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Results for “Interdecadal variability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Impacts of the Pacific–Japan and Circumglobal Teleconnection Patterns on the Interdecadal Variability of the East Asian Summer Monsoon

Based on the Twentieth Century Reanalysis (20CR) dataset, the dominant modes of interdecadal variability of the East Asian summer monsoon (EASM) are investigated through a multivariate empirical orthogonal function analysis (MV-EOF). The first mode (EA1) is characterized by an anomalous cyclone centered over Taiwan and an anomalous anticyclone centered over the Bohai Sea. These phenomena are part of the meridional wave–like teleconnection pattern propagating poleward from the southern tropical western North Pacific (WNP), referred to as the interdecadal Pacific–Japan (PJ) pattern. The interdecadal PJ pattern is driven by negative anomalous convective heating over the southern tropical WNP, which is associated with the interdecadal Pacific oscillation (IPO) and the interdecadal Indian Ocean basin mode (IOBM). The amplitude of the EA1 and its contribution to the total variance of the EASM decrease remarkably after the 1960s. The second MV-EOF mode (EA2) is characterized by cyclone anomalies extending from northeastern China to Japan, which are part of a circumglobal wave train. Given the spatial scale of the wave train in the zonal direction (wavenumber 5), as well as the fact that it possesses barotropic structures and propagates along the Northern Hemispheric jet stream, it is referred to herein as the interdecadal circumglobal teleconnection (CGT) pattern. The interdecadal CGT pattern is associated with the forcing from the Atlantic multidecadal oscillation (AMO). Though the interdecadal PJ and CGT patterns are derived from the 20CR dataset, they are carefully verified through comparisons with various observational and reanalysis datasets from different perspectives.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Likely accelerated weakening of Atlantic overturning circulation emerges in optimal salinity fingerprint

The long-term response of the Atlantic meridional overturning circulation (AMOC) to anthropogenic forcing has been difficult to detect from the short direct measurements available due to strong interdecadal variability. Here, we present observational and modeling evidence for a likely accelerated weakening of the AMOC since the 1980s under the combined forcing of anthropogenic greenhouse gases and aerosols. This likely accelerated AMOC weakening signal can be detected in the AMOC fingerprint of salinity pileup remotely in the South Atlantic, but not in the classic warming hole fingerprint locally in the North Atlantic, because the latter is contaminated by the “noise” of interdecadal variability. Our optimal salinity fingerprint retains much of the signal of the long-term AMOC trend response to anthropogenic forcing, while dynamically filtering out shorter climate variability. Given the ongoing anthropogenic forcing, our study indicates a potential further acceleration of AMOC weakening with associated climate impacts in the coming decades.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Subsurface Nonlinear Dynamical Heating and ENSO Asymmetry

Abstract This study presents evidence of interannual to interdecadal variabilities residing in the subsurface nonlinear dynamical heating (NDH) along the equatorial Pacific thermocline based on ocean reanalysis products. In association with a flattened thermocline and drastic halt of the Equatorial Undercurrent, the NDH increases sharply right after a peak of the strong El Niño, reducing the linear anomalous advective subsurface cooling by 30%. As the result, subsurface cold signals in the west are significantly weakened as it reaches the easternmost Pacific, causing less surface cooling in the east and thus weakening the subsequent La Niña. Therefore, the subsurface NDH contributes to asymmetry in both the magnitude and structure between El Niño and La Niña. The acute positive subsurface NDH associated with strong El Niño events leads to substantial variations in its decadal means and serves as a potential source for tropical Pacific decadal to interdecadal variabilities.

