CDP Annual Workshop 2022
CLIVAR Climate Dynamics Panel
CLIVAR Climate Dynamics Panel (CDP) annual workshop:
External versus internal variability on decadal and longer time scales
Session 1: Isolate the relative contributions of external and internal variability to observed decadal and longer variability
Session 2: Modulation of internal variability by external forcings
Session 3: Progress in narrowing observational and modeling uncertainties in external and internal variability
Session 4: Effects of external and internal variability on extreme events
More info: https://www.clivar.org/events/clivar-climate-dynamics-panel-cdp-annual-workshop-external-versus-internal-variability
Filter displayed posters (113 keywords)
timeslot2 (27)
ECS (23)
timeslot1 (12)
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Internal variability (3)
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2C target year (1)
AMOC (1)
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Antarctic sea ice (1)
Arctic (1)
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Arctic Sea-ice and Arctic Amplification (1)
Atlantic Multidecadal Variability (1)
Atlantic Multidecadal Variability (AMV) (1)
Beaufort Sea High (1)
CESM LENS (1)
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Greenland blocking (1)
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North Atlantic Oscillation (1)
North Atlantic Oscillation (NAO) (1)
Northward heat transport (1)
PDO (1)
Pacemaker eksperiments (1)
Pacific Decadal Variability (1)
Past climates (1)
Pinatubo (1)
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Predictability (1)
RCM simulation large ensemble (1)
Rainfall Onset & Cessation (1)
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SST (1)
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Sahel (1)
Seasonal to Decadal (1)
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bayesian inference (1)
carbon (1)
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coupled feedbacks (1)
decadal trends (1)
decadal variability (1)
detectability (1)
emergence (1)
external Forcing (1)
global warming (1)
inter-model diversity (1)
interdecadal variability (1)
internal variability (1)
intrabasin teleconnections (1)
jet stream (1)
large-ensemble runs (1)
multi year climate prediction (1)
nonlinear climate change (1)
observational coonstraint (1)
ocean (1)
oxygen (1)
rainfall (1)
rainfall decline (1)
regional climate change (1)
sea-level rise (1)
signal emergence (1)
simple climate models (1)
stratosphere (1)
surface solar radiation (1)
teleconnection (1)
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tropical Pacific (1)
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tropical-Arctic teleconnections (1)
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Show Posters:
▼ Session 1 Back to top
The Nonlinear Northern Hemisphere Stratospheric Temperature Response to External Radiative Forcing in Decadal Climate Simulations
Abdullah A. Fahad, Andrea Molod, Dimitris Menemenlis, Patrick Heimbach, Atanas Trayanov, Ehud Strobach, Lawrence Coy, Krzysztof Wargan
Abstract
To predict the future climate on multiyear timescales, it is crucial to understand how the changing external radiative forcing (CO2 and Ozone) drives the climate and impacts the skill of intra-seasonal to multiyear climate prediction. In this study, we use a 1-degree configuration of the GEOS-MITgcm coupled general circulation model to understand the response to different levels of observed external forcing from past decades. We ran `perpetual' experiments for 1992, 2000, and 2020, each with their respective year’s external forcing. Results of the perpetual simulations showed that the Northern Hemisphere polar stratospheric temperature increases from 1992 to 2000, whereas it decreases from 2000 to 2020. We further conducted a 10-member ensemble of transient climate simulations for the 1992-2020 period with observed external forcing and found a similar positive temperature trend from 1992 to 2000 and a negative trend from 2000 to 2020. This is in contrast to the general expectation that the stratosphere cools as CO2 increases. A similar opposing pattern of temperature trends exists in reanalyses and CMIP6 historical simulations with a well-resolved stratosphere. Analysis of the results showed that the external forcing change during the years 1992-2000 increases the tropical diabatic heating, and intensifies the wave activity related meridional heat transport to the Northern Hemisphere mid to high-latitudes, which, in turn, increases the polar stratospheric temperature. In contrast, during the 2000-2020 period the meridional heat transport decreases, contributing to a decrease in the polar stratospheric temperature. The long-wave radiation change in these periods responds to the changing temperature and so doesn't play a significant role in driving them.
Presented by
Abdullah A. Fahad
<a.fahad@nasa.gov>
Institution
NASA Goddard Space Flight Center, GMAO, MD, US
Keywords
stratosphere, Seasonal to Decadal, multi year climate prediction, nonlinear climate change, ECS, timeslot2
Separating internal and external global temperature variability using a Bayesian stochastic energy balance framework
Beatrice Ellerhoff, Maybritt Schillinger, Robert Scheichl, Kira Rehfeld
Abstract
Climate variability is of vital importance for living conditions on Earth. Underlying mechanisms and the relative contribution of externally-forced and internally-generated temperature variability remain partly elusive, especially on decadal to centennial timescales. However, there is a lack of easily applicable and robust numerical frameworks to isolate different contributions to climate variability across timescales. We present a novel approach to separate internal and externally-forced temperature variations by combining conceptual climate models with Bayesian inference and spectral methods. Presenting the “ClimBayes” software package in R, we emulate the internal and externally-forced variability of global temperature for a set of climate model simulations for the last millennium. Our physics-informed emulation approximates the target variability closely and allows us to contrast contributions to the variance on interannual to centennial scales, and from climate models of varying complexity. We expect our developed framework to help diagnose different contributions to climate variability across scales and, therefore, advance reliable simulations of long-term variability.
Presented by
Beatrice Ellerhoff
<beatrice-marie.ellerhoff@uni-tuebingen.de>
Institution
Geo- and Environmental Research Center, University of Tübingen, Germany
Other Affiliations
Seminar for Statistics of the Department of Mathematics at ETH Zurich, Institute of Applied Mathematics and Interdisciplinary Center for Scientific Computing (IWR) at Heidelberg University
Keywords
climate variability, bayesian inference, simple climate models, ECS, timeslot1
Internally Generated and Externally Forced Multidecadal Oceanic Modes and Their Influence on the Summer Rainfall over East Asia
Dong Si and Aixue Hu
Abstract
By analyzing simulations from a unique Community Earth System Model (CESM) Large Ensemble (CESM-LE) project, it is shown that the interdecadal Pacific oscillation (IPO) is primarily an internally generated oceanic variability, while the Atlantic multidecadal oscillation (AMO) may be an oceanic variability generated by internal oceanic processes and modulated by external forcing in the twentieth century. Although the observed relationship between IPO and the Yangtze–Huaihe River valley (YHRV) summer rainfall in China is well simulated in both the preindustrial control and the twentieth-century ensemble simulation, none of the twentieth-century ensemble members can reproduce the observed time evolution of both the IPO and YHRV rainfall on multidecadal time scales. On the other hand, although CESM-LE cannot reproduce the observed relationship between the AMO and Huanghe River valley (HRV) summer rainfall of China in the preindustrial control simulation, this relationship in the twentieth-century simulations is well reproduced, indicating the important role of the interaction between the internal processes and the external forcing to realistically simulate the AMO and HRV rainfall.
Presented by
Dong Si
Institution
Institute of Atmospheric Physics, Chinese Academy of Sciences
Other Affiliations
CGD/NCAR
Keywords
timeslot1
Unforced Trends and Variability of Surface Solar Radiation
Doris Folini, Boriana Chtirkova, Lucas Ferreira Correa, Martin Wild
Abstract
Surface solar radiation (SSR) is a of key relevance for the surface energy balance of the planet. It is well documented that SSR varies on decadal time scales. In Europe, for example, observations show a decreasing trend of SSR from the 1960s to the 1980s, followed by an increasing trend in subsequent decades. Changing anthoropgenic aerosol emissions are an accepted, major contribution to these variations. More debated is the contribution of internal variability to these observed, decadal scale changes.
Using CMIP pre-industrial control simulations it can be shown that the statistical properties of annual mean SSR are such that the standard deviation of the time series and decadal trends of the time series are closely related. The probability of occurrence of a trend of any length and strength can then be estimated based on the standard deviation of the time series. Statistical properties of much shorter observed SSR time series are in line with modeled time series, allowing to link the model results to real world data. The model results can then be used to estimate potential contributions from internal variability to observed decadal scale trends.
Using CMIP pre-industrial control simulations it can be shown that the statistical properties of annual mean SSR are such that the standard deviation of the time series and decadal trends of the time series are closely related. The probability of occurrence of a trend of any length and strength can then be estimated based on the standard deviation of the time series. Statistical properties of much shorter observed SSR time series are in line with modeled time series, allowing to link the model results to real world data. The model results can then be used to estimate potential contributions from internal variability to observed decadal scale trends.
