| 1. |
- Kageyama, Masa, et al.
(författare)
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A multi-model CMIP6-PMIP4 study of Arctic sea ice at 127 ka : sea ice data compilation and model differences
- 2021
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 17:1, s. 37-62
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Tidskriftsartikel (refereegranskat)abstract
- The Last Interglacial period (LIG) is a period with increased summer insolation at high northern latitudes, which results in strong changes in the terrestrial and marine cryosphere. Understanding the mechanisms for this response via climate modelling and comparing the models' representation of climate reconstructions is one of the objectives set up by the Paleoclimate Modelling Intercomparison Project for its contribution to the sixth phase of the Coupled Model Intercomparison Project. Here we analyse the results from 16 climate models in terms of Arctic sea ice. The multi-model mean reduction in minimum sea ice area from the pre industrial period (PI) to the LIG reaches 50 % (multi-model mean LIG area is 3.20×106 km2, compared to 6.46×106 km2 for the PI). On the other hand, there is little change for the maximum sea ice area (which is 15–16×106 km2 for both the PI and the LIG. To evaluate the model results we synthesise LIG sea ice data from marine cores collected in the Arctic Ocean, Nordic Seas and northern North Atlantic. The reconstructions for the northern North Atlantic show year-round ice-free conditions, and most models yield results in agreement with these reconstructions. Model–data disagreement appear for the sites in the Nordic Seas close to Greenland and at the edge of the Arctic Ocean. The northernmost site with good chronology, for which a sea ice concentration larger than 75 % is reconstructed even in summer, discriminates those models which simulate too little sea ice. However, the remaining models appear to simulate too much sea ice over the two sites south of the northernmost one, for which the reconstructed sea ice cover is seasonal. Hence models either underestimate or overestimate sea ice cover for the LIG, and their bias does not appear to be related to their bias for the pre-industrial period. Drivers for the inter-model differences are different phasing of the up and down short-wave anomalies over the Arctic Ocean, which are associated with differences in model albedo; possible cloud property differences, in terms of optical depth; and LIG ocean circulation changes which occur for some, but not all, LIG simulations. Finally, we note that inter-comparisons between the LIG simulations and simulations for future climate with moderate (1 % yr−1) CO2 increase show a relationship between LIG sea ice and sea ice simulated under CO2 increase around the years of doubling CO2. The LIG may therefore yield insight into likely 21st century Arctic sea ice changes using these LIG simulations.
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| 2. |
- Otto-Bliesner, Bette L., et al.
(författare)
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Large-scale features of Last Interglacial climate : results from evaluating the lig127k simulations for the Coupled Model Intercomparison Project (CMIP6)–Paleoclimate Modeling Intercomparison Project (PMIP4)
- 2021
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 17:1, s. 63-94
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Tidskriftsartikel (refereegranskat)abstract
- The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to the Coupled Model Intercomparison Project (CMIP6) is the Tier 1 Last Interglacial experiment for 127 000 years ago (lig127k), designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models as for the future and following a common experimental protocol. Here we present a first analysis of a multi-model ensemble of 17 climate models, all of which have completed the CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. The equilibrium climate sensitivity (ECS) of these models varies from 1.8 to 5.6 ∘C. The seasonal character of the insolation anomalies results in strong summer warming over the Northern Hemisphere continents in the lig127k ensemble as compared to the CMIP6 piControl and much-reduced minimum sea ice in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than the CMIP6 midHolocene simulations as expected from the larger insolation anomalies at 127 than 6 ka.New synthesis for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and for precipitation over the Northern Hemisphere continents. The model–data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions.The CMIP6–Paleoclimate Modeling Intercomparison Project (PMIP4) lig127k simulations, in combination with the proxy record, improve our confidence in future projections of monsoons, surface temperature, and Arctic sea ice, thus providing a key target for model evaluation and optimization.
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| 3. |
- Sicard, Marie, et al.
