ALBERT

Description: Simulations with the Max Planck Institute Earth System Model (MPI-ESM) are used to study the sensitivity of the AMOC and the deep ocean water masses during the Last Glacial Maximum to different sets of forcings. Analysing the individual contributions of the glacial forcings reveals that the ice sheets cause an increase of the overturning strength and a deepening of the North Atlantic Deep Water (NADW) cell, while the low greenhouse gas (GHG) concentrations cause the overturning strength to decrease and the NADW cell to shoal. The effect of the orbital configuration is negligible. The effects of the ice sheets and the GHG reduction balance each other in the deep ocean so that no shoaling of the NADW cell is simulated in the full glacial state. Experiments in which different GHG concentrations with linearly decreasing radiative forcing are applied to a setup with glacial ice sheets and orbital configuration show that GHG concentrations below the glacial level are necessary to cause a shoaling of the NADW cell with respect to the preindustrial state in MPI-ESM. For a pCO2 of 149 ppm, the simulated overturning state and the deep ocean water masses are in best agreement with the glacial state inferred from proxy data. Sensitivity studies confirm that brine release and shelf convection in the Southern Ocean are key processes for the shoaling of the NADW cell. Shoaling occurs only when Southern Ocean shelf water contributes significantly to the formation of Antarctic Bottom Water.

Description: Simulations with the Max Planck Institute Earth System Model (MPI-ESM) are used to study the sensitivity of the AMOC and the deep-ocean water masses during the Last Glacial Maximum to different sets of forcings. Analysing the individual contributions of the glacial forcings reveals that the ice sheets cause an increase in the overturning strength and a deepening of the North Atlantic Deep Water (NADW) cell, while the low greenhouse gas (GHG) concentrations cause a decrease in overturning strength and a shoaling of the NADW cell. The effect of the orbital configuration is negligible. The effects of the ice sheets and the GHG reduction balance each other in the deep ocean so that no shoaling of the NADW cell is simulated in the full glacial state. Experiments in which different GHG concentrations with linearly decreasing radiative forcing are applied to a setup with glacial ice sheets and orbital configuration show that GHG concentrations below the glacial level are necessary to cause a shoaling of the NADW cell with respect to the pre-industrial state in MPI-ESM. For a pCO2 of 149 ppm, the simulated overturning state and the deep-ocean water masses are in best agreement with the glacial state inferred from proxy data. Sensitivity studies confirm that brine release and shelf convection in the Southern Ocean are key processes for the shoaling of the NADW cell. Shoaling occurs only when Southern Ocean shelf water contributes significantly to the formation of Antarctic Bottom Water.

Description: Modeling is an important tool for understanding AMOC on all timescales. Mechanistic studies of modern AMOC variability have been hampered by a lack of consistency between free-running models and the sensitivity of AMOC to resolution and parameterization. Recent work within the framework of the phase two Coordinated Ocean- Reference Experiments (CORE-II) addresses this issue head on, looking at model differences of AMOC mean state and interannual variability. One consistent feature across the models is that AMOC mean transport is related to mixed layer depths and Labrador Sea salt content, whereas interannual variability is primarily associated with Labrador Sea temperature anomalies. This is consistent with the hypothesized importance of salt balance for AMOC variability on geological timescales. The simulated relationships between AMOC and subsurface temperature anomalies in fully coupled climate models reveal subsurface AMOC fingerprints that could be used to reconstruct historical AMOC variations at low frequency.With the lack of long-term AMOC observations, models of ocean state that assimilate observational data have been explored as a way to reconstruct AMOC, but comparisons between models indicate they are quite variable in their AMOC representations. Karspeck et al. (2015) found that historical reconstructions of AMOC in such models are sensitive to the details of the data assimilation procedure. The ocean data assimilation community continues to address these issues through improved models and methods for estimating and representing error information.Two objectives of paleoclimate modeling are 1) to provide mechanistic information for interpretation of paleoclimate observations, and 2) to test the ability of predictive models to simulate Earth's climate under different background forcing states. In a good example of the first objective, Schmittner and Lund (2015) and Menviel et al. (2014) provided key information about the proxy signals expected under freshwater disturbance of AMOC, which were used to support the paleoclimate observations made by Henry et al. (2016). In an example of the second objective, Muglia and Schmittner (2015) analyzed Third Paleoclimate Modeling Intercomparison Project (PMIP3) models of the Last Glacial Maximum (LGM) and found consistently more intense and deeper AMOC transports relative to preindustrial simulations, counter to the paleoclimate consensus of LGM conditions, indicating that some processes are not well represented in the PMIP3 models. One challenge is to find adequate paleo observations against which to test these models. PMIP is now in phase 4 (part of CMIP6), which includes experiments covering five periods in Earth's history: the last millennium, last glacial maximum, last interglacial, and the mid-Pliocene. Newly compiled paleoclimate datasets from the PAGES2k project, more transient simulations, and participation of isotope enabled models planned for CMIP6PMIP4 will enable richer paleo data-model comparisons in the near future.