Presented by
Doris Folini
Institution
ETH Zurich, Institute for Atmospheric and Climate Science
Keywords
surface solar radiation, internal variability, decadal trends, timeslot2
The Mount Pinatubo “Gulp” Long-lasting impacts on ocean oxygen and carbon
Amanda R. Fay, Galen A. McKinley*, Nicole S. Lovenduski, Yassir Eddebbar, Michael N. Levy, Matthew C. Long, Holly Olivarez, Rea R. Rustagi
Abstract
It is well known that large volcanic eruptions drive significant climate perturbations such as major anomalies in surface radiative fluxes and widespread cooling of the upper ocean, and recent studies suggest that these eruptions also drive important variability in air-sea carbon and oxygen fluxes. Using the CESM Large Ensemble framework, we isolate impacts on ocean carbon and oxygen from Mt. Pinatubo’s June 1991 eruption. Mt Pinatubo forced significant trends in surface fluxes and especially in interior inventories of heat, carbon and oxygen. Changes last multiple years in the upper ocean and permanently modify integrated ocean heat, carbon and oxygen inventories. Oxygen anomalies appear immediately post-eruption and penetrate to the deep ocean. In contrast, the response of carbon takes 2-3 years to fully emerge, and the impact is focused in the upper 150m. Additionally, we see the eruption’s impact on oxygen is dominant in both the tropics and northern high latitudes, likely due to ventilation. The carbon signal is predominantly surface bound and focused in the tropics, likely driven by solubility changes and with strong links to ENSO variability forced by the eruption. In the Southern Ocean, we find only modest forced impacts on the oxygen and carbon inventories.
Presented by
Galen McKinley
Institution
Columbia University and Lamont-Doherty Earth Observatory
Other Affiliations
U. Colorado, Boulder; NCAR; Scripps
Keywords
Volcano, Pinatubo, CESM LENS, ocean, carbon, oxygen, timeslot2
Investigating the forced and free global-mean surface temperature variations in CMIP6 historical simulations
Harun A. Rashid
Abstract
Estimating the near-term anthropogenic climate change signal has many policy implications, yet this has proven to be difficult because of the presence of large internal climate variability (ICV). Many studies have attempted to estimate the anthropogenic signal, mainly by ensemble averaging climate and earth system model simulations. However, the signal thus estimated contains both the anthropogenic signal and the externally forced natural variability. Here, we develop a multiple linear regression (MLR) model to efficiently decompose the historical global mean surface-air temperatures (GMSTs) into its forced and free components. The forced component is then further separated into the anthropogenic and naturally forced signals and the free component into contributions from Pacific and North Atlantic ICV. We apply this method to GMSTs from observations and an ensemble of CMIP6 simulations. We find that the anthropogenic signal explains 83% of the observed GMST variance over the historical period. Most CMIP6 models underestimate this anthropogenic contribution (median explained variance is 67%), but compare better with observations when the North Atlantic regional contribution is included in the anthropogenic signal (median 77%). The ICV contributions to the GMST variance are ~8% for observations and ~7% for the models (median). The models’ GMST responses to the external forcings and ICV vary widely, with the two responses being oppositely related (r=-0.89). The North Atlantic drives the free GMST variability in observations, whereas the Pacific drives this in most CMIP6 models due to stronger than observed simulated GMST-Pacific ICV relationships.
Presented by
Harun Rashid
<harun.rashid@csiro.au>
Institution
CSIRO Oceans and Atmosphere, Melbourne, Australia
Keywords
timeslot1
Two Distinct Modes of Climate Responses to the Anthropogenic Aerosol Forcing Changes
Jia-Rui Shi; Young-Oh Kwon; Susan Wijffels
Abstract
Unlike greenhouse gases (GHGs), anthropogenic aerosol (AA) concentrations have increased and then decreased over the past century or so, with the timing of the peak concentration varying in different regions. To date, it has been challenging to separate the climate impact of AAs from that due to GHGs and background internal variability. We use a pattern recognition method, taking advantage of spatiotemporal covariance information, to isolate the forced patterns for the surface ocean and associated atmospheric variables from the all-but-one forcing Community Earth System Model ensembles. We find that the aerosol-forced responses are dominated by two leading modes, with one associated with the historical increase and future decrease of global mean aerosol concentrations (dominated by the Northern Hemisphere sources) and the other due to the transition of the primary sources of AA from the west to the east and also from Northern Hemisphere extratropical regions to tropical regions. In particular, the aerosol transition effect, to some extent compensating the global mean effect, exhibits a zonal asymmetry in the surface temperature and salinity responses. We also show that this transition effect dominates the total AA effect during recent decades, e.g., 1967–2007.
Presented by
Jia-Rui Shi
Institution
Woods Hole Oceanographic Institution
Keywords
ECS, timeslot2
The role of external forcing for centennial climate variability
Juergen Bader and Johann Jungclaus
Abstract
Knowledge of the amplitude and causes of surface temperature variability is essential for attributing and predicting temperature changes.
Instrumental temperature records are too short to reliably determine surface temperature variability on multidecadal and centennial time-scales.
Unfortunately, variability estimates using proxy data and climate model simulations do not agree in magnitude, with simulations showing substantially smaller variability.
Here we show that two transient Holocene climate simulations - performed with the same climate model - differ significantly in terms of the amplitude of temperature variability on long time-scales.
The difference in the centennial variability between the two integrations is due to the external forcing. While both simulations are driven with orbital and greenhouse gas forcing, one simulation
is additionally forced by stratospheric volcanic aerosol distribution and spectral variations of solar irradiance.
Our results provide an indication of possible causes for the amplitude differences between proxy and model based temperature variability on long time scales.
Presented by
Juergen Bader
Institution
Max-Planck-Institut fuer Meteorologie
Keywords
external Forcing, climate variability, volcano
Pacific contributions to decadal surface temperature trends in the Arctic during the 20th century
Lea Svendsen, Noel Keenlyside, Morven Muilwijk, Ingo Bethke, Nour-Eddine Omrani, Yongqi Gao
Abstract
Instrumental records suggest multidecadal variability in Arctic surface temperature throughout the twentieth century. This variability is caused by a combination of external forcing and internal variability, but their relative importance remains unclear. Since the early twentieth century Arctic warming has been linked to decadal variability in the Pacific, we hypothesize that the Pacific could impact decadal temperature trends in the Arctic throughout the twentieth century. To investigate this, we compare two ensembles of historical all-forcing twentieth century simulations with the Norwegian Earth System Model (NorESM): (1) a fully coupled ensemble and (2) a wind-stress pacemaker ensemble where momentum flux anomalies from reanalysis are prescribed over the Indo-Pacific Ocean to constrain Pacific sea surface temperature variability. By comparing these two ensembles, we isolate the externally forced signal from that forced by Pacific variability. We find that the combined effect of tropical and extratropical Pacific decadal variability can explain up to ~ 50% of the observed decadal surface temperature trends in the Arctic. The Pacific-Arctic connection involves both lower tropospheric horizontal advection and subsidence-induced adiabatic heating, mediated by Aleutian Low variations. This link is detected across the twentieth century, but the response in Arctic surface temperature is moderated by external forcing and surface feedbacks. Our results also indicate that increased ocean heat transport from the Atlantic to the Arctic could have compensated for the impact of a cooling Pacific at the turn of the twenty-first century. These results have implications for understanding the present Arctic warming and future climate variations.
Presented by
Lea Svendsen
<lea.svendsen@uib.no>
Institution
Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Norway, ECS, timeslot2
Keywords
Pacific Decadal Variability, Arctic, teleconnections, Pacemaker eksperiments, decadal variability, ECS, timeslot2
Revisiting the existence of the global warming slowdown during the early 21st century
Meng Wei, Zhenya Song, Qi Shu, Xiaodan Yang, Yajuan Song, Fangli Qiao*
Abstract
There are heated debates on the existence of the global warming slowdown during the early twenty-first century. Although efforts have been made to clarify or reconcile the controversy over this issue, it is not explicitly addressed, restricting the understanding of global temperature change particularly under the background of increasing greenhouse gas concentrations. Here, using extensive temperature datasets, we comprehensively reexamine the existence of the slowdown under all existing definitions during all decadal-scale periods spanning 1990–2017. Results show that the short-term linear trend–dependent definitions of slowdown make its identification severely suffer from the period selection bias, which largely explains the controversy over its existence. Also, the controversy is further aggravated by the significant impacts of the differences between various datasets on the recent temperature trend and the different baselines for measuring slowdown prescribed by various definitions. However, when the focus is shifted from specific periods to the probability of slowdown events, we find the probability is significantly higher in the 2000s than in the 1990s, regardless of which definition and dataset are adopted. This supports a slowdown during the early twenty-first century relative to the warming surge in the late twentieth century, despite higher greenhouse gas concentrations. Furthermore, we demonstrate that this decadal-scale slowdown is not incompatible with the centennial-scale anthropogenic warming trend, which has been accelerating since 1850 and never pauses or slows. This work partly reconciles the controversy over the existence of the warming slowdown and the discrepancy between the slowdown and anthropogenic warming.
