Tier 1 Sea Ice Changes
Synthesis
Related diagnostics
Sea Ice Concentration Change (NH)
| Variables | avg_siconc |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | 0-1 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary high
The figure illustrates the projected change in annual mean sea ice concentration (SIC) in the Northern Hemisphere between the baseline (1990-2014) and the near-future (2040-2049) under the SSP3-7.0 scenario for IFS-FESOM and IFS-NEMO models.
Key Findings
- Both models project a decline in annual mean sea ice concentration, primarily concentrated in the marginal ice zones.
- The most significant reductions (indicated by negative anomalies approaching or exceeding -0.2) occur in the Barents and Kara Seas, as well as Baffin Bay.
- The central Arctic Ocean exhibits minimal change in annual mean concentration, suggesting that winter refreezing remains sufficient to maintain high average cover despite potential summer losses.
Spatial Patterns
Sea ice retreat is spatially asymmetric, heavily dominated by losses in the Atlantic sector (Barents, Kara, and Greenland Seas). There is also noticeable decline in the Baffin Bay/Labrador Sea region. In contrast, the annual mean concentration in the central Arctic basin remains relatively stable (close to zero change), indicating that the ice pack persists year-round on average in this timeframe.
Model Agreement
There is strong qualitative and quantitative agreement between IFS-FESOM and IFS-NEMO. Both models identify identical regions of sea ice loss with comparable magnitudes, reinforcing the robustness of the projected response to forcing in these high-resolution configurations.
Physical Interpretation
The pattern is consistent with the 'Atlantification' of the Arctic, where the intrusion of warm Atlantic water into the Barents and Kara Seas accelerates sea ice melt. The general retreat along the ice edge is driven by Arctic Amplification (enhanced polar warming). The stability of the central annual mean reflects the dominance of the winter season in the annual average, where temperatures likely remain low enough for 100% concentration despite thinning.
Caveats
- The use of annual means obscures seasonal variability; summer (September) sea ice loss is likely much more extensive than the annual average suggests.
- The color scale limits (+/- 0.2) are likely saturated in areas like the Barents Sea, where the loss of sea ice concentration often exceeds 20% in future scenarios.
Sea Ice Concentration Change (SH)
| Variables | avg_siconc |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | 0-1 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary high
Comparison of Antarctic sea ice concentration (SIC) changes between 1990-2014 and 2040-2049 under SSP3-7.0 shows divergent behaviors; IFS-NEMO projects widespread circum-Antarctic loss, whereas IFS-FESOM predicts a localized but substantial increase in the Weddell Sea sector amidst broader declines.
Key Findings
- IFS-NEMO exhibits a coherent annular pattern of sea ice loss, with concentration decreases of -0.1 to -0.2 evident in the Ross, Amundsen, and Bellingshausen sectors.
- IFS-FESOM displays a stark dipole in response: while the Ross and East Antarctic sectors show declines similar to NEMO, the Weddell Sea Gyre shows a strong positive SIC anomaly (increase > +0.15).
- The magnitude of mean SIC change generally remains within ±0.2 for this mid-century time slice, suggesting gradual rather than catastrophic loss in these high-resolution runs.
Spatial Patterns
In IFS-NEMO, the marginal ice zone retreats relatively uniformly around East Antarctica and the Pacific sector. In contrast, IFS-FESOM features a large, intense region of sea ice growth extending northeast from the Antarctic Peninsula into the Weddell Sea, flanked by areas of ice loss along the continental margin.
Model Agreement
The models agree on the sign of change (negative) for the East Antarctic, Ross, and Amundsen sectors. There is strong disagreement in the Weddell Sea sector, where IFS-NEMO simulates decline while IFS-FESOM simulates expansion.
Physical Interpretation
The widespread loss in both models is driven by thermodynamic warming of the atmosphere and ocean under SSP3-7.0. The anomalous sea ice expansion in the IFS-FESOM Weddell Sea is likely a signature of projected upper-ocean freshening (via increased precipitation or meltwater) leading to enhanced stratification. This stratification can shut down deep convection (if present in the baseline), isolating the surface from warm deep waters and facilitating surface cooling and ice expansion—a mechanism often referred to as the 'polynya shutdown' effect.
