Toekenningen RAPID Climate Change
Eind 2004 is de financiering voor 4 projecten van de Joint NL/NO/UK RAPID met Nederlandse onderzoekers rondgekomen:
- Variations of the Atlantic Meridional Ocerturning Circulation during rapid climate changes: calibration, modelling and palaeoceanographic observations (VAMOC)
- Mass balance and fresh water contribution of the Greenland ice sheet: a combined modelling and observational approach
- To what extent was the Little Ice Age a result of change in the thermohaline circulation?
- Impact of changing freshwater flows on the thermohaline circulation and European climate: analysis and modelling of the last glaciation
Abstracts of Joint NL/NO/UK proposals 2004
Variations of the Atlantic Meridional Ocerturning Circulation during rapid climate changes: calibration, modelling and palaeoceanographic observations (VAMOC)
Elderfield, Univ.Cambridge
McCave, Galy, Pomies, Greaves Univ.Cambridge
Dokken, Jansen, Kleiven, Andersson, e.a. Univ.Bergen
Brummer, Van
Weering, van Aken NIOZ
Ganssen, Kroon, Davies, Jung VU-FALW
Shephard ,
Univ. Southampton
Our ability to understand the potential for future abrupt changes in climate is limited by our lack of understanding of the processes that control them. The climate system appears to operate in quasi-stable modes, and may switch from one mode to another within a few decades. Recent evidence suggest that abrupt climate changes often occur when gradual causes push the earth system across a threshold. Studies, using paleo data, of past climate suggest that large and rapid (as fast as 10-20 years) changes have occurred and that changes in the Atlantic Meridional Overturning Circulation (AMOC) are a major contributing factor. A better understanding of the processes that “drive” the AMOC is of key importance. Examination of proxy data for the hydrography of the N. Atlantic has suggested 3 modes of operation of the MOC, modern, peak glacial and meltwater pulse modes. The meltwater event mode is the most severe in terms of regional atmospheric temperature drop and cessation of deep meridional overturning In the project we propose to test the hypothesis that rapid climate transitions are always associated with changes in overturning rate in the Nordic Seas. This will make a major contribution to understanding what might happen with increased greenhouse gas levels and glocal warming.
Mass balance and fresh water contribution of the Greenland ice sheet: a combined modelling and observational approach
Van den Broeke, UU-IMAU
van Meijgaard KNMI
Bamber, Univ. Bristol
Johannessen, Nansen Center
The thermohaline circulation is a global ocean circulation, driven by differences in the density of the sea water that is controlled by temperature (thermal) and salinity (haline). In the north Atlantic, the thermohaline circulation transports warm and salty water to the north, where it, together with the North Atlantic Drift (the north-eastern most extension of the Gulfstream), contributes to the warm sea surface along the coast of western Europe and to the relatively mild European winters. From ice cores drilled in Greenland, there is evidence that rapid climate changes took place during the last glacial (the period roughly from 100,000 to 20,000 years before present): over a period of just several decades, northern European winter temperature dropped by as much as 10 degrees for periods typically lasting 1000 years. The present explanation is that large, pulse-like freshwater fluxes (probably from icebergs that originated from the continental ice sheets) were released into the north Atlantic where they weakened or shut down the thermohaline circulation. In a warmer greenhouse climate, it is also likely that the freshwater flux into the north Atlantic will increase; using a scenario of doubling CO2 within the next 70 years, most atmospheric models predict an increase in precipitation in high latitudes. One of the great uncertainties in these projections is the role of the Greenland ice sheet, which is situated in the middle of the area of interest. We know so little about the variability in its meltwater production and its sensitivity to regional warming that its contribution to the problem of the north Atlantic thermohaline circulation is often ignored, in spite of the fact that the Greenland ice sheet contains enough water to rise global sea level by 6 m! In this proposed research we will quantify in detail how, where and when the Greenland ice sheet has fed fresh water through iceberg calving, subglacial melting and meltwater runoff into the surrounding ocean during the last half century. The melting and runoff is calculated using a coupled snow - atmosphere model that is run over Greenland at very high resolution (11 km in the horizontal), which will take about 1 year on a supercomputer to run! The resulting data will be used by the oceanographical community as a boundary condition for their models of the north-Atlantic thermohaline circulation.
To what extent was the Little Ice Age a result of change in the thermohaline circulation?
Osborn, Univ.East Anglia
van de Schrier, Briffa Univ.East Anglia
Weber, Barkmeijer KNMI
For a full understanding of the global climate system, it is imperative to integrate research on empirical climate reconstruction with physical modelling studies of the Earth’s climate, using numerical models of varying complexity to address important questions about the attribution of past and future climate changes to specific natural and anthropogenic factors. The focus of this project is on testing various hypotheses about the possible causes of the Little Ice Age. A carefully-designed set of model experiments (incorporating novel methods of assimilating information on climate time scales) is proposed, with the outputs assessed through comparison against empirical palaeoclimate evidence for climate variations over the past millennium. Specifically, we will explore whether the Little Ice Age climate could have been generated by one or more of the following factors: a weakening of the Atlantic thermohaline circulation; the persistence of a generally negative North Atlan tic Oscillation; or reduced radiat ive forcing (by increased volcanic activity, reduced solar insolation and lower greenhouse gas concentrations relative to the present). The proposed project will involve a 3-year collaboration between the University of East Anglia (UK) and the Royal Netherlands Meteorological Institute (Netherlands).
Impact of changing freshwater flows on the thermohaline circulation and European climate: analysis and modelling of the last glaciation
Harrison Univ.Bristol
Valdes Univ.Bristol,
Mangerud, Svendsen,
Jansen, Dokken, Univ.Bergen
Weber KNMI, Renssen, Vandenberghe
VU-FALW
Changes in the amount and location of river and meltwater discharge to the North Atlantic and Arctic Oceans could profoundly affect the thermohaline circulation and thus the climate of Europe. Abrupt changes in ocean circulation, and the location of North Atlantic Deep Water (NADW) formation, have been recorded during the last 21,000 years. Palaeodata and modelling suggest these changes may have been caused by ice-sheet dynamics (changing meltwater inputs, blocking/unblocking of river channels) and by climate change affecting continental runoff and river discharge. A concerted effort is planned to understand past changes in NADW formation and to explore the risk of comparable changes taking place in the future. Our approach involves using two efficient coupled ocean-atmosphere-vegetation models to explore the impacts of a range of possible freshwater-flux scenarios representing different intervals during the last deglaciation. New reconstructions of Eurasian ice-sheet deglaciation history will be used to i nform the choice of scenarios. The plausibility of the simulations will be evaluated using a 4D reconstruction of the ocean during the deglaciation and palaeoenvironmental records of regional climates over the northern continents, prior to using the models to examine the consequences of potential future changes in freshwater fluxes on ocean circulation and climate.