Presented by
Meng Wei
Institution
First Institute of Oceanography and Key Laboratory of Marine Science and Numerical Modeling, Ministry of Natural Resource
Keywords
ECS, timeslot1
Sensitivity of the Middle East and North Africa (MENA) to External and Internal Variability
Muhammad Mubashar Dogar
Abstract
The Middle East and North Africa (MENA) regional climate appears to be extremely sensitive to volcanic eruptions. For example the winter cooling after the 1991 Pinatubo eruption far exceeded the mean hemispheric temperature anomaly, even causing snowfall in Israel. To better understand MENA climate variability, the climate responses to the El Chichón and Pinatubo volcanic eruptions are analyzed using observations, National Centers for Environmental Prediction Climate Forecast System Reanalysis, and the output from the Geophysical Fluid Dynamics Laboratory’s High-Resolution Atmospheric Model. A multiple regression analysis both for the observations and the model output is performed to separate out the contributions from climate trends, El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian summer monsoon, and volcanic aerosols. Strong regional temperature and precipitation responses over the MENA region are found in both winter (DJF) and summer (JJA). The model and the observations both show that a positive NAO and ENSO amplify the MENA volcanic winter cooling. In boreal summer, the patterns of changing temperature and precipitation suggest a weakening and southward shift of the Intertropical Convergence Zone, caused by volcanic surface cooling and post-eruption weakening of the Indian and West African monsoons. The model captures the main features of the climate response; however, it underestimates the total cooling, especially in winter compared to the observations. The conducted analysis sheds light on the internal mechanisms of MENA climate variability and helps to selectively diagnose the model deficiencies.
Presented by
Muhammad Mubashar Ahmad Dogar
Institution
Faculty of Environmental Earth Science, Hokkaido University, Japan
Keywords
ECS, timeslot2
Coupled stratosphere-troposphere-Atlantic multidecadal oscillation and its importance for near-future climate projection
Nour-Eddine Omrani, Noel Keenlyside, Katja Matthes, Lina Boljka, Davide Zanchettin, Johann H. Jungclaus5 and Sandro W. Lubis
Abstract
Northern Hemisphere (NH) climate has experienced various coherent wintertime multidecadal climate trends in stratosphere, troposphere, ocean, and cryosphere. However, the overall mechanistic framework linking these trends is not well established. Here we show, using long-term transient forced coupled climate simulation, that large parts of the coherent NH-multidecadal changes can be understood within a damped coupled stratosphere/troposphere/ocean-oscillation framework. Wave-induced downward propagating positive stratosphere/troposphere-coupled Northern Annular Mode (NAM) and associated stratospheric cooling initiate delayed thermohaline strengthening of Atlantic overturning circulation and extratropical Atlantic-gyres. These increase the poleward oceanic heat transport leading to Arctic sea-ice melting, Arctic warming amplification, and large-scale Atlantic warming, which in turn initiates wave-induced downward propagating negative NAM and stratospheric warming and therefore reverse the oscillation phase.
This coupled variability improves the performance of statistical models. Using the configuration with the best predictors and assuming that the climate change will continue, the projected near future climate shows further weakening of North Atlantic Oscillation, North Atlantic cooling and hiatus in wintertime North Atlantic-Arctic sea-ice and global surface temperature just like the 1950s–1970s.
Presented by
Nour-Eddine Omrani
Institution
Bjerknes Centre for Climate Research, University of Bergen, Bergen, Norway
Keywords
North Atlantic Oscillation (NAO), Atlantic Multidecadal Variability (AMV), Arctic Sea-ice and Arctic Amplification, Stratosphere/Troposphere coupling. Global warming, timeslot2
Impact of volcanic eruptions in CMIP6 decadal prediction systems: a multi-model analysis.
Bilbao, R., Athanasiadis, P., Hermanson, L., Mignot, J., Nicoli, D., Sospedra-Alfonso, R., Swingedouw, D., Wu, X., Yeager, S., and Ortega, P
Abstract
In recent decades three major volcanic eruptions of different intensity have occurred: Mount Agung (1963), El Chichón (1982) and Mount Pinatubo (1991), with reported climate impacts on seasonal-to-decadal timescales and providing a high prediction potential. The Decadal Climate Prediction Project component C (DCPP-C) includes a protocol to investigate the impact of such volcanic eruptions on decadal prediction, which consists in performing initialised sets of predictions just before the three historical volcanic eruptions, but in which the volcanic aerosol forcing is excluded. The impact of the volcanic eruptions is therefore determined by comparing these new forecasts with those included in the corresponding retrospective prediction experiment DCPP-A, which include historical volcanic aerosol forcing. Here we present the results from six CMIP6 decadal prediction systems (CanESM5, CESM1, EC-Earth3, HadGEM3, IPSL-CM6A and CMCC-CM2-SR5). The global mean temperature cooling is comparable among models and consistent with previous studies. The surface temperature response pattern in the first years is similar across all the models and for the individual volcanic eruptions. At later forecast times (years 6-9), differences among the models and eruptions emerge. Results show that the volcanic eruptions impact the atmospheric and oceanic dynamics, as shown in previous studies, although some differences across models emerge.
Presented by
Roberto Bilbao
Institution
Barcelona Supercomputing Center
Keywords
Climate Prediction, Volcanic Eruptions, ECS, timeslot1
Decrease of the dynamical and spatial variability of the Euro-Atlantic eddy-driven jet stream under global warming
Robin Noyelle, Vivien Guette, Akim Viennet, Davide Faranda
Abstract
The atmospheric eddy-driven jet stream is one of the main features of the mid-latitude climatology. Although zonal in climatological mean, the jet stream meanders at meteorological time scales. The jet and its variability have been under great scrutiny in the past years for their suspected role in the triggering of extreme events in mid-latitude regions. Because of its natural variability, the impact of climate change on the jet remains elusive and discussed. Here we develop a new approach for studying the jet by seeing it as a 1D object. We assess the past dynamical properties of this representation of the jet in ERA5 and ERA20C reanalysis data using new indicators from dynamical system theory. Our results suggest a significant decrease of the dynamical and spatial variabilities of the position of the North Atlantic eddy-driven jet stream with global warming. We also show a small increase in the persistence of the jet. Finally, even after controlling for the natural variability of the climate system we show an increase in the mean latitudinal position and mean speed of the jet.
Presented by
Robin Noyelle
Institution
Laboratoire des Sciences du Climat et de l'Environnement (LSE-IPSL)
Keywords
jet stream, global warming, interdecadal variability, timeslot1
Understanding surface warming trend in East Asia and a role of internal variability
Sae-Yoon Oh, Sang-Wook Yeh, In-Hong Park
Abstract
Recent studies suggest that global warming sensitivity varies on a regional scale, yet there is a large uncertainty to clarify the influences of external forcing and internal variability on regional climate change. Therefore, it is necessary to understand the characteristics of regional scale warming in the observations as well as analyzing climate models. In this study, we analyzed the observed annual-mean surface temperature trends in East Asia for 1900-2021. The regional surface temperature in East Asia shows that there are distinct periods when it increase or decrease despite a steady increase in carbon dioxide concentration since 1900. The trend patterns of sea surface temperature are investigated in each period and examined the role of ocean basins in East Asian warming trend. In addition, we analyze the Max Planck Institute Grand Ensemble (MPI-GE) which is a large ensemble of a single model to understand the effect of internal variability on regional trend patterns in East Asia under the global warming.
Presented by
Sae-Yoon Oh
Institution
Hanyang University, Korea
Keywords
timeslot2
Internal variability influences model-satellite differences in the rate of tropical tropospheric warming
Stephen Po-Chedley, Elizabeth A. Barnes, Céline J. W. Bonfils, John T. Fasullo, Zachary M. Labe, Benjamin D. Santer, Nicholas Siler
Abstract
Observations of surface and tropospheric temperature change since the late-1970s exhibit less warming than the average warming in coupled climate model simulations, particularly in the tropical troposphere. One possible explanation for differential model-versus-observed warming is that the average model sensitivity to greenhouse gas forcing is too large. Another possibility is that satellite observations underestimate tropospheric warming. Recent work has also demonstrated that deficiencies in the aerosol forcing enhance model warming and that natural internal climate variability has reduced satellite-era warming in the observed record. Each of these factors needs to be assessed to determine their contribution to model-versus-observed differences in the rate of tropical and global mean warming.