Caveats
- The 10-year averaging period (2040-2049) is relatively short and may be heavily influenced by internal multi-decadal variability (e.g., IPO) rather than just the forced climate signal.
- The analysis lacks baseline climatology; if IFS-FESOM had a large open-ocean polynya bias in the historical period, the 'increase' is merely a correction of that bias rather than true expansion beyond observed variability.
Sea Ice Concentration Seasonal Change — IFS-FESOM
| Variables | avg_siconc |
|---|---|
| Models | ifs-fesom |
| Units | 0-1 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary medium
The figure displays the projected seasonal changes in sea ice concentration (SICONC) for the IFS-FESOM model between the historical baseline (1990–2014) and the near-future (2040–2049) under the SSP3-7.0 scenario. It contrasts a widespread thermodynamic reduction in Arctic winter sea ice with a complex, regionally specific signal in the Antarctic, dominated by a strong increase in the Weddell Sea concentration during austral winter.
Key Findings
- Arctic Sea Ice (DJF): Extensive decline in sea ice concentration is observed along the marginal ice zones, specifically in the Barents Sea, Sea of Okhotsk, Labrador Sea, and the Bering Sea.
- Antarctic Sea Ice (JJA): A pronounced positive anomaly (increase > 20%) is evident in the central Weddell Sea, indicating a substantial localized increase in sea ice concentration.
- Southern Ocean Zonal Asymmetry: While the Weddell Gyre region shows sea ice growth, the outer fringes of the Antarctic sea ice pack (e.g., Atlantic and Indian sectors) exhibit concentration decreases, suggesting a retreat of the ice edge despite the interior increase.
Spatial Patterns
In the Northern Hemisphere (DJF), negative anomalies are strictly confined to the retreating ice edges, consistent with 'Atlantification' and warming. In the Southern Hemisphere (JJA), the pattern is dipolar in the Atlantic sector: a core of strong positive change in the Weddell Gyre surrounded by a band of negative change at the northernmost ice extent. The Ross Sea sector shows weaker, mixed signals.
Model Agreement
The Arctic sea ice loss is a robust feature consistent with the CMIP6 multi-model ensemble and physical expectations of polar amplification. However, the strong positive anomaly in the Weddell Sea is likely specific to IFS-FESOM's representation of Southern Ocean deep convection; many models show broad Antarctic decline, but high-resolution models can exhibit distinct behavior regarding open-ocean polynyas (e.g., the closing of a historical polynya in the future period).
Physical Interpretation
The Arctic pattern is driven by thermodynamic warming and ocean heat transport, preventing ice formation in marginal seas. The anomalous increase in the Weddell Sea (JJA) likely results from changes in ocean stratification or the suppression of deep convection (closure of a Weddell Sea polynya) in the future climate state, possibly linked to surface freshening which stabilizes the water column and isolates warm Deep Water from the surface.
Caveats
- The 10-year averaging period (2040–2049) is relatively short and may be heavily influenced by decadal internal variability (e.g., Southern Ocean convection cycles) rather than purely forced trends.
- The strong Antarctic positive signal may represent model drift or a bias correction from the historical state (e.g., an overly active polynya in the baseline) rather than a response to radiative forcing.
Sea Ice Concentration Seasonal Change — IFS-NEMO
| Variables | avg_siconc |
|---|---|
| Models | ifs-nemo |
| Units | 0-1 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary medium
The figure illustrates the projected seasonal changes in sea ice concentration (siconc) for the IFS-NEMO model under SSP3-7.0, comparing the 2040–2049 mean to the 1990–2014 baseline. It highlights a contrast between thermodynamically driven ice loss in the Arctic marginal zones and complex, dynamically driven dipoles of ice gain and loss in the Southern Ocean.
Key Findings
- Arctic sea ice shows consistent decreases (negative anomalies ~-0.15 to -0.20) in the Barents and Greenland Seas during boreal winter (DJF) and in Hudson Bay/Canadian Archipelago during boreal summer (JJA).
- The Southern Ocean exhibits significant regional heterogeneity, particularly in austral winter (JJA), with a large area of increased sea ice concentration (> +0.15) in the Weddell/Ross Sea sectors contrasting with decreases elsewhere.
