Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum

Schmittner, Andreas; Urban, Nathan M.; Shakun, Jeremy D.; Mahowald, N. M.; Clark, Peter U.; Bartlein, Patrick J.; Mix, Alan C; Rosell-Melé, Antoni

doi:10.1126/science.1203513

Cited by 233 publications

(209 citation statements)

References 98 publications

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“…Furthermore, in our approach we include changes in land ice sheet (albedo forcing or R [LI] ), while Yin and Berger (2012) There exist some intrinsic uncertainties in our approach based on the underlying data sets, which are not included in the Monte Carlo statistic. For example, the global temperature anomaly in the LGM still disagrees in various approaches (Annan and Hargreaves, 2013;Schmittner et al, 2011;Schmidt et al, 2014), and Pliocene sea level and ice-sheet dynamics are still a matter of debate (Rohling et al, 2014;Dolan et al, 2015;Koenig et al, 2015;Rovere et al, 2014;de Boer et al, 2015). Taking these issues into account might lead to changes in our quantitative estimates but not necessarily to a revision of our main finding of state dependency in S [CO 2 ,LI] .…”

Section: Martínezmentioning

confidence: 62%

On the state dependency of the equilibrium climate sensitivity during the last 5 million years

et al. 2015

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Abstract.It is still an open question how equilibrium warming in response to increasing radiative forcing -the specific equilibrium climate sensitivity S -depends on background climate. We here present palaeodata-based evidence on the state dependency of S, by using CO 2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO 2 radiative forcing depends on the CO 2 data set used. This nonlinearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of icesheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO 2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S [CO 2 ,LI] , for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S [CO 2 ,LI] is on average ∼ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6-5 Myr BP) the CO 2 data uncertainties prevent a well-supported calculation for S [CO 2 ,LI] , but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S [CO 2 ,LI] , was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO 2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large.

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Section: Martínezmentioning

confidence: 62%

On the state dependency of the equilibrium climate sensitivity during the last 5 million years

et al. 2015

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“…Consistent with proxy data for the LGM, the prescribed atmospheric cooling is polar amplified, ranging from 2 • C in the tropics to 6 • C around Antarctica (14,15). All other boundary conditions are held fixed.…”

Section: Significancementioning

confidence: 68%

“…Significant uncertainty also exists in the spatial pattern of atmospheric temperature change between the present and LGM (14,15). We consider two sensitivity experiments, which represent extreme cases: one where atmospheric cooling is restricted to the Southern Hemisphere (experiment "LGM dTSH" in Table 1) and one where a globally constant cooling is applied (experiment "LGM dTconst").…”

Section: Sensitivity Experimentsmentioning

confidence: 99%

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

Jansen

2016

Proc. Natl. Acad. Sci. U.S.A.

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Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 • C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.LGM | AMOC | stratification | cooling | sea-ice T he deep ocean today is ventilated mainly by two water masses. North Atlantic deep water (NADW) is formed in the North Atlantic before flowing southward at a depth of about 2-3 km and eventually rising back up to the surface in the Southern Ocean. Antarctic bottom water (AABW) is formed around Antarctica and spreads northward into the abyssal basins. The AABW that makes it into the Atlantic then slowly upwells into the lower NADW before returning southward and resurfacing again around Antarctica (1, 2). The glacial equivalent of NADW was likely confined to shallower depths, leaving more of the deep Atlantic filled with water masses originating primarily from around Antarctica (3-5). Moreover, the two water masses appear more distinct, with less mixing between them (6).Multiple studies have pointed toward the potential importance of sea ice and surface buoyancy fluxes around Antarctica in controlling changes in the deep ocean stratification and circulation between the present and Last Glacial Maximum (LGM) (7-11). Specifically, we recently showed that enhanced buoyancy loss around Antarctica is expected to lead to an increase in the abyssal stratification, an upward shift of NADW, and a clearer separation between NADW and southward-flowing AABW (11)-all in agreement with inferences made for differences in circulation and stratification between the present and LGM (3,6,12,13). This gives rise to the hypothesis that strong cooling around Antarctica led to an increased net freezing...

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“…Paleoecological data such as fossil pollen, diatoms, and marine foraminifera are the backbone of continental-to global-scale paleoclimatic reconstructions developed to benchmark climate models and assess feedbacks within the earth system (CLIMAP Project Members, 1976;Wright et al, 1993;MARGO Project Members, 2009;Bartlein et al, 2011;Shakun et al, 2012;Viau et al, 2012;Marcott et al, 2013;Trouet et al, 2013) and constrain estimates of climate sensitivity (Schmittner et al, 2011). Paleoecological data help establish ecosystem baselines and trajectories for managers seeking to conserve species and ecosystems of concern (Whitehouse et al, 2008;Dietl et al, 2015;Panagiotakopulu and Buchan, 2015;Clarke and Lynch, 2016;Barnosky et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

The Neotoma Paleoecology Database, a multiproxy, international, community-curated data resource

et al. 2018

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The Neotoma Paleoecology Database is a community-curated data resource that supports interdisciplinary global change research by enabling broad-scale studies of taxon and community diversity, distributions, and dynamics during the large environmental changes of the past. By consolidating many kinds of data into a common repository, Neotoma lowers costs of paleodata management, makes paleoecological data openly available, and offers a high-quality, curated resource. Neotoma's distributed scientific governance model is flexible and scalable, with many open pathways for participation by new members, data contributors, stewards, and research communities. The Neotoma data model supports, or can be extended to support, any kind of paleoecological or paleoenvironmental data from sedimentary archives. Data additions to Neotoma are growing and now include >3.8 million observations, >17,000 datasets, and >9200 sites. Dataset types currently include fossil pollen, vertebrates, diatoms, ostracodes, macroinvertebrates, plant macrofossils, insects, testate amoebae, geochronological data, and the recently added organic biomarkers, stable isotopes, and specimen-level data. Multiple avenues exist to obtain Neotoma data, including the Explorer map-based interface, an application programming interface, the neotoma R package, and digital object identifiers. As the volume and variety of scientific data grow, community-curated data resources such as Neotoma have become foundational infrastructure for big data science.

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Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum

Cited by 233 publications

References 98 publications

On the state dependency of the equilibrium climate sensitivity during the last 5 million years

On the state dependency of the equilibrium climate sensitivity during the last 5 million years

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

The Neotoma Paleoecology Database, a multiproxy, international, community-curated data resource

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