.. _icon_model_historical_projection: Historical and Projection Simulations ############################################## The ICON historical and projection experiment consists of two simulations: a historical simulation covering 1990–2014 and a projection simulation covering 2015–2039 (SSP3-7.0, ongoing). The projection is a direct continuation of the historical simulation. Both the atmosphere and ocean use a horizontal grid resolution of 5km (public ICON grid id: R02B09). +----------+------------------------------------+--------------+-------------+------------------------------------------------+-----------------------------------+ | Model | Spatial Resolution | Time | Realization | Experiment ID | DestinE Data Lake (bridge site) | +==========+====================================+==============+=============+================================================+===================================+ | ICON | 5km atmosphere; 5km ocean | 1990-2014 | 1 | climatedt-gen2-icon-baseline-hist-5km-r1 | LUMI data bridge | +----------+------------------------------------+--------------+-------------+------------------------------------------------+-----------------------------------+ | ICON | 5km atmosphere; 5km ocean | 2015–2039 | 1 | climatedt-gen2-icon-projections-ssp370-5km-r1 | LUMI data bridge | | | | *(ongoing)* | | | | +----------+------------------------------------+--------------+-------------+------------------------------------------------+-----------------------------------+ Forcing data ------------ Global mean concentrations of greenhouse gases, ozone, and aerosols follow their respective values for each simulated year. For the historical simulation, the standardized CMIP6 forcing that follows observations is used as climatology. The projection uses the Shared Socioeconomic Pathway (SSP) 3-7.0 scenario from the ScenarioMIP as forcing. The ocean initial state (1990-01-01) is taken from a spun-up ocean model run with climatology forcing as described in :ref:`icon_initial_conditions_and_forcing`. The atmosphere, solid moisture, snow cover, and soil and surface temperature are derived from the operational analysis of the European Centre for Medium-Range Weather Forecast (ECMWF) without being spun up for the chosen start date and interpolated onto the horizontal grid at a pre-processing step. For evaluation of these simulations, see :ref:`evaluation_icon`. .. Performance is particularly strong (PI < 0.5) for specific humidity, winds, air temperature, and sea surface salinity. .. Temperature-related variables over land and ocean show weaker performance (PI ~1.5), reflecting a persistent cold bias that also affects precipitation and radiation. .. .. _1: .. .. figure:: ../../../../evaluation/general_evaluation/figures/climate_metrics.performance_indices.climatedt-o25.1.ICON.historical-1990.r1.png .. :align: center .. :width: 100% .. Performance Index table for the historical simulation. Performance values refer to the mean of CMIP6 models, with values below 1 indicating improved performance and values above 1 degraded performance. .. The cold bias is evident in the Gregory plot (:numref:`2`, right panel), which relates global mean 2 m temperature to the top-of-atmosphere (TOA) energy imbalance over the simulation period. .. In 1990, ERA5 has a global mean temperature of 14.24°C, while ICON is colder by ~0.6°C and exhibits a negative TOA imbalance of ~−0.59 W m\ :sup:`-2`. .. ICON lies outside the ERA5 temperature spread throughout the simulation, confirming a persistent cold bias. .. At TOA, global net radiation rapidly falls within the CERES range, indicating a fast atmospheric adjustment. .. .. _2: .. .. figure:: ../../../../evaluation/mn5/figures/ICON-Historical_SSP370_Tco2559_timeseries_Gregory_absoluteT-ICON.png .. :align: center .. :width: 100% .. Left\: Time series of the globally averaged annual surface air temperature in ERA5 and the historical and scenario ICON simulations. Fit-lines representing the trends over the overlap period between ERA5 and the simulations are also included. Middle\: Same figure but for the timeseries of the net heat fluxes at the top of the atmosphere (TOA), including observations from CERES. Right\: Gregory plot of the combined ICON simulations. The mean values and ranges of the observed TOA fluxes and global mean surface air temperatures are included for reference. .. Near-surface