Tier 1 Cloud Radiative Effect
Synthesis
Related diagnostics
LW CRE Change
| Variables | avg_tnswrf, avg_tnswrfcs, avg_tnlwrf, avg_tnlwrfcs |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | W/m2 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | ΔLW CRE = Δ(allsky LW) − Δ(clearsky LW) at TOA. |
Summary high
The figure displays the projected change in Top-of-Atmosphere (TOA) Longwave Cloud Radiative Effect (LW CRE) for the 2040s (SSP3-7.0) relative to the 1990-2014 baseline, highlighting a dominant Arctic warming signal and complex shifts in tropical convection.
Key Findings
- A robust, high-magnitude positive anomaly (> +3 W/m²) covers the Arctic Ocean in both models, indicating a strong positive cloud feedback associated with sea-ice retreat.
- Significant negative anomalies (blue, -2 to -4 W/m²) are observed over the Maritime Continent and the Amazon Basin (particularly in IFS-FESOM), suggesting suppressed deep convection and reduced high-cloud cover in these regions.
- IFS-NEMO exhibits a distinct, intense positive anomaly band across the tropical Atlantic and a strong dipole in the Indian Ocean that is much more muted in IFS-FESOM.
Spatial Patterns
The high latitudes, particularly the Arctic, show widespread positive LW CRE changes. The tropics exhibit zonal asymmetry suggestive of circulation shifts: a weakening or eastward shift of the Walker circulation (drying Maritime Continent, wetter Central Pacific/Western Indian Ocean). The subtropics show broad regions of weak negative anomalies, consistent with the widening of the Hadley cells and stabilization of the troposphere.
Model Agreement
Both models agree on the sign and location of the Arctic amplification and the drying signal over the Maritime Continent. However, they disagree significantly on the magnitude of tropical convective responses; IFS-NEMO predicts much sharper and more intense positive anomalies in the Tropical Atlantic ITCZ and the Western Indian Ocean compared to the more diffuse patterns in IFS-FESOM, likely stemming from differences in Ocean Mean State (SST) between the NEMO and FESOM components.
Physical Interpretation
In the Arctic, the positive LW CRE change is driven by increased cloud fraction and moisture flux over warming, open waters (sea-ice loss), which traps more outgoing longwave radiation. In the tropics, the patterns reflect a reorganization of deep convection: blue regions (e.g., Amazon, Indonesia) indicate reduced cloud top height or fraction (subsidence/drying), while red regions indicate intensified deep convection and higher cloud tops, likely driven by localized SST warming patterns and an El Niño-like mean state response.
Caveats
- The analysis considers only the Longwave component; Shortwave (SW) CRE changes often oppose LW changes, so the Net CRE impact cannot be fully determined from this figure alone.
- The future averaging period (2040-2049) is relatively short (10 years), meaning internal decadal variability could partially obscure or amplify the forced anthropogenic climate signal compared to a 30-year climatology.
Net CRE Change
| Variables | avg_tnswrf, avg_tnswrfcs, avg_tnlwrf, avg_tnlwrfcs |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | W/m2 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | ΔNet CRE = ΔSW CRE + ΔLW CRE. |
Summary high
The figure displays the projected change in Net Cloud Radiative Effect (CRE) at the Top of Atmosphere for the 2040–2049 period relative to 1990–2014 under SSP3-7.0, showing a mix of positive and negative feedbacks with strong inter-model consistency.
Key Findings
- Widespread positive CRE anomalies (warming, +2 to +4 W/m²) are observed over the eastern subtropical ocean basins (N.E. Pacific, S.E. Atlantic, S.E. Pacific), indicating a reduction in marine stratocumulus cloud decks.
- A distinct band of negative CRE anomalies (cooling, -2 to -4 W/m²) dominates the Southern Ocean between 50°S and 60°S, consistent with increased cloud albedo.
- Tropical land masses, particularly the Amazon Basin and Central Africa, exhibit strong positive anomalies, suggesting reduced cloud cover and potential drying.
- The North Atlantic exhibits a complex response, with IFS-FESOM showing widespread positive anomalies while IFS-NEMO retains a region of negative CRE change south of Greenland.
