Glossary
A reference glossary for the terms used across this section. Every page in the section links here for any term defined below. If you find a term we should define and haven’t, click “Edit this page” in the footer to suggest it.
Climate science terms
AR6 — the IPCC’s Sixth Assessment Report. Working Group I (physical science basis) was published 2021; Working Group II (impacts, adaptation, vulnerability) in 2022; Working Group III (mitigation) in 2022; Synthesis Report in 2023. The current reference cycle for climate-science assessment. AR7 is in progress.
Baseline — see Reference period.
Bias correction — adjusting a climate model’s output to better match observed climate over a historical reference period. See the Bias correction page.
Climate projection — a future climate simulation conditional on a specific emissions scenario. Projection ≠ prediction — projections are scenario-dependent. See the Projections primer.
Climate sensitivity (ECS) — Equilibrium Climate Sensitivity. The warming a climate model reaches at equilibrium for a doubling of atmospheric CO₂. A fundamental property of how strongly a model represents climate feedbacks (water vapour, clouds, ice-albedo). The real climate’s ECS is assessed by IPCC AR6 at 2.5–4.0 °C (likely range) or 2.0–5.0 °C (very-likely range).
CMIP — Coupled Model Intercomparison Project. The international framework that coordinates climate-model experiments world-wide. CMIP6 is the current generation (feeds AR6); CMIP7 is in design (will feed AR7).
CORDEX — Coordinated Regional Climate Downscaling Experiment. The WCRP initiative producing dynamically-downscaled regional climate-model runs. Has an Africa domain (CORDEX-AFR-22 / AFR-44; CORDEX-CORE).
Downscaling — methods to translate a coarse-resolution global climate model output to a finer resolution useful for regional / local analysis. Two main families: statistical and dynamical. See Downscaling.
Ensemble — a collection of climate models, all run under the same scenario, treated as samples from the space of plausible futures. The ensemble mean is the central estimate; the ensemble spread (e.g. ±1 standard deviation) is the model-disagreement uncertainty.
GCM — General (or Global) Climate Model. The mathematical models that simulate the global climate system.
Hot model problem — the observation that some CMIP6 models (notably CanESM5) have climate sensitivities above the AR6 very-likely assessed range, leading them to over-project warming for impact studies. See Why models disagree §“Hot model problem”.
Internal variability — the climate’s own year-to-year and decade-to-decade noise, unrelated to forcing. ENSO, NAO, and other modes are forms of internal variability. One of the three sources of projection uncertainty.
NEX-GDDP-CMIP6 — NASA’s downscaled product based on the CMIP6 archive. 18 models, statistically downscaled to 0.25° resolution. The Adaptation Atlas’s primary projection data source.
Predicate pushdown — (data engineering term, appears in technical references) a query optimisation where filters are applied at the data source rather than after the data is loaded. Relevant to how the Atlas serves projection data efficiently to your browser.
Reanalysis — a historical climate dataset produced by running a frozen-version weather forecast model with all available observations assimilated. Not the same as direct observation — it’s a model-assisted gridded estimate. ERA5, MERRA-2, JRA-55 are the major reanalyses.
RCM — Regional Climate Model. A finer-resolution model that takes a global GCM as input and produces a higher-resolution regional simulation. The basis of CORDEX.
Reference period (or baseline) — the multi-year window of past climate against which present or future climate change is measured. Three reference periods turn up in African work: 1850–1900 (IPCC pre-industrial anchor, used for the Paris targets); 1991–2020 (WMO operational normal, used in the Atlas’s Recent Changes view and in WMO reporting); 1995–2014 (CMIP6 standard, used in NEX-GDDP-CMIP6 and the Atlas’s Future Projections view). The Atlas uses two different periods on purpose — see Baselines and reference periods.
r1i1p1f1 — the standard “first physical ensemble member” of a CMIP6 model run. The first of typically several realisations of a model; each realisation differs only in initial conditions, sampling internal variability. The Adaptation Atlas uses this realisation across all 18 models for consistency.
Scenario — a future trajectory of emissions / land use / socioeconomic development. SSP1-2.6 is “sustainability”; SSP2-4.5 is “middle of the road”; SSP3-7.0 is “regional rivalry”; SSP5-8.5 is “fossil-fuelled development.”
SSP — Shared Socioeconomic Pathway. The CMIP6 scenarios are SSPx-y.z (e.g. SSP2-4.5) — x is the socioeconomic narrative (1-5), y.z is the radiative forcing level in W/m² at 2100.
TCR — Transient Climate Response. The warming a model reaches at the moment of CO₂ doubling under a 1 % per year increase. A second climate-sensitivity metric (alongside ECS).
Walker Circulation — the equatorial Pacific east-west atmospheric circulation that connects sea-surface temperature patterns to remote rainfall. The mechanism implicated in the East African Paradox.
Acronyms — quick reference
| Abbrev. | Full name |
|---|---|
| AOGCM | Atmosphere-Ocean General Circulation Model |
| AR5 / AR6 / AR7 | IPCC Fifth / Sixth / Seventh Assessment Report |
| BCSD | Bias-Correction Spatial Disaggregation |
| CHIRPS | Climate Hazards Group InfraRed Precipitation with Stations |
| CHIRTS | Climate Hazards Group InfraRed Temperature with Stations |
| CMIP | Coupled Model Intercomparison Project |
| CORDEX | Coordinated Regional Climate Downscaling Experiment |
| ECS | Equilibrium Climate Sensitivity |
| ESM | Earth System Model |
| GCM | General / Global Climate Model |
| GHACOF | Greater Horn of Africa Climate Outlook Forum |
| ICPAC | IGAD Climate Prediction and Applications Centre |
| IPCC | Intergovernmental Panel on Climate Change |
| ISIMIP | Inter-Sectoral Impact Model Intercomparison Project |
| NDC | Nationally Determined Contribution (UNFCCC) |
| NEX | NASA Earth Exchange |
| NEX-GDDP | NEX Global Daily Downscaled Projections |
| NMHS | National Meteorological / Hydrological Service |
| RCM | Regional Climate Model |
| SSP | Shared Socioeconomic Pathway |
| TCR | Transient Climate Response |
| WCRP | World Climate Research Programme |
| WMO | World Meteorological Organization |