In this analysis, we seek to quantify the contribution of internal variability to satellite-era (1979 – 2014) tropical tropospheric warming. We apply a range of techniques, including linear regression and neural network analysis, to large model initial condition ensembles to quantify and separate the forced and unforced component of tropospheric warming. We demonstrate that we can accurately partition the internal variability and forced components of tropospheric warming in climate models using the pattern of surface temperature change as a predictor. In applying these techniques to observations, our results suggest that internal variability has offset the forced component of tropical tropospheric warming (1979 – 2014) by approximately 25%. These results indicate that internal variability must be accounted for when evaluating climate models and when inferring transient and equilibrium climate sensitivity from the observed record.
In this analysis, we seek to quantify the contribution of internal variability to satellite-era (1979 – 2014) tropical tropospheric warming. We apply a range of techniques, including linear regression and neural network analysis, to large model initial condition ensembles to quantify and separate the forced and unforced component of tropospheric warming. We demonstrate that we can accurately partition the internal variability and forced components of tropospheric warming in climate models using the pattern of surface temperature change as a predictor. In applying these techniques to observations, our results suggest that internal variability has offset the forced component of tropical tropospheric warming (1979 – 2014) by approximately 25%. These results indicate that internal variability must be accounted for when evaluating climate models and when inferring transient and equilibrium climate sensitivity from the observed record.
Presented by
Stephen Po-Chedley
Institution
Lawrence Livermore National Laboratory
Other Affiliations
National Center for Atmospheric Research, Boulder, CO 80305, USA; College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA; Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA; Joint Institute for Regional Earth System Science & Engineering, University of California – Los Angeles, Los Angeles, CA, USA
Keywords
ECS, timeslot2
The relative roles of external forcing and internal variability on multi-decadal rainfall variability and change over south-west of Australia
Surendra P. Rauniyar, Pandora Hope and Scott B. Power, Michael Grose
Abstract
The south-west of Australia (SWA) has experienced an unprecedented decline (20%) in cool season (May-October) rainfall for the recent 20-year period (2001-2020) relative to the 1901-1960 period average. The cool season rainfall contributes about 70% to annual rainfall over SWA and any significant changes in rainfall have huge impacts on agriculture, tourism, and the environment across the region. Here, we used outputs from CMIP5 and CMIP6 models under different forcing conditions (i.e., pre-industrial, historical and future - under different emissions pathways) to: (i) quantify the likely contribution of external forcing to the recent observed drying, (ii) explore the time of emergence of the climate change signal in rainfall over this part of the world, (iii) estimate future rainfall, and (iv) examine whether there will ever be wet years in future taking both external forcing and internal climate variability into account.
We found a near zero probability that such a large decline in 20-year average rainfall could occur just due to decadal natural variability in the observed time-series. According to models, about half of the observed post-2000 decline is due to external forcing, with greenhouse gases driving the decline and other factors working against that signal. The forced signal has already emerged at the end of the 20th century and there is a 99% probability that the next 20-year period will be drier than the pre-industrial average. The multi-model median (MMM) rainfall decline at the end of the century is outside the range of internal variability in the pre-industrial climate regardless of emission scenario. However, the forced drying could be limited to ~20 % of 1901-1960 average rainfall under a very low emission pathway, rather than the more than 30 % decline under a high emissions scenario. We are currently investigating the large-ensemble members from climate model simulations to better understand the likely change in the frequency of wet years in coming years and decades.
We found a near zero probability that such a large decline in 20-year average rainfall could occur just due to decadal natural variability in the observed time-series. According to models, about half of the observed post-2000 decline is due to external forcing, with greenhouse gases driving the decline and other factors working against that signal. The forced signal has already emerged at the end of the 20th century and there is a 99% probability that the next 20-year period will be drier than the pre-industrial average. The multi-model median (MMM) rainfall decline at the end of the century is outside the range of internal variability in the pre-industrial climate regardless of emission scenario. However, the forced drying could be limited to ~20 % of 1901-1960 average rainfall under a very low emission pathway, rather than the more than 30 % decline under a high emissions scenario. We are currently investigating the large-ensemble members from climate model simulations to better understand the likely change in the frequency of wet years in coming years and decades.
Presented by
Surendra Rauniyar
<surendra.rauniyar@bom.gov.au>
Institution
Australian Bureau of Meteorology, Melbourne, Australia
Keywords
climate change, rainfall decline, signal emergence, large-ensemble runs, timeslot1, ECS
Evaluation of external forcing and initial conditions contributions to decadal predictions of the INMCM5 climate model
Vasilisa Vorobyeva, Andrey Gritsun, Maria Tarasevich, Evgeny Volodin
Abstract
Decadal hindcasts were conducted using the Marchuk Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS) INMCM5 climate model initialized on November 1st for each year over the 41-yr period 1980-2020. Initial state of atmosphere, ocean and land is prescribed using the anomaly initialization method. The INM RAS climate model skill in decadal predictions for up to 5 years is evaluated. Predictability of large-scale modes of climate variability on timescales from a season to 5 years ahead with the INMCM5 climate model is studied. The spatial anomaly correlation coefficients of the 0-300m layer average water temperature and the temporal anomaly correlation coefficient for the Arctic sea ice area will be calculated for different time intervals of 1-5 years using the results of decadal hindcasts, historical experiments and their extensions for the SSP3-7.0 scenario. The contributions of initial conditions and external forcing in anomaly correlation coefficients will be evaluated.
Presented by
Vasilisa Vorobyeva
<VVorobyeva@yandex.ru>
Institution
Marchuk Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS)
Other Affiliations
Hydrometeorological Research Center of Russian Federation (Hydrometcenter of Russia), Moscow Institute of Physics and Technology (MIPT NRU)
Keywords
Climate model, Decadal predictions, External forcing, Initial conditions, Large-scale modes, Long-term variability, ECS, timeslot2
Antarctic Sea Ice Multidecadal Variability and Predictability in GFDL SPEAR_LO Model
Yushi Morioka, Liping Zhang, Thomas L. Delworth, Xiaosong Yang, Fanrong Zeng, Masami Nonaka, Swadhin K. Behera
Abstract
Using the GFDL’s new coupled model (SPEAR_LO) constrained by atmospheric reanalysis and observed sea surface temperature, physical processes controlling Antarctic sea ice multidecadal variability and predictability are investigated with a focus on relative roles of internal variabilities such as the Southern Ocean deep convection and surface wind variability. The 63-year (1958-2020) SPEAR_LO reanalysis reproduces the Antarctic sea ice multidecadal variability with two high sea ice periods (1960s-early 1970s and 2000s-early 2010s) and one low sea ice period (late 1970s-1990s), although the SPEAR_LO model overestimates the sea ice decrease over the Weddell Sea around the 1980s. In the SPEAR_LO reanalysis, the low sea ice state is largely due to an occurrence of the Southern Ocean deep convection that induces anomalous warming of the upper ocean. During the high sea ice period (post-2000s), the deep convection weakens, so that the surface wind variability starts to play a greater role in the sea ice increase. The decadal reforecast initialized from the SPEAR_LO reanalysis demonstrates that the Antarctic sea ice multidecadal variability can be skillfully predicted 6-10 years in advance. Ensemble members with a stronger deep convection tend to predict a larger sea ice decrease in the 1980s, whereas the members with a larger surface wind variability tend to predict a larger sea ice increase after the 2000s. Therefore, skillful predictions of the Antarctic sea ice multidecadal variability require accurate simulation and prediction of both the Southern Ocean deep convection and the surface wind variability in the SPEAR_LO model.
Presented by
Yushi Morioka
Institution
JAMSTEC/VAiG/APL
Other Affiliations
NOAA/GFDL, Princeton University/AOS
Keywords
Antarctic sea ice, Multidecadal variability, Predictability, timeslot2
Temporary slowdowns in decadal warming predictions by a neural network
Zachary M. Labe and Elizabeth A. Barnes
Abstract
In addition to the long-term warming trend from externally-forced climate change, the global mean surface temperature (GMST) record exhibits substantial interannual to decadal variability. To explore the predictability of temporary slowdowns in future climate warming, we apply an artificial neural network (ANN) to data from the Community Earth System Model Version 2 Large Ensemble Community Project. Here, an ANN is tasked with predicting the onset of a slowdown in the rate of the GMST trend by using maps of upper ocean heat content. Through a machine learning explainability method, we then find the ANN is learning patterns of anomalous ocean heat content that resemble transitions in the phase of the Interdecadal Pacific Oscillation to make correct slowdown predictions. Finally, we examine the validity of our ANN architecture by evaluating input data from real-world observations and find that our ANN is successfully able to predict the early 2000s hiatus-like period. In agreement with recent work, we find that machine learning tools offer the opportunity to further improve our understanding of decadal climate variability and prediction.
