Ensemble Simulation of the Last Millennium using the Comprehensive COSMOS Earth System Model Jungclaus, J.H. Jungclaus, J.H. sensitivity earth science/paleoclimate/paleoclimatic modeling (latitude,null,null,degree north,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/paleoclimatic modeling (surface air temperature,null,null,kelvin,null,paleoclimatic modeling,null,null,N,2 meter air temperature) earth science/paleoclimate/paleoclimatic modeling (precipitation,null,null,kilogram per square meter per second,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/paleoclimatic modeling (age,null,null,year Common Era,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/paleoclimatic modeling (surface temperature,null,null,kelvin,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/paleoclimatic modeling (sea level pressure,null,null,pascal,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/paleoclimatic modeling (longitude,null,null,degree east,null,paleoclimatic modeling,null,null,N,null) earth science/paleoclimate/model earth science/paleoclimate/model (Global>LATITUDE >LONGITUDE ) A long-standing task in climate research has been to distinguish between anthropogenic climate change and natural climate variability. A prerequisite for fulfilling this task is the understanding of the relative roles of external drivers and internal variability of climate and the carbon cycle. Here, we present the first ensemble simulations over the last 1200 years with a comprehensive Earth system model including a fully interactive carbon cycle. Applying up-to-date reconstructions of external forcing including the recent low-amplitude estimates of solar variations, the ensemble simulations reproduce temperature evolutions consistent with the range of reconstructions. The 20th-century warming trend stands out against all pre-industrial trends within the ensemble. Volcanic eruptions are necessary to explain variations in pre-industrial climate such as the Little Ice Age; yet only the strongest, repeated eruptions lead to cooling trends that differ significantly from the internal variability across all ensemble members. The simulated atmospheric CO2 concentrations exhibit a stable carbon cycle over the pre-industrial era with multi-centennial variations somewhat smaller than in the observational records. Early land-cover changes have modulated atmospheric CO2 concentrations only slightly. We provide a model-based quantification of the sensitivity (termed γ) of the global carbon cycle to temperature for a variety of climate and forcing conditions. We diagnose a distinct dependence of γ on the forcing strength and time-scales involved, thus providing a possible explanation for the systematic difference in the observational estimates for different segments of the last millennium. STUDY NOTES: The data is all monthly means on a 96 x 48 gaussian grid. Experiment ID Length Description mil0001_EH5_mm 800-3800 yr. 800 control experiment mil0002_EH5_mm 800-2100 land use change only (best guess) mil0005_EH5_mm 800-2005 solar forcing only mil0006_EH5_mm 800-2005 solar forcing only (scaled to 0.25% amp.) mil0007_EH5_mm 800-2100 as mil0002, only biogeochemical influence of land cover changes mil0008_EH5_mm 1860-2100 as mil002, plus fossil fuel emissions mil0009_EH5_mm 800-2005 Volcanoes only mil0010_EH5_mm 800-2005 full forcing (ensemble member 1) mil0012_EH5_mm 800-2005 full forcing (ensemble member 2) mil0013_EH5_mm 800-2005 full forcing (ensemble member 3) mil0014_EH5_mm 800-2005 full forcing (ensemble member 4) mil0015_EH5_mm 800-2005 full forcing (ensemble member 5) mil0021_EH5_mm 800-2100 full forcing using solar forcing of Bard (ensemble member 1) mil0025_EH5_mm 800-2100 full forcing using solar forcing of Bard (ensemble member 2) mil0026_EH5_mm 800-2100 full forcing using solar forcing of Bard (ensemble member 3) NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Jungclaus, J.H. 2011-03-14 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/10477 https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/ https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/MILL-COSMOS-readme.txt https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/ https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/MILL-COSMOS-readme.txt English https://www.ncdc.noaa.gov/paleo/study/10477 https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/ https://www1.ncdc.noaa.gov/pub/data/paleo/gcmoutput/mpi/MILL-COSMOS-readme.txt Jungclaus, J.H., S.J. Lorenz, C. Timmreck, C.H. Reick, V. Brovkin, K. Six, J. Segschneider, M.A. Giorgetta, T.J. Crowley, J. Pongratz, N.A. Krivova, L.E. Vieira, S.K. Solanki, D. Klocke, M. Botzet, M. Esch, V. Gayler, H. Haak, T.J. Raddatz, E. Roeckner, R. Schnur, H. Widmann, M. Claussen, B. Stevens and J. Marotzke. 2010. Climate and carbon-cycle variability over the last millennium. Clim. Past, 6, 723-737, doi:10.5194/cp-6-723-2010 START YEAR: 800 AD * END YEAR: 2100 AD -180 -90 180 90