Evaluation Global Mean Time Series CMIP6
CMIP6 Multi-Model Mean Context
Comparison with CMIP6 ensemble mean from 10 members.
Contributing models: ACCESS-ESM1-5, AWI-CM-1-1-MR, CNRM-CM6-1, CNRM-ESM2-1, EC-Earth3, GISS-E2-1-G, INM-CM5-0, IPSL-CM6A-LR, MPI-ESM1-2-LR, MRI-ESM2-0
Synthesis
Related diagnostics
10m U Wind Global Mean Time Series
| Variables | avg_10u |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | m/s |
| Period | 1990–2014 |
Summary high
Global mean time series of 10m zonal wind (U wind) from 1990 to 2015, comparing high-resolution DestinE models (IFS-FESOM, IFS-NEMO, ICON) against ERA5 observations and the CMIP6 multi-model mean.
Key Findings
- ICON exhibits a systematic positive (westerly) bias of approximately 0.2 to 0.3 m/s in the global mean compared to ERA5.
- IFS-NEMO shows a persistent negative (easterly) bias of roughly 0.1 m/s relative to observations.
- IFS-FESOM performs best among the high-resolution models, closely tracking the long-term mean state of both ERA5 and the CMIP6 multi-model mean.
- Observations show a distinct decadal variability that is not temporally matched by the models, which is expected for free-running coupled simulations.
Spatial Patterns
While this is a global mean time series, the temporal dimension reveals strong, persistent offsets in the climatological mean state among the models. High-frequency (monthly) variance appears similar in amplitude across all models and observations, but the smoothed interannual signals highlight a wide spread in the baseline global zonal flow.
Model Agreement
Inter-model agreement is low regarding the mean state, with a roughly 0.4 m/s spread separating the most westerly-biased model (ICON) from the most easterly-biased model (IFS-NEMO). IFS-FESOM agrees well with the ERA5 mean state and the CMIP6 MMM baseline.
Physical Interpretation
The global mean 10m U wind is naturally negative due to the area-weighted dominance of tropical easterly trade winds over mid-latitude westerlies. The systematic positive bias in ICON implies that it simulates either overly weak tropical easterlies or excessively strong mid-latitude westerlies. Conversely, IFS-NEMO's negative bias suggests overly strong trades or weak westerlies. These offsets are likely tied to differences in atmospheric boundary layer drag formulations, sub-grid orographic parameterizations, or the simulated latitudinal positions of the mid-latitude eddy-driven jets.
Caveats
- Because these are free-running historical coupled simulations, they generate their own internal climate variability; therefore, they are not expected to capture the specific chronological timing of decadal shifts seen in ERA5.
- A globally averaged U wind metric can mask large, spatially compensating regional biases between the tropics and extratropics.
10m V Wind Global Mean Time Series
| Variables | avg_10v |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | m/s |
| Period | 1990–2014 |
Summary high
This figure displays the area-weighted global mean time series of 10m meridional wind (V-wind), highlighting the annual mean offsets and the strong seasonal cycle amplitude for high-resolution models compared to ERA5 and the CMIP6 multi-model mean.
Key Findings
- The global mean 10m V-wind exhibits a pronounced seasonal cycle ranging from roughly -0.4 m/s to 0.8 m/s, driven by the seasonal migration of global atmospheric circulation patterns.
- IFS-FESOM shows excellent agreement with ERA5 for both the annual mean (~0.18 m/s) and the amplitude of the seasonal cycle.
- IFS-NEMO displays a systematic positive bias in the annual mean (~0.25 m/s), while ICON exhibits a systematic negative bias (~0.1 m/s) and overestimates the magnitude of the seasonal troughs.
Spatial Patterns
The temporal series is dominated by the annual cycle. Positive peaks (boreal summer) occur when cross-equatorial southerly flow into the Northern Hemisphere ITCZ is maximized. Negative troughs (boreal winter) correspond to enhanced northerly flow into the Southern Hemisphere. The net positive annual mean indicates a global asymmetry, driven by the mean position of the ITCZ being north of the equator.
Model Agreement
Inter-model agreement is moderate regarding the annual mean. IFS-FESOM closely tracks ERA5 observations. IFS-NEMO has a consistent positive offset, and ICON has a consistent negative offset compared to both ERA5 and the CMIP6 multi-model mean. All models capture the phase of the seasonal cycle accurately, though ICON slightly overestimates the boreal winter northerly extremes.
Physical Interpretation
The global mean V-wind is primarily governed by the position and strength of the Hadley circulation and the Intertropical Convergence Zone (ITCZ). The seasonal cycle reflects the interhemispheric mass transport as the ITCZ migrates across the equator. The net positive annual mean reflects the climatological position of the ITCZ at roughly 5°N, drawing southeast trade winds across the equator and yielding a net southerly global component.
