Global impacts of recent Southern Ocean cooling

Proceedings of the National Academy of Sciences, Journal Year: 2023, Volume and Issue: 120(30)

Published: July 17, 2023

Since the beginning of satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed cooling has previously been reported to minimal impact on tropical Pacific, efficiency this teleconnection recently shown be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model intercomparison paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and other SST anomalies constrained follow observations. We reveal in stronger (and more realistic) feedbacks, including Antarctic sea-ice expansion, southeastern Pacific cooling, northward-shifted Hadley circulation, Aleutian low weakening, North Our results therefore suggest decrease might contributed cooler conditions eastern recent decades.

Language: Английский

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Colder Eastern Equatorial Pacific and Stronger Walker Circulation in the Early 21st Century: Separating the Forced Response to Global Warming From Natural Variability

Geophysical Research Letters, Journal Year: 2023, Volume and Issue: 50(3)

Published: Jan. 21, 2023

Abstract Since the early 1990s Pacific Walker circulation shows a multi‐decadal strengthening, which contradicts future model projections. Whether this trend, evident in many climate indices especially before 2015 El Niño, reflects coupled ocean‐atmosphere response to global warming or negative phase of Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature trends during 1980–2020 are dominated by three signals: spatially uniform PDO pattern, and Northern Hemisphere‐Indo‐West pattern. The latter closely resembles transient ocean thermostat‐like emerging subset CMIP6 models, cooling central‐eastern equatorial but western tropical Indian Ocean. Together with PDO, pattern drives strengthening band. Historical simulations appear underestimate contributing models' inability replicate cell strengthening.

Language: Английский

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Origin, importance, and predictive limits of internal climate variability

Environmental Research Climate, Journal Year: 2023, Volume and Issue: 2(2), P. 023001 - 023001

Published: April 21, 2023

Abstract Adaptation to climate change has now become a necessity for many regions. Yet, adaptation planning at regional scales over the next few decades is challenging given contingencies originating from combination of different sources projection uncertainty, chief among them internal variability. Here, we review causes and consequences variability, how it can be quantified accounted in uncertainty assessments, what research questions remain most pertinent better understand its predictive limits science society. This perspective argues putting variability into spotlight intensifying collaborations between modeling application communities.

Language: Английский

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Possible shift in controls of the tropical Pacific surface warming pattern

Nature, Journal Year: 2024, Volume and Issue: 630(8016), P. 315 - 324

Published: June 12, 2024

Language: Английский

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Sea-surface temperature pattern effects have slowed global warming and biased warming-based constraints on climate sensitivity

Proceedings of the National Academy of Sciences, Journal Year: 2024, Volume and Issue: 121(12)

Published: March 11, 2024

The observed rate of global warming since the 1970s has been proposed as a strong constraint on equilibrium climate sensitivity (ECS) and transient response (TCR)—key metrics to greenhouse-gas forcing. Using CMIP5/6 models, we show that inter-model relationship between these (the basis for constraint) arises from similarity in patterns within producing an effective (EffCS) governing recent is comparable value ECS long-term under CO 2 However, historical simulations do not reproduce patterns. When driven by patterns, even high models produce low EffCS values consistent with rate. inability thus results bias modeled sensitivity. Correcting this means wide ranges TCR extending higher than previously recognized. These findings are corroborated energy balance model coupled (CESM1-CAM5) better replicate via tropospheric wind nudging or Antarctic meltwater fluxes. Because fail simulate warming-based constraints ECS, TCR, projected biased low. reinforce unique pattern slowed global-mean over decades how will evolve future represents major source uncertainty projections.

Language: Английский

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Contribution of anthropogenic aerosols to persistent La Niña-like conditions in the early 21st century

Proceedings of the National Academy of Sciences, Journal Year: 2024, Volume and Issue: 121(5)

Published: Jan. 22, 2024

The discrepancy between the observed lack of surface warming in eastern equatorial Pacific and climate model projections an El Niño-like pattern confronts research community. While anthropogenic aerosols have been suggested as a cause, prolonged cooling trend over appears conflict with Northern Hemisphere aerosol emission reduction since 1980s. Here, using CESM, we show that superposition fast slow responses to change—an increase followed by decrease—can sustain La Niña-like condition for longer time than expected. rapid adjustment Hadley Cell triggers joint feedback low clouds, wind, evaporation, sea temperature Southeast Pacific, leading wedge-shaped extends central Pacific. Meanwhile, northern subtropical cell gradually intensifies, resulting subsurface lasts decades.