- Counter-intuitive sea ice increases are observed in the Bering Sea and Sea of Okhotsk during DJF, suggesting regional cooling or freshwater-induced stratification in the model's 2040s climatology.
- The central Arctic basin shows minimal change (near zero) in both seasons, indicating the ice pack remains saturated (near 100% concentration) in this model for the 2040s timeframe despite warming.
Spatial Patterns
In the Northern Hemisphere, patterns are zonally asymmetric, with losses concentrated in the North Atlantic sector (Barents/Labrador) and slight gains in the North Pacific sector (Bering). The Southern Hemisphere displays a strong dipole structure in the Antarctic sea ice zone, particularly during JJA, indicating a redistribution of ice rather than uniform retreat.
Model Agreement
The Arctic retreat in the North Atlantic sector aligns with the broad CMIP6 ensemble consensus. However, the regional sea ice expansion in the Southern Ocean and North Pacific is likely specific to the IFS-NEMO realization, potentially diverging from coarser standard-resolution models that tend to show more uniform decline.
Physical Interpretation
Arctic losses are driven by thermodynamic warming and Arctic Amplification. The Southern Ocean anomalies likely result from dynamic factors resolved at high resolution (5 km), such as shifts in wind stress (Southern Annular Mode) or mesoscale eddy transport, and potentially increased surface stratification (freshwater capping) which inhibits the upwelling of warm deep water, favoring ice formation.
Caveats
- The future averaging period (2040–2049) is relatively short (10 years), making the results susceptible to decadal internal variability which can mask or amplify the forced climate signal.
- The presence of positive sea ice anomalies (blue regions) may indicate model drift or initialization shock common in high-resolution coupled simulations, rather than a robust forced response.
Sea Ice Thickness Change (NH)
| Variables | avg_sithick |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary high
The figure illustrates the projected change in annual mean sea ice thickness in the Northern Hemisphere between the historical period (1990-2014) and the near-future (2040-2049) under the SSP3-7.0 scenario, as simulated by IFS-FESOM and IFS-NEMO.
Key Findings
- Both models project significant sea ice thinning, with maximum losses exceeding 0.5 m in specific regions.
- The primary region of thickness loss is concentrated in the Central Arctic, specifically north of Greenland and the Canadian Archipelago (the 'Last Ice Area').
- Marginal seas (e.g., Barents, Kara, Laptev) and the Eurasian Basin show negligible absolute thickness change (near 0 m) compared to the central basin.
Spatial Patterns
The spatial pattern of thinning is highly asymmetrical, dominated by a strong negative anomaly (white/pale pink shading) in the Lincoln Sea and north of Ellesmere Island. In contrast, the vast majority of the Arctic Ocean and sub-polar seas show the background blue color, indicating little to no change in mean thickness. This suggests the signal is dominated by the reduction of thick multi-year ice rather than widespread thinning of first-year ice.
Model Agreement
There is high agreement between IFS-FESOM and IFS-NEMO regarding the location and magnitude of the thinning. Both models isolate the loss to the multi-year ice region. IFS-NEMO displays slightly sharper gradients and more resolved features within the narrow straits of the Canadian Archipelago compared to IFS-FESOM, likely due to differences in grid discretization in complex coastlines.
Physical Interpretation
The observed pattern is driven by the thermodynamic melting and dynamic export of the Arctic's thickest multi-year ice. Under SSP3-7.0 warming, the reservoir of thick ice north of Greenland thins significantly or is replaced by thinner seasonal ice. The lack of strong signals in the marginal seas implies that while ice extent may decrease, the absolute reduction in thickness is small because the ice there is already relatively thin (seasonal).
Caveats
- The color map is counter-intuitive for a difference plot: the zero-value background is blue, while negative values (thinning) are white/pink. This obscures potential small positive anomalies.
- The analysis compares a near-future decadal mean (2040s) to a historical baseline; internal variability may still influence the magnitude of local changes over this relatively short timeframe.