Spatial Patterns
The data reveals a distinct zonal asymmetry in the Southern Hemisphere, characterized by a 'brightening' (negative trend) belt over the Southern Ocean. In the tropics, a horseshoe-like pattern in the Pacific and dipoles over South America indicate shifts in the ITCZ and SPCZ. Over land, the Northern Hemisphere mid-to-high latitudes show mixed signals, while major tropical rainforest regions show coherent positive trends.
Model Agreement
Agreement is structurally high between IFS-FESOM and IFS-NEMO, as both share the IFS atmospheric component. Discrepancies are most notable in the North Atlantic and Arctic, where IFS-FESOM projects stronger positive feedbacks, likely due to differences in sea ice decline and SST evolution driven by the differing ocean model formulations (unstructured FESOM vs. structured NEMO).
Physical Interpretation
The positive anomalies in the subtropics likely result from the 'spread of dry zones' and thermodynamic suppression of low-level clouds (positive shortwave feedback). The negative anomalies in the Southern Ocean are characteristic of the optical depth feedback, where warming induces a phase change from ice to supercooled liquid water, increasing cloud reflectivity. The positive signal over the Amazon implies a reduction in convective cloud cover.
Caveats
- Net CRE aggregates Shortwave (SW) and Longwave (LW) effects; decomposing these is required to distinguish between albedo changes and cloud-top height changes.
- High-latitude signals (Arctic/Antarctic) include contributions from surface albedo masking (sea-ice loss) which complicates the isolation of pure cloud feedbacks.
SW CRE Change
| Variables | avg_tnswrf, avg_tnswrfcs, avg_tnlwrf, avg_tnlwrfcs |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | W/m2 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | ΔSWE CRE = Δ(allsky SW) − Δ(clearsky SW) at TOA. |
Summary high
The figure illustrates the projected change in Shortwave Cloud Radiative Effect (SW CRE) at the Top of Atmosphere between the near-future (2040-2049) and historical baseline (1990-2014) for two coupled climate models, IFS-FESOM and IFS-NEMO. Both models predict a net positive SW CRE change (warming effect) over most subtropical oceans and major landmasses, contrasted by negative changes (cooling effect) over high-latitude oceans.
Key Findings
- Widespread positive SW CRE anomalies (+2 to +6 W/m²) are observed over eastern subtropical ocean basins (e.g., off Peru, Namibia, California), indicating a reduction in marine stratocumulus cloud reflection.
- Strong positive anomalies over the Amazon Basin and Southern Africa suggest a reduction in convective cloud cover associated with regional drying.
- Significant negative SW CRE anomalies (<-4 W/m²) dominate the Arctic Ocean and bands of the Southern Ocean, implying increased cloud reflection or cloud fraction in these warming high-latitude regions.
- The Central Pacific exhibits positive anomalies, indicating a weakening of cloud reflection likely tied to shifts in the ITCZ/SPCZ.
Spatial Patterns
The maps display a distinct zonal structure: high-latitude bands of negative change (blue) indicating increased cloud shielding; subtropical and tropical bands of positive change (red) indicating reduced cloudiness. Notable regional features include intense positive anomalies over the Amazon and Indonesia, and a 'warming hole' signature (negative anomaly) in the North Atlantic, particularly visible in IFS-FESOM.
Model Agreement
Agreement is very high between IFS-FESOM and IFS-NEMO, consistent with their shared atmospheric component (IFS). Subtle discrepancies exist in the North Atlantic subpolar gyre and the Southern Ocean (approx. 60°S), where IFS-NEMO shows a more continuous zonal band of negative anomalies while IFS-FESOM is more patchy, likely reflecting differences in ocean circulation and sea-ice handling between the finite-element (FESOM) and finite-difference (NEMO) ocean cores.
Physical Interpretation
In the subtropics, the positive anomalies are driven by the positive low-cloud feedback mechanism, where warming SSTs cause marine stratocumulus decks to dissipate or thin. Over land (Amazon/S. Africa), reduced evapotranspiration and drying lead to fewer convective clouds. In the Arctic, the negative signal is driven by sea-ice loss exposing open water, which enhances surface moisture fluxes and low-level cloud formation; the darker surface also increases the contrast between cloudy and clear skies, mathematically amplifying the negative CRE.
Caveats
- The analysis period (2040-2049) is relatively short (10 years), meaning internal variability (e.g., ENSO phases) could influence the mean state compared to a longer climatology.
- Interpretation of CRE change in the Arctic is complicated by the simultaneous drastic reduction in clear-sky surface albedo due to sea-ice melt.