Community Simulations of the last Millennium


Coordinator: Johann Jungclaus, MPI-M   Opens window for sending emailmail

The last millennium is the best-documented period of climate change in a multi-century time frame. Climate has varied considerably during the late Holocene and these changes left their traces in history (Medieval Climate Optimum, Little Ice Age). However, the relative magnitude of natural fluctuations due to internal variability of the Earth’s climate system and to variations in the external forcings (sun, orbital, volcanic) and the present global warming, attributed to anthropogenic greenhouse gases, is still under debate (Figure 1). Since reconstructions of the past climate beyond the instrumental record have to rely on relatively sparse data sources, numerical model simulations are necessary to investigate the underlying causes of climate change. Moreover, model simulated climate data can be used to validate reconstruction methods.


For the first time, sufficient computational resources are available to carry out millennial-scale simulations with a comprehensive Earth System Model (ESM).





Figure 1: 1000-year temperature record from 10 different reconstructions; source:



To bundle the expertise in atmosphere, land, and ocean modeling at MPI-M, the Millennium simulations have been granted the status of an Integrated Project. Moreover, Millennium has been defined a principle science activity of the Community Earth System Modeling ( initiative.


To discriminate between internal variability, natural external forcing (orbital, solar, volcanic), and the anthropogenic-induced land-use-change and greenhouse-gas forcing, simulations are carried out with an IPCC-AR4-type ESM that allows for an interactive simulation of the carbon cycle and will make use of new reconstructions of the external forcings. Due to the internal variability in the climate system and its non-linear evolution, it is necessary to carry out several experiments with the same forcing, but with slightly different initial conditions (ensemble simulations).


The results expected from the simulations will allow to

  • comprehensively evaluate the model used for climate projection in the framework of past variability

  • to explore in-depth the role of solar, volcanic, and land-use-change forcing and their relative role in the 20th warming

  • to investigate interannual, multi-decadal to multi-century climate variability, atmospheric modes (e.g. NAO, ENSO), and ocean circulation changes

  • to assess regional climate change and regional/global scale teleconnections

  • to identify regional „hot-spots“ where climate change manifests itself particularly

  • to evaluate the model’s low frequency ecosystem feedbacks

  • to test statistical methods


The forced model simulations cover the period 800AD to present and will be extended into the 21st century using IPCC scenarios. A list of sub-projects is available (>>).

The Earth System Model:


The Max Planck Institute Earth System Model (MPI-ESM) consists of the atmosphere model ECHAM5, the ocean model MPIOM and modules for land vegetation (JSBACH) and ocean biogeochemistry (HAMOCC). The model setup enables the interactive simulation of the carbon cycle.


The model set-up:


Model experiments are carried out using the MPI-ESM model with ECHAM5 in T31/L19 and MPIOM in GR3.0/L40 resolution. In the framework of the upcoming CMIP5 long-term integrations, a higher resolution set-up will be applied. More information on the model and the external forcing reconstruction can be found here.

Millennium experiments

In the framework of the project, an extensive data set has been produced. First, we created a 3000-year unforced control experiment (mil0001) as a reference. We conducted an ensemble of five simulations (E1 = mil0010, mil0012, mil0013, mil0014, mil0015) spanning the time 800 AD to 2005 AD, applying reconstructions of natural forcing (volcanic aerosols and Total Solar Irradiance, TSI) and anthropogenic forcing (land-cover-changes, greenhouse gas emissions) that represent the most recent state-of-the-art. Solar variations over the last centuries have recently been argued to be much smaller than previously thought (Lean, 2005; Wang et al., 2005; Steinhilber et al., 2009) and we applied as our standard forcing a reconstruction with only ca. 0.1% TSI change from the Maunder Minimum to present. To account for uncertainty in the amplitude in solar forcing and to enable comparison with earlier model studies, we ran a second ensemble (E2 = mil0021, mil0025, mil0026) of three simulations with a Maunder Minimum reduction of 0.25%. In addition, we have performed sensitivity experiments with just one external forcing at a time (see table 1).

Exp. ID




yr. 800 control



Land-use-change only (best guess)



Land-use-change only (max. est.)



