High-resolution simulations of twocold palaeo climates in Europe: MIS 3 and LGM
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
The study of past climate is important because it increases our understandingof how the climate system works. Past climate is often reconstructed by us-ing proxies (that is observations of things that tell something about past cli-mate, for example tree rings, pollen in lake sediments and fossils). Modelsimulations of past climate further increases the knowledge since it has thepossibility to gap the space and time between the sparse and scattered proxyobservations, since a model simulation gives relatively continuous infor-mation about the whole simulated area. Model simulations can also giveinternally coherent information about parameters that is not easily recon-structed from proxies (for example heat fluxes).In this thesis two periods in the past are simulated by climate models: theMarine Isotope Stage 3 (MIS 3), 44 000 years ago, and the Last GlacialMaximum (LGM), 21 000 years ago. Both periods are characterised by lowtemperature, low sea level and low level of carbon dioxide. The topographyin northern Europe is dominated by ice sheets covering Iceland, Norway andparts of Sweden at MIS3; and more extensive ice sheets covering Iceland,Scandinavia, the British Isles and Northern Germany at LGM. These periodsare firstly simulated by a global climate model. Those simulations are subse-quently used in a regional climate model to increase the level of detail overEurope. To make the regional climate model simulation more realistic vege-tation simulated by a dynamical vegetation model is used in the regionalclimate model.The climate models simulate European climates much colder than today,especially at LGM. The temperature differences ranges from 5 to 45 °Ccolder than today; the largest differences being at the ice sheets where theperennial ice cover and the high altitude keep temperatures low. Precipita-tion is reduced with as much as almost 100 % in northern Europe due toreduced evaporation. Precipitation is increased with as much as 100 % inparts of southern Europe due to changes in atmospheric circulation. Thesimulations are in broad agreement with proxies, although there are differ-ences.The vegetation model simulates tundra like vegetation (herbs and shrubs) inthe ice-free parts of central and southern Europe. The eastern parts of Europeare dominated by needle-leaved trees. The short and cool summers limitvegetation. The simulated vegetation is in broad agreement with reconstruc-tions.Sensitivity studies of vegetation show that changed vegetation can changethe monthly mean temperature with 1-3 °C in some seasons and regions. Theresponse depends on regional surface characteristics. Sensitivity studies ofice sheets show that the simulated climate is consistent with the assumptionsabout the ice sheet extent made in the simulation. The simulated climate iscold enough in northern Europe to support the ice sheet, and warm enough insouthern Europe to prevent the ice sheet from expanding in this direction. Aremoval of the ice sheet would only have an effect on the local scale in thevicinity of the ice sheet, but this experiment did not include changes in thelarge-scale global atmospheric circulation.Although the regional climate model simulations are to a large degree de-pending on the global climate model simulations they provide new infor-mation. When comparing proxies with model data or studying local/regionalclimatic features (such as the interplay between climate and vegetation) highhorizontal resolution, as in the regional climate model, is important.
Place, publisher, year, edition, pages
Meteorologiska institutionen , 2015.
Palaeo climate, climate, climate model, proxy data, LGM, MIS 3
Meteorology and Atmospheric Sciences
Research subject Meteorology
IdentifiersURN: urn:nbn:se:su:diva-124347OAI: oai:DiVA.org:su-124347DiVA: diva2:885280
2015-12-15, C609, 11:15 (English)
Kjellström, ErikNilsson, JohanZhang, Qiong
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