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Coupled Simulations of the Greenland Ice Sheet: Eemian

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Coupled Simulations of the Greenland Ice Sheet: Eemian Coupled simulations of the Greenland ice sheet: Eemian Alexander Robinson CESM Workshop, Cross Working Group Session Monday, 17 June 2019 Greenland during the Eemian Camp Century NEEM • Eemian age (130-115 kyr ago) ice found at Summit and NEEM, Summit deposited upstream. • DYE-3 and Camp Century show tenuous DYE-3 evidence for ice but no climatic information. Credit: NASA Greenland during the Eemian Camp Century NEEM • Southern ice sheet remained intact given significant glacial Summit discharge and only a small increase in DYE-3 pollen. Credit: NASA MIS-5 MIS-11 kyr ago Reyes et al. (2014) Greenland during the Eemian Camp Century NEEM • Southern ice sheet remained intact given significant glacial Summit discharge and only a small increase in DYE-3 pollen. Credit: NASA Greenland during the Eemian Camp Century NEEM • Southern ice sheet remained intact given significant glacial Summit discharge and only a small increase in DYE-3 pollen. • Temperatures were warmer than today… Credit: NASA Greenland during the Eemian Capron et al. (2014) • Data show peak warming up to Multi-model 5°C around 129 kyr ago, sustained mean (Bakker et al., 2013) anomalies through the Eemian. X • Climate models cannot capture X this transient pattern so far. X X Greenland during the Eemian • Summit and NEEM δ18O signals are remarkably similar. • Reconstructed warming reaches 6- 8°C assuming no ice elevation changes. • Seasonality? δ18O conversion? How can we reconcile models and reconstructions? • Transient coupled climate – ice sheet simulations • Ensembles to test uncertainty Methods Robinson et al., 2010 REMBO *Temperature Daily melt *Annual accum. SICOPOLIS climate model *Precipitation model *Annual ablation *Annual temp. Greve, 1997 *Albedo scaling *Surface elevation *Land/ice mask Low resolution High resolution (100 km grid) (20km grid) • Physically based, yet simple and fast (250 ka in 10 hr) • Includes albedo and elevation feedbacks • Shows expected response of climate to large topographic changes • Forced by CO2, insolation and regional temp. anomaly t Insolation-temperature M 1 a S c T melt (ITM) equation s wLm Comparing with Eemian targets Comparing with Eemian targets Comparing with Eemian targets Comparing with Eemian targets Transient snapshots (best simulation) Transient snapshots (best simulation) Transient snapshots (best simulation) Transient snapshots (best simulation) Comparing with Eemian targets Caveats • Changes in atmospheric 126 ka ago circulation and sea ice could affect precipitation. • δ18O may not be a consistent proxy of temperature through time. • Missing local negative feedbacks and fast ice advection may reduce retreat. Summary • Global simulations are difficult to reconcile with prolonged warming in Greenland data. • Early warming of 3-5°C may be enough to trigger smb-albedo and melt-elevation feedbacks. • So far, an elevation reduction is needed to explain late Eemian temperature anomalies. • Magnitudes of feedbacks between elevation, temperature, precipitation and melt are key to the amount of Eemian ice sheet retreat. Thanks! Credit: NASA.
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