Solar only



Solar only (scaled to 0.25% amp.)



as mil002, only biogeochemical influence of land cover changes



as mil002, plus fossil fuel emmissions



Volcanoes only



E1: all forcings expt. 1



E1: all forcings expt. 2



E1: all forcings expt. 3



E1: all forcings expt. 4



E1: all forcings expt. 5



Scenario ext. mil0010



Scenario ext. Mil0012



Scenario ext. Mil0013



Scenario ext. Mil0014



Scenario extension mil0015



E2: All forcing expt. 1



E2: All forcing expt. 2



E2: All forcing expt. 3



Table 1: List of the Millennium experiment carried out with the MPI-M ESM at T31/GR3 resolution


Control integration


The first suite of experiments is carried out using the low-resolution version. After a multi-millennia spin-up the control integration was launched on February 26, 2008. In this run there is no external forcing and the orbital parameters are fixed to those for the year 800.


The 2000-year integration shows that the model exhibits a stable climate and compares well with other pre-industrial control integrations. Analyzes of the control simulation are underway including an assessment of internal variability on various time scales. European temperatures from the model agree well with the 500-year reconstruction of Luterbacher et al. (2004) (Figure 2).


Figure 2: European winter (DJF) surface air temperatures (land points only) from the Millennium control experiment (upper) and the Luterbacher et al. (2004) reconstruction. Thin lines: annual, thick lines: 11-year running mean.

Full forcing experiment

Over time-intervals from decades to centuries, simulated NH temperatures (Fig. 3) from all ensemble members differ significantly from the range of internal variability defined by the control experiment. Strong volcanic eruptions, particularly the cumulative effect of several volcanoes around the most severe eruptions in 1258 AD, 1453 AD, and 1815 AD, leave a long-lasting imprint on NH climate. Note that the generally somewhat cooler mean states in the ensembles are a result of the absence of volcanic aerosol forcing in the control run. Modulation by changing solar irradiance is more pronounced in the E2 ensemble where we identify the largest pre-industrial temperature anomalies in the 15th century during a superposition of the 1453 AD Kuwae eruption and the Spörer-Minimum (1450-1550 AD) in TSI. Overall, the simulations show the warmest pre-industrial NH temperatures around 1050-1250 AD and in the late 18th century while cold anomalies prevail during the 13th, 15th, 17th and early 19th centuries. In contrast to the E1 experiments, the E2 ensemble exhibits a notable MWP that is associated with the peak in the solar forcing in the 12th century.


Figure 3: Evolution of simulated temperature over the last 1200 years: Northern Hemisphere 2m land temperature anomalies w.r.t. the 1961-1990 mean for ensembles E1 (red) and E2 (blue) in comparison with the range of reconstructions (gray scale, redrawn from Jansen et al. (2007). Black horizontal lines indicate the control experiment mean and its 5th-95th percentile range. Green horizontal bars indicate periods where the ensembles do not overlap with each other. Time series are smoothed by a 31-yr running mean. Crosses at the right axis denote the ensemble means (annual average) at the end of the simulation (2005)
Both model ensembles exhibit relatively stable CO2 concentrations (Fig. 4 a) over the pre-industrial era. During the 20th century, the full forcing runs reproduce the observed increase in atmospheric CO2 similar to other carbon-cycle models (Figure 2 b). The E1 realisations fall below the ±1 ppm 5-95 percentile variability of the control run only after the very strong 1258 AD volcanic eruption, and rise above the control run variability only from the early 18th century on. The E2 realisations simulate CO2 significantly high during the MWP and significantly low during the LIA, akin to the NH temperatures, but none of the simulations reaches the amplitude suggested by the Law Dome data.

Solar radiation changes, land-cover changes, and volcanic eruptions have competing impacts on the carbon budget and on atmospheric CO2 concentration as demonstrated by experiments where just one forcing component was applied (Fig. 4 b). Solar forcing modulates atmospheric CO2 as can be most clearly seen in the experiment with the stronger amplitude TSI reconstruction. However, while the E2 ensemble gives generally lower CO2 concentrations throughout the LIA (Fig. 4 a), the pronounced drop in the early 17th century can not be associated with solar forcing because both TSI (Fig. 1 a) and CO2 (Fig 4 b, dark blue line) records show a positive anomaly around 1610 AD. Before 1700 AD, land cover changes modulate the CO2 record only by a few ppm, slightly exceeding the range of internal variability.


Figure 4.  CO2 concentrations (31-year running mean) from (a) ensembles E1 (red) and E2 (blue) in comparison with a compilation of ice core reconstructions (grey shading). Black horizontal lines denote the control experiment mean and its 5th-95th percentile range, (b) the respective CO2 concentrations from the experiments forced by one single component, i.e. standard solar forcing (red), strong solar forcing (blue), land-cover change (green), and volcanic aerosols (purple).