Language: Английский

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Opinion: Why all emergent constraints are wrong but some are useful – a machine learning perspective

Atmospheric chemistry and physics, Journal Year: 2025, Volume and Issue: 25(4), P. 2365 - 2384

Published: Feb. 21, 2025

Abstract. Global climate change projections are subject to substantial modelling uncertainties. A variety of emergent constraints, as well several other statistical model evaluation approaches, have been suggested address these However, they remain heavily debated in the science community. Still, central idea relate future already observable quantities has no real substitute. Here, we highlight validation perspective predictive skill machine learning community a promising alternative viewpoint. Specifically, argue for quantitative approaches which each constraining relationship can be evaluated comprehensively based on out-of-sample test data – top qualitative physical plausibility arguments that commonplace justification new constraints. Building this perspective, review ideas types controlling-factor analyses (CFAs). The principal behind CFAs is use find climate-invariant relationships historical hold approximately under strong scenarios. On basis existing archives, validated perfect-climate-model frameworks. From such three reasons: (a) objectively both past and data, (b) provide more direct and, by design, physically plausible links between observations potential climates, (c) take high-dimensional complex into account functions learned constrain response. We demonstrate advantages two recently published CFA examples form constraints feedback mechanisms (clouds, stratospheric water vapour) discuss further challenges opportunities using example rapid adjustment mechanism (aerosol–cloud interactions). avenues work, including strategies non-linearity, tackle blind spots ensembles, integrate helpful priors Bayesian methods, leverage physics-informed learning, enhance robustness through causal discovery inference.

Language: Английский

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Antarctic Ice‐Sheet Meltwater Reduces Transient Warming and Climate Sensitivity Through the Sea‐Surface Temperature Pattern Effect

Geophysical Research Letters, Journal Year: 2022, Volume and Issue: 49(24)

Published: Dec. 14, 2022

Abstract Coupled global climate models (GCMs) generally fail to reproduce the observed sea‐surface temperature (SST) trend pattern since 1980s. The model‐observation discrepancies may arise in part from lack of realistic Antarctic ice‐sheet meltwater input GCMs. Here we employ two sets CESM1‐CAM5 simulations forced by anomalous fluxes over 1980–2013 and through 21st century. Both show a reduced warming rate an SST that better resembles observations. drives surface cooling Southern Ocean tropical southeast Pacific, turn increasing low‐cloud cover driving radiative feedbacks become more stabilizing (corresponding lower effective sensitivity). These feedback changes can contribute as substantially ocean heat uptake efficiency reducing rate. Accurately projecting historical future thus requires improved representation its impacts.

Language: Английский

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The future of the El Niño–Southern Oscillation: using large ensembles to illuminate time-varying responses and inter-model differences

Earth System Dynamics, Journal Year: 2023, Volume and Issue: 14(2), P. 413 - 431

Published: April 14, 2023

Abstract. Future changes in the El Niño–Southern Oscillation (ENSO) are uncertain, both because future projections differ between climate models and large internal variability of ENSO clouds diagnosis forced observations individual model simulations. By leveraging 14 single initial-condition ensembles (SMILEs), we robustly isolate time-evolving response sea surface temperature (SST) to anthropogenic forcing from each SMILE. We find nonlinear time many considerable inter-model differences projected mean-state tropical Pacific zonal SST gradient. demonstrate a linear relationship change gradient, although gradient often occur later 21st century than variability, which can lead departures relationship. Single-forcing SMILEs show potential contribution (aerosols greenhouse gases) historical while observed strengthening sits on edge spread for those single-forcing available. Our results highlight value investigating time-dependent responses projections. The found importance characterizing this behavior, as it implies that impacts may vary dramatically throughout century.

Language: Английский

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Steady global surface warming from 1973 to 2022 but increased warming rate after 1990

Communications Earth & Environment, Journal Year: 2023, Volume and Issue: 4(1)

Published: Nov. 1, 2023

Abstract The change in global mean surface temperature is a crucial and broadly used indicator of the evolution climate change. Any decadal scale changes warming rate are however obfuscated by internal variability. Here we show that increase through recent La Nina influenced years (2022) consistent with 50-year trend 0.18 °C/decade. We use an Earth System Model based tool to filter out modulations sea-surface patterns find rates four major data series. However, also clear indications, all observational series, step-up since around 1990. CMIP6 models generally do not capture this observed combination long-term increase.

Language: Английский

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