temperature .. ^^^^^^^^^^^^^^^^^^^^^^^^ .. :numref:`3` further illustrates the cold bias in ICON. .. ICON displays a cold bias over the tropics (land and ocean) and a warm bias over land above the mid-latitudes. .. The land warm bias is likely linked to the Louis turbulence scheme, which enhances vertical mixing and increases surface temperatures. .. In the Pacific basin, ICON exhibits a cold tongue bias, which is also present in :ref:`icon_model_control`, suggesting an issue with the ocean spin-up. .. ICON's regional biases are comparable to the CMIP6 multi-model mean over both land and ocean. Biases in eastern boundary upwelling regions (e.g. Humboldt, Benguela) are reduced relative to CMIP6, likely due to the higher model resolution. .. .. _3: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_tas_annual_bias_combined_cropped.png .. :align: center .. :width: 100% .. Spatial maps of the climatological biases of annual surface air temperature in the historical ICON simulation and the CMIP6 multi-model mean. Biases are computed against Berkeley Earth climatology over the period 1990–2014. .. Mean sea level pressure exhibits large-scale biases (:numref:`1`), with strong negative biases over the Southern Ocean, positive biases over the tropics, and slight negative biases over the Northern Hemisphere mid-latitudes (:numref:`4`). The origin of these biases remains under investigation. .. .. _4: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_psl_annual_bias_combined_cropped.png .. :align: center .. :width: 100% .. Spatial maps of the climatological biases of annual mean sea level pressure in the historical ICON simulation and the CMIP6 multi-model mean. Biases are computed against ERA5 climatology over the period 1990–2014. .. The tropical cold tongue bias shifts the intertropical convergence zone (ITCZ) and associated rainfall. .. :numref:`5` shows the regional bias of ICON in comparison to MSWEP, and the CMIP6 multi-model mean. .. ICON produces a double ITCZ structure in the Pacific, consistent with a displacement driven by altered SST gradients. .. The shift of the Atlantic rainband reduces precipitation over the Amazon, resulting in a pronounced negative bias. .. Over the maritime continent and warm pool, ICON shows a positive and negative bias, respectively. .. .. _5: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_pr_annual_bias_combined_cropped.png .. :align: center .. :width: 100% .. Spatial maps of the climatological biases of annual precipitation in the historical ICON simulation and the CMIP6 multi-model mean. Biases are computed against MSWEP climatology over the period 1990–2014. .. :numref:`6` shows the global mean TOA energy imbalance from 1990 to 2014, with CERES observations available from 2000 onwards. .. ICON captures the seasonal cycle accurately, and its annual mean is closer to CERES than the CMIP6 multi-model mean. .. Consistent with :numref:`2`, ICON shows a negative energy imbalance at the start and a fast atmospheric adjustment. .. .. _6: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_radiation_imbalance_timeseries.png .. :align: center .. :width: 100% .. Time series of the global-mean net top-of-atmosphere radiation (Earth’s energy imbalance) from 1990 to 2014, comparing ICON with CERES observations and the CMIP6 multi-model mean. .. .. In accordance with :numref:`1`, ICON displays less sea ice compared with the observation data set (OSI-SAF and PIOMAS) as depicted in :numref:`7` and :numref:`8`. .. .. ICON has a stronger seasonal cycle in the Northern Hemisphere for sea-ice extent and volume, even if its shifted to lower values. .. .. However, it shows a similar seasonal cycle in the Southern Hemisphere for sea-ice extent, but a weaker seasonal cycle in the Northern Hemisphere. .. .. ICON shows a negative sea ice extent trend (reduction) of about 0.56 million km\ :sup:`-2` per decade in the Northern Hemisphere, comparable to OSI-SAF. .. .. In the Southern Hemisphere, ICON displays a neutral trend while OSI-SAF has a positive trend of 0.31 million km\ :sup:`-2`. .. .. ICON displays a negative sea ice volume trend (reduction) in the Southern and Northern Hemisphere of about 141 and 132 km\ :sup:`-3` per decade, respectively, weaker than GIOMAS and PIOMAS observed trends, 246 and 396 km\ :sup:`-3` per decade, respectively. .. Consistent with :numref:`1`, ICON