(författare)
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Similarities and Differences in Arctic Sea-Ice Loss During the Solar-Forced Last Interglacial Warming (127 Kyr BP) and CO2-Forced Future Warming
- 2023
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 50:24
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Tidskriftsartikel (refereegranskat)abstract
- Based on a 7-member global circulation model ensemble from CMIP6/PMIP4, we compare the regional distribution of Arctic sea ice between a simulation representing the Last Interglacial (LIG) climate, with solar-forced warming, and an idealized future CO2-forced simulation with a similar annual sea-ice volume. The two simulations feature small but robust differences in the Central Arctic and Baffin Bay during summer, and larger differences at the sea-ice margins in the sub-Arctic Atlantic and North Pacific sectors during winter. Our results indicate that, under both forcings, sea ice persists north of Greenland until late summer, suggesting that the assumption that this region is the Last Ice Area is robust and holds for other climate states. However, we show that processes influencing sea-ice distribution in winter, such as Atlantification and sea-ice drift, differ and need to be further investigated.
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| 4. |
- Sime, Louise C., et al.
(författare)
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Summer surface air temperature proxies point to near-sea-ice-free conditions in the Arctic at 127 ka
- 2023
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Ingår i: Climate of the Past. - 1814-9324 .- 1814-9332. ; 19:4, s. 883-900
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Tidskriftsartikel (refereegranskat)abstract
- The Last Interglacial (LIG) period, which had higher summer solar insolation than today, has been suggested as the last time that Arctic summers were ice free. However, the latest suite of Coupled Modelling Intercomparison Project 6 Paleoclimate (CMIP6-PMIP4) simulations of the LIG produce a wide range of Arctic summer minimum sea ice area (SIA) results, with a 30% to 96% reduction from the pre-industrial (PI) period. Sea ice proxies are also currently neither abundant nor consistent enough to determine the most realistic state. Here we estimate LIG minimum SIA indirectly through the use of 21 proxy records for LIG summer surface air temperature (SSAT) and 11 CMIP6-PMIP4 models for the LIG. We use two approaches. First, we use two tests to determine how skilful models are at simulating reconstructed Delta SSAT from proxy records (where Delta refers to LIG-PI). This identifies a positive correlation between model skill and the magnitude of Delta SIA: the most reliable models simulate a larger sea ice reduction. Averaging the two most skilful models yields an average SIA of 1 :3 x 10(6) km(2) for the LIG. This equates to a 4 :5 x 10(6) km(2) or 79% SIA reduction from the PI to the LIG. Second, across the 11 models, the averaged Delta SSAT at the 21 proxy locations and the pan-Arctic average Delta SSAT are inversely correlated with Delta SIA ( r = - 0.86 and 0.79, respectively). In other words, the models show that a larger Arctic warming is associated with a greater sea ice reduction. Using the proxy-record-averaged Delta SSAT of 4 :5 +/- 1 :7K and the relationship between Delta SSAT and Delta SIA suggests an estimated sea ice reduction of 4:2 +/- 1:4 x 10(6) km(2) or about 74% less sea ice than the PI period. The mean proxy-location Delta SSAT is well correlated with the Arctic-wide Delta SSAT north of 60 degrees N (r = D 0:97), and this relationship is used to show that the mean proxy record Delta SSAT is equivalent to an Arctic-wide warming of 3 :7 +/- 1 :5K at the LIG compared to the PI period. Applying this Arctic-wide Delta SSAT and its modelled relationship to Delta SIA, results in a similar estimate of LIG sea ice reduction of 4 :1 +/- 1 :2 x 10(6) km(2). These LIG climatological minimum SIA of 1.3 to 1.5 x 10(6) km(2) are close to the definition of a summer ice-free Arctic, which is a maximum sea ice extent of less than 1 x 10(6) km(2). The results of this study thus suggest that the Arctic likely experienced a mixture of ice-free and near-ice-free summers during the LIG.
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