Hayashi, Michiya↗
DOE OSTI2017

Interdecadal Climate Variations Controlling the Water Level of Lake Qinghai over the Tibetan Plateau

Using observed and reanalysis research, the pronounced interdecadal variations of Lake Qinghai (LQH) water levels and associated climate factors were diagnosed. From the 1960s to the early 2000s, the water level of LQH in the Tibetan Plateau has experienced a continual decline of 3 m but has since increased considerably. A water budget assessment of the LQH watershed implied that the water vapor flux divergence ∇•Q is the dominant atmospheric process modulating precipitation and subsequently the lake volume change ΔV. The marked interdecadal variability in ΔV and ∇•Q and was found to be related to the North Pacific (NP) and Pacific decadal oscillation (PDO) modes during the cold season (November–March). Through empirical orthogonal function (EOF) and regression analyses, the water vapor sink over the LQH watershed also responds critically to the summer Eurasian wave train modulated by the low-frequency variability associated with the cold season NP and PDO modes. Removal of these variability modes (NP, PDO, and the Eurasian wave train) led to a residual uptrend in the hydrological variables of ΔV, ∇•Q and precipitation, corresponding to the net water level increase. Attribution analysis using the Coupled Model Intercomparison Project phase 5 (CMIP5) single-forcing experiments shows that the simulations driven by greenhouse gas forcing produced a significant increase in the LQH precipitation, while anthropogenic aerosols generated a minor wetting trend as well.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Global teleconnections influencing large-scale drought in the United States using SVDI

Understanding recent large-scale drought patterns and the mechanisms producing extreme drought events is vital for future drought forecasts and understanding future drought risks. Increasingly, vapor pressure deficit (VPD) has been used as an important measure of evaporative demand and proxy for drought detection. In this study, VPD is used to calculate the new Standardized VPD Drought Index (SVDI) with NASA North American Land Data Assimilation System (NLDAS) data. Previous studies have shown that SVDI accurately identifies the timing and magnitude short-term droughts in the United States (U.S). In the present study, SVDI is now used to identify large-scale drought patterns between 1980 and 2021 and drought variability driven by selected global teleconnections originating in the Pacific and Atlantic Oceans. Spatial drought characteristics were extracted from SVDI using empirical orthogonal function (EOF) analysis. Then a k-means clustering algorithm was applied to both EOF principal components and primary teleconnections, including the El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) to identify drought events driven by the Pacific Ocean. Results show that the SVDI is useful in evaluating large-scale drought variability in the U.S. related to global teleconnections, and that mechanisms influencing summer drought patterns in the Western and Southwestern U.S. are driven by a tropical-extratropical interactions originating in the equatorial Pacific Ocean related to ENSO dynamics with interdecadal variability modulated by PDO. The large-scale droughts in the Central and Southern U.S., like those in 2011 and 2012, on the other hand, are driven by the North Pacific Ocean warm pool during a strong negative PDO, which subsequently influenced variability in the Bermuda-Azores High in the Atlantic Ocean. In summer 2011, the Bermuda-Azores High weakened, reducing the onshore winds and moisture transport along the eastern Gulf of Mexico and contributing to ongoing drought in the region. The Northern Pacific and Atlantic Ocean sea surface temperatures (SSTs) have increased between 1980 and 2021. In conclusion, as SSTs continue to rise in the Northern Pacific Ocean, one consequence of the coupled North Pacific warm pool and atmospheric dynamics, is to increase summer drought variability over a large region in the southern and midwestern U.S. under global warming.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Impact of Lateral Mixing in the Ocean on El Nino in a Suite of Fully Coupled Climate Models

Abstract We examine the dependence of the amplitude of the El Nino‐Southern Oscillation (ENSO) on the mixing coefficient parameterizing the lateral mixing of tracers (A Redi ) The value of this coefficient is very uncertain, ranging in Earth System Models between a few hundred and a few thousand m 2 s −1 , with some observational estimates showing even higher values. A suite of simulations is made with two spatially varying distributions of A Redi derived from satellite observations as well as four simulations where a spatially constant A Redi is varied over a factor of 6. Surprisingly, larger values of A Redi result in stronger ENSO variability despite the higher mixing coefficients producing more efficient lateral diffusive damping of anomalies. This is because lateral mixing also warms the cold tongue, increasing vertical temperature gradients and decreasing horizontal temperature gradients. Larger vertical temperature gradients make sea surface temperatures more responsive to atmospheric forcing, while smaller horizontal temperature gradients shift the location of convection and make the atmosphere more responsive to sea surface temperature anomalies. The last effect holds across simulations as well as within individual simulations and thus also helps to explain interdecadal variability in ENSO amplitude. By contrast, a previously proposed anticorrelation between the amplitude interannual and annual variability does not hold across simulations, although it does hold within simulations. The propagation of thermocline depth anomalies is relatively insensitive to the value of A Redi . Properly specifying the lateral mixing along the equator (including distinguishing the impacts of subgridscale turbulence and tropical instability waves) appears essential to simulating ENSO.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Dryland climate change: Recent progress and challenges: Dryland Climate Change

