Tier 1 SST Patterns

2 figures · 1990–2014 → 2040–2049

Synthesis

Projected mid-century warming is punctuated by an AMOC-induced North Atlantic cooling hole (-1.5 K) and intense heating hotspots (>2 K) in Western Boundary Current extensions and Arctic marginal seas.
Under SSP3-7.0, high-resolution coupled simulations (IFS-FESOM, IFS-NEMO) project a highly heterogeneous SST response for the 2040–2049 period, characterized by a robust North Atlantic Warming Hole (NAWH) and intense warming in Western Boundary Current (WBC) extensions. The NAWH manifests as a regional cooling of up to -1.5 K south of Greenland, physically consistent with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and reduced northward heat transport. Conversely, the Gulf Stream and Kuroshio extensions exhibit warming rates exceeding +2 K—approximately 2 to 3 times the global average—indicating a poleward shift and intensification of subtropical gyres. Arctic amplification is distinct, with marginal seas (Barents, Kara) displaying warming ratios exceeding 3 relative to the global mean, driven by localized sea-ice loss and positive albedo feedbacks. While structural agreement is strong regarding Northern Hemisphere dynamics, notable discrepancies emerge in the Southern Ocean. Both models depict delayed warming (ratios <1) attributable to deep mixing and continuous upwelling, but IFS-FESOM resolves sharper, filamentary thermal structures in the Agulhas Retroflection, likely a result of its unstructured grid resolution. IFS-NEMO diverges by predicting a specific cooling anomaly (~-1 K) in the Amundsen/Bellingshausen sector that is largely absent in IFS-FESOM, suggesting model sensitivities regarding Southern Ocean deep-water formation or ice-shelf coupling parameterizations.

Related diagnostics

amoc_strength sea_ice_concentration ocean_heat_transport

SST Change (Annual)

SST Change (Annual)
Variables avg_tos
Models ifs-fesom, ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method Future mean minus historical mean of avg_tos.

Summary high

The figure illustrates projected annual Sea Surface Temperature (SST) changes for the 2040–2049 period relative to 1990–2014 under the SSP3-7.0 scenario for two high-resolution coupled models, IFS-FESOM and IFS-NEMO. Both models exhibit a classic pattern of global warming punctuated by a prominent North Atlantic 'warming hole' and enhanced warming in western boundary currents and high latitudes.

Key Findings

  • A distinct North Atlantic Warming Hole (NAWH) is present in both models, showing regional cooling of up to -1.5 K south of Greenland/Iceland despite global warming.
  • Intense warming exceeding the colorbar saturation (> 2 K) is observed in the Gulf Stream extension, Kuroshio Extension, and the Nordic/Barents Seas.
  • IFS-FESOM displays sharper, filament-like warming structures in the Southern Ocean and Agulhas Retroflection compared to IFS-NEMO.
  • IFS-NEMO shows a pronounced cooling patch (~-1 K) in the Pacific sector of the Southern Ocean (Amundsen/Bellingshausen Sea region) which is largely absent or weaker in IFS-FESOM.

Spatial Patterns

Warming is hemispherically asymmetric, with the Northern Hemisphere high latitudes warming faster than the Southern Hemisphere (Arctic Amplification). Western Boundary Currents (Gulf Stream, Kuroshio, Brazil-Malvinas, Agulhas) appear as narrow bands of intense warming, suggesting a poleward shift of these fronts. The tropical oceans show broad warming of 0.8–1.2 K. A 'warming hole' dipole structure is evident in the North Atlantic, where the subpolar gyre cools while the Gulf Stream path warms significantly.

Model Agreement

There is strong agreement on the large-scale forced response: general tropical warming, Arctic amplification, and the location of the North Atlantic warming hole. Disagreements arise in the Southern Ocean, where IFS-NEMO predicts a localized cooling area not seen in IFS-FESOM, and in the textural details of the warming, where IFS-FESOM resolves finer eddy-scale thermal anomalies, likely due to the unstructured grid's effective resolution in dynamically active regions.

Physical Interpretation

The North Atlantic warming hole is the fingerprint of a weakening Atlantic Meridional Overturning Circulation (AMOC), leading to reduced northward heat transport. The extreme warming in the Nordic Seas and Arctic is driven by sea-ice loss and albedo feedback. The bands of high warming along Western Boundary Currents are consistent with a poleward shift and intensification of the subtropical gyres under climate change. The delayed warming in the Southern Ocean results from deep mixing and the upwelling of unmodified deep waters.

Caveats

  • The 10-year averaging period (2040-2049) is short, meaning internal decadal variability (e.g., ENSO, IPO, AMV) may contaminate the anthropogenic signal.
  • The color scale saturates at ±2 K, obscuring the maximum magnitude of warming in the Arctic and WBC extensions.

Normalized SST Pattern

Normalized SST Pattern
Variables avg_tos
Models ifs-fesom, ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method ΔSST / mean(ΔSST). HealPix equal-area cells, simple .mean() is used.

Summary high

The figure displays normalized Sea Surface Temperature (SST) change patterns for IFS-FESOM and IFS-NEMO under the SSP3-7.0 scenario (2040-2049 vs 1990-2014), highlighting distinct regions of amplified warming in Western Boundary Currents and high latitudes versus suppressed warming in the North Atlantic and Southern Ocean.

Key Findings

  • Both models exhibit a prominent 'warming hole' (normalized ratio < 0) in the subpolar North Atlantic, indicative of AMOC weakening.
  • Western Boundary Current extensions (Gulf Stream and Kuroshio-Oyashio) show warming rates 2-3 times the global average.
  • Marginal sea ice zones (Barents, Kara, Okhotsk, Hudson Bay) display the highest warming ratios (> 3) due to ice-albedo feedbacks.
  • The Southern Ocean generally warms slower than the global mean (ratio < 1), with IFS-NEMO showing a more pronounced cooling signal in the Weddell Sea sector.

Spatial Patterns

The maps reveal strong hemispheric asymmetry. The Northern Hemisphere is dominated by polar amplification in marginal seas and hotspots along western boundary currents. The North Atlantic features a distinct minimum south of Greenland. The Southern Hemisphere is characterized by delayed warming (ratios 0–1) in the Southern Ocean, punctuated by a band of high warming in the Agulhas Return Current region (~40°S). Eastern boundary upwelling systems (e.g., Humboldt, California) also show suppressed warming ratios.

Model Agreement

There is high structural agreement between IFS-FESOM and IFS-NEMO regarding the location of major hotspots (Kuroshio, Gulf Stream) and the North Atlantic warming hole. Discrepancies are evident in the Southern Ocean, particularly the Weddell Sea, where IFS-NEMO depicts a stronger negative anomaly than IFS-FESOM, likely due to differences in deep water formation or ice-ocean coupling implementation.

Physical Interpretation

The North Atlantic warming hole is physically consistent with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) reducing northward heat transport. Extreme warming in the Barents/Kara seas is driven by sea-ice loss and the resulting albedo feedback. The hotspots in the Gulf Stream and Kuroshio extensions likely reflect a poleward shift or intensification of these currents. The delayed warming in the Southern Ocean is typical of regions with deep mixed layers and continuous upwelling of cold deep waters.

Caveats

  • The 10-year averaging period (2040-2049) is relatively short, meaning internal decadal variability could partially obscure the forced climate change signal.
  • The analysis is limited to the mid-century timeframe; patterns, particularly in the Southern Ocean, may evolve differently on centennial scales.