Presented by
Zachary Labe
Institution
Colorado State University
Other Affiliations
NOAA GFDL and Princeton University
Keywords
Neural Networks, Decadal Prediction, Climate Variability, Large Ensembles, Explainable AI, Climate Change, ECS, timeslot2
▼ Session 2 Back to top
Volcanic eruptions and multi-decadal Indo-Pacific variability amplify extreme Indian Ocean Dipole events in Last Millennium Ensemble simulations
Benjamin H. Tiger, Caroline C. Ummenhofer
Abstract
The tropical Indian Ocean is warming faster than any other basin, and its interannual climate variability is projected to become more extreme under future emissions scenarios with substantial impacts on developing Indian Ocean rim countries. Therefore, it has become increasingly important to understand the drivers of regional precipitation in a changing climate. Intense volcanic eruptions can have significant climate impacts and serve as a useful natural experiment for better understanding the effects of abrupt, externally forced climate change. Previous work has found that volcanic forcing can induce changes in pantropical atmospheric and oceanic circulation regimes, favoring the formation of El Niño conditions in the equatorial Pacific. The volcanic response in the tropical Indian Ocean is much less well constrained. Here, I use the Community Earth System Model Last Millennium Ensemble (CESM-LME) to investigate the response of the Indian Ocean Dipole (IOD) to intense volcanic eruptions from 850-2005 CE. Post-eruption spatial composites show a strong negative IOD (nIOD) developing in the boreal fall of eruption years. This response is associated with low-level westerly anomalies across the basin and anomalously warm SSTs in the Sunda Strait upwelling region. The magnitude of nIOD tracks eruption intensity, with the most intense eruptions driving the largest decreases in values of the Dipole Mode Index (DMI) well beyond the range of natural variability. This response occurs regardless of the hemisphere of eruption. Post-eruption timeseries composites show a long-term damped oscillatory response in the DMI with excursions significantly beyond the range of natural variability that can take multiple years to return to pre-eruptive baselines. Moreover, the state of the Interdecadal Pacific Oscillation (IPO) at the time of eruption modulates the IOD response to intense eruptions, with negative (positive) IPO phasing favoring more negative (positive) DMI values. The effects of initial IPO phasing result in statistically significant differences in the distribution of the resulting post-eruption DMI. This suggests that the mean state of the Indo-Pacific is an important preconditioning control on the tropical Indian Ocean’s response to volcanic forcing.
Presented by
Benjamin H. Tiger
<tigerb@mit.edu>
Institution
Massachusetts Institute of Technology
Other Affiliations
Woods Hole Oceanographic Institution
Keywords
ECS, timeslot2
Interannual variability in the tropical Indian Ocean simulated by the Palaeoclimate Model Intercomparison Project
Chris Brierley, Kaustubh Thirumalai, Edward Grindrod, Jonathan Barnsley
Abstract
The Indian Ocean exhibits multiple modes of interannual climate variability, whose future behaviour is uncertain. According to climate simulations, global warming induces a mean sea surface temperature (SST) change reminiscent of the positive mode of the Indian Ocean Dipole (IOD), alongside a stronger Indian Summer Monsoon and northward displacement of the Intertropical Convergence Zone. Recent analysis of glacial climates has uncovered an additional El Nino-like equatorial mode in the Indian Ocean, which could also emerge in future warm states. Here we explore changes in the tropical Indian Ocean simulated by the Palaeoclimate Model Intercomparison Project (PMIP4). These simulations are performed by an ensemble of models contributing to the Coupled Model Intercomparison Project 6, and over four coordinated experiments: three past periods - the mid-Holocene (6000 years ago), the last glacial maximum (21,000 years ago), the last interglacial (127,000 years ago) - and an idealised forcing scenario to examine the impact of greenhouse forcing. The two interglacial experiments are used to characterise the role of orbital variations on the seasonal cycle, whilst the other pair focus on responses to large changes in global temperature.
Orbitally-driven damping of ENSO during both mid-Holocene and last interglacial causes a damping of the Indian Ocean Basin Mode. Additionally, the mid-Holocene sees a weakening of the Dipole, but this is not seen during the last interglacial. Changes in the amplitude of both the dipole and basin modes are more ambiguous at the last glacial maximum, which featured a larger role for greenhouse gas changes rather than orbital forcing. The SST pattern of the Indian Ocean Dipole also has orbital variations with the cold pole extending along the Equator.
Orbitally-driven damping of ENSO during both mid-Holocene and last interglacial causes a damping of the Indian Ocean Basin Mode. Additionally, the mid-Holocene sees a weakening of the Dipole, but this is not seen during the last interglacial. Changes in the amplitude of both the dipole and basin modes are more ambiguous at the last glacial maximum, which featured a larger role for greenhouse gas changes rather than orbital forcing. The SST pattern of the Indian Ocean Dipole also has orbital variations with the cold pole extending along the Equator.
Presented by
Chris Brierley
Institution
University College London & University of Arizona
Keywords
Indian Ocean Dipole, Past climates, timeslot2
Large-scale emergence of regional changes in year-to-year temperature variability by the end of the 21st century
Dirk Olonscheck, Andrew Schurer, Lucie Lücke & Gabi Hegerl
Abstract
Global warming is expected to not only impact mean temperatures but also temperature variability, substantially altering climate extremes. Here we show that human-caused changes in internal year-to-year temperature variability are expected to emerge from the unforced range by the end of the 21st century across climate model initial-condition large ensembles forced with a strong global warming scenario. Different simulated changes in globally averaged regional temperature variability between models can be explained by a trade-off between strong increases in variability on tropical land and substantial decreases in high latitudes, both shown by most models. This latitudinal pattern of temperature variability change is consistent with loss of sea ice in high latitudes and changes in vegetation cover in the tropics. Instrumental records are broadly in line with this emerging pattern, but have data gaps in key regions. Paleoclimate proxy reconstructions support the simulated magnitude and distribution of temperature variability. Our findings strengthen the need for urgent mitigation to avoid unprecedented changes in temperature variability.
Presented by
Dirk Olonscheck
Institution
University of Edinburgh, School of GeoSciences, UK
Other Affiliations
Max Planck Institute for Meteorology, Germany
Keywords
Climate variability, regional climate change, emergence, SMILEs, ECS, timeslot2
Widespread changes in surface temperature persistence under climate change
Jingyuan Li, David W. J. Thompson
Abstract
Climate change has been and will be accompanied by widespread changes in surface temperature. It is clear that these changes include global-wide increases in mean surface temperature and changes in temperature variance that are more regionally-dependent. It is less clear whether they also include changes in the persistence of surface temperature. This is important as the effects of weather events on ecosystems and society depend critically on the length of the event. Here we provide an extensive survey of the response of surface temperature persistence to climate change over the twenty-first century from the output of 150 simulations run on four different Earth system models, and from simulations run on simplified models with varying representations of radiative processes and large-scale dynamics. Together, the results indicate that climate change simulations are marked by widespread changes in surface temperature persistence that are generally most robust over ocean areas and arise due to a seemingly broad range of physical processes. The findings point to both the robustness of widespread changes in persistence under climate change, and the critical need to better understand, simulate and constrain such changes.
Presented by
Jingyuan Li
Institution
Scripps Institution of Oceanography
Other Affiliations
Colorado State University, University of East Anglia
Keywords
timeslot2
Understanding the role of internal climate variability and anthropogenic forcing on the Paris Agreement target of 2C in climate models
Sang-Wook Yeh and In-Hong Park
Abstract
The Paris Agreement adopted a 1.5°C/2°C of global mean surface temperature (GMST) increase limit. Since then, the science community has tried to understand the physical factors modulating the near-term global warming rates. According to previous studies, the Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5/CMIP6) climate models show a wide inter-model diversity of simulating the year when the GMST reaches to the Paris Agreement of 1.5°C/2°C. In this study, we analyzed CMIP6 climate models with different Shared Socioeconomic Pathways (SSP) scenarios to understand the role of internal climate variability and anthropogenic forcing on the 2°C target year simulated in climate models. Indeed, climate models with a high emission scenario (SSP8.5) simulate the earliest 2°C target year. In addition, we found that the inter-model spread of simulated 2C target year is variable to different SSP scenarios. When the SSP scenario is strong, their inter-model spread is weak. To understand the details, we further examined the MPI grand ensemble (MPI-GE) simulations and analyzed the dynamical processes on the role of internal climate variability and anthropogenic forcing to determine the Paris Agreement target of 2°C
Presented by
Sang-Wook Yeh
Institution
Hanyang University
Keywords
Internal climate variability, 2C target year, inter-model diversity, SSP scenarios, timeslot1
Does the Indian summer monsoon modulate the Arctic sea ice?