Caveats
- A global mean of a vector wind component is highly susceptible to compensating errors; regional biases in opposite hemispheres or differing wind belts can cancel each other out.
- Small differences in the global mean (e.g., 0.1 m/s) may mask significant regional circulation errors that require spatial bias maps to properly identify.
2m Temperature Global Mean Time Series
| Variables | avg_2t |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | K |
| Period | 1990–2014 |
Summary high
The figure displays the global mean 2m temperature time series from 1990 to 2014, showing both monthly values (seasonal cycle) and smoothed interannual variations for three high-resolution models compared to observations and the CMIP6 multi-model mean.
Key Findings
- IFS-FESOM shows excellent agreement with observations (ERA5) and the CMIP6 multi-model mean, accurately capturing both the climatological mean and the long-term trend.
- ICON exhibits a persistent and significant cold bias of approximately 0.5-1.0 K globally compared to observations.
- IFS-NEMO displays a slight cold bias (0.2-0.4 K) but generally tracks the interannual variability of the observations well.
Spatial Patterns
The time series reveals a distinct seasonal cycle superimposed on a long-term warming trend. A temporary cooling dip is visible around 1992-1993 across most datasets, corresponding to the climatic impact of the Mt. Pinatubo eruption. ICON's monthly time series (thin green line) shows particularly deep minima, indicating its cold bias is exacerbated during the global winter (Northern Hemisphere winter).
Model Agreement
IFS-FESOM and the CMIP6 MMM agree exceptionally well with the observational reference. IFS-NEMO is marginally colder, while ICON diverges significantly with a pronounced cold bias. Interannual variability is generally consistent across all models.
Physical Interpretation
The persistent global cold bias in ICON suggests a systematic offset in the global energy budget, potentially driven by excessive low cloud cover (higher planetary albedo), biases in aerosol forcing, or an overestimation of sea ice extent/surface albedo in polar regions. The excellent performance of IFS-FESOM indicates well-tuned atmospheric physics and surface coupling at high resolution.
Caveats
- Global mean metrics can mask large compensating regional biases; a near-zero global bias does not imply zero regional errors.
- The 25-year period is relatively short for robustly evaluating long-term climate sensitivity or low-frequency multi-decadal variability.
Surface Sensible Heat Flux Global Mean Time Series
| Variables | avg_ishf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of surface sensible heat flux for three high-resolution models compared to ERA5 reanalysis from 1990 to 2015, highlighting both the smoothed annual means and the monthly seasonal cycles.
Key Findings
- All three models overestimate the magnitude of the global mean upward sensible heat flux (shown as more negative values) relative to ERA5.
- IFS-FESOM and IFS-NEMO exhibit similar behavior, with a moderate bias (~1.5 W/m2 more negative) and seasonal cycle amplitudes that closely parallel the reanalysis.
- ICON shows a pronounced negative bias (~3.5 W/m2) and a substantially exaggerated seasonal cycle amplitude compared to both the IFS-based models and ERA5.
Spatial Patterns
As a global mean time series, spatial patterns are aggregated; however, the temporal patterns show that while all models correctly capture the phasing of the global seasonal cycle, ICON's seasonal amplitude swings much wider (from roughly -16 to -24 W/m2) than ERA5 (roughly -14.5 to -19 W/m2).
Model Agreement
There is high agreement between IFS-FESOM and IFS-NEMO, which track each other closely in both mean state and variability, reflecting their shared atmospheric component. ICON diverges significantly, acting as an outlier in both annual mean bias and seasonal amplitude.
Physical Interpretation
The stronger upward sensible heat fluxes (more negative values) in the models imply simulated surface temperatures that are too warm relative to the overlying near-surface air, or excessively strong turbulent mixing in the boundary layer. ICON's exaggerated seasonal cycle strongly points to overly sensitive parameterizations in its land surface model or boundary layer scheme responding to seasonal changes in solar insolation.
Caveats
- Surface sensible heat flux is not directly assimilated but rather derived from parameterizations in ERA5, meaning the 'observational' baseline carries its own model-dependent uncertainties.
- Global mean metrics can obscure significant compensating regional biases, such as differing performance over land versus ocean.
Mean Sea Level Pressure Global Mean Time Series
| Variables | avg_msl |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | Pa |
| Period | 1990–2014 |
Summary high
The figure presents the 1990–2014 time series of global mean sea level pressure (MSLP), comparing the temporal evolution, interannual variability, and seasonal cycle amplitude of total atmospheric mass in high-resolution models against ERA5 and the CMIP6 multi-model mean.
Key Findings
- ICON exhibits a systematic negative bias of approximately 35–40 Pa in its baseline global mean MSLP compared to ERA5 and the IFS configurations.
- IFS-FESOM and IFS-NEMO accurately reproduce the climatological mean MSLP of ERA5, but their smoothed annual means exhibit less interannual and decadal variability than the reanalysis.
