In the Global Climate division, large-scale climate variability is studied, including the effects of climate change. The research activities in the group focus on quantifying decadal to centennial climate variability, studying feedbacks in the earth system, development of global climate scenario’s and development of monthly, seasonal and decadal predictions. The group maintains global climate models of intermediate complexity and develops a state-of-the-art earth system model (EC-EARTH) as research tool and as tool for developing climate scenario’s. The group is internationally recognized in the fields of climate extremes, thermohaline circulation, tropical variability, atmospheric dynamics and land processes.

02-01-2012: Acceleration of land surface model devlopement over a decade of GLASS. Bart van den Hurk et al, Bulletin of the American Meteorological Society; doi: 10.1175/BAMS-D-11-00007.1

The Global Land Atmosphere System Study has ushered in an era in which LSMs for numerical weather and climate prediction now incorporate complex vegetation responses, detailed hydrology, dynamic snowpack evolution, urban processes, and more. This overview paper gives a historical overview of the GLASS panel activities and its current and future role in land surface model development and evaluation.

02-01-20112: Soil moisture effects on seasonal temperature and precipitation forecast scores in Europe. Van den Hurk, B.J.J.M., F. Doblas-Reyes, G. Balsamo, R.D. Koster, S.I. Seneviratne en H. Camargo Jr,; Clim. Dyn., 2010, doi:10.1007/s00382-010-0956-2.

The Second Global Land Atmosphere Coupling Experiment (GLACE2) is designed to explore the improvement of forecast skill of summertime temperature and precipitation up to 8 weeks ahead by using realistic soil moisture initialization. We show that for temperature the skill does indeed increase up to 6 weeks, but areas with (statistically significant) lower skill also exist at longer lead times for the European continent. The skill improvement is smaller than shown earlier for the US, partly because of a lower potential predictability of the European climate at seasonal time scales. Selection of extreme soil moisture conditions or a subset of models with similar initial soil moisture conditions does improve the forecast skill, and sporadic positive effects are also demonstrated for precipitation. Using realistic initial soil moisture data increases the interannual variability of temperature compared to the control simulations in the South-Central European area at longer lead times. Also better temperature forecasts are generated in a remote area in Western Europe. However, the covered range of forecast dates (1986 – 1995) is too short to isolate a clear physical mechanism for this remote correlation.

24-05-2011: The construction of a Central Netherlands temperature, G. van der Schrier(1), A. van Ulden(*), and G. J. van Oldenborgh(1)
(1)KNMI, P.O. Box 201, 3730 AE De Bilt, The Netherlands; (*) †

Abstract. The Central Netherlands Temperature (CNT) is a monthly daily mean temperature series constructed from homogenized time series from the centre of the Netherlands. The purpose of this series is to offer a homogeneous time series representative of a larger area in order to study large-scale temperature changes. It will also facilitate a comparison with climate models, which resolve similar scales. 
Read more on http://www.clim-past.net/7/527/2011/cp-7-527-2011.html

23-05-2011: Krimpend ijs op Arctische eilanden hoofdrolspeler in zeespiegelstijging, A.S. Gardner (DOASS) and B. Wouters (KNMI).

Smeltende gletsjers en ijskappen op de Canadese arctische eilanden spelen een veel grotere rol in de hedendaagse zeespiegelstijging dan tot zover werd aangenomen, volgens een internationale studie die op 20 April in Nature is verschenen. Tijdens de eerste drie jaar van de studie, van 2004 tot 2006, verloren de gletsjers en ijskappen in de regio jaarlijks gemiddeld 30 kubieke kilometer aan water. Dit verdrievoudigde zich tussen 2006 en 2009 tot 90 kubieke kilometer, oftewel 90 biljoen liter water per jaar. Tijdens de hele 6 jaar van de studie steeg de zeespiegel door het verdwijnende ijs wereldwijd gemiddeld met 1 millimeter.

14-04-2011: Regionale zeespiegelveranderingen in de eenentwintigste eeuw, C. Katsman (KNMI), A. Slangen (IMAU/UU), R. van de Wal (IMAU/UU), B. Vermeersen, R. Riva (TU Delft).

04-01-2011: EC-Earth: A seamless prediction system in action, W. Hazeleger et al, Bulletin of American Meteorological Society
http://journals.ametsoc.org/doi/abs/10.1175/2010BAMS2877.1

In a recent paper in BAMS we publish the project, the consortium and the model EC-Earth. EC-Earth is a state-of-the-art climate model based on ECMWFs seasonal forecast system. We present a seamless prediction strategy in which numerical weather forecasting strategies and climate predictions and projections are linked. The strategy of model development is illustrated by upgrading EC-Earth using both new model cycles of ECMWF and by including new earth system components developed at universities and institutions. We show that the coupled model performs well compared to CMIP3 models, in particular the atmospheric states. We also indicate that the slight changes that we implemented to get stable radiation balance did not affect the medium range weather forecasting capabilities. An example of a new snow scheme that is developed in the EC-Earth framework and that is now implemented in the ECMWF model is shown. The model is used for climate research and generating climate projections and predictions.

01-11-2010: The stability of the MOC as diagnosed from model projections for pre-industrial, present and future climates

Paleoclimatic proxy data of the last glacial cycle show evidence of abrupt climate changes that are associated with major reorganizations of the Atlantic Meridional Overturning Circulation (MOC). The stability of the MOC was investigated for various climate scenario runs, using data from the CMIP3 archive of coupled atmosphere-ocean models. Apart from atmospheric feedbacks, the sign of the salt flux into the Atlantic basin that is carried by the MOC determines whether the MOC is in a stable regime with only one equilibrium, or in a regime where abrupt transitions between two stable states are possible. The amplitude of the salt advection feedback was analyzed by diagnosing the freshwater and salt budgets for the combined Atlantic and Arctic basins. Consistent with the finding that almost all coupled climate models recover from hosing experiments, it was found that most models feature a negative salt advection feedback in their pre-industrial climate, excluding the existence of a stable off-state for the MOC. There is strong evidence that the "real" MOC resides in the multiple equilibrium regime, indicating that those models are biased towards too stable conditions. All models feature enhanced evaporation over the Atlantic basin in future, warmer climates, but for a moderate increase in radiative forcing (B1 and 2 CO2 scenarios), there is a decrease of the fresh water flux carried by the MOC into the Atlantic, making the MOC less stable in the future. (Drijfhout, et al)

01-11-2010: Greenland's contribution to global sea-level rise by the end of the 21st century.

The largest uncertainty in future sea-level rise scenarios stems from the calving, or ice discharge from large ice sheets. Present-day ice sheet models are unable to simulate ice flow dynamics and the recently observed speed-up of outlet glaciers. A simple parameterization of increased flow in outlet glaciers was implemented in a positive degree day model, which decreases the bias in surface height. With this parameterization we have been able to simulate the Greenland ice-sheet evolution of the last 100,000 years. The uncertainty in Greenland's contribution to future sea-level rise was estimated by driving the model with high resolution output of the RAMO-model and adding temperature and precipitation anomalies from an ensemble of model simulations from the CMIP3 archive. We estimate the maximum mass loss in 2100 to be equivalent to 17 cm sea-level rise, higher than the IPCC AR4 estimate, but lower than high-end estimates by the Delta Committee and other expert elicitation. The reason is that ice flow velocities saturate for long-lasting enhanced lubrication (decreased friction) as the surface height gradient in the enhanced outflow regime strongly diminishes, counteracting the decrease in bottom friction. (Grand Graversen, et al)