simulates less sea ice than OSI-SAF observations (:numref:`7`). .. ICON reproduces a strong seasonal cycle, but with systematically lower values. In the Southern Hemisphere, it shows a similar seasonal cycle to observations, while the Northern Hemisphere seasonal amplitude is underestimated. .. ICON shows a negative sea ice extent trend of about 0.56 million km\ :sup:`2` per decade in the Northern Hemisphere, comparable to OSI-SAF. In the Southern Hemisphere, ICON displays a neutral trend, whereas OSI-SAF shows a positive trend of ~0.31 million km\ :sup:`2` per decade. .. .. _7: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_sea_ice_extent_timeseries.png .. :align: center .. :width: 100% .. Time series of monthly and annual-mean sea ice extent for the Northern and Southern Hemispheres, comparing ICON against OSI-SAF satellite observations and a CMIP6 multi-model ensemble. .. .. rubric:: Further evaluation .. Additional evaluation plots for the ICON simulations are available .. in the `Climate DT Evaluation Charts `_. .. .. _8: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_sea_ice_volume_timeseries.png .. :align: center .. :width: 100% .. Time series (monthly and annual-mean) of the sea-ice volume for the Northern and Southern Hemispheres from 1990 to 2014. .. ICON in green, the multi-model mean of CMIP6 in dashed gray, and PIOMAS (Arctic) and GIOMAS (Antarctic) observations dataset in black. .. :numref:`9` displays a Hovmoeller diagram of the global mean temperature anomalies of the 3D structure of the ocean. .. As in the ClimateDT simulation :ref:`icon_model_control`, the cold bias development of ICON is clearly observed. .. The cold bias has a strong seasonal cycle located in the near-surface, between 0 and 100 m. .. Between 100 and 200 m depth, ICON shows a warm bias, likely a response of the ocean to its heat distribution from the surface through deepening of the thermocline or enhanced vertical mixing. .. The deep ocean remains relatively stable. .. .. _9: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_en4_thetao_hovmoller_anom1_combined.png .. :align: center .. :width: 100% .. Time-depth Hovmöller diagrams of global-mean ocean temperature anomalies relative to the initial EN4 observational state from 1990 to 2014. .. Over the 700 m layer deep (:numref:`10`), the cold bias is observed in the first months towards the first years, where ICON shows an agreement with the observational dataset EN4. .. Until 2003, ICON has a similar volume-weighted mean ocean temperature but does not shows the warming trend in EN4 from 2003, remaining colder. .. In comparison to :numref:`9`, the temperature contrast of the bias between different depths seems to compensate for each other, but later the cold bias becomes more persistent. .. Between 700 and 2000 m depth, ICON is colder than EN4 by about 0.06°C with a similar warming trend. .. However, between 2000 and the bottom of the ocean, ICON is slightly warmer with a warming trend, which is not observed in EN4. .. .. _10: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_nk_en4_thetao_depth_timeseries.png .. :align: center .. :width: 100% .. Volume-weighted mean ocean temperature time series for three depth layers (0–700 m, 700–2000 m, 2000 m–bottom) from 1990 to 2014. .. ICON in green and EN4 v4.2.2 observations in black. .. ClimateDT Projection Evaluation .. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. We evaluate the near-surface temperature evolution of yearly and monthly means with their respective trend using the mean over 1995-1999 as a reference for ICON and ERA5, assuming that the period over 1990-1995 as a spin-up. .. ICON displays a similar trend as ERA5 of about 0.19°C per decade in the ClimateDT historical simulation (2000-2014). .. However, in the ClimateDT projection simulation, ICON displays a muted increase in near-surface temperature, deviating from the ERA5 trend between 2015 and 2024. .. ICON suggests a stronger increase in temperature in its projection beyond 2024 with a trend of 0.85 K per decade. .. .. _11: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_2t_timeseries_anomalies_hisproj.png .. :align: center .. :width: 100% .. Time series (monthly and annual-mean) of the near-surface temperature for the ClimateDT simulation, historical (1990 to 2014) and projection (2015-2029). .. ICON in blue and ERA5 in gray. .. Even