Drylands are home to more than 38% of the world's population and are one of the most sensitive areas to climate change and human activities. This review describes recent progress in dryland climate change research. Recent findings indicate that the long-term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions, while anthropogenic aerosols exert small effects but alter its attributions. Atmosphere-land interactions determine the intensity of regional response. The largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. The global pattern and interdecadal variability of aridity changes are modulated by oceanic oscillations. The different phases of those oceanic oscillations induce significant changes in land-sea and north-south thermal contrasts, which affect the intensity of the westerlies and planetary waves and the blocking frequency, thereby altering global changes in temperature and precipitation. During 1948–2008, the drylands in the Americas became wetter due to enhanced westerlies, whereas the drylands in the Eastern Hemisphere became drier because of the weakened East Asian summer monsoon. Drylands as defined by the AI have expanded over the last 60 years and are projected to expand in the 21st century. The largest expansion of drylands has occurred in semiarid regions since the early 1960s. Dryland expansion will lead to reduced carbon sequestration and enhanced regional warming. The increasing aridity, enhanced warming, and rapidly growing population will exacerbate the risk of land degradation and desertification in the near future in developing countries.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

How Tropical Pacific Surface Cooling Contributed to Accelerated Sea Ice Melt from 2007 to 2012 as Ice is Thinned by Anthropogenic Forcing

Over the past 40 years the Arctic sea ice minimum in September has declined. The period between 2007 and 2012 showed accelerated melt contributed to the record minima of 2007 and 2012. Here, observational and model evidence shows that the changes in summer sea ice since the 2000s reflects a continuous anthropogenically forced melting masked by interdecadal variability of Arctic atmospheric circulation. This variation is partially driven by teleconnections originating from sea surface temperature (SST) changes in the east-central tropical Pacific via a Rossby wave train propagating into the Arctic (hereafter referred to as the “Pacific-Arctic teleconnection (PARC)”), which represents the leading internal mode connecting the pole to lower latitudes. This mode has contributed to accelerated warming and Arctic sea ice loss from 2007 to 2012, followed by slower declines in recent years, resulting in the appearance of a slowdown over the past 11 years. A pacemaker model simulation, in which we specify observed SST in the tropical eastern Pacific, demonstrates a physically plausible mechanism for the PARC mode. However, the model-based PARC mechanism is considerably weaker and only partially accounts for the observed acceleration of sea ice loss from 2007 to 2012. Further research is needed to identify the reasons for model limitations in reproducing the PARC mode.

Baxter, Ian↗
DOE OSTI2020

Northern Hemisphere Winter Air Temperature Patterns and Their Associated Atmospheric and Ocean Conditions

The Northern Hemisphere (NH) has experienced winter Arctic warming and continental cooling in recent decades, but the dominant patterns in winter surface air temperature (SAT) are not well understood. Here, a self-organizing map (SOM) analysis is performed to identify the leading patterns in winter daily SAT fields from 1979 to 2018, and their associated atmospheric and ocean conditions are also examined. Three distinct winter SAT patterns with two phases of nearly opposite signs and a time scale of 7–12 days are found: one pattern exhibits concurrent SAT anomalies of the same sign over North America (NA) and northern Eurasia, while the other two patterns show SAT anomalies of opposite signs between, respectively, NA and the Bering Sea, and the Kara Sea and East Asia (EA). Winter SAT variations may arise from changes in the SOM frequencies. Specifically, the observed increasing trends of winter cold extremes over NA, central Eurasia, and EA during 1998–2013 can be understood as a result of the increasing occurrences of some specific SAT patterns. These SOMs are closely related to poleward advection of midlatitude warm air and equatorward movements of polar cold airmass. These meridional displacements of cold and warm airmasses cause concurrent anomalies over different regions not only in SAT but also in water vapor and surface downward longwave radiation. Anomalous sea surface temperatures in the tropical Pacific, midlatitude North Pacific, and North Atlantic and anomalous Arctic sea ice concentrations also concur to support and maintain the anomalous atmospheric circulation that causes the SAT anomalies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Evaluation of the atmosphere–land–ocean–sea ice interface processes in the Regional Arctic System Model version 1 (RASM1) using local and globally gridded observations