Suchithra Sundaram and David M.Holland
Abstract
A substantial change in the Arctic climate, particularly a rapid decline of September Arctic sea ice, has occurred over the past few decades. The exact reasons for such drastic changes are still unknown. But studies suggest anthropogenic drivers, natural processes with the climate system - the internal variability, and a combination of both play a significant role in the rapid decline of Arctic sea ice. The present study focus on the influence of one of the natural variabilities of the climate system, the teleconnections associated with the Indian Summer Monsoon (ISM), and its relationship to September Arctic sea ice. This study uses 50 years (1951-2000) of NCEP/NCAR reanalysis data, APHRODITE precipitation data, Gridded Monthly Sea Ice Extent and Concentration, 1850 Onward, V2, and HadISST sea-ice concentration data. The analysis shows that, during many strong (weak) ISM years, the Arctic sea ice increased (decreased), particularly over the Chukchi and Beaufort Seas. The study proposes a physical mechanism to explain this unique feature. It has shown that the ISM plays a significant role in causing a positive (negative) North Atlantic Oscillation (NAO) during strong (weak) ISM years through the monsoon-desert mechanism associated with monsoonal heating. Simultaneously, the NAO during a strong (weak) ISM causes weakening (strengthening) of the Beaufort Sea High (BSH). The strength of the BSH modulates the Arctic atmospheric circulation by affecting the cold air advection and direction of the transpolar drift stream, leading to the generation of more (less) sea ice over the Chukchi-Beaufort Sea region during strong (weak) ISM years. The study illustrates a new atmospheric teleconnection between the tropics and the Arctic and indicates a role in the predictability of Arctic sea ice.
Presented by
Suchithra Sundaram
Institution
New York University Abu Dhabi, UAE
Other Affiliations
Courant Institute of Mathematical Sciences, New York University , USA
Keywords
Polar climate variability, Indian Summer Monsoon, Internal variability, Teleconnections, North Atlantic Oscillation, Beaufort Sea High, timeslot2
Are multidecadal climate modes in the Northern Hemisphere connected?
Tyler Fenske, Amy Clement
Abstract
Previous studies documented possible connections between low frequency climate modes in
the Northern Hemisphere ocean basins. We use observed sea surface temperatures and 270
large ensemble climate model simulations, which allows for improved methods of separating
external and internal variability, such as removing the ensemble mean from each simulation.
Detrending methods for observations have also improved since some of these previous
studies were conducted. We also devise a modiLed statistical test using bootstrapping that is
tuned speciLcally to this analysis. With these tools, we reexamine relationships among these
modes. While previous studies have argued for the existence of an inter-basin link, our results
suggest that any internal connections between these modes are indistinguishable from
random noise. Further, we show that external forcing affects each region in similar ways. This
suggests that anthropogenic warming can cause an indirect link between the two basins,
confounding the interpretation of a potential relationship.
Presented by
Tyler Fenske
Institution
University of Miami, Rosenstiel School of Marine, Atmosphere, and Earth Sciences
Keywords
PDO, AMV, Inter-basin, Large ensembles, ECS, timeslot2
Fast and Slow Responses of the Tropical Pacific to Radiative Forcing in Northern High Latitudes
Yen-Ting Hwang, Hung-Yi Tseng, Shang-Ping Xie, Yu-Heng Tseng, Sarah M. Kang, Matthew T. Luongo, and Ian Eisenman
Abstract
Anthropogenic aerosol forcing, Antarctica ozone hole, and greenhouse gases have all been suggested to affect the observed trend in sea surface temperature patterns. And yet, a mechanistic understanding of the sea surface temperature pattern responses to regional radiative forcing is lacking. Motivated by previous studies highlighting the distinct tropical responses to extratropical forcing between slab ocean model and dynamical ocean model simulations, this study investigates the role of the ocean in shaping the transient evolution of tropical Pacific SST responses to northern high latitude solar forcings in CESM 1.2. Two distinct stages are identified through running a large number of ensemble members. (1) A hemispherically asymmetric pattern similar to the equilibrium response in the slab ocean simulations is observed in the first three years. Despite the forcing being a northern high latitude heating, an anomalous cooling occurs in the Southeast Pacific and extends toward the central equatorial Pacific. The strengthened zonal SST gradient along the equator enhances the easterlies and drives anomalous Ekman transport divergence, which is confined to the equator, and leads to the amplified anomalous cooling in the 50m mixed layer heat budget analysis. (2) A hemispherically symmetric pattern that starts around one decade after the forcing is imposed, quicker than the timescale of the oceanic ventilation, and persists to the end of the fully coupled simulations is observed. An ocean energy budget analysis above 200m attributes the gradual warming in the equatorial region to the anomalous meridional heat convergence associated with weakening of the northern subtropical cell. Our results highlight the role of ocean dynamics in shaping the tropical SST pattern under idealized hemispherically asymmetric forcing. The results thus have implications for understanding the SST pattern evolutions in historical simulations and future projections under anthropogenic aerosol forcing.
Presented by
Yen-Ting Hwang
Institution
National Taiwan University
Other Affiliations
University of California San Diego, Ulsan National Institute of Science and Technology
Keywords
tropical SST pattern, teleconnection, timeslot2
Understanding the role of greenhouse gas forcing leading to a long-term positive trend of Arctic Oscillation
Yong-Cheol Jeong, Sang-Wook Yeh, Guojian Wang, Hyerim Kim and Se-Yong Song
Abstract
Arctic oscillation (AO) is the most dominant atmospheric variability in Northern Hemisphere (NH) during the boreal winter, and it affects surface winter climate over mid-to-high latitudes in the NH. Therefore, it is important to understand how AO changes under global warming. Because there is still debate on whether AO will show a positive or negative trend under global warming, additional studies should be done. To contribute this, we conduct two idealized experiments with 30 ensemble members using GFDL-CM2.1 climate model. In the first experiment, which is referred to as CO2_Exp, historical (1951 – 2019) CO2 concentration is prescribed and climatological SST is restored in the Arctic region (north of 65°N) to exclude an impact of the Arctic warming. Outside the Arctic region, the ocean is fully coupled with the atmosphere in the experiment. In the second experiment, which is referred to as Arctic_Exp, a fixed CO2 concentration is prescribed and the historical sea surface temperature (SST) is restored in the Arctic region to isolate an impact of the Arctic warming. As a result, AO has a long-term positive trend in CO2_Exp, and negative trend in Arctic_Exp. Given that the observed AO has a long-term positive trend, this result may imply that the impact of CO2 increase is more dominant than that of Arctic warming in the observation. We also investigate the physical mechanisms of how CO2 increase is able to induce a long-term positive trend of AO.
Presented by
Yong-Cheol Jeong
Institution
Hanyang University, Department of Marine Science and Convergence Engineering
Other Affiliations
Center for Southern Hemisphere Oceans Research (CSHOR), CSIRO Oceans and Atmosphere, Hobart, TAS, Australia, Frontier Science Center for Deep Ocean Multispheres and Earth System and Physical Oceanography Laboratory, Ocean University of China, Qingdao, China, Qingdao National Laboratory for Marine Science and Technology (QNLM), Qingdao, China
Keywords
Arctic Oscillation, CO2 forcing, Long-term trend, ECS, timeslot1
▼ Session 3 Back to top
Assessing the role of internal variability in projections of northern Europe wintertime climate change at near-term (2020-2040) using a storyline approach
Aurélien Liné, Christophe Cassou, Rym Msadek
Abstract
Climate fluctuates under the dual influence of external forcings and internal variability linked to the intrinsic properties of the climate system. The weight of internal variability gets stronger at regional scale and at near-term, e.g. for the next 20-30 years, and can significantly modulate the forced response, as assessed in the latest IPCC report. In this study, we focus on northern Europe wintertime climate changes projected for the 2020-2040 period, using large ensembles of historical and SSP simulations produced by 6 coupled models. Based on analyses of variance, we show that about 80% of the total uncertainty is attributable to internal variability, the rest being explained by model uncertainty in the forced response, while the scenario uncertainty is strictly marginal. We further explore, assess, and communicate the internal variability role through the determination of physical storylines, defined as self-consistent and plausible unfoldings of a physical trajectory, conditioned on specific explanatory elements, here drivers of internal variability. We identify the two main drivers, namely the Atlantic Multidecadal Variability (AMV) and the North Atlantic Oscillation (NAO), and accordingly define 4 storylines that correspond to the combination of these two drivers' changes. In the high-impact storyline, where both AMV and NAO concurrently switch to positive phase, warming is strongly amplified, about one standard deviation above the forced response, precipitation significantly increases, snow cover is reduced, and cold waves defined as 10-yr return period events gets 6 times less frequent. When AMV and NAO turn negative at once, internal variability partly cancels out the forced response, leading to weak climate changes over the next two decades over Northern Europe. Extreme cold events only get 2 times less frequent. This confirms the importance of accounting for internal variability in risk planning and adaptation strategies at regional scale.
