Coupled Model Intercomparison Project
The Coupled Model Intercomparison Project (CMIP) is a standardized framework for coordinating and comparing simulations from global coupled ocean-atmosphere climate models, organized under the World Climate Research Programme's (WCRP) Working Group on Coupled Modelling (WGCM).[1][2] Initiated in the early 1990s as the coupled analog to the Atmospheric Model Intercomparison Project (AMIP), CMIP facilitates multi-model ensembles to evaluate climate variability, model performance against observations, and projections of future changes driven by factors such as greenhouse gas emissions.[3][4] Through successive phases—CMIP1 to CMIP6, with CMIP7 planning underway—the project has produced vast datasets that underpin assessments by the Intergovernmental Panel on Climate Change (IPCC), enabling systematic identification of model strengths and persistent systematic biases, such as in sea surface temperatures and precipitation patterns.[5][6] Key achievements include the standardization of diagnostic experiments and scenario-based projections, like those using Shared Socioeconomic Pathways in CMIP6, which have advanced understanding of climate sensitivity and inter-model spread despite challenges in fully resolving observed trends.[7][8]Background
Definition and Objectives
The Coupled Model Intercomparison Project (CMIP) is an international collaborative framework for coordinating and standardizing simulations from global coupled atmosphere-ocean general circulation models, and later Earth system models, to evaluate climate variability and projections. Initiated in 1995 by the Working Group on Coupled Modelling (WGCM) under the World Climate Research Programme (WCRP), CMIP serves as the analog to the Atmospheric Model Intercomparison Project (AMIP) but extends to fully coupled ocean-atmosphere systems, enabling assessments of interactions across Earth's climate components including land, sea ice, and biogeochemical cycles.[3][9] The core objective of CMIP is to enhance understanding of past, present, and future climate changes driven by natural variability or anthropogenic forcings through multi-model intercomparisons, which reveal robust patterns amid model uncertainties. By defining common experimental protocols—such as control runs, idealized forcing scenarios (e.g., abrupt quadrupling of atmospheric CO₂), and historical simulations—CMIP facilitates direct comparisons of outputs from dozens of modeling groups, typically over 50 centers by recent phases, to quantify ensemble means, spread, and discrepancies attributable to parameterization differences or resolution variations.[9][3] This approach supports model evaluation against observations, identification of systematic biases (e.g., in tropical precipitation or cloud feedbacks), and iterative improvements in model physics and resolution.[9] Additionally, CMIP aims to generate standardized, open-access datasets for broader scientific analysis, policy assessments, and IPCC reports, addressing questions on climate sensitivity, regional impacts, and forcing-response relationships while highlighting limitations from model simplifications or incomplete process representations. The Program for Climate Model Diagnosis and Intercomparison (PCMDI) at Lawrence Livermore National Laboratory provides infrastructural support, including data archiving and analysis tools, to WGCM in scoping experiments and disseminating results.[3][9]Organizational Framework
The Coupled Model Intercomparison Project (CMIP) operates as a coordinated international effort under the World Climate Research Programme (WCRP), specifically within its Earth System Modelling and Observations (ESMO) core project.[9] It is overseen by the CMIP Panel, which guides the project's experimental design, endorses subsidiary Model Intercomparison Projects (MIPs), and coordinates participation from global modeling groups.[9] The Working Group on Coupled Modelling (WGCM), a WCRP panel established to advance coupled climate models, provides strategic direction and reviews model developments to support CMIP's objectives.[10] Technical infrastructure is managed by the WCRP ESMO Infrastructure Panel (WIP), which standardizes data protocols, facilitates archiving through the Earth System Grid Federation (ESGF), and ensures accessibility of simulation outputs exceeding 14 petabytes in recent phases.[9] Over 50 modeling centers have contributed to phases like CMIP6, submitting simulations according to defined protocols for core diagnostics, historical runs, and scenario experiments.[9] This structure evolved to address growing complexity, with task teams now aiding CMIP7 design and emphasizing streamlined coordination for timely data delivery expected in early 2026.[9]Historical Phases
Early Phases (CMIP1 and CMIP2)
