge, sustained investment for observational advances from laboratory experiments, new probe development, next-generation instruments space needed. Greater emphasis on work, which has apparently declined over past decades relative other areas research, argued be an essential ingredient improving process-level understanding. More systematic use natural observations constrain schemes also advocated. Because it generally difficult quantify individual these directly, presents inverse can viewed standpoint Bayesian statistics. Following idea, probabilistic framework proposed combines elements statistical physical modeling. Besides providing rigorous constraint schemes, there added benefit quantifying systematically. Finally, broader hierarchical approach accelerate improvements leveraging described paper related modeling (using schemes), experimentation, observations, methods.

Language: Английский

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Framing, Context, and Methods

Cambridge University Press eBooks, Journal Year: 2023, Volume and Issue: unknown, P. 147 - 286

Published: June 29, 2023

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Language: Английский

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Latest climate models confirm need for urgent mitigation

Nature Climate Change, Journal Year: 2019, Volume and Issue: 10(1), P. 7 - 10

Published: Dec. 2, 2019

Language: Английский

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Quantifying Progress Across Different CMIP Phases With the ESMValTool

Journal of Geophysical Research Atmospheres, Journal Year: 2020, Volume and Issue: 125(21)

Published: Oct. 19, 2020

Abstract More than 40 model groups worldwide are participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), providing a new and rich source of information to better understand past, present, future climate change. Here, we use Earth System Evaluation Tool (ESMValTool) assess performance CMIP6 ensemble compared previous generations CMIP3 CMIP5. While CMIP5 models did not capture observed pause increase global mean surface temperature between 1998 2013, historical simulations agree well with recent increase, but some have difficulties reproducing record second half twentieth century. systematic biases annual precipitation remain multimodel mean, individual high‐resolution versions show significant reductions many long‐standing biases. Some improvements also found vertical temperature, water vapor, zonal wind speed distributions, root‐mean‐square errors for selected fields generally smaller reduced intermodel spread higher average skill correlation patterns relative observations. An emerging property is effective sensitivity an increased range 2.3 5.6 K. A possible reason this cloud representation resulting stronger shortwave feedbacks their predecessor versions.

Language: Английский

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Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles

Atmospheric chemistry and physics, Journal Year: 2021, Volume and Issue: 21(2), P. 665 - 679

Published: Jan. 18, 2021

Abstract. Shallow clouds covering vast areas of the world's middle- and high-latitude oceans play a key role in dampening global temperature rise associated with CO2. These clouds, which contain both ice supercooled water, respond to warming world by transitioning state more liquid water greater albedo, resulting negative “cloud-phase” climate feedback component. Here we argue that magnitude cloud-phase component depends on amount nature small fraction aerosol particles can nucleate crystals. We propose concerted research effort is required reduce substantial uncertainties related poorly understood sources, concentration, seasonal cycles these ice-nucleating (INPs) their rudimentary treatment models. The topic important because many models may have overestimated feedback, those better representation shallow oceanic predict substantially larger warming. make case understanding present-day INP population cold sector cyclone systems particularly critical for defining cloud phase therefore how also need develop predictive capability future emissions sinks warmer less snow potentially stronger sources.

Language: Английский

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