- All evaluated models overestimate the amplitude of the seasonal cycle of global MSLP, with ICON showing an amplitude (~80 Pa) roughly twice as large as ERA5 (~40 Pa).
Spatial Patterns
Temporally, the data is dominated by a strong seasonal cycle (shown by the thin lines) driven by global moisture fluctuations. The smoothed annual means (thick lines) reveal that ERA5 undergoes low-frequency decadal variability (e.g., rising from 1993 to 2006) that the free-running models remain generally too flat to capture, lacking similar internal variance.
Model Agreement
IFS-FESOM and IFS-NEMO are in excellent agreement with each other, both successfully capturing the long-term mean of ERA5 and the CMIP6 MMM. ICON is a distinct outlier among the high-resolution models due to its persistent negative mass offset and exaggerated seasonal cycle.
Physical Interpretation
Global mean MSLP is a proxy for total atmospheric mass. Because dry air mass is conserved, temporal fluctuations in global MSLP are primarily driven by changes in integrated atmospheric water vapor (moisture loading). The persistent low bias in ICON suggests either a lower prescribed dry air mass at initialization or a severe global dry bias. The overestimated seasonal amplitudes in the models indicate an exaggerated seasonal fluctuation in global atmospheric moisture compared to observations, likely linked to the hydrological cycle over Northern Hemisphere landmasses.
Caveats
- Global mean MSLP calculations are highly sensitive to the extrapolation methods used to reduce surface pressure to sea level over high topography, which can introduce artificial offsets.
- Different modeling centers may use slightly different constants for total dry atmospheric mass during initialization, creating baseline offsets (like ICON's) that are arbitrary and do not necessarily degrade dynamical performance.
Surface Downwelling Longwave Global Mean Time Series
| Variables | avg_sdlwrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
Global mean time series of surface downwelling longwave radiation from 1990–2014, comparing DestinE high-resolution models against ERA5 observations and the CMIP6 multi-model mean.
Key Findings
- ICON and IFS-NEMO accurately capture the observed global mean of ~339 W/m², improving upon the persistent positive bias present in the CMIP6 MMM.
- IFS-FESOM exhibits a positive drift throughout the simulated period, resulting in an overestimation of ~3-4 W/m² by 2014.
- All models correctly capture the transient reduction in downwelling longwave radiation following the 1991 Mount Pinatubo eruption.
Spatial Patterns
The temporal evolution is dominated by a strong global seasonal cycle with an amplitude of approximately 20-25 W/m². The smoothed annual means reveal a slight multi-decadal upward trend in observations, which is significantly exaggerated in IFS-FESOM and the CMIP6 MMM.
Model Agreement
ICON and IFS-NEMO show excellent agreement with observations in both mean state and interannual variability. In contrast, IFS-FESOM diverges from the other high-resolution models and observations after 2000, aligning more closely with the positively biased CMIP6 MMM.
Physical Interpretation
Surface downwelling longwave radiation is primarily controlled by lower tropospheric temperature, water vapor concentration, and low-level cloud cover. The positive bias in IFS-FESOM and CMIP6 MMM likely stems from an overestimation of boundary layer moisture or excessive optically thick low clouds. ICON and IFS-NEMO appear to better represent these thermodynamic and cloud-radiative processes at high resolution.
Caveats
- ERA5 surface radiative fluxes are model-derived reanalysis products rather than direct satellite observations (like CERES EBAF), introducing inherent model-dependent uncertainties.
- Global mean metrics can obscure compensating regional biases in cloud cover and atmospheric humidity.
Surface Downwelling Shortwave Global Mean Time Series
| Variables | avg_sdswrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of surface downwelling shortwave radiation from 1990 to 2014, highlighting the performance of high-resolution DestinE models against ERA5 reanalysis and the CMIP6 multi-model mean.
Key Findings
- The CMIP6 multi-model mean exhibits a systematic positive bias of approximately 3-4 W/m2 compared to ERA5 observations.
- The high-resolution DestinE models significantly reduce this bias, with ICON showing excellent agreement with the observed global mean.
- IFS-FESOM and IFS-NEMO display a slight negative bias (roughly 2-3 W/m2) relative to ERA5.
- A distinct temporary reduction in shortwave radiation is visible across observations and all models between 1991 and 1993, corresponding to the Mt. Pinatubo eruption.
Spatial Patterns
The time series is dominated by a strong, regular seasonal cycle driven by the hemispheric asymmetry of Earth's landmasses and seasonal cloud cover variations. Interannual variability is prominent in the early 1990s due to volcanic forcing.
Model Agreement
ICON agrees exceptionally well with the ERA5 reference in terms of the annual mean magnitude. IFS-FESOM and IFS-NEMO track each other closely but are slightly dimmer than observations. All high-resolution models represent a clear improvement over the CMIP6 ensemble mean, which systematically overestimates surface shortwave.