The Regional Arctic System Model version 1 (RASM1) has been developed to provide high-resolution simulations of the Arctic atmosphere–ocean–sea ice–land system. Here, we provide a baseline for the capability of RASM to simulate interface processes by comparing retrospective simulations from RASM1 for 1990–2014 with the Community Earth System Model version 1 (CESM1) and the spread across three recent reanalyses. Evaluations of surface and 2 m air temperature, surface radiative and turbulent fluxes, precipitation, and snow depth in the various models and reanalyses are performed using global and regional datasets and a variety of in situ datasets, including flux towers over land, ship cruises over oceans, and a field experiment over sea ice. These evaluations reveal that RASM1 simulates precipitation that is similar to CESM1, reanalyses, and satellite gauge combined precipitation datasets over all river basins within the RASM domain. Snow depth in RASM is closer to upscaled surface observations over a flatter region than in more mountainous terrain in Alaska. The sea ice–atmosphere interface is well simulated in regards to radiation fluxes, which generally fall within observational uncertainty. RASM1 monthly mean surface temperature and radiation biases are shown to be due to biases in the simulated mean diurnal cycle. At some locations, a minimal monthly mean bias is shown to be due to the compensation of roughly equal but opposite biases between daytime and nighttime, whereas this is not the case at locations where the monthly mean bias is higher in magnitude. These biases are derived from errors in the diurnal cycle of the energy balance (radiative and turbulent flux) components. Therefore, the key to advancing the simulation of SAT and the surface energy budget would be to improve the representation of the diurnal cycle of radiative and turbulent fluxes. The development of RASM2 aims to address these biases. Still, an advantage of RASM1 is that it captures the interannual and interdecadal variability in the climate of the Arctic region, which global models like CESM cannot do.

58 GEOSCIENCES↗
DOE OSTI2018

On the relative roles of the atmosphere and ocean in the Atlantic Multi-decadal Variability

The relative roles of the ocean and the atmosphere in driving the Atlantic Multi-decadal Oscillation (AMO) are investigated by isolating the AMO components forced by anomalous surface heat fluxes and ocean dynamics in a fully- and partially-coupled experiments. The impact of the ocean-dynamics-forced SST on air-sea interaction is disabled in the partially-coupled experiment in order to isolate the atmosphere-forced variability. In the partially-coupled experiment, the ocean-forced AMO component exhibits a strong multi-decadal variability (25- to 50-yr periods), while the atmosphere-forced component has weak multi-decadal variability. This ocean-forced variability is imprinted on the fully-coupled surface heat fluxes, which however, damp the ocean-forced SST variability inducing them, so that the fully-coupled AMO multi-decadal power is only slightly stronger than that forced by the atmosphere alone. Our results suggest that the multi-decadal variability of the AMO is largely driven by ocean dynamics, but its power is also determined by the strength air-sea coupling.

Garuba, Oluwayemi A.↗
DOE OSTI2016

West African monsoon decadal variability and surface-related forcings: second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

