Project

Discipline

Pollen; Climate models; Paleoclimate; Atmospheric dynamics; Holocene; Climate

Lead
Projet HORNET: Reconstitutions climatiques de l’Hémisphère Nord extratropical au cours de l’Holocène à partir de données polliniquesLes enregistrements des changements du climat de la Terre avant l’époque moderne nous aident à comprendre le système climatique global au delà de notre perspective historique étriquée. Ces enregistrements peuvent aussi être utilisés pour tester et évaluer la fiabilité des modèles climatiques sur lesquels nos prédictions des changements climatiques à venir sont basées. Il a été montré que les modèles actuels ont des difficultés à reproduire un grand nombre d’aspects des changements climatiques qui ont eu lieu au cours de l’Holocène (la dernière période interglaciaire qui couvre les 12000 dernières années).
Lay summary
Le principal objectif de ce projet consiste à améliorer notre compréhension des changements climatiques qui ont eu lieu au cours de l’Holocène en créant les toutes premières reconstitutions spatialement et saisonnièrement explicites du climat de l’Hémisphère Nord extratropical au cours des 12000 dernières années. Pour ce faire, nous utiliserons des enregistrements polliniques fossiles provenant de plus de 3000 lacs et tourbières répartis à travers notre zone d’étude, ce qui nous permettra de mettre en évidence comment le climat a changé via son impact sur la végétation. En reconstituant la configuration spatiale des anomalies hivernales et estivales des températures et des précipitations, et en les comparant avec celles dérivées des simulations mais aussi avec des configurations modernes de circulation atmosphérique, nous espérons déterminer le rôle relatif de la dynamique de l’atmosphère sur le climat au cours de l’Holocène.  Ce projet va reconstituer les changements climatiques de l’Holocène avec une résolution spatiale et saisonnière inédite. Ces résultats vont nous aider à comprendre comment le climat a changé à l’échelle régionale, ce qui permettra par la suite d’améliorer la capacité des modèles à prédire les futurs changements climatiques à l’échelle régionale.

Direct link to Lay Summary

Last update: 01.02.2017

Number	Title	Start	Funding scheme

Data-model comparisons of Holocene climate provide an ideal basis for evaluating climate model performance outside of modern climate variability, being recent enough that boundary conditions and forcings are well known, while well-dated palaeoclimate archives are abundant enough that past climate can be comprehensively reconstructed. To date, efforts to reconstruct the spatial patterns of Holocene climate change have been mainly focused on the mid-Holocene, but significant problems have already been identified in data-model comparisons. For instance, Hargreaves et al. (2013) reported for the very latest CMIP5 models that “..our results for the mid-Holocene are substantially negative, with the models failing to reproduce the observed changes with any degree of skill”. The reasons for these data-model discrepancies are not entirely clear, but the applicants have shown that the regional patterns of climate anomalies that are poorly represented in climate models may be explained by seasonal changes in atmospheric dynamics, a model weakness also found in simulations of modern climate (Mauri et al., 2014). The HORNET project will investigate these data-model discrepancies, including the potential role of atmospheric dynamics, by providing the first quantitative gridded climate reconstruction for the entire Northern Hemisphere extra-tropical landmass for the last 12,000 years based on pollen data. This will be achieved by leveraging fossil pollen data from over 3000 sites from North America, Europe and Asia, most of which are already available from existing public pollen databases. The reconstruction will use a common pollen-climate methodology to provide consistent and comprehensive estimates of uncertainties, and will be independently evaluated against existing reconstructions based on other proxies, as well as other pollen-climate techniques. The results will be fully documented and both managed and made public using a new map-based visualization tool developed within the project. This tool will allow both primary pollen and climate data from the HORNET project to be viewed on a site-by-site basis, whilst also providing a more general resource for the study of Holocene climate by also showing other climate reconstructions from other studies. A key scientific objective of the HORNET project will be to use data to identify the relative contribution of the summer and winter seasons to Northern Hemisphere interglacial warming, and particularly the relative role of an orbitally driven increase in insolation in summer, and a dynamically driven increase in the pole-ward heat flux in winter. The role of atmospheric dynamics will be investigated by comparison with comparable patterns of regional climate anomalies generated by modern analogue circulation patterns. The project will make available a high quality gridded and seasonally resolved reconstruction of Northern Hemisphere climate change during the Holocene that will provide a state-of-the-art baseline for climate model evaluation, and particularly to evaluate the ability of models to reproduce regional climate change, which remains a key uncertainty in simulations of future climate change (Stocker et al., 2013).The HORNET project will promote collaboration and community participation in the project through 3 workshops on 1) pollen-climate reconstruction methods, 2) quantitative records of Holocene climate change, and 3) Holocene data-model comparisons and understanding data-model discrepancies.