Physical Interpretation
Global mean surface downwelling shortwave radiation is primarily modulated by cloud fraction and cloud optical properties. The positive bias in CMIP6 MMM likely reflects a common underestimation of cloud cover or optical thickness in conventional models. The improved performance of the ~5 km models, particularly ICON, suggests that explicitly resolving deep convection and fine-scale cloud structures leads to more realistic atmospheric transmissivity. The 1991-1993 dip is a direct physical response to increased scattering by stratospheric sulfate aerosols from the Mt. Pinatubo eruption.
Caveats
- ERA5 surface radiation fields are heavily dependent on the reanalysis model's own cloud parameterizations; direct satellite observations like CERES EBAF (available post-2000) would provide a more robust observational constraint.
- A highly accurate global mean can sometimes result from compensating regional biases (e.g., too cloudy in the tropics, too clear in the extratropics), which are masked in a global average.
Surface Latent Heat Flux Global Mean Time Series
| Variables | avg_slhtf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
Global mean time series of surface latent heat flux reveals that IFS-coupled models systematically overestimate the magnitude of upward flux (evaporation) compared to ERA5, whereas the ICON model shows close agreement with the reanalysis after 2000.
Key Findings
- IFS-FESOM and IFS-NEMO consistently simulate a stronger upward latent heat flux (more negative by ~2-4 W/m2) than ERA5 throughout the 1990-2015 period.
- ICON demonstrates the best overall agreement with ERA5, particularly from 2000 onwards where the smoothed timeseries closely track each other.
- ERA5 exhibits a distinct structural shift towards more negative values around 1998-2000, a feature not replicated by the free-running climate models, suggesting an artifact related to observing system changes in the reanalysis.
Spatial Patterns
This diagnostic presents global mean temporal evolution rather than spatial patterns. High-frequency (likely monthly) variability is captured by all models with amplitudes comparable to ERA5, while the smoothed low-frequency signal highlights systematic model offsets.
Model Agreement
The two IFS-based models (FESOM and NEMO) show strong inter-model agreement, both exhibiting a systematic bias toward excessive global evaporation. ICON diverges from the IFS models, simulating weaker evaporation that aligns well with the observational reference in the 21st century.
Physical Interpretation
The persistent negative bias (stronger upward flux) in the IFS models indicates excessive global surface evaporation, which implies excessive surface latent cooling and an overly active hydrological cycle. The abrupt shift in the ERA5 timeseries in the late 1990s is likely a non-physical artifact driven by the assimilation of new satellite observing systems (e.g., AMSU-A), a known issue in reanalysis flux products.
Caveats
- Surface latent heat flux in ERA5 is a modeled variable strongly influenced by parameterizations and shifting data assimilation inputs, meaning it should be treated with caution as an absolute 'truth', particularly across satellite era transitions.
- A global mean metric may mask large, compensating regional biases; spatial maps are necessary to identify whether the excessive evaporation in IFS models originates from the tropics or mid-latitudes.
Surface Net Longwave Radiation Global Mean Time Series
| Variables | avg_snlwrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
Global mean time series of surface net longwave radiation from 1990 to 2014, revealing that all three high-resolution coupled models exhibit a systematic positive bias (weaker net surface cooling) compared to the ERA5 reanalysis.
Key Findings
- All three models consistently underestimate the magnitude of net surface longwave cooling by approximately 1 to 2 W/m2 relative to ERA5.
- The models exhibit strong inter-model agreement in their climatological means, tightly clustering around -56.5 W/m2, distinct from the ERA5 baseline of approximately -58 W/m2.
- Both the models and ERA5 show a slight upward trend (toward less negative values) over the 25-year period, consistent with greenhouse gas accumulation.
- The amplitude of interannual variability in the models matches observations well, though the phasing differs, as expected for free-running coupled simulations.
Spatial Patterns
As a global mean time series, spatial patterns are integrated out. However, temporally, a persistent systematic offset is maintained throughout the entire 1990-2014 period. High-frequency (monthly) and low-frequency (annual) variances in the models are comparable in magnitude to the ERA5 reanalysis.
Model Agreement
Inter-model agreement is notably high, with IFS-FESOM, IFS-NEMO, and ICON tracking closely together and differing by less than ~0.5 W/m2 in their annual means. Model-observation agreement is comparatively poor due to the persistent 1-2 W/m2 positive bias shared by all models.
Physical Interpretation
Net surface longwave radiation represents the balance between upward emission (governed by surface temperature and emissivity) and downward emission (governed by atmospheric temperature, greenhouse gases, and cloud cover). The positive bias (less negative net flux) indicates weaker surface cooling. This is typically driven by excessive downwelling longwave radiation—often due to an overestimation of optically thick low clouds or atmospheric column moisture—or insufficient upwelling longwave radiation resulting from cold surface temperature biases.