Presented by
Aurélien Liné
Institution
Cerfacs/CECI, UMR 5318, Climate Modelling and Global Change Team, Toulouse, France
Other Affiliations
Institut National Polytechnique de Toulouse
Keywords
Climate change, Internal variability, Near-term, Storylines, Europe, AMV, NAO, ECS, timeslot2
Recent Atlantic Multidecadal Variability and its tropical impacts are driven by external forcings
Chengfei He*, Amy C. Clement, Sydney Kramer, Mark A. Cane, Lisa N. Murphy, Jeremy M. Klavans, Tyler M. Fenske
Abstract
Changes in the decadal climate variability are as vital to society as are changes in climate trends.
Though observations show a clear link between the Atlantic multidecadal variability (AMV) and the North Atlantic hurricane variability and Sahel rainfall, the source of their formation remains highly uncertain. Anthropogenic forcings, such as aerosol emissions, are thought to set the pace and amplitude of the AMV and its tropical impacts, however, prevailing thoughts consider AMV and its impacts are regulated by internal oceanic and atmospheric dynamics. Here, we use a grand model composite from the CMIP6 to investigate recent tropical Atlantic variability. We show, after removing an sea surface temperature (SST) bias induced by greenhouse gas, the simulated AMV and its impacts are highly consistent with observations, which are driven by natural forcing and anthropogenic aerosols since 1950. The AMV affects the Sahel rainfall and hurricane variability via tropical SST gradient. The forced asymmetric tropical SST anomaly excites a Gill-type response locally, including a low-level westerly that favors the Sahel rainfall and a high-level easterly that perturbs the vertical wind shear (VWS) and hence hurricane activity. The diabatic heating released by the Sahel rainfall further causes a planetary Rossby wave, in favor of VWS and inducing global impacts via atmospheric teleconnection.
Presented by
Chengfei He
Institution
University of Miami
Keywords
AMV, Hurricane, Sahel, AMOC, ECS, timeslot2
How discrepancies between observations and climate models of large-scale wind-driven Greenland melt influence sea-level rise projections
Daniel Topal, Qinghua Ding, Thomas J Ballinger, Edward Hanna, Xavier Fettweis, Zhe Li, Ildiko Pieczka
Abstract
While climate models project that Greenland ice sheet (GrIS) melt will continue to accelerate with climate change, models exhibit limitations in capturing observed connections between GrIS melt and changes in high-latitude atmospheric circulation. Here we impose observed Arctic winds in a fully-coupled climate model with fixed anthropogenic forcing to quantify the influence of the rotational component of large-scale atmospheric circulation variability over the Arctic on the temperature field and the surface mass/energy balances through adiabatic processes. We show that recent changes involving mid-to-upper-tropospheric anticyclonic wind anomalies – linked with tropical forcing – explain half of the observed Greenland surface warming and ice loss acceleration since 1990, suggesting a pathway for large-scale winds to potentially enhance sea-level rise by ~0.2 mm/year per decade. We further reveal fingerprints of this observed teleconnection in paleo-reanalyses spanning the past 400 years, which heightens concern about model limitations to capture wind-driven adiabatic processes associated with GrIS melt.
Presented by
Daniel Topal
<topal.daniel@csfk.org>
Institution
Research Centre for Astronomy and Earth Sciences, Institute for Geological and Geochemical Research
Other Affiliations
University of California Santa Barbara
Keywords
sea-level rise, Greenland blocking, tropical-Arctic teleconnections, ECS, timeslot1
Observational constraints on the externally-forced water cycle response to past and future human activities
Hervé Douville, Saïd Qasmi and Aurélien Ribes
Abstract
Changes in the terrestrial water cycle due to global warming remain highly uncertain, even in the latest generation of climate models. While global temperature projections can be constrained with the observed historical warming, such observational constraints have not been used so far to narrow uncertainties in the forced water cycle response due to the lack of reliable observations and the lower signal-to-noise ratio than for temperature changes. Here, we highlight the possibility to constrain global water cycle changes with both temperature and hydrological variables. The first example is about both recent and future global changes in total precipitable water. Most state-of-the-art global climate models tend to overestimate the global atmospheric moistening whose projected range can be narrowed by up to 39% at the end of the 21st century. Our best-guess estimate of 7% per °C of global warming is consistent with the Clausius-Clapeyron relationship and the projected increase in the intensity of heavy precipitation events. The second example relates to near-surface relative humidity globally averaged over land. Compared to the raw CMIP6 model outputs, our results highlight a robust land surface drying, with a substantial (up to 37%) narrowing of the 5-95% confidence interval at the end of the 21st century. This finding has strong implications for the projection of drought events and further supports the urgent need for adaptation measures in the water and agriculture sector.
Presented by
Hervé Douville
Institution
Météo-France/CNRM
Other Affiliations
CNRS
Keywords
Forced response, observational coonstraint, timeslot2
Large ensemble of MIROC6 for understanding internal and externally forced variability in the climate system
Hideo Shiogama1, Hiroaki Tatebe2, Manabu Abe2, Miki Arai3, Yukiko Imada4, Yu Kosaka5, Michiya Hayashi1 and Masahiro Watanabe3
Abstract
Large ensembles can provide useful tools for understanding internal and externally forced variability in the climate system. By using the MIROC6 atmosphere-ocean global climate model, we are performing the large ensembles described below to understand historical climate change and examine uncertainties of future climate change projections. We are publishing the output data of these large ensembles in the earth system grid to foster research in wide communities.
We have already published the output data of the 50-member ensembles for 3 of 4 Tier 1 experiments of Scenario Model Intercomparison Project (ScenarioMIP): SSP1-2.6, SSP2-4.5 and SSP5-8.5. We have a plan to increase the ensemble size of the last one of Tier 1 experiment, SSP3-7.0, from 3 to 50. Because large ensembles are crucial to investigate differences in extreme events between the 1.5°C and 2.0°C warmer climates according to the Paris Agreement goals, we have also produced the 50- member ensemble of SSP1-1.9.
To understand historical climate changes, we have performed large ensemble simulations of the Detection and Attribution Model Intercomparion Project (DAMIP) experiments. We have already completed the 50-member historical simulations of well-mixed greenhouse gases only (hist-GHG), natural-forcing (solar and volcanic) only (hist-nat) and anthropogenic aerosol only (hist-aer) experiments, which are Tier 1 of DAMIP. We are also performing the 10-member ensembles of volcanic only (hist-volc), solar only (hist-sol), stratospheric ozone only (hist-stratO3) and stratosphere and troposphere only (hist-totalO3) experiments, which are Tiers 2 or 3 of DAMIP. Future simulations of well-mixed greenhouse gases only (ssp245-GHG) and aerosol only (ssp245-aer) under the SSP2-4.5 scenario have been extended to 50 members. To contribute to the Large Ensemble Single Forcing Model Intercomparison Project (LESFMIP), we are performing historical land use land cover change only simulations (hist-lu, 10-members).
Here we explain the design of this ‘one of largest ensembles in the world’ and show some examples of analyses.