Sea Ice Thickness Change (SH)
| Variables | avg_sithick |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary medium
This diagnostic shows the projected annual mean sea ice thickness change in the Southern Hemisphere between the historical baseline (1990-2014) and the near-future (2040-2049) under the SSP3-7.0 scenario for IFS-FESOM and IFS-NEMO. Both models predict a reduction in sea ice thickness around Antarctica, with IFS-NEMO projecting significantly stronger and more localized thinning than the more diffuse signals in IFS-FESOM.
Key Findings
- Both models consistently project sea ice thinning (negative thickness change) across the Antarctic sea ice zone.
- IFS-NEMO shows marked thickness reductions, reaching magnitudes of -0.3 m to -0.5 m, particularly in the Weddell and Ross Sea sectors.
- IFS-FESOM simulates a much weaker signal, with diffuse thinning generally less than -0.2 m restricted to the immediate coastal margins.
- No regions of significant sea ice thickening (dark blue) are observed in either model.
Spatial Patterns
The thinning is concentrically located around the Antarctic continent. IFS-NEMO displays distinct, spatially heterogeneous patches of loss (lighter/white regions) in the Weddell Gyre and Ross Sea, indicative of changes in perennial ice zones or specific circulation features. In contrast, IFS-FESOM presents a smooth, 'washed-out' halo of minor thinning with little regional differentiation.
Model Agreement
The models agree on the sign of the change (loss) but disagree substantially on magnitude and spatial structure. IFS-NEMO appears more sensitive to the warming forcing in the Southern Ocean. This discrepancy may stem from differences in ocean-ice coupling, vertical mixing schemes (regulating heat flux from the Warm Deep Water), or the specific sea ice rheology implementations in the finite-element (FESOM) versus finite-difference/volume (NEMO) frameworks.
Physical Interpretation
The widespread thinning is driven by radiative forcing under SSP3-7.0, leading to warmer atmospheric temperatures and, crucially in the Southern Ocean, increased ocean heat content. The thinning likely represents a combination of reduced thermodynamic growth during winter and increased basal melt. The stronger signal in NEMO suggests it may be simulating stronger ventilation of warm sub-surface waters or has a more sensitive ice thermodynamics scheme compared to FESOM.
Caveats
- The color scale (-0.6 to +0.6 m) is centered on a medium blue (0 m), making slight thinning appear as subtle lighting changes; care must be taken to distinguish open ocean (zero change) from slight ice loss.
- The analysis is based on annual means, which smears out potentially larger seasonal differences (e.g., winter maximum thickness vs. summer minimum).
- Southern Hemisphere sea ice is typically thinner than Arctic ice, so a loss of 0.5 m represents a very large fractional reduction in volume.
Sea Ice Thickness Seasonal Change — IFS-FESOM
| Variables | avg_sithick |
|---|---|
| Models | ifs-fesom |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary high
IFS-FESOM projects widespread reduction in sea ice thickness across both poles by the 2040s under SSP3-7.0, with the most pronounced thinning occurring in the Central Arctic and north of Greenland.
Key Findings
- Arctic sea ice exhibits significant thinning (anomalies of -0.4 to -0.8 m) in both winter (DJF) and summer (JJA), particularly in the Central Arctic Basin.
- The 'Last Ice Area' north of the Canadian Arctic Archipelago and Greenland shows substantial thickness loss, indicating a decline in multi-year ice retention.
- Antarctic sea ice thickness decreases are more moderate than in the Arctic, with widespread thinning visible in the Weddell and Ross Seas during austral winter (JJA).
Spatial Patterns
In the Arctic, thinning is concentrically focused in the high latitudes, affecting the Transpolar Drift stream and the thick ice zone north of Greenland. In the Antarctic (JJA), thinning is observed along the continental margins and within the pack ice of the Weddell Sea, while open ocean regions remain largely unchanged (zero anomaly).
Model Agreement
Only IFS-FESOM is presented in this specific figure, preventing direct inter-model comparison. However, the projected Arctic thinning aligns qualitatively with the broader CMIP6 HighResMIP ensemble consensus on declining sea ice volume.
Physical Interpretation
The patterns are driven by Arctic amplification and thermodynamic melting. The strong negative anomalies north of Greenland suggest the loss of thick, deformed multi-year ice due to warmer atmospheric and oceanic temperatures. In the Antarctic, ocean heat uptake and warmer surface air temperatures likely limit winter accretion.