The Coupled Model Intercomparison Project (CMIP) was established in 1995 by the Working Group on Coupled Modelling (WGCM) under the World Climate Research Programme (WCRP) to standardize and compare simulations from global coupled ocean-atmosphere general circulation models (GCMs).[11][9] CMIP1, initiated in 1996, focused on control experiments where external forcings such as CO2 concentrations and solar irradiance were held constant at pre-industrial levels to assess models' ability to simulate mean climatology without transient changes.[11][12] These runs, analogous to the earlier Atmospheric Model Intercomparison Project (AMIP) but extended to fully coupled systems, involved 15 participating models and emphasized evaluation of equilibrium climate states, including systematic biases in sea surface temperatures and flux adjustments used by many models to mitigate drift.[13][14] CMIP2, announced on January 7, 1997, expanded the framework to include transient forcing experiments, specifically a 1% per year compound increase in atmospheric CO2 concentrations over 80 years, reaching doubling around year 70.[15] This phase aimed to intercompare models' climate sensitivity, the time-evolving response to radiative forcing, and the influence of flux adjustments on sensitivity estimates, with optional paired control runs and equilibrium 2xCO2 mixed-layer ocean experiments for context.[15] Seventeen to 18 models contributed data, representing groups from Australia (2), Canada (1), France (2), Germany (3), Japan (2), the United Kingdom (1), and the United States (7), with approximately half employing flux corrections.[15] Outputs included expanded diagnostic fields beyond CMIP1, enabling analyses of inter-model spread in surface temperature, precipitation, and ocean heat uptake.[15] Results from both phases informed the Intergovernmental Panel on Climate Change's Third Assessment Report (2001), particularly in evaluating model performance for present-day climate and projecting transient responses to greenhouse gas increases, highlighting persistent challenges like excessive ocean drift in non-flux-adjusted models and variability in equilibrium sensitivity estimates ranging from 1.5°C to over 6°C.[12] These early efforts laid the groundwork for standardized protocols but revealed limitations in data volume and experiment design, prompting subsequent phases to incorporate historical simulations and ensemble approaches.[11]CMIP Phase 3
The Coupled Model Intercomparison Project Phase 3 (CMIP3) represented a significant expansion in coordinated climate modeling efforts, building on earlier phases by emphasizing multi-model ensembles for evaluating 20th- and 21st-century climate simulations. Initiated under the World Climate Research Programme's Working Group on Coupled Modelling (WCRP WGCM), CMIP3 focused on archiving output from coupled ocean-atmosphere general circulation models (GCMs) to support research into the physical climate system, including atmosphere, land, ocean, and sea ice components.[8] Data collection commenced in 2004, with primary submissions occurring between 2005 and 2006, enabling standardized comparisons of model performance against observations and projections of future climate change.[16] This phase marked the first large-scale effort to produce a comprehensive, openly accessible multimodel dataset tailored for the Intergovernmental Panel on Climate Change's (IPCC) Fourth Assessment Report (AR4), published in 2007.[17] Seventeen modeling groups from twelve countries contributed simulations from 24 distinct models to the CMIP3 archive, hosted by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) at Lawrence Livermore National Laboratory.[16] These contributions included equilibrium climate sensitivity estimates, transient simulations, and variability analyses, allowing for robust assessment of intermodel spread in key metrics such as global temperature response to radiative forcing.[8] The dataset's scale—exceeding 30 terabytes by early 2005 and growing to over 36 terabytes by 2009—facilitated peer-reviewed analyses by thousands of researchers, with more than 250 journal publications emerging from its use by July 2009.[16][8] CMIP3 defined twelve core experiments to standardize model forcings and outputs, including the 20th-century simulation (20c3m) incorporating anthropogenic and natural forcings such as greenhouse gases, aerosols, solar variability, and volcanic activity from 1870 to 2000.[16] Future-oriented runs encompassed Special Report on Emissions Scenarios (SRES) projections under pathways A1B, A2, and B1, extending to 2100, alongside commitment experiments to isolate thermal inertia effects post-forcing stabilization.