Caveats
- ERA5 surface radiative fluxes are modeled products rather than direct observations and carry their own uncertainties, meaning the 'bias' may partially reflect reanalysis errors.
- Because these are free-running coupled models, their internal climate variability (e.g., ENSO events) is not phase-locked to historical observations, so matching exact peaks and troughs is not expected.
- Analyzing the net longwave flux obscures compensating errors; investigating the individual upwelling and downwelling components is necessary to isolate the exact physical driver.
Surface Net Longwave Radiation (Clear-Sky) Global Mean Time Series
| Variables | avg_snlwrfcs |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
Global mean time series of clear-sky surface net longwave radiation from 1990 to 2014, evaluating IFS-FESOM, IFS-NEMO, and ICON models against ERA5 reanalysis.
Key Findings
- ICON exhibits a pronounced negative bias of approximately -5 W/m2, significantly overestimating clear-sky net surface longwave cooling.
- IFS-NEMO shows the best agreement with ERA5, with only a slight positive bias of roughly +0.5 to +1.0 W/m2.
- IFS-FESOM maintains a consistent positive bias of about +1.5 to +2.0 W/m2 relative to observations.
- All models accurately capture the seasonal cycle amplitude and key interannual variability, including the notable global minimum around 1992-1993.
Spatial Patterns
While spatial patterns are integrated out, the temporal evolution reveals a robust seasonal cycle driven by Northern Hemisphere continental temperature fluctuations. Subtle decadal trends and multi-year anomalies (such as the 1992-1993 dip, likely associated with the Mt. Pinatubo eruption's impact on temperature and moisture) are well-reproduced in the temporal structure of all models.
Model Agreement
The models diverge substantially in their absolute climatological mean states, spanning a ~7 W/m2 range. However, they demonstrate excellent agreement with each other and with ERA5 regarding the phase and amplitude of both seasonal and interannual variability. The two IFS-based models group much closer to the ERA5 baseline, whereas ICON is a distinct outlier.
Physical Interpretation
Clear-sky surface net longwave radiation is governed by the balance between upward emission (controlled by surface skin temperature) and downward emission (controlled by lower tropospheric temperature and water vapor). ICON's strongly negative bias (excessive net surface cooling) strongly suggests either a warm bias in surface skin temperature or a dry/cold bias in the lower troposphere, which would reduce downwelling longwave radiation. Conversely, the slight positive biases in the IFS models imply mildly excessive lower-tropospheric moisture/temperature or cooler surface temperatures.
Caveats
- ERA5 is a reanalysis product, and its clear-sky radiative fluxes depend on the underlying IFS model's radiative transfer scheme and moisture assimilation, which may share inherent similarities with the DestinE IFS configurations.
- Differences in how 'clear-sky' is defined and sampled (e.g., Method II vs. clear-sky radiative transfer calls) between the models and ERA5 can introduce methodological artifacts into the comparison.
Surface Net Shortwave Radiation Global Mean Time Series
| Variables | avg_snswrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of surface net shortwave radiation from 1990 to roughly 2015, featuring both the raw seasonal cycle and smoothed interannual variations for three high-resolution models compared to ERA5.
Key Findings
- All models exhibit a systematic negative bias in global mean surface net shortwave radiation of approximately 1 to 2 W/m2 relative to ERA5.
- The 1991 Mt. Pinatubo eruption signal (a sharp decrease in 1992-1993) is distinctly captured by the IFS-based models and ERA5, but is much more muted in ICON.
- The negative bias in the models' annual means is primarily driven by an underestimation of the seasonal maximums, as seen in the amplitude of the thin lines.
Spatial Patterns
Temporally, the data is dominated by a strong seasonal cycle. ERA5 (faint grey line) exhibits seasonal peaks exceeding 170 W/m2, whereas the models' seasonal peaks generally only reach 167-168 W/m2. Interannually, a prominent dip occurs in 1992-1993 due to volcanic forcing.
Model Agreement
IFS-FESOM and IFS-NEMO show excellent agreement with each other, maintaining a consistent ~2 W/m2 negative bias throughout the period. ICON diverges from the IFS models; it exhibits a muted volcanic response in the early 1990s but trends closer to observations (within ~1 W/m2) in the later half of the time series.
Physical Interpretation
The pervasive negative bias in surface net shortwave radiation implies that the models either have too much cloud cover, overly reflective clouds, excessive aerosol optical depth, or higher surface albedos than ERA5. The distinct response to the Pinatubo eruption highlights differences in how volcanic aerosols and their radiative impacts are parameterized between the IFS and ICON atmospheric models.
Caveats
- ERA5 surface radiation fields are model-derived forecasts and can themselves contain biases; comparison against direct satellite products like CERES EBAF would provide a more robust observational baseline.
- Global mean metrics obscure compensating regional biases (e.g., between the tropics and poles, or land and ocean).
