Papers by Didier Swingedouw
Nature Communications
The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom W... more The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom Water, which contributes up to ~25% of the Antarctic Bottom Water. This major polynya is closely linked to the presence of the Mertz Glacier Tongue that traps pack ice upstream. In 2010, the Mertz Glacier calved a massive iceberg, deeply impacting local sea ice conditions and dense shelf water formation. Here we provide the first detailed 250-year long reconstruction of local sea ice and bottom water conditions. Spectral analysis of the data sets reveals large and abrupt changes in sea surface and bottom water conditions with a ~70-year cyclicity, associated with the Mertz Glacier Tongue calving and regrowth dynamics. Geological data and atmospheric reanalysis, however, suggest that sea ice conditions in the polynya were also very sensitive to changes in surface winds in relation to the recent intensification of the Southern Annular Mode.
Nature, 2015
The North Atlantic Oscillation (NAO) is the major source of variability in winter atmospheric cir... more The North Atlantic Oscillation (NAO) is the major source of variability in winter atmospheric circulation in the Northern Hemisphere, with large impacts on temperature, precipitation and storm tracks, and therefore also on strategic sectors such as insurance, renewable energy production, crop yields and water management. Recent developments in dynamical methods offer promise to improve seasonal NAO predictions, but assessing potential predictability on multi-annual timescales requires documentation of past low-frequency variability in the NAO. A recent bi-proxy NAO reconstruction spanning the past millennium suggested that long-lasting positive NAO conditions were established during medieval times, explaining the particularly warm conditions in Europe during this period; however, these conclusions are debated. Here, we present a yearly NAO reconstruction for the past millennium, based on an initial selection of 48 annually resolved proxy records distributed around the Atlantic Ocean and built through an ensemble of multivariate regressions. We validate the approach in six past-millennium climate simulations, and show that our reconstruction outperforms the bi-proxy index. The final reconstruction shows no persistent positive NAO during the medieval period, but suggests that positive phases were dominant during the thirteenth and fourteenth centuries. The reconstruction also reveals that a positive NAO emerges two years after strong volcanic eruptions, consistent with results obtained from models and satellite observations for the Mt Pinatubo eruption in the Philippines.
Proceedings of the National Academy of Sciences, 2015
Abrupt transitions of regional climate in response to the gradual rise in atmospheric greenhouse ... more Abrupt transitions of regional climate in response to the gradual rise in atmospheric greenhouse gas concentrations are notoriously difficult to foresee. However, such events could be particularly challenging in view of the capacity required for society and ecosystems to adapt to them. We present, to our knowledge, the first systematic screening of the massive climate model ensemble informing the recent Intergovernmental Panel on Climate Change report, and reveal evidence of 37 forced regional abrupt changes in the ocean, sea ice, snow cover, permafrost, and terrestrial biosphere that arise after a certain global temperature increase. Eighteen out of 37 events occur for global warming levels of less than 2°, a threshold sometimes presented as a safe limit. Although most models predict one or more such events, any specific occurrence typically appears in only a few models. We find no compelling evidence for a general relation between the overall number of abrupt shifts and the level of global warming. However, we do note that abrupt changes in ocean circulation occur more often for moderate warming (less than 2°), whereas over land they occur more often for warming larger than 2°. Using a basic proportion test, however, we find that the number of abrupt shifts identified in Representative Concentration Pathway (RCP) 8.5 scenarios is significantly larger than in other scenarios of lower radiative forcing. This suggests the potential for a gradual trend of destabilization of the climate with respect to such shifts, due to increasing global mean temperature change.
Studying the climate of the last millennium gives the possibility to assess a pre-industrial peri... more Studying the climate of the last millennium gives the possibility to assess a pre-industrial period of several centuries more and more documented through surface temperature reconstructions. The Northern Hemisphere temperature reconstructions show common secular pattern reflecting the so-called Medieval Climate Anomaly and the Little Ice Age and understanding the causes of such events is a key issue in understanding natural
The behaviour of the thermohaline circulation at the Last Glacial Maximum (LGM) and its sensitivi... more The behaviour of the thermohaline circulation at the Last Glacial Maximum (LGM) and its sensitivity to fresh water forcing at mid to high latitudes in the North Atlantic has extensively been studied with Earth system models of Intermediate Complexity (EMICS). There are far less studies based on fully coupled ocean-atmosphere general circulation models. In the present work, we use the IPSL ocean-atmosphere general circulation model in the same version as the one used in the last IPCC exercise. We study two LGM simulations, one starting with an active Atlantic Meridional Overturning Circulation (AMOC), the other starting with a shut down (AMOC). At the time of writing, after more tha 500 years of integration for each run, both circulations are stable. We will investigate the reasons of this stability and examine the climate differences between these two states. These will be compared to the results of a transient run between the 2 states.
Climate of the Past Discussions, 2014
La Météorologie, 2007
Le 4e rapport du Groupe intergouvernemental d'experts su... more Le 4e rapport du Groupe intergouvernemental d'experts sur l'évolution du climat (Giec), récemment paru, propose une évaluation remise à jour des éléments scientifiques, techniques et socio-économiques permettant une meilleure compréhension du ...
Uploads
Papers by Didier Swingedouw