The Sahel climate system had experienced one of the strongest interdecadal climate variabilities and the longest drought on the planet in the twentieth century. Most modeling studies on the decadal variability of the Sahel climate so far have focused on the role of anomalies in either sea surface temperature (SST), land surface processes, or aerosols concentration. The Second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II) is designed to improve understanding of the possible roles and feedback of SST, land use land cover change (LULCC), and aerosols forcings in the Sahel climate system at seasonal to decadal scales. The WAMME II strategy is to apply observationally based anomaly forcing, i.e., “idealized but realistic” forcing, in simulations by general circulation models’ (GCMs) and regional climate models’ (RCMs) to test the relative impacts of such forcings in producing/amplifying the Sahelian seasonal and decadal climate variability, including the 20th century drought. To test individual ocean’s SST effect, a special approach in the experimental design is taken to avoid undermine its effect. This is the first multi-model experiment specifically designed to simultaneously evaluate relative contributions of multiple-external forcings to the Sahel drought. This paper presents the major results and preliminary findings of the WAMME II SST experiment, including each ocean’s contribution to the global SST effect, as well as comparison of the SST effect with the LULCC effect. The common empirical orthogonal functions and other analyses are applied to assess and comprehend the discrepancies among the models. In general, the WAMME II models have reached a consensus on SST’s major contribution to the great Sahel drought and show that with the maximum possible SST forcing, it can produce up to 60% of the absolute amount of precipitation difference between the 1980s and the 1950s. This paper has 3 also delineated the role of SSTs in triggering and maintaining the Sahel drought, suggesting a potential predictability of WAM development linked to SST. Among different ocean basins, the Pacific and Indian Ocean SSTs have the greatest impact on the 1980s drought. The WAMME II, however, fails to reach a consensus on the role of the Mediterranean Sea SST. The changes in circulation, moisture flux convergence, and associated surface energy balances are the main mechanisms for the SST effect. The paper also compares the SST effect with the LULCC effects. It is shown that the prescribed land forcing produces about 40% of the precipitation difference between the 1980s and the 1950s, which is less than SST contribution but still of first order in the Sahel climate system. The role of land surface processes in responding to and amplifying the drought has also been identified. The results demonstrate that catastrophic consequences likely occur in the regional climate when SST anomalies in individual ocean basins and in land conditions combine synergistically to favor drought. Due to limited ensemble members, aerosol effects are not compared. Since the SST and land forcing in the real world are likely smaller than specified in this study, further investigations on the effects of aerosols as well as of other external forcings, such as greenhouse gases, and of atmospheric internal variability, are necessary. Moreover, although the WAMEE II models support a general consensus on SST and LULCC effects, there are still large discrepancies in how these models produce the Sahel drought in the 1980s. Better atmospheric observational and analysis data including more processes and components are necessary to validate and constrain models, and to guide further model development and improvement.

Xue, Yongkang (ORCID:0000000261699631)↗
DOE OSTI2017

Internally Generated and Externally Forced Multidecadal Oceanic Modes and Their Influence on the Summer Rainfall over East Asia

Abstract Interdecadal oceanic variabilities can be generated from both internal and external processes, and these variabilities can significantly modulate climate on global and regional scales, including the warming slowdown in the early twenty-first century and rainfall in East Asia. 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 because of the unpredictable nature of IPO 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, and the chance of reproducing the observed time evolution of both AMO and HRV rainfall is about 30%, indicating the important role of the interaction between the internal processes and the external forcing to realistically simulate the AMO and HRV rainfall.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Freshwater Flux Variability Lengthens the Period of the Low-Frequency AMOC Variability

Atlantic Meridional Overturning Circulation (AMOC) exhibits interdecadal to multidecadal variability, yet the extent to which the surface freshwater flux (FWF) variability affects the AMOC variability remains unclear. This study isolates the contribution of FWF variability in modulating AMOC through a partially coupled experiment, in which the FWF effect from the atmosphere and sea ice are disabled. It is demonstrated that the FWF effect can remarkably enhance the persistence of positive salinity anomalies in the Labrador Sea, and sustain the dense water formation that was initiated by the cold temperature anomalies. Therefore, the FWF variability serves as a positive feedback on AMOC and lengthens the period of the AMOC oscillation. Further lead-lag regressions of atmospheric and oceanic variables onto the AMOC time series illuminate that the persistent salinity anomalies are generated through two pathways: i) the phase lag between temperature and salinity anomalies in the Labrador Sea; and ii) a downstream propagation of extra high-salinity anomaly along the East Greenland Current, due to the reduced sea ice melting flux associated with an atmosphere forcing over the southern Greenland tip.