Surface Net Shortwave Radiation (Clear-Sky) Global Mean Time Series
| Variables | avg_snswrfcs |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
Global mean time series of clear-sky surface net shortwave radiation from 1990 to 2015, highlighting steady baseline offsets among models and the prominent multi-year signal from the 1991 Mount Pinatubo eruption.
Key Findings
- All models successfully capture the transient reduction and subsequent recovery in surface shortwave radiation caused by the 1991 Mount Pinatubo volcanic eruption.
- ICON displays a systematic positive bias of approximately 1.5-2.0 W/m2 relative to ERA5 observations throughout the time series.
- IFS-FESOM and IFS-NEMO exhibit a systematic negative bias of roughly 2.5 W/m2 compared to ERA5, with nearly identical performance to one another.
Spatial Patterns
Temporally, the data is dominated by the annual seasonal cycle (thin lines) and the significant 1991-1994 interannual dip in the annual mean (thick lines) corresponding to the injection of stratospheric aerosols by Mount Pinatubo.
Model Agreement
IFS-FESOM and IFS-NEMO are in virtually perfect agreement, demonstrating that the ocean coupling choice has negligible impact on this atmospheric/surface metric. ICON diverges significantly from the IFS models, with observations lying squarely between the ICON (high) and IFS (low) estimates.
Physical Interpretation
Because clouds are excluded from clear-sky metrics, the mean biases are primarily driven by differences in prescribed background aerosol climatologies, atmospheric absorbers (like water vapor), and global mean surface albedo (such as snow and sea ice extent). The accurate capture of the 1991 dip confirms that all models correctly ingest transient stratospheric volcanic aerosol forcing.
Caveats
- The observational reference used is ERA5, a reanalysis product that relies on its own radiative transfer model and aerosol/albedo assumptions, which may differ from direct satellite measurements like CERES.
- The calculation of 'clear-sky' fluxes in models depends heavily on how clear-sky conditions are computationally defined and sampled compared to the reanalysis.
Total Cloud Cover Global Mean Time Series
| Variables | avg_tcc |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | % |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of total cloud cover from 1990 to 2015, comparing high-resolution DestinE models (ifs-fesom, ifs-nemo), the CMIP6 multi-model mean, and ERA5 observations.
Key Findings
- ERA5 observations show a distinct multidecadal variation, with total cloud cover dipping to ~62.2% around 2000 and subsequently increasing to ~63.4% by 2012.
- Both ifs-fesom and ifs-nemo exhibit a persistent positive bias of 0.5% to 1.5% in global cloud fraction compared to the pre-2010 ERA5 baseline.
- None of the models, including the CMIP6 MMM and the high-resolution DestinE models, capture the post-2000 upward trend seen in the ERA5 reanalysis, instead simulating stable, flat trajectories.
Spatial Patterns
The temporal patterns reveal strong, consistent high-frequency (monthly/seasonal) variability of roughly 3-4% amplitude (thin lines) across all models and observations. At decadal timescales, models exhibit flat climatologies, whereas ERA5 demonstrates a pronounced structural trend change post-2000.
Model Agreement
The models agree on a stable multidecadal trajectory but disagree on the absolute magnitude. The CMIP6 MMM aligns closely with the 1990-2000 ERA5 mean (~62.3%), whereas ifs-fesom (~63.4%) and ifs-nemo (~63.8%) consistently overestimate total cloud cover. ifs-fesom only converges with ERA5 late in the time series due to the uncaptured upward trend in the observational dataset.
Physical Interpretation
The positive bias in IFS-based models relative to CMIP6 points to parameterization sensitivities in macrophysics or convection schemes favoring excessive cloud formation or longevity, which are not explicitly resolved even at ~5km resolution. Furthermore, the inability of any model (high-resolution or CMIP6) to reproduce the ERA5 trend strongly suggests that the post-2000 ERA5 increase is an artifact of changes in the assimilated satellite observing system (e.g., the transition to newer satellite instruments around 1998-2002), rather than a genuine physical climate forcing response.
Caveats
- ERA5 cloud cover is a reanalysis product known to contain spurious trends related to historical changes in satellite observing systems, limiting its reliability as 'truth' for decadal cloud cover trends.
- Although the prompt metadata lists ICON as an evaluated model, it is missing from the figure's legend and plotted data.
TOA Net Longwave Radiation Global Mean Time Series
| Variables | avg_tnlwrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of TOA net longwave radiation from 1990 to 2014, revealing that all three high-resolution models systematically underestimate the magnitude of outgoing longwave radiation (OLR) compared to ERA5 reanalysis.
Key Findings
- All models exhibit a positive bias in net TOA longwave radiation (underestimating OLR) ranging from approximately 1.5 to 3.8 W/m2 relative to ERA5.
- ifs-fesom demonstrates the best agreement with observations, with a mean bias of ~1.5 W/m2, whereas icon has the largest bias at ~3.8 W/m2.