[16] Control simulations provided baselines without external forcings, enabling detection of internal variability. These protocols ensured consistency in variables like surface temperature, precipitation, and sea-level pressure, with outputs adhering to IPCC-standard requirements for monthly and daily means.[8] The PCMDI archive made CMIP3 data freely available for non-commercial research via the Earth System Grid (ESG) portal, FTP, and OPeNDAP protocols, amassing over 536 terabytes of downloads from more than 2,500 registered users by 2009.[8] This infrastructure underpinned AR4's Working Group I assessments, where multimodel means informed projections of warming ranges (e.g., 1.8–4.0°C by 2100 under various SRES scenarios) and regional patterns, while highlighting uncertainties in cloud feedbacks and ocean heat uptake.[17] Despite advances, later evaluations noted CMIP3 models' tendencies to overestimate tropical precipitation and underestimate Arctic sea ice decline compared to observations, informing refinements in subsequent phases.[8]CMIP Phase 5
CMIP5, the fifth phase of the Coupled Model Intercomparison Project, was endorsed by the World Climate Research Programme's Working Group on Coupled Modelling in September 2008 and provided a coordinated framework for climate simulations underpinning the Intergovernmental Panel on Climate Change's Fifth Assessment Report (AR5), published in 2013.[4][18] It engaged 20 international climate modeling groups, yielding outputs from coupled atmosphere-ocean general circulation models and Earth system models to evaluate mechanisms driving model divergences, particularly in cloud and carbon cycle feedbacks, and to probe decadal-scale climate predictability.[4] First model outputs became available in February 2011, aligning with AR5 deadlines including a July 2012 paper submission cutoff and a March 2013 publication deadline for citations.[4] The protocol outlined 35 experiments, encompassing core diagnostics for baseline model behavior, historical runs from 1850 to at least 2012 incorporating observed greenhouse gas concentrations, aerosols, solar variability, and volcanic forcings, and idealized tests such as abrupt quadrupling of atmospheric CO2 (abrupt4xCO2) for equilibrium climate sensitivity and 1% annual CO2 increase (1pctCO2) for transient responses.[18][19] Future projections utilized four Representative Concentration Pathways (RCPs), quantifying radiative forcings in 2100 relative to pre-industrial levels: RCP2.6 (~2.6 W/m², stringent mitigation), RCP4.5 (~4.5 W/m², intermediate stabilization post-2100), RCP6.0 (~6.0 W/m², higher stabilization), and RCP8.5 (~8.5 W/m², rising emissions without policy intervention).[20] Decadal prediction experiments, initialized from observed ocean and atmosphere states around 1960–2012, extended short-term forecasts to assess near-term variability.[19] These simulations supported AR5's analyses of 20th-century climate fidelity against observations, attribution of warming to anthropogenic forcings, and projections of global temperature increases (e.g., likely 1.0–3.7°C by 2100 under RCP2.6–8.5 across models), regional patterns, and extremes, while revealing persistent intermodel spreads in equilibrium climate sensitivity (typically 2–4.5°C) due to unresolved cloud-aerosol interactions.[21] Enhanced metadata standards via the METAFOR initiative improved data interoperability, with archives hosted on the Earth System Grid Federation for global access, though model resolutions varied (e.g., horizontal grids from ~1° to 3°), limiting uniformity in process representation.[4]CMIP Phase 6
The Coupled Model Intercomparison Project Phase 6 (CMIP6) represents an expansion in scope and complexity over prior phases, with experimental design formalized in 2016 to support coordinated simulations across global modeling centers.[22] Coordinated by the World Climate Research Programme's Working Group on Coupled Modelling (WGCM) and hosted by the Program for Climate Model Diagnosis and Intercomparison (PCMDI), CMIP6 emphasized a federated structure including core Diagnostic Experiments (DECK)—such as pre-industrial control (piControl) and Atmospheric Model Intercomparison Project (AMIP) runs—alongside historical simulations spanning 1850 to the near-present using observed forcings.[22][2] This phase incorporated 23 endorsed Model Intercomparison Projects (MIPs), addressing specialized topics like aerosol-cloud interactions (AERMIP), high-resolution modeling (HighResMIP), and polar amplification (Polar MIP).[23] CMIP6 targeted four key science questions: the origins and consequences of systematic model biases; assessment of future climate changes amid variability, predictability, and forcing uncertainties; process-level understanding for model improvement; and regional-scale climate responses.