Jungclaus, J. H., Lorenz, S. J., Timmreck, C., Reick, C. H., Brovkin, V., Six, K., Segschneider, J., Giorgetta, M. A., Crowley, T. J., Pongratz, J., Krivova, N. A., Vieira, L. E., Solanki, S. K., Klocke, D., Botzet, M., Esch, M., Gayler, V., Haak, H., Raddatz, T. J., Roeckner, E., Schnur, R., Widmann, H., Claussen, M., Stevens, B., and Marotzke, J.: Climate and carbon-cycle variability over the last millennium, Clim. Past, 6, 723-737, doi:10.5194/cp-6-723-2010, 2010





Friedrich, T., A. Timmermann, A. Abe-Ouchi, N. R. Bates, M. O. Chikamoto, M. J. Church, J. E. Dore, D. K. Gledhill, M. Gonzalez-Davila, M. Heinemann, T. Ilyina, J. H. Jungclaus, E. McLeod, A. Mouchet, and J. M. Santana-Casiano, 2012: Detecting regional anthropogenic trends in ocean acidification against natural variability. Nature Clim. Change, 2(3), 167–171. 10.1038/nclimate1372


Henriksson, S., P. Räisänen, J. Silén and A. Laaksonen, 2012: Quasiperiodic climate variability with a period of 50–80 years: Fourier analysis of measurements and Earth System Model simulations. Climate Dynamics. doi: 10.1007/s00382-012-1341-0, in press.


Hind, A. and A. Moberg. Past millennial solar forcing magnitude. Climate Dynamics, 2012, doi: 10.1007/s00382-012-1526-6.


Hind, A., Moberg, A., and Sundberg, R.: Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 2: A pseudo-proxy study addressing the amplitude of solar forcing, Clim. Past, 8, 1355-1365, doi:10.5194/cp-8-1355-2012, 2012.


Lehner, F., C. C. Raible and T. F. Stocker, 2012: Testing the robustness of a precipitation proxy-based North Atlantic Oscillation reconstruction. Quaternary Science Reviews, 45, 85-94. doi: 10.1016/j.quascirev.2012.04.025

Man, W., T. Zhou, and J. Jungclaus, 2012: Simulation of the East Asian Summer Monsoon during the Last Millennium with the MPI Earth System Model. J. Climate. doi: 10.1175/JCLI-D-11-00462.1, in press.


Menary, M., W. Park, K. Lohmann, M. Vellinga, M. Palmer, M. Latif and J. Jungclaus, 2012: A multimodel comparison of centennial Atlantic meridional overturning circulation variability. Climate Dynamics, 38, 2377-2388. doi: 10.1007/s00382-011-1172-4


Pongratz, J., and K. Caldeira. Attribution of atmospheric CO2 and temperature increases to regions: importance of preindustrial land use change. Environmental Research Letters, 7(3):034001+, 2012, doi: 10.1088/1748-9326/7/3/034001


Zanchettin, D., A. Rubino, D. Matei, O. Bothe and J. Jungclaus, 2012: Multidecadal-to-centennial SST variability in the MPI-ESM simulation ensemble for the last millennium. Climate Dynamics. doi: 10.1007/s00382-012-1361-9, in press.


Zhang, D., R. Blender and K. Fraedrich, 2012: Volcanoes and ENSO in millennium simulations: global impacts and regional reconstructions in East Asia. Theoretical and Applied Climatology. doi: 10.1007/s00704-012-0670-6, in press.





Bye, J., K. Fraedrich, E. Kirk, S. Schubert, and X. Zhu, 2011: Random walk lengths of about 30 years in global climate. Geophysical Research Letters, 38, L05806, doi:10.1029/2010GL046333


Franke, J., J. Fidel González-Rouco, David Frank, and Nicholas E. Graham, 2011: 200years of european temperature variability: insights from and tests of the proxy surrogate reconstruction analog method. Climate Dynamics, 37(1), 133–150. doi: 10.1007/s00382-010-0802-6


F.J. González-Rouco, L. Fernández-Donado, C.C. Raible, D. Barriopedro , J. Luterbacher, J.H. Jungclaus, D. Swingedouw, J. Servonnat, E. Zorita, S. Wagner and C.M. Ammann (2011): Medieval Climate Anomaly to Little Ice Age transition as  simulated by current climate models, PAGES News, 19, 7-8.