though ICON has a cold bias, :numref:`11` suggests that it displays a similar warming trend to ERA5. .. However, the regional pattern of changes between the ClimateDT ICON projection simulation and ERA5 with respect to the ClimateDT historical period (1990-2014) is different (:numref:`12`). .. ERA5 shows a strong warming in the northern hemisphere and a cooling near the southern ocean, eastern Pacific, and in the subpolar gyre (north Atlantic). .. In contrast, ICON shows a more intense warming over the poles and a distinct cooling pattern than ERA5, with cooling in the tropical Pacific ocean basin and Africa, and India. .. The cold tongue biases observed in the ClimateDT historical simulation (:numref:`3`) seem to intensify, especially in the cold tongue and coastal region of the western USA (:numref:`13`). .. Beyond 2024, ICON suggests a stronger warming in the northern hemisphere, especially over land, and the cooling and more localized subpolar gyre cooling in the north Atlantic — a signature of AMOC slowdown. .. .. _12: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_bias_2D_2t_delta_proj_hist.png .. :align: center .. :width: 100% .. Near-surface temperature regional changes with respect to ClimateDT historical simulation period (1990-2014) for ERA5 (left column) and ClimateDT ICON projection simulation (right column). .. .. _13: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_bias_2D_sst_delta_proj_hist.png .. :align: center .. :width: 100% .. Sea surface temperature regional (SST) changes with respect to ClimateDT historical simulation period (1990-2014) for ERA5 (left column) and ClimateDT ICON projection simulation (right column). .. In the ClimateDT projection simulation, ICON displays a bias in precipitation with respect to MSWEP of about -.3 mm d\ :sup:`-1` with a weaker seasonal cycle (:numref:`14`) as observed in the ClimateDT historical simulation (:numref:`5`). .. We compare the trend of the ClimateDT historical and projection simulation using the mean over 1995-1999 as a reference for ICON and ERA5, treating 1990-1995 is a spin-up. .. ICON displays a neutral trend in the increase of precipitation between 1990 and 2024, and a slight increase in its trend from 2025 towards the end of the ClimateDT projection simulation. .. In contrast, MSWEP shows a positive trend of about 0.4 mm d\ :sup:`-1` between 2000 and 2014, followed by a decrease with a later increase in precipitation between 2015 and 2024. .. The increase and decrease of precipitation observed in MSWEP are not present in the ICON simulation, which could be due to internal variability in the precipitation observational dataset. .. We further evaluate the intensification of the hydrological cycle, relative change of precipitation to temperature change with respect to the Climate DT historical period, which is expected to be between 1-3%. .. MSWEP displays an intensification of the hydrological cycle of about 0.99% per 1K over the period of 2015 and 2024, while ICON has a lower value 0.55% per 1K. .. Beyond 2025, ICON shows an increase in the intensification of the hydrological cycle of about 0.85% per 1K, which relates to the increase in the precipitation trend in this period. .. .. _14: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_pr_timeseries_anomalies_hisproj.png .. :align: center .. :width: 100% .. Time series (monthly and annual-mean) of precipitation for the ClimateDT simulation, historical (1990 to 2014) and projection (2015-2029). .. ICON in blue and MSWEP in gray. .. We compare the regional changes of ICON and MSWEP with respect to the ClimateDT historical simulation period (:numref:`15`). .. Over the ITCZ region in the Pacific Ocean basin, ICON shows a decrease in precipitation over 2015 and 2024 and an increase in the edges of the cold tongue, which could be internal changes of the circulation pattern. .. Beyond 2025, ICON shows an increase of precipitation over the Pacific ITCZ, specifically over the eastern Pacific. .. Over the Atlantic and the Amazon forest, ICON shows a decrease in precipitation. .. .. _15: .. .. figure:: ../../../../evaluation/levante/Fig/ICON_bias_2D_pr_delta_proj_hist.png .. :align: center .. :width: 100% .. Precipitation regional changes with respect to ClimateDT historical simulation period (1990-2014) for MSWEP (left column) and ClimateDT ICON projection simulation (right column).