[22] Unlike CMIP5's reliance on Representative Concentration Pathways (RCPs), CMIP6's Scenario Model Intercomparison Project (ScenarioMIP) integrated Shared Socioeconomic Pathways (SSPs) with radiative forcing levels (e.g., SSP1-2.6, SSP5-8.5), enabling exploration of coupled human-Earth system dynamics and a broader range of plausible futures.[22] Simulations encouraged higher spatial resolutions (e.g., ~100 km for atmosphere/ocean) and greater use of Earth system models (ESMs) incorporating biogeochemical cycles.[22] Over 49 modeling groups contributed from 132 registered models, producing outputs from 322 experiments archived via the Earth System Grid Federation (ESGF), totaling approximately 24.5 petabytes across 6.4 million datasets.[24] Data production occurred primarily between 2015 and 2021, with CMIP6 serving as the foundational dataset for the Intergovernmental Panel on Climate Change's Sixth Assessment Report (AR6), published in 2021-2022.[25] Notable advancements included refined representations of clouds, aerosols, and ocean dynamics, though inter-model spread in equilibrium climate sensitivity increased compared to CMIP5, with some models exceeding 5°C for doubled CO2.[22][26]CMIP Phase 7
CMIP Phase 7 (CMIP7), coordinated by the World Climate Research Programme (WCRP), is the forthcoming iteration of the Coupled Model Intercomparison Project, emphasizing a continuous, evolving framework to support ongoing climate assessments and research.[27] As of October 2025, it remains in early organizational stages, with planning initiated following the completion of CMIP6 data releases, building on lessons from prior phases to enhance model coordination and data accessibility.[28] The phase introduces a "Fast Track" subset of experiments, including the Assessment Fast Track, designed to deliver targeted simulations for timely policy-relevant outputs, such as those informing the IPCC Seventh Assessment Report (AR7).[29] CMIP7 is motivated by four fundamental research questions: (1) patterns of sea surface change, (2) changing weather patterns, (3) the water-carbon-climate nexus, and (4) risks of tipping points.[27] To address these, the phase expands the Core Diagnostic Experiments (DECK) to include updated baselines such as historical simulations, Earth system model historical runs (esm-hist), pre-industrial climate controls (piClim-control), anthropogenic forcing experiments (piClim-anthro), and abrupt 4xCO2 forcing (piClim-4xCO2), endorsed by the Working Group on Coupled Modelling (WGCM) in March 2024.[27] Key advances feature a shift toward CO2-emissions-driven experiments (e.g., flat10 scenarios maintaining constant emissions), new scenario sets encompassing low, medium, and high emissions pathways, and sustained endorsement of 35 community-led Model Intercomparison Projects (MIPs).[29] [30] Forcing datasets have been updated to cover at least through 2021, with prototype versions available by late 2024 to facilitate model runs.[31] The CMIP7 Data Request is under development via the Harmonised Thematic Variables process, managed by a dedicated task team, to standardize output variables across experiments.[32] Initial model output data are anticipated starting in late 2025, aligning with an ambitious timeline that accounts for modeling center capacities and uncertainties in AR7 scheduling.[33] Enhanced protocols, including the Essential Model Documentation standard, aim to improve transparency and reproducibility, while the CMIP International Project Office provides ongoing support for infrastructure and community engagement.[29] This structure prioritizes periodic data releases over a single large archive, enabling iterative refinements based on emerging scientific needs.[30]Methodology and Experiments
Core Diagnostic Experiments (DECK)
The Core Diagnostic Experiments (DECK), an acronym for Diagnostic, Evaluation and Characterization of Klima, form the foundational set of simulations required for all models participating in the Coupled Model Intercomparison Project (CMIP). These experiments establish a standardized baseline to characterize each model's climatology, internal variability, and response to radiative forcing, enabling direct inter-model comparisons independent of specific scenario assumptions.[23][34] Introduced in CMIP5 and retained in subsequent phases including CMIP6, the DECK ensures continuity across phases by mandating a minimal set of idealized and control runs that document basic model behavior before more complex simulations.[22] This core requirement facilitates evaluation of model fidelity against observations and paleoclimate proxies, while isolating equilibrium and transient climate sensitivities.