- The models generally capture the phase of the seasonal cycle but slightly overestimate its peak-to-peak amplitude compared to the observational baseline.
Spatial Patterns
Temporally, the models show a brief initial adjustment period between 1990 and 1993, particularly noticeable in the icon model, before stabilizing into a consistent multi-decadal mean bias. The thin lines reveal that models slightly exaggerate the seasonal extremes of OLR relative to ERA5.
Model Agreement
The models agree on the direction of the bias (too little OLR) but diverge considerably in magnitude. The IFS-based models (ifs-fesom and ifs-nemo) exhibit similar interannual variability, reflecting their shared atmospheric physics, yet maintain a constant offset of ~1 W/m2 from each other. icon stands out as the greatest outlier.
Physical Interpretation
An underestimation of OLR (a positive bias in net TOA longwave) suggests that the models may be trapping too much longwave radiation in the atmosphere. This is typically driven by excessive high cloud fraction, a globally cold bias in surface or tropospheric temperatures, or an overestimation of atmospheric water vapor.
Caveats
- ERA5 is a reanalysis product; comparing against direct satellite-based radiation observations like CERES (EBAF) would provide a more robust baseline for TOA fluxes.
- Global mean metrics can obscure large, compensating regional biases, such as tropical high-cloud errors canceling out extratropical clear-sky emission biases.
TOA Net Longwave Radiation (Clear-Sky) Global Mean Time Series
| Variables | avg_tnlwrfcs |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of clear-sky TOA net longwave radiation from 1990 to 2014, revealing that the high-resolution models generally underestimate clear-sky outgoing longwave radiation (exhibiting less negative net values) compared to ERA5.
Key Findings
- IFS-FESOM is the best-performing model, tracking ERA5 closely with only a minor positive bias of ~0.5-1 W/m2.
- ICON displays the largest systematic bias, consistently underestimating clear-sky outgoing longwave radiation by roughly 2-4 W/m2.
- All models accurately capture the amplitude and phase of the seasonal cycle, as well as key interannual variability such as the 1992-1993 anomaly.
Spatial Patterns
The temporal pattern is dominated by a strong seasonal cycle, with the most negative values (highest outgoing longwave radiation) occurring during the Northern Hemisphere summer, driven by thermal emission from warmer NH landmasses. A prominent interannual shift toward less negative values is visible in 1992-1993, capturing the radiative impact of the Mt. Pinatubo eruption.
Model Agreement
The models show excellent agreement with each other and with observations regarding temporal variability, including both seasonal and interannual timescales. However, they diverge in their climatological mean states, with IFS-FESOM closely matching ERA5 while IFS-NEMO and ICON exhibit persistent positive mean biases.
Physical Interpretation
TOA net clear-sky longwave radiation represents the outgoing longwave radiation (OLR) without cloud effects. The positive bias (less negative values) in models like ICON and IFS-NEMO indicates insufficient clear-sky OLR. This is typically driven by either a cold bias in global surface temperatures (reducing surface emission) or a moist bias in atmospheric column water vapor, which excessively enhances the clear-sky greenhouse effect and traps more radiation.
Caveats
- ERA5 clear-sky radiative fluxes are derived from a forecast model rather than direct observation, and may contain their own biases compared to satellite products like CERES.
- A global mean time series can obscure compensating regional biases, such as opposing errors in the deep tropics versus the extratropics.
TOA Net Shortwave Radiation Global Mean Time Series
| Variables | avg_tnswrf |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure displays the global mean time series of TOA net shortwave radiation from 1990 to 2014, highlighting systematic model underestimations and the transient impact of the Mount Pinatubo eruption.
Key Findings
- All evaluated models systematically underestimate global mean TOA net shortwave radiation compared to ERA5 observations.
- ICON exhibits the largest negative bias (approximately 3-4 W/m2), whereas IFS-FESOM and IFS-NEMO show a smaller bias (approximately 1.5-2 W/m2).
- All models successfully reproduce the significant reduction in net shortwave radiation during 1992-1993, corresponding to the volcanic forcing from the 1991 Mount Pinatubo eruption.
Spatial Patterns
Temporally, the data exhibits a prominent seasonal cycle driven by the asymmetric distribution of land, ocean, and clouds between hemispheres, superimposed on a relatively stable long-term mean outside the short-lived Pinatubo aerosol anomaly.
Model Agreement
IFS-FESOM and IFS-NEMO show high inter-model agreement, directly reflecting their shared IFS atmospheric component. ICON has a distinctly lower mean state. While all models agree well with the observed temporal variability, phasing, and response to volcanic forcing, they unanimously fail to capture the absolute observed magnitude.