Caveats
- The color map background (ocean blue) is visually similar to the 'zero change' and 'slight positive' values, potentially obscuring small positive anomalies.
- The analysis is limited to a single model realization without assessing internal variability.
Sea Ice Thickness Seasonal Change — IFS-NEMO
| Variables | avg_sithick |
|---|---|
| Models | ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary high
IFS-NEMO projects widespread reduction in sea ice thickness in both hemispheres by 2040-2049 (SSP3-7.0) relative to 1990-2014, with Arctic thinning exceeding 0.6 m in extensive regions.
Key Findings
- Pronounced Arctic winter (DJF) thinning (>0.6 m) in marginal seas, specifically Hudson Bay, Baffin Bay, and the Barents/Kara Seas.
- Significant Arctic summer (JJA) thinning extending into the Central Arctic basin and the region north of Greenland ('Last Ice Area').
- Antarctic sea ice thickness decreases in a circum-polar band at the winter ice edge (JJA) and within the summer remnant pack (DJF).
Spatial Patterns
The patterns follow the seasonal sea ice cycle: DJF (Arctic winter) losses are concentrated in the first-year ice zones of the marginal seas, while JJA (Arctic summer) losses impact the perennial ice of the central basin. In the Southern Hemisphere, a distinct band of thinning traces the retreat of the maximum winter extent in JJA.
Model Agreement
While only IFS-NEMO is shown, the projection of widespread thinning and polar amplification aligns with the broader CMIP6 HighResMIP ensemble under high-emission scenarios.
Physical Interpretation
Anthropogenic warming drives thermodynamic ice loss. In the Arctic, winter thinning is driven by delayed freeze-up (ocean heat content) and warmer atmospheric temperatures. Summer thinning is amplified by the ice-albedo feedback, accelerating the melt of multi-year ice.
Caveats
- The color scale saturates at -0.6 m, likely masking significantly larger thickness reductions in the Canadian Archipelago and Central Arctic.
- Internal decadal variability may influence the specific magnitude of change between the 1990-2014 and 2040-2049 windows.
Sea Ice Volume per Area Change (NH)
| Variables | avg_sivol |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary high
By 2040-2049 under SSP3-7.0, both IFS-FESOM and IFS-NEMO project a widespread reduction in Arctic sea ice volume per unit area (effective thickness), with the most pronounced thinning occurring in the Central Arctic and the region north of Greenland.
Key Findings
- Significant sea ice thinning (volume per area reduction) of 0.4 m to over 0.6 m is observed in the Central Arctic Basin relative to the 1990-2014 baseline.
- The most intense volume loss is concentrated in the 'Last Ice Area' north of the Canadian Archipelago and Greenland, indicating a degradation of the thickest multi-year ice reservoirs.
- Marginal increases in volume per area are visible in the East Greenland Current export pathway in IFS-FESOM, suggesting dynamic piling or enhanced export of thicker ice, a feature less prominent in IFS-NEMO.
Spatial Patterns
The spatial pattern is characterized by central basin losses and near-neutral changes in the peripheral shelf seas (e.g., Barents, Kara Seas), likely where baseline ice is already thin or seasonal. The maximum negative anomalies align with the climatological location of multi-year ice. IFS-FESOM displays localized positive anomalies (blue) along the sea ice edge in the North Atlantic sector, contrasting with the more uniform decline in IFS-NEMO.
Model Agreement
Both models strongly agree on the sign and primary region of sea ice thinning (Central Arctic). However, IFS-NEMO predicts a slightly more coherent and geographically extensive thinning signal in the central basin. Disagreements appear in the marginal ice zones (specifically the Fram Strait outflow), potentially reflecting differences in sea ice rheology or grid-dependent advection schemes between the finite-element (FESOM) and finite-difference (NEMO) ocean components.
Physical Interpretation
The patterns are driven primarily by thermodynamic forcing associated with Arctic Amplification, where elevated atmospheric and oceanic heat fluxes melt existing ice. The substantial loss north of Greenland implies that thermodynamic melting is outpacing the dynamic convergence that historically builds thick ice in that region. The thinning reflects a transition from a multi-year ice pack to a thinner, more seasonal first-year ice regime.