[23] The DECK comprises four principal experiments: the pre-industrial control (piControl), abrupt quadrupling of atmospheric CO2 concentration (abrupt-4xCO2), 1% per year compounded increase in CO2 (1pctCO2), and the Atmosphere Model Intercomparison Project (AMIP) simulation. Each is designed with precise protocols for initial conditions, forcings, and integration lengths to minimize variability in setup across modeling groups. For instance, piControl and the CO2 perturbation experiments branch from a stable pre-industrial state, using fixed radiative forcings representative of 1850 conditions, including constant greenhouse gases, aerosols, solar irradiance, and land use.[34][22] These simulations typically span centuries to capture long-term drifts and variability, with piControl requiring at least 500 years to adequately sample unforced internal climate modes such as El Niño-Southern Oscillation or decadal oscillations.[23] The piControl experiment maintains constant pre-industrial forcings to simulate the unperturbed Earth system, serving as a reference for detecting forced signals in other runs and quantifying internal variability that can mask anthropogenic trends.[23] It allows assessment of model drift from initial conditions and provides a baseline climatology for comparison with historical simulations. The abrupt-4xCO2 experiment, initialized from year 1 of piControl, instantaneously quadruples CO2 concentration and holds it fixed thereafter, typically for 150 years or longer; this isolates the equilibrium response to a step forcing, enabling estimation of equilibrium climate sensitivity (ECS) through methods like radiative forcing regression on global mean surface temperature.[34][22] Similarly, the 1pctCO2 experiment increases CO2 by 1% annually from pre-industrial levels for 140 years (reaching 4xCO2), followed by stabilization or extension; it quantifies transient climate response (TCR), the warming at the time of CO2 doubling under gradual forcing, which is crucial for projecting near-term climate changes.[23] The AMIP experiment decouples the atmosphere-ocean general circulation model by prescribing observed sea surface temperatures (SSTs), sea ice, and continental conditions from 1870 or 1979 to present (e.g., 1979–2014 in CMIP6), with evolving historical forcings; this validates the atmospheric component's realism against reanalyses and observations, identifying biases in precipitation, clouds, or dynamics before full coupling.[34] Collectively, DECK outputs support diagnostics like effective radiative forcing, feedback analysis, and energy budget closure, with data standardized via the Earth System Grid Federation for interoperability.[22] While these experiments prioritize idealized perturbations over real-world complexity, they underpin CMIP's value by providing robust, reproducible benchmarks for model improvement and uncertainty quantification in climate sensitivity.[23]Historical and Scenario Simulations
The historical simulations within the Coupled Model Intercomparison Project (CMIP) require participating climate models to integrate from pre-industrial conditions, typically starting in 1850, through to the recent past using time-varying observed forcings. These forcings encompass anthropogenic greenhouse gas concentrations, short-lived climate forcers like aerosols and tropospheric ozone, natural variability from solar irradiance and volcanic eruptions, and land use changes derived from historical datasets.[35] In CMIP6, the standard historical period spans 1850–2014, enabling direct evaluation of model outputs against instrumental records for metrics such as global mean surface temperature, sea level rise, and regional precipitation patterns.[36] Earlier phases, such as CMIP5, extended historical runs to 2005 or 2014 with similar forcings, while CMIP3 focused on 1871–2000 to align with available observations.[4] These simulations form the "entry card" for model participation, quantifying reproducibility of 20th-century warming—estimated at 0.6–1.0°C globally—and identifying biases in phenomena like the Atlantic Multidecadal Oscillation.[37] Historical runs connect directly to the Core Diagnostic Experiments (DECK) by initializing from control simulations (e.g., pre-industrial 1850 conditions) and provide baselines for attributing observed changes to specific forcings. For instance, models driven by all forcings versus natural-only forcings demonstrate that anthropogenic influences dominate post-1950 temperature trends, with multi-model ensembles showing a forced response of approximately 0.7°C from 1850–2014.[22] Data from these simulations, archived via the Earth System Grid Federation, support analyses of internal variability versus forced signals, though inter-model spread in aerosol effects can exceed 0.5°C in regional means.[34] Scenario simulations extend historical integrations into the future (e.g., 2015–2100 or beyond) under prescribed radiative forcing pathways to explore potential climate outcomes. In CMIP5, the Representative Concentration Pathways (RCPs) defined four trajectories—RCP2.6 (peak forcing ~3 W/m² stabilizing near 2.6 W/m² by 2100), RCP4.5, RCP6.0, and RCP8.5 (increasing to ~8.5 W/m²)—focusing on end-of-century forcings without explicit socio-economic narratives.