58 GEOSCIENCES↗
DOE OSTI2015

Interannual to decadal climate variability of sea salt aerosols in the coupled climate model CESM1.0

This study reported herein examines multi-year climate variability associated with sea salt aerosols and their contribution to the variability of shortwave cloud forcing (SWCF) using a 150-year simulation for pre-industrial conditions of the Community Earth System Model version 1.0 (CESM1). The results suggest that changes in sea salt and related cloud and radiative properties on interannual timescales are dominated by the ENSO cycle. Sea salt variability on longer (interdecadal) timescales is associated with low-frequency Pacific ocean variability similar to the interdecadal Pacific Oscillation (IPO), but does not show a statistically significant spectral peak. A multivariate regression suggests that sea salt aerosol variability may contribute to SWCF variability in the tropical Pacific, explaining up to 25-35% of the variance in that region. Elsewhere, there is only a small aerosol influence on SWCF through modifying cloud droplet number and liquid water path that contributes to the change of cloud effective radius and cloud optical depth (and hence cloud albedo), producing a multi-year aerosol-cloud-wind interaction.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Robust Anthropogenic Signal Identified in the Seasonal Cycle of Tropospheric Temperature

Previous work identified an anthropogenic fingerprint pattern in T AC (x, t), the amplitude of the seasonal cycle of mid- to upper-tropospheric temperature (TMT), but did not explicitly consider whether fingerprint identification in satellite T AC (x, t) data could have been influenced by real-world multidecadal internal variability (MIV). Here we address this question here using large ensembles (LEs) performed with five climate models. LEs provide many different sequences of internal variability noise superimposed on an underlying forced signal. Despite differences in historical external forcings, climate sensitivity, and MIV properties of the five models, their T AC (x, t) fingerprints are similar and statistically identifiable in 239 of the 240 LE realizations of historical climate change. Comparing simulated and observed variability spectra reveals that consistent fingerprint identification is unlikely to be biased by model underestimates of observed MIV. Even in the presence of large (factor of 3–4) intermodel and inter-realization differences in the amplitude of MIV, the anthropogenic fingerprints of seasonal cycle changes are robustly identifiable in models and satellite data. This is primarily due to the fact that the distinctive, global-scale fingerprint patterns are spatially dissimilar to the smaller-scale patterns of internal T AC (x, t) variability associated with the Atlantic multidecadal oscillation and El Niño–Southern Oscillation. The robustness of the seasonal cycle detection and attribution results shown here, taken together with the evidence from idealized aquaplanet simulations, suggest that basic physical processes are dictating a common pattern of forced T AC (x, t) changes in observations and in the five LEs. The key processes involved include GHG-induced expansion of the tropics, lapse-rate changes, land surface drying, and sea ice decrease.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Forced Component Estimation Statistical Method Intercomparison Project (ForceSMIP)

Anthropogenic climate change is unfolding rapidly, yet its regional manifestation can be obscured by internal variability. A primary goal of climate science is to identify the externally forced climate response from among the noise of internal variability. Separating the forced response from internal variability can be addressed in climate models by using a large ensemble to average over different possible realizations of internal variability. However, with only one realization of the real world, it is a major challenge to isolate the forced response directly in observations. In the Forced Component Estimation Statistical Method Intercomparison Project (ForceSMIP), contributors used existing and newly developed statistical and machine learning methods to estimate the forced response over 1950–2022 within individual realizations of the climate system. Participants used neural networks, linear inverse models, fingerprinting methods, and low-frequency component analysis, among other approaches. These methods were trained using large ensembles from multiple climate models and then applied to observations. Here, we evaluate method performance within large ensembles and investigate the estimates of the forced response in observations. Our results show that many different types of methods are skillful for estimating the forced response in climate models, though the relative skill of individual methods varies depending on the variable and evaluation metric. Methods with comparable skill in models can give a wide range of estimates of the forced response pattern in observations, illustrating the epistemic uncertainty in forced response estimates. ForceSMIP gives new insights into the forced response in observations, its uncertainty, and methods for its estimation.

Climate attribution↗