Junk, C. and Claussen, M.: Simulated climate variability in the region of Rapa Nui during the last millennium, Clim. Past, 7, 579-586, doi:10.5194/cp-7-579-2011, 2011.


J. Pongratz, K. Caldeira, C.H. Reick, and M. Claussen (2011). Coupled climate-carbon simulations indicate minor global effects of wars and epidemics on atmospheric CO2 between AD 800 and 1850. The Holocene, doi: 10.1177/0959683610386981.


G.A. Schmidt, J.H. Jungclaus, C.M. Ammann, E. Bard, P. Braconnot, T.J. Crowley, G. Delaygue, F. Joos, N.A. Krivova, R. Muscheler, B.L. Otto-Bliesner, J. Pongratz, D.T. Shindell, S.K. Solanki, F. Steinhilber, and L.E.A. Vieira (2011). Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0). Geosci. Model Dev., 4, pp. 33–45, doi:10.5194/gmd-4-33-2011.


Zanchettin, D, C Timmreck, H-F Graf, A Rubino, S Lorenz, K Lohmann, K Krüger, JH Jungclaus (2011) Bi-decadal variability excited in the coupled ocean–atmosphere system by strong tropical volcanic eruptions. Climate Dynamics, online first. doi: 10.1007/s00382-011-1167-1


Blender, R., Zhu, X., Zhang, D., Fraedrich, K. Yangtze Runoff, Precipitation, and the East Asian Monsoonin a 2800years Climate Control Simulation, Quaternary International (2010), doi: 10.1016/j.quaint.2010.10.017

Brovkin, V., Lorenz, S. J., Jungclaus, J., Raddatz, T., Timmreck, C., Reick, C. H., Segschneider, J. and Six, K. (2010), Sensitivity of a coupled climate-carbon cycle model to large volcanic eruptions during the last millennium. Tellus B, 62: 674–681. doi: 10.1111/j.1600-0889.2010.00471.x

Pongratz, J., C. H. Reick, T. Raddatz, and M. Claussen (2010), Biogeophysical versus biogeochemical climate response to historical anthropogenic land cover change, Geophys. Res. Lett., 37, L08702, doi:10.1029/2010GL043010.

Reick, C. H., Raddatz, T., Pongratz, J. and Claussen, M. (2010), Contribution of anthropogenic land cover change emissions to pre-industrial atmospheric CO2. Tellus B, 62: 329–336. doi: 10.1111/j.1600-0889.2010.00479.x

Zanchettin, D., A. Rubino, and J. H. Jungclaus (2010), Intermittent multidecadal-to-centennial fluctuations dominate global temperature evolution over the last millennium, Geophys. Res. Lett., 37, L14702, doi:10.1029/2010GL043717.

Zhang, D., R. Blender, X. Zhu, and K. Fraedrich 2010: Temperature variability in China in an ensemble simulaton for the last 1200 years. Theoretical and Applied Climatology, doi: 10.1007/s00704-010-0305-8.    

Zhu, Xiuhua, Klaus Fraedrich, Zhengyu Liu, Richard Blender, 2010: A Demonstration of Long-Term Memory and Climate Predictability. J. Climate, 23, 5021–5029. doi: 10.1175/2010JCLI3370.1


Pongratz, J., T. Raddatz, C. H. Reick, M. Esch, and M. Claussen (2009), Radiative forcing from anthropogenic land cover change since A.D. 800, Geophys. Res. Lett., 36, L02709, doi:10.1029/2008GL036394.

Pongratz, J., C. H. Reick, T. Raddatz, and M. Claussen (2009), Effects of anthropogenic land cover change on the carbon cycle of the last millennium, Global Biogeochem. Cycles, 23, GB4001, doi:10.1029/2009GB003488.

Timmreck, C., S. J. Lorenz, T. J. Crowley, S. Kinne, T. J. Raddatz, M. A. Thomas, and J. H. Jungclaus (2009), Limited temperature response to the very large AD 1258 volcanic eruption, Geophys. Res. Lett., 36, L21708, doi:10.1029/2009GL040083.


Pongratz, J., C. Reick, T. Raddatz, and M. Claussen (2008), A reconstruction of global agricultural areas and land cover for the last millennium, Global Biogeochem. Cycles, 22, GB3018, doi:10.1029/2007GB003153.