Caveats
- The colorbar range (-0.6 to +0.6 m) saturates in the regions of peak loss (Central Arctic), obscuring the maximum magnitude of thinning which likely exceeds 0.6 m.
- The analysis relies on a single realization per model; without an ensemble, it is difficult to separate the forced climate response from internal decadal variability.
Sea Ice Volume per Area Change (SH)
| Variables | avg_sivol |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Future mean minus historical mean. |
Summary high
Comparison of projected Antarctic sea ice volume per area change (2040–2049 vs 1990–2014) under SSP3-7.0, revealing a striking disparity in sensitivity between the IFS-FESOM and IFS-NEMO coupled models.
Key Findings
- IFS-NEMO projects widespread sea ice thinning and volume loss across the Southern Ocean seasonal ice zone.
- IFS-FESOM exhibits a negligible response, with volume changes remaining close to zero across most of the domain.
- The magnitude of loss in IFS-NEMO appears to range between -0.2 m and -0.4 m in key sectors, whereas IFS-FESOM changes are barely detectable.
- No regions of sea ice volume increase (dark blue) are observed in either model.
Spatial Patterns
IFS-NEMO displays a distinct circumpolar 'halo' of negative anomalies (lighter colors indicating -0.2 to -0.4 m change), most pronounced in the Weddell and Ross Sea sectors. In contrast, IFS-FESOM shows only very faint, localized thinning restricted to the immediate Antarctic coastline, with the open ocean signal indistinguishable from zero.
Model Agreement
Low agreement regarding sensitivity. While both agree on the sign (no growth), IFS-NEMO predicts substantial decline while IFS-FESOM suggests near-stability. This divergence likely stems from differences in Southern Ocean vertical mixing parameterizations, sea ice thermodynamics, or baseline ice thickness distributions between the unstructured (FESOM) and structured (NEMO) ocean components.
Physical Interpretation
The negative anomalies in IFS-NEMO reflect the expected thermodynamic response to anthropogenic warming (SSP3-7.0), driven by increased atmospheric temperatures and likely enhanced basal melting from Warm Deep Water. The muted response in IFS-FESOM suggests strong stratification preventing ocean heat release, a cold bias in the Southern Ocean, or significantly different sea ice dynamics on the unstructured mesh.
Caveats
- The 10-year averaging period (2040–2049) is relatively short and may be influenced by high internal decadal variability in the Southern Ocean.
- The colormap center (0 m) is a medium blue, making small negative anomalies (lighter blue/white) visually subtle against the background.
- Without baseline climatology, it is unclear if IFS-FESOM's lack of change is due to resilience or a lack of sea ice in the historical period (though the latter is unlikely for a major climate model).
Sea Ice Volume per Area Seasonal Change — IFS-FESOM
| Variables | avg_sivol |
|---|---|
| Models | ifs-fesom |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary high
The figure illustrates the seasonal change in sea ice volume per area (equivalent thickness) for the IFS-FESOM model, comparing the future period 2040-2049 (SSP3-7.0) against the historical baseline 1990-2014. The data reveals a widespread reduction in sea ice volume in both hemispheres, with the most pronounced thinning occurring in the central Arctic during boreal summer.
Key Findings
- Arctic sea ice volume exhibits significant reductions in both seasons, with DJF losses concentrated in marginal seas (Hudson Bay, Sea of Okhotsk) and JJA losses dominated by thinning of multi-year ice in the Central Arctic.
- The Central Arctic during JJA shows a reduction in effective thickness exceeding 0.4 m across the basin, indicating a substantial decline in the perennial ice pack.
- Antarctic sea ice changes in JJA (austral winter) are characterized by thinning/retreat at the outer ice margins, while some interior coastal regions show localized, heterogeneous areas of volume increase (blue patches).
Spatial Patterns
In the Arctic, the pattern is basin-wide thinning, with the 'Last Ice Area' north of the Canadian Archipelago showing strong negative anomalies in JJA. In the Antarctic, the pattern is zonally asymmetric; the ice edge generally retreats (pink bands), particularly in the Indian and Pacific sectors, while the Weddell Gyre and parts of the Ross Sea exhibit complex patches of thickening (blue) likely driven by dynamic redistribution or local freshwater feedbacks.