[4] CMIP6's Scenario Model Intercomparison Project (ScenarioMIP) refines this by integrating Shared Socio-economic Pathways (SSPs) with forcing levels, yielding scenarios like SSP1-1.9 (low emissions, net-zero by 2050), SSP1-2.6, SSP2-4.5 (middle-of-the-road), SSP3-7.0 (regional rivalry, high emissions), and SSP5-8.5 (fossil-fueled development).[38] These drive multi-model projections for impacts assessment, with ensembles revealing equilibrium climate sensitivity influencing warming ranges (e.g., 1.5–4.5°C across models under SSP2-4.5).[39] ScenarioMIP emphasizes tiered experiments: Tier 1 for core long-term projections (e.g., 2015–2100), Tier 2 for variability-focused runs, and Tier 3 for low-likelihood, high-impact cases like abrupt aerosol reductions.[38] This structure allows quantification of uncertainty from emissions, land use, and biogeochemical feedbacks, with historical-to-scenario transitions ensuring continuity in ocean heat uptake and carbon cycle states. For CMIP7 planning as of 2024, scenarios may incorporate updated SSPs with extended timelines to 2300 for long-term commitments.[40] Outputs inform probabilistic projections, though model spread in transient climate response (e.g., 1.2–2.5°C per CO2 doubling) underscores ongoing challenges in constraining future sea ice loss or extreme event frequencies.[41]Endorsed Model Intercomparison Projects (MIPs)
The Endorsed Model Intercomparison Projects (MIPs) extend the core CMIP framework by coordinating specialized simulations and diagnostics to probe targeted climate processes, feedbacks, and forcings not comprehensively addressed in the Diagnostic Experiments (DECK) or historical runs. These projects underwent a formal endorsement process by the World Climate Research Programme's (WCRP) Working Group on Coupled Modelling (WGCM) and CMIP Panel, requiring proposals to align with CMIP's overarching science questions—such as radiative forcings, climate variability, and future projections—while demonstrating links to DECK baselines, resource feasibility, and multi-model participation (typically at least 10 groups committing to priority experiments). Endorsement ensures standardized protocols for experiment design, variable output, and analysis, enabling robust intercomparisons that reveal model strengths, biases, and uncertainties.[22][42] In CMIP6, launched in 2016, 21 MIPs received endorsement between 2014 and mid-2015, comprising 17 simulation-based MIPs and 4 diagnostic MIPs that primarily specify additional output requests from existing simulations rather than new integrations. These MIPs collectively generated petabytes of data, supporting assessments like the Intergovernmental Panel on Climate Change's Sixth Assessment Report by quantifying uncertainties in areas such as aerosol effects on clouds, land-use impacts on biogeochemistry, and ocean heat uptake dynamics. Participation varied, with popular MIPs like ScenarioMIP involving over 30 models, while niche ones like SolarMIP drew fewer but focused contributions.[22][42] Prominent CMIP6-endorsed MIPs include:| Acronym | Full Name | Primary Focus |
|---|---|---|
| AerChemMIP | Aerosols and Chemistry Model Intercomparison Project | Interactive atmospheric chemistry, aerosol-radiation and aerosol-cloud interactions, and their climate forcing. |
| C4MIP | Coupled Climate–Carbon Cycle Model Intercomparison Project | Terrestrial and ocean carbon cycle feedbacks to CO₂ and climate change. |
| DAMIP | Detection and Attribution Model Intercomparison Project | Single-forcing experiments to attribute historical and future changes to specific drivers like greenhouse gases or ozone.[22] |
| DCPP | Decadal Climate Prediction Project | Initialized predictions on seasonal-to-decadal timescales, evaluating predictability from internal variability and external forcings. |
| GeoMIP | Geoengineering Model Intercomparison Project | Solar radiation management simulations to assess engineered climate interventions. |
| HighResMIP | High Resolution Model Intercomparison Project | Effects of increased horizontal resolution (≤50 km atmosphere, ≤10 km ocean) on mean climate and variability. |
| ISMIP6 | Ice Sheet Model Intercomparison Project for CMIP6 | Greenland and Antarctic ice sheet contributions to sea-level rise under forcing scenarios.[14] |
| LUMIP | Land-Use Model Intercomparison Project | Biogeophysical and biogeochemical impacts of land-use and land-cover changes. |
| ScenarioMIP | Scenario Model Intercomparison Project | Tiered future projections under Shared Socioeconomic Pathways (SSPs) for long-term climate change assessment.[39] |