Physical Interpretation
The negative bias in TOA net shortwave radiation indicates that the models reflect too much incoming solar radiation (an overestimated planetary albedo). In climate models, this is typically driven by excessive low-level cloud cover or overly high cloud optical depth (e.g., too much liquid water). The temporary 1992-1993 dip accurately physically reflects the increased scattering of shortwave radiation by stratospheric sulfate aerosols injected by Mount Pinatubo.
Caveats
- ERA5 is a reanalysis product; evaluating against direct satellite-derived datasets like CERES-EBAF (though only available post-2000) is generally preferred for TOA radiative fluxes.
- Global mean time series can obscure large, compensating regional biases, such as models being too reflective in the tropics but insufficiently reflective over the Southern Ocean.
TOA Net Shortwave Radiation (Clear-Sky) Global Mean Time Series
| Variables | avg_tnswrfcs |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | W/m2 |
| Period | 1990–2014 |
Summary high
The figure shows the global mean time series of clear-sky TOA net shortwave radiation from 1990 to 2015, highlighting a persistent negative bias in all models and a distinct transient response to the 1991 Mount Pinatubo eruption.
Key Findings
- All models exhibit a persistent negative bias in global mean clear-sky TOA net shortwave radiation relative to observations, ranging from ~1.5 W/m² (ICON) to ~3 W/m² (IFS models).
- The IFS-FESOM and IFS-NEMO time series are virtually identical, indicating that the clear-sky shortwave bias is driven entirely by the shared atmospheric component (IFS).
- Both models and observations clearly capture the abrupt ~4 W/m² reduction and subsequent multi-year recovery associated with stratospheric aerosols from the Mount Pinatubo eruption.
Spatial Patterns
The time series is dominated by a strong seasonal cycle driven by the hemispheric asymmetry in clear-sky albedo (landmass, desert, and cryosphere distribution). Interannual variability is largely defined by the sharp drop in 1991-1992 due to Pinatubo, with stable long-term climatologies thereafter.
Model Agreement
There is a near-perfect agreement between the two IFS-based models, highlighting the insensitivity of global clear-sky TOA fluxes to the underlying ocean model. ICON demonstrates better agreement with observations, showing a smaller negative bias than the IFS models, though all models underestimate the clear-sky net shortwave flux.
Physical Interpretation
The negative bias in clear-sky net shortwave radiation implies that the models reflect too much solar radiation back to space (higher clear-sky planetary albedo). This typically points to overly bright surface albedos (e.g., in deserts, snow, or sea ice parameterizations) or excessive atmospheric scattering from aerosols and Rayleigh scattering. The accurate reproduction of the Pinatubo signal demonstrates that the prescribed stratospheric aerosol optical depth forcing is functioning correctly.
Caveats
- Observational clear-sky fluxes (whether from ERA5 or satellite products like CERES) depend heavily on the accuracy of cloud-masking algorithms, which can misclassify thin cirrus or heavy aerosol layers as clouds.
- The pre-Pinatubo baseline is short, making it slightly difficult to assess the exact equilibrium climatology of the models prior to the eruption.
Total Precipitation Rate Global Mean Time Series
| Variables | avg_tprate |
|---|---|
| Models | IFS-FESOM, IFS-NEMO, ICON |
| Obs Dataset | ERA5 |
| Units | kg/m2/s |
| Period | 1990–2014 |
Summary high
Global mean total precipitation rate time series from 1990–2014 showing all three high-resolution DestinE models overestimating precipitation relative to ERA5.
Key Findings
- All evaluated models (ICON, IFS-FESOM, IFS-NEMO) exhibit a positive global mean precipitation bias compared to ERA5.
- ICON shows the largest positive bias (~3.6e-5 kg/m2/s), while IFS-FESOM and IFS-NEMO are closer to the CMIP6 multi-model mean (~3.45e-5 kg/m2/s).
- ERA5 observations show a marked dip in the early 1990s and a subsequent upward trend, whereas the models depict a relatively flat long-term mean.
Spatial Patterns
Temporally, the models exhibit a stable climatological mean with regular seasonal cycles, lacking the decadal upward trend present in the ERA5 reanalysis from the early 1990s to the 2010s.
Model Agreement
Models agree on an overly active global hydrological cycle relative to ERA5. IFS-FESOM and IFS-NEMO agree well with each other and the CMIP6 MMM, while ICON diverges with a significantly higher global precipitation rate.
Physical Interpretation
The persistent positive bias reflects an overly active global hydrological cycle, a common issue in climate models related to boundary layer and convective parameterizations, as well as atmospheric energy balance constraints. The ERA5 dip in 1992-1993 reflects radiative cooling and reduced evaporation following the Mt. Pinatubo eruption, a signal that is weaker in the model outputs.
Caveats
- ERA5 precipitation is a model-derived forecast variable rather than a direct observation, and is known to have its own uncertainties and temporal discontinuities.
- The early 1990s period in the simulations may be affected by coupled model spin-up adjustments, complicating the interpretation of early trends.