Presented by
Hideo Shiogama
<shiogama.hideo@nies.go.jp>
Institution
(1) National Institute for Environmental Studies (2) Japan Agency for Marine-Earth Science and Technology (3) Atmosphere and Ocean Research Institute, the University of Tokyo (4) Meteorological Research Institute (5) Research Center for Advanced Science and Technology, the University of Tokyo
Keywords
Large ensmeble, timeslot1
Warm phase of AMV damps ENSO through weakened thermocline feedback
Paloma Trascasa Castro, Yohan Ruprich Robert, Fred Castruccio and Amanda Maycock
Abstract
Interactions between ocean basins affect El Niño–Southern Oscillation (ENSO), altering its impacts on society. Here, we explore the effect of Atlantic Multidecadal Variability (AMV) on ENSO behavior using idealized experiments performed with the NCAR-CESM1 model. Comparing warm (AMV+) to cold (AMV−) AMV conditions, we find that ENSO sea surface temperature (SST) anomalies are reduced by ∼10% and ENSO precipitation anomalies are shifted to the west during El Niño and east during La Niña. Using the Bjerknes stability index, we attribute the reduction in ENSO variability to a weakened thermocline feedback in boreal autumn. In AMV+, the Walker circulation and trade winds strengthen over the tropical Pacific, increasing the background zonal SST gradient. The background changes shift ENSO anomalies westwards, with wind stress anomalies more confined to the west. We suggest the changes in ENSO-wind stress decrease the strength of the thermocline feedback in the east, eventually reducing ENSO growth rate.
Presented by
Paloma Trascasa-Castro
<ee17pt@leeds.ac.uk>
Institution
University of Leeds, Barcelona Supercomputing Center
Keywords
ENSO, AMV, coupled feedbacks, intrabasin teleconnections, ECS, timeslot2
Ensemble bias correction of climate simulations: preserving internal variability
Pradeebane Vaittinada Ayar [1, 2], Mathieu Vrac [1] , Alain Mailhot [2]
Abstract
Climate simulations often need to be adjusted (i.e., corrected) before any climate change impacts studies. However usual bias correction approaches do not differentiate the bias from the different uncertainties of the climate simulations: scenario uncertainty, model uncertainty and internal variability. In particular, in the case of a multi-run ensemble of simulations (i.e., multiple runs of one model), correcting, as usual, each member separately, would mix up the model biases with its internal variability. In this study, two ensemble bias correction approaches preserving the internal variability of the initial ensemble are proposed. These “Ensemble bias correction” (EnsBC) approaches are assessed and compared to the approach where each ensemble member is corrected separately, using precipitation and temperature series at two locations in North America from a multi-member regional climate ensemble. The preservation of the internal variability is assessed in terms of monthly mean and hourly quantiles. Besides, the preservation of the internal variability in a changing climate is evaluated. Results show that, contrary to the usual approach, the proposed ensemble bias correction approaches adequately preserve the internal variability even in changing climate. Moreover, the climate change signal given by the original ensemble is also conserved by both approaches.
Presented by
Pradeebane Vaittinada Ayar
Institution
[1] Laboratoire des Sciences du Climat et l’Environnement (LSCE-IPSL) CNRS/CEA/UVSQ, UMR8212, Université Paris-Saclay, 91190 Gif-sur-Yvette, France
Other Affiliations
[2] Institut national de la recherche scientifique, Centre Eau Terre Environnement, Québec, Canada
Keywords
RCM simulation large ensemble, Ensemble bias correction, Internal variability, timeslot2
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Influence of the Atlantic Multidecadal Variability and of Soil Moisture on Extreme Heatwaves in Europe
Valeria Mascolo$^1$, Clément Le Priol$^1$, Freddy Bouchet$^1$, Fabio d'Andrea$^2$
Abstract
Presented by
Clément LE PRIOL
Institution
1: Ecole Normale Supérieure de Lyon ; 2 Laboratoire de Météorologie dynamique, IPSL, France
Keywords
Atlantic Multidecadal Variability, Soil Moisture, Heatwaves, ECS, timeslot2
Ocean-atmosphere processes in response to Climate Change in the tropical South Atlantic
Isabelle Vilela, Noel Keenlyside, Dóris Veleda, Thiago Silva, Janini Pereira
Abstract
The Atlantic Meridional Overturning Circulation (AMOC) is responsible for transporting large amounts of heat in the ocean, which affects the Intertropical Convergence Zone position, with further consequences for weather and climate. This work investigates the historical and climate projections variability of AMOC heat transport and its impacts on the rainfall over the Tropical South Atlantic and in the Eastern Northeast of Brazil (ENEB). The analyses were applied considering greenhouse gas increase by using extended global-warming simulations of the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the scenarios of Shared Socioeconomic Pathways (SSPs) 126, 245, and 585, respectively.
The potential temperature and rainfall differences between the SSPs scenarios and the historical in the tropical South Atlantic show an increase in the following years. In the warming upper ocean, it is possible to identify a decrease in heat transport in response to an AMOC shutdown by comparing the CMIP6 simulation with historical AMOC from ORAS4. Further, the increased rainfall projections for all optimistic, realistic, and pessimistic scenarios are triggered by tropical South Atlantic warming and due to the AMOC slowdown in future projection models. The cross-wavelet analysis indicates a co-variability between the AMOC heat transport and the continental rainfall over ENEB, mainly on the annual timescale, with some moderate seasonal and weaker interannual relationships.
Presented by
Isabelle Vilela
<isabelle.vilelaoliveira@ufpe.br>
Institution
Federal University of Pernambuco
Other Affiliations
Uib, APAC, UFBA
Keywords
Northward heat transport, AMOC weakening, rainfall, Eastern Northeast of Brazil, ECS, timeslot2
Emergence of climate change in the tropical Pacific
Jun Ying, Mat Collins, Wenjv Cai, Axel Timmermann, Ping Huang, Dake Chen, and Karl Stein
Abstract
Future changes in the mean climate of the tropical Pacific and characteristics of the El Niño–Southern Oscillation (ENSO) are established as likely. Determining the time of emergence (ToE) of climate change signals from the natural variability is critical for mitigation strategies and adaptation planning. Here, using a multi-model ensemble, we find that the annual-mean sea surface temperature (SST) signal has already emerged across much of the tropical Pacific, appearing last in the east. The signal of a wetter annual-mean rainfall in the east is expected to emerge by mid-century, with some sensitivity to emission scenario. However, the ENSO-related rainfall variability signal is projected to emerge by ~ 2040 regardless of emission scenario, ~ 30 years earlier than ENSO-related SST variability signal at ~ 2070. Our results are instructive for the detection of climate change signals and reinforce the rapidly emerging risks of ENSO-induced climate extremes regardless of mitigation actions.
Presented by
Jun Ying
Institution
State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources
Keywords
Time of emergence, SST, ENSO, detectability, tropical Pacific, ECS, timeslot1
Understanding Modes of Climate Variability during Extreme Dry Climatic Seasons in the Greater Horn of Africa (GHA) region
Vincent O. Otieno, Herbert Misiani, and Lydia Gachai
Abstract
Weather/Climate forecast/prediction, as an art and science, is one of the most valuable skill in climate science and most cherished and loathed in almost equal measures in Africa and more so Greater Horn of Africa as most economic activities are dependent on climate conditions (rainfall and temperature). To that extent the forecast skill need to be meticulous not to deviate much from the actual event. In addition, the most valuable elements of forecast are the onset which heralds the beginning of the season and the seasonal rainfall distribution which is a precursor to the expected performance of the season. The GHA region has four established climatic regimes; December-January-February (DJF), mainly experience in the southern part of the GHA region; March-April-May (MAM) and October-NovemberDecember, which are the major rainfall season of the equatorial GHA region; and June-JulyAugust-September (JJAS) which is the main rainfall season in the northern part of GHA mainly Ethiopia and part of South Sudan and Sudan. These rainfall regimes define the economic life lines of the regions. A good rainfall season; that is, with rainfall onset on time and well distributed over the season is generally a sign of bumper harvest and food security. Any deviation from the expectation of the two elements especially rainfall is considered a failure in season and herald food insecurity in the region. While the frequency of heavy precipitation is projected to increase, dry climatic conditions are also expected to be longer as climate change. Nonetheless the determination of the extent to which climate change influences an individual weather or climate event is still challenging. It involves consideration of a host of possible natural and anthropogenic factors (e.g., large-scale circulation, internal modes of climate variability, anthropogenic climate change, aerosol effects) that combine to produce the specific conditions of an event. Skilful prediction of these extreme events therefore require a thorough understanding of the drives of climate variability in the region and how they behave/will behave in the phase climate change. This work therefore seek to understand effects of large scale and mesoscale variability on extreme events, how these climatic modes of variability evolve prior to, and during extreme climatic periods. In this first part of our study we will analyze observational data from various climate centers to isolate and understand the various modes of climate variability and their influence in the region. We hope our work will contribute to skillful prediction of extreme climatic events.
Presented by
Vincent Otieno
Institution
Technical University of Kenya, Department of Geoscience and Environment
Keywords
Rainfall Onset & Cessation, Drought, SST forcing, Negative Indian Ocean Dipole (IOD), ECS, timeslot2