Model Agreement
This figure displays only IFS-FESOM. While inter-model comparison is not possible from this image alone, the projected Arctic decline is consistent with the broader CMIP6 ensemble response to SSP3-7.0 radiative forcing. The complex Antarctic patterns reflect the high-resolution, unstructured grid's ability to resolve mesoscale eddies and bathymetric steering.
Physical Interpretation
The pervasive Arctic thinning is driven by thermodynamic melting enhanced by Arctic amplification and the ice-albedo feedback. The seasonal shift in Arctic loss (marginal seas in winter vs. central basin in summer) reflects the retreat of the seasonal ice line. In the Southern Ocean, the dipole of marginal loss and coastal thickening suggests a combination of warmer surface waters eroding the edge and changing wind stress (possibly SAM-related) or meltwater stratification enhancing freezing or piling up ice near the continent.
Caveats
- The color bar scale (±0.6 m) likely saturates in regions of heavy multi-year ice loss, potentially masking the full magnitude of the decline.
- The 10-year averaging period (2040-2049) is relatively short, meaning internal decadal variability could still significantly influence the specific spatial patterns, particularly in the highly variable Antarctic system.
- Sea ice volume per area combines thickness and concentration; distinguishing between thinning ice and reduced areal coverage is not possible from this variable alone.
Sea Ice Volume per Area Seasonal Change — IFS-NEMO
| Variables | avg_sivol |
|---|---|
| Models | ifs-nemo |
| Units | m |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | Per-season future mean minus historical mean. |
Summary high
The figure illustrates the projected mid-century (2040–2049) change in sea ice volume per area (equivalent to mean thickness) relative to the historical baseline (1990–2014) for the IFS-NEMO model under the SSP3-7.0 scenario. It reveals widespread reductions in sea ice thickness in both hemispheres, with the most pronounced loss occurring in the Arctic marginal seas during winter and the central Arctic basin during summer.
Key Findings
- Widespread thinning of Arctic sea ice is evident in both seasons, with volume per area decreases exceeding 0.4 m (saturation of the color scale) in many regions.
- During boreal winter (DJF), sea ice loss is concentrated in the marginal ice zones, specifically Hudson Bay, the Sea of Okhotsk, and the Barents/Kara Seas.
- During boreal summer (JJA), significant thinning extends throughout the central Arctic Basin, indicating a transition toward thinner, potentially seasonal ice cover.
- In the Southern Hemisphere, substantial sea ice loss is projected in the Weddell Sea and Bellingshausen/Amundsen Seas during austral winter (JJA), while changes in other Antarctic sectors are more heterogeneous or muted.
Spatial Patterns
In the Northern Hemisphere, the pattern follows the seasonal retreat of the ice edge: DJF losses highlight the 'Atlanticization' of the Barents Sea and retreat in sub-Arctic basins (Hudson, Okhotsk), while JJA losses are pan-Arctic. In the Southern Hemisphere, the most notable feature is a strong reduction in ice volume in the Weddell Sea gyre region during JJA, with more localized coastal thinning evident in DJF.
Model Agreement
Only IFS-NEMO is visualized in this specific figure, preventing direct inter-model comparison. However, the projected decline in Arctic sea ice volume and the specific retreat in the Barents Sea are consistent with the broader CMIP6 ensemble behavior under high-warming scenarios (SSP3-7.0).
Physical Interpretation
The patterns are driven by thermodynamic forcing from increased greenhouse gases, leading to ocean and atmospheric warming. In the Arctic, the ice-albedo feedback amplifies summer melt in the central basin. The winter loss in marginal seas is likely driven by warmer Atlantic and Pacific water inflows and delayed freeze-up. The localized loss in the Weddell Sea may indicate changes in ocean stratification, wind-driven upwelling of warm Circumpolar Deep Water, or reduced sea ice production in this model.
Caveats
- The colorbar scale (±0.4 m) is likely saturated in regions of heavy multi-year ice loss, potentially under-representing the magnitude of the decline in the central Arctic.
- The future averaging period (10 years: 2040–2049) is relatively short compared to the baseline (25 years), meaning internal decadal variability could partially influence the apparent climate change signal, particularly in the highly variable Antarctic system.