Evaluation of coupled ocean-atmosphere simulations of the mid-Holocene using palaeovegetation data from the northern hemisphere extratropics

• Published in: Climate dynamics Vol. 31; no. 7-8; pp. 871 - 890
• Main Authors: Wohlfahrt, J, Harrison, S. P, Braconnot, P, Hewitt, C. D, Kitoh, A, Mikolajewicz, U, Otto-Bliesner, B. L, Weber, S. L
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01-12-2008; Springer-Verlag; Springer; Springer Nature B.V; Springer Verlag
• Subjects: Atmosphere; Atmospheric sciences; Biogeography; Boreal forests; Climate model evaluation; Climate science; Climatology; Continental interfaces, environment; Data-model comparisons; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Extratropical climates; Geochemistry; Geophysics/Geodesy; Growing season; Holocene; Latitude; Marine; Marine and continental quaternary; Mid-continental aridity; Mid-Holocene; Ocean feedback; Ocean, Atmosphere; Ocean-atmosphere interaction; Oceanography; Paleobotany; Paleoclimate; Paleontology; Pollen reconstructions of vegetation; Sciences of the Universe; Simulation; Surficial geology; Temperate forests; Tundra-taiga boundary; Vegetation; Winter; Eurasia; Europe; North America; ANE, Europe; PNE, Eurasia; Mid-continental aridity; Tundra–taiga boundary; Climate model evaluation; Mid-Holocene; Ocean feedback; Data-model comparisons; Pollen reconstructions of vegetation; Extratropical climates; Quaternary; vegetation; digital simulation; upper Quaternary; North America; forests; paleoclimate; feedback; paleobotany; Northern Hemisphere; middle Holocene; cooling; warming; Cenozoic; Phanerozoic; atmospheric circulation; Holocene; ocean circulation
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-008-0415-5

We have used the BIOME4 biogeography-biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean-atmosphere general circulation models to mid-Holocene changes in orbital forcing in the mid- to high-latitudes of the northern hemisphere. All the models produce: (a) a northward shift of the northern limit of boreal forest, in response to simulated summer warming in high-latitudes. The northward shift is markedly asymmetric, with larger shifts in Eurasia than in North America; (b) an expansion of xerophytic vegetation in mid-continental North America and Eurasia, in response to increased temperatures during the growing season; (c) a northward expansion of temperate forests in eastern North America, in response to simulated winter warming. The northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in North America are supported by palaeovegetation data. The expansion of xerophytic vegetation in mid-continental North America is consistent with palaeodata, although the extent may be over-estimated. The simulated expansion of xerophytic vegetation in Eurasia is not supported by the data. Analysis of an asynchronous coupling of one model to an equilibrium-vegetation model suggests vegetation feedback exacerbates this mid-continental drying and produces conditions more unlike the observations. Not all features of the simulations are robust: some models produce winter warming over Europe while others produce winter cooling. As a result, some models show a northward shift of temperate forests (consistent with, though less marked than, the expansion shown by data) and others produce a reduction in temperate forests. Elucidation of the cause of such differences is a focus of the current phase of the Palaeoclimate Modelling Intercomparison Project.