Description: Simulations with the Max Planck Institute Earth System Model (MPI-ESM) are used to study the sensitivity of the AMOC and the deep-ocean water masses during the Last Glacial Maximum to different sets of forcings. Analysing the individual contributions of the glacial forcings reveals that the ice sheets cause an increase in the overturning strength and a deepening of the North Atlantic Deep Water (NADW) cell, while the low greenhouse gas (GHG) concentrations cause a decrease in overturning strength and a shoaling of the NADW cell. The effect of the orbital configuration is negligible. The effects of the ice sheets and the GHG reduction balance each other in the deep ocean so that no shoaling of the NADW cell is simulated in the full glacial state. Experiments in which different GHG concentrations with linearly decreasing radiative forcing are applied to a setup with glacial ice sheets and orbital configuration show that GHG concentrations below the glacial level are necessary to cause a shoaling of the NADW cell with respect to the pre-industrial state in MPI-ESM. For a pCO2 of 149 ppm, the simulated overturning state and the deep-ocean water masses are in best agreement with the glacial state inferred from proxy data. Sensitivity studies confirm that brine release and shelf convection in the Southern Ocean are key processes for the shoaling of the NADW cell. Shoaling occurs only when Southern Ocean shelf water contributes significantly to the formation of Antarctic Bottom Water.

Description: Last December, Paris was the host city for the 21st Conference of the Parties (COP21) of the United Nations Framework Convention on Climate Change (UNFCCC). Representatives of 195 countries met to dispute a legally binding climate agreement – a highly complex process involving thousands of politicians, scientists and activists, that to date has taken over two decades. The director ensemble “Rimini Protokoll” re-enacted this mammoth-scale drama of diplomacy in the play “Weltklimakonferenz” (World Climate Conference) at the “Deutsches Schauspielhaus” theatre in Hamburg, Germany. Since the opening night (21st Nov. 2014), the play has been performed 16 times, reaching an audience of over 9000. All performers in the play were experts and scientists at different stages of their careers, including PhD students, journalists and professors. Each spectator took on the identity of a delegate of one of the 195 participating countries. We will present the project and the performance, thereby highlighting the role of and the interaction between the spectators and early career scientists. In a nutshell the play went as follows (https://vimeo.com/137817619); after an opening ceremony, the audience was divided up into seven groups, each of which was given advice by experts in several different briefings. These informed on country-specific challenges caused by the social and economic situation, possible future climatic changes and negotiating tactics. In addition, the delegations had bilateral meetings, enabling them to exchange views and experiences with one another. Towards the end of the play each delegation was asked to submit a national commitment to greenhouse gas reduction and a financial contribution to the Green Climate Fund. Based on these national commitments, the final plenum revealed whether or not the delegations had managed to submit reductions compatible with restricting global warming to 2°C compared to pre-industrial times. Due to their direct personal involvement in the play, each spectator was confronted with the full complexity and challenge of a climate change conference: Revealing the "culprit" - in other words the causes of climate change – is all about facts. In contrast, when developing options for action, the matter at hand is ultimately values. Which risks should the world community take on? What cost is it prepared to accept to protect the population in areas menaced by droughts or floods? These are all decisions based on political, economic, and indeed ethical issues. Based on feedback from spectators both during and after the performance, we will discuss to what extent the performance managed to convey the complexity of the question at hand and to what extent the spectators actually took on the role of their given country. The spectators were not the only ones to be put out of their comfort zone during the performance. Also the experts had to, in cooperation with the directors, think carefully on how to find the right balance between scientific integrity and a captivating dramaturgy, ultimately leading to a performance that would be informative, thought-provoking, as well as enjoyable.