Sensitivity of the last glacial inception to initial and boundary conditions: lessons from a coupled climate-ice sheet model
Notice bibliographique
Résumé
Proxy data indicate that the last glacial inception started at approximately 115ka BP when boreal summer insolation reached its minimum. At that time, large ice sheets started to form in Northern Canada. A number of models of different complexities have been employed to simulate the last glacial inception; however, complex climate models did not incorporate interactive ice sheets. Here, a state-of-art Earth System Model AWI-ESM-2.2 (Gierz et al., 2020, GMDD), composed of AWI-ESM-2.0 (Sidorenko et al., 2019) that now includes the Parallel Ice Sheet Model PISM (The PISM authors, 2016), was utilized to study the potential causes of the inception. By conducting different sensitivity experiments, we investigated the effect of initial conditions, different surface mass balance schemes, greenhouse gas (GHG) concentration, ocean circulation, and model resolution on the last glacial inception. Two experiments were conducted under 115 ka BP orbital and radiative forcing to examine the effect of initial conditions: one without interactive ice sheets but with fixed preindustrial topography, and the other with interactive ice sheets that include initial snow cover over two small regions in northeastern and northwestern Canada. The first experiment failed to produce a permanent appearance of snow over North America. The second experiment simulated a further growth of ice sheets over northeastern and northwestern Canada. In these experiments, the initial ice sheets provide important feedbacks to cause North America ice sheet growth: the snow-albedo feedback and elevation effect of orography reinforce the cooling in the region initially covered by snow or ice. We compared an empirically-based positive-degree-day (PDD) scheme, which estimates surface melt as a function of temperature, with a more physically-based diurnal energy balance model (dEBM) (Krebs-Kanzow et al., 2018), which also takes changes in shortwave radiation into account and implicitly resolves a diurnal freeze-melt cycle. Both simulations showed a tendency of ice sheet growth in Northern Canada ice sheet. The experiment employing the dEBM model for surface mass balance had a larger magnitude in SMB, resulting in faster development of the ice sheet. Another experiment with a lowered GHG concentration was carried out to investigate the role of GHG, suggesting that GHG changes also contribute to a cooling state. Two additional experiments also explored the effect of changed ocean circulation and atmosphere dynamics and their contribution to the inception, as well as the effect of an improved resolution in the atmosphere model. In summary, our findings imply that initial conditions have a significant impact on simulating the inception. We conclude that the incorporation of an ice sheet model into the Earth system is an important step forward to provide a more realistic simulation of glacial inception and to uncover its potential causes.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,002 | 0,006 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,001 | 0,001 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,002 | 0,001 |
| Science ouverte | 0,002 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».