AMOC Recovery in CMIP Future Scenarios

The authors discuss the CMIP future scenarios RCP4.5 and RCP8.5 they redo with the AWI-ESM, a model that basis on AWI-CM (Rankow et al., 2018, Sidorenko et al., 2015) but includes interactive vegetation and an interactive Northern Hemispheric ice sheet model. The focus of the paper is on the effects of the melt-induced fresh water on the Atlantic meridional overturning circulation (AMOC). 

The results indicate, that AMOC is slowing down in both experiments, with and without included interactive ice sheet into the model system, for both future scenarios but starts to recover at the end of the 21st century (RCP4.5) and at the beginning of the 22nd century (RCP8.5), respectively.

Nevertheless, an interactive ice sheet model adds a strong decadal variability on the freshwater release, as a compensating effect, when the surface runoff is reduced by high accumulation rates.

The authors argue, that experiments that aim to parameterize the Greenland freshwater release by freshwater hosing have to be assessed critically, as this compensating effect is missing in climate models without interactive ice sheets. Moreover, they discuss, that the increasing net evaporation over the Atlantic and the resulting increase of the salinity may be the main driver of the AMOC recovery.

Fig.Time series of 11-year means and spatial changes of the Greenland Ice Sheet in the coupled simulations; shaded areas indicate 1 standard deviation. (a) The ice sheet’s total volume expressed as sea-level rise potential, (b) surface runoff from the icesheet model, (c) surface accumulation, (d) discharge, (e) the ice sheet’s total volume change, (f) surface runoff from the atmosphere model. For CTRL only the last 100 years are shown; (g and h) anomaly of ice sheet’s thickness for 2170 – 2199 for RCP4.5-ice and RCP8.5-ice respectively, (i and j) the ice sheet’s surface mass balance for 2170 – 2199 for RCP4.5-ice and RCP8.5-ice respectively. 

Ackermann, L. , Danek, C. , Gierz, P. and Lohmann, G. (2020) AMOC Recovery in a Multicentennial Scenario Using a Coupled Atmosphere‐Ocean‐Ice Sheet Model. Geophysical Research Letters, 47 (16). e2019GL086810. DOI 10.1029/2019GL086810.

Natural methane emissions – from the glacial to the present In a new study in Climate of the Past Kleinen, Mikolajewicz, and Brovkin (Max Planck Institute for Meteorology), were able to show that the changes in methane concentration between the Last Glacial Maximum (LGM, about 20000 years ago) and the preindustrial late Holocene (PI), 300 years ago, can be explained entirely by changes in the natural methane emissions caused by environmental changes.   Natural net emissions of methane in the present-day climate. Credit: Thomas Kleinen Kleinen, Thomas , Mikolajewicz, Uwe und Brovkin, Victor (2020) Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period. Climate of the Past, 16 (2). pp. 575-595. DOI 10.5194/cp-16-575-2020. Source: Max Planck Institute for Meteorology

PalMod I Highlights

 

Freshwater release and elevation loss affect climate during Heinrich events

 

A team of researchers around Dr. Florian Ziemen at the Max Planck Institute for Meteorology found that Heinrich events, climate changes during the last ice age, were caused by a succession of the effects of two mechanisms: iceberg calving, having effects on the ocean, and ice sheet elevation loss, having effects on the atmosphere. Using a novel model setup, they were able to study the relationship between the two individual effects. They were the first to observe the succession of both effects in one simulation.

Citation: Ziemen, F., Kapsch, M.-L., Klockmann, M., & Mikolajewicz, U. (2019). Heinrich events show two-stage climate response in transient glacial simulations. Climate of the Past, 15, 153-168. doi:10.5194/cp-15-153-2019

How cold was Antarctica during the last ice age?   [August 2018]  In a recent study by scientists from the Alfred Wegener Institute together with French colleagues temperature changes in Antarctica during the last ice age have been reconstructed. Ice core data and model results indicate a much stronger cooling of West Antarctica than East Antarctica during that time. Furthermore, the study enabled a new estimate of Antarctic ice sheet height changes during this past climate stage. The results of this study have been recently published in Nature Communications. Citation: Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer; Martin Werner, Jean Jouzel, Valérie Masson-Delmotte & Gerrit Lohmann; Nature Communicationsvolume 9, Article number: 3537 (2018)

 

Coastal erosion in the Arctic intensifies global warming Sea level rise in the past led to the release of greenhouse gases from permafrost [September 2018]  The loss of arctic permafrost deposits by coastal erosion could amplify climate warming via the greenhouse effect. A study using sediment samples from the Sea of Okhotsk on the eastern coast of Russia led by AWI researchers revealed that the loss of Arctic permafrost at the end of the last glacial period led to repeated sudden increases in the carbon dioxide concentration in the atmosphere. press release (AWI) Citation: Winterfeld, M. et al., Deglacial mobilization of pre-aged terrestrial carbon from degrading permafrost. Nat. Commun. 9, 3666 doi: 10.1038/s41467-018-06080-w (2018).

 

Sea level fall during glaciation stabilized atmospheric CO2 by enhanced volcanic degassing   [Juli 2017] Throughout the last 800,000 years, Antarctic temperatures and atmospheric carbon dioxide concentrations showed a similar evolution. However, this was different during the transition to the last ice age: approximately 80,000 years ago, temperature declined, while the carbon dioxide content of the atmosphere remained relatively stable. An international research team led by the GEOMAR Helmholtz Centre for Ocean Research Kiel and the Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research has now discovered that a falling sea level may have caused enhanced volcanic activity in the ocean, which can explain the anomaly. The results are published today in the journal Nature Communications. press release (AWI) Citation: Hasenclever, J. et al. Sea level fall during glaciation stabilized atmospheric CO2 by enhanced volcanic degassing. Nat. Commun. 8, 15867 doi: 10.1038/ncomms15867 (2017).

All PalMod publications are listed here.