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Jeffrey Baggenstos Daniel present the Glacial to Last Maximum the from imbalance radiative ’s a onw oatmthsbe aet uniyPI(let PRI quantify to made the been as Up has such phases. attempt cooling warming, no pos- global mean fluxes was now, during PRI global imbalance radiative to negative the energy of and global that the periods dictates , the about inference during Logical affect known itive past. is even the warm- little in may anthropogenic However, Merid- current and (13). the (12) exhibit the than locally ing of higher which strength rates change (AMOC), warming the Circulation rapid in Overturning of climate ional variations times past as to well from related as (11), gained the deglaciation be last include can These imbalance changes. radiation of etary variability spatial and assess (8–10). temporal fluxes to large radiative difficult the underlying the is to measurements due integrated satellite today, globally even from The m. PRI 2,000 of of depth signal ocean an refs. to (OHC; down content 3–7) heat as ocean well the as of measurements (2) continuous radiometers space-borne to 0.50 calibrated to 2001 carefully estimated using from current been the has decade For imbalance the (1). 2010—the times state period—specifically, all the warming at describes balance global energy that planetary there- parameter by is the It climate of absorbed space. fundamental into energy back a radiates solar fore the between energy difference and Earth the to amounts G paleoclimate factor also picture. may the uncertain, into albeit deep- balance, coverage, radiative cloud Atlantic global in North the changes on in while impact changes their rapid and ocean formation to in water changes due net likely to uptake, related are heat peaks these W·m that 0.4 conclude We to Circulation. 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M.H., D.B., and measurements; T.K., J.S., contributions: Author ytmt h oa nrycneti ietypootoa to turn, proportional in loss, directly ice Continental is mass. climate content ice the continental energy in of con- change total part the the this the of of to waning contribution and system The waxing sheets. the ice with tinental associated the OHC—namely, heat the heat as latent second importance improved comparable a and of heat scales, is resolution time reservoir oceanic temporal glacial/ the high On has (20). at of precision it past changes 19), the quantify (18, in to the reservoir thermometry in possible ocean improvements warm- become mean With global 17). now gas ongoing (16, noble ocean the of the More during by method diffusion. up heat of and taken excess is transport advection the ing efficient by of and interior 90% capacity ocean than heat the high into its heat to due system the over 16). studies 15, energy-balance (5, in y that 20,000 neglected small last safely so be are changes can temporal they its Moreover, flux. the of radiation of rate heat- components geothermal the all to (typically due of ing equal available content energy exactly heat The (8). the must system of climate time sum in the energy of point to change any Due atmospheric atmosphere. at upper the the boundary across flux of radiation net top the the the conservation, paleo- the inferring at reconstruct to budget and prox- way of radiation only direct change the method is of energy indirect imbalance lack flux system the necessary a Thus, total fluxes. to (LGM; the radiative due deglacia- determining Maximum global ka), past recent Glacial (∼10 of most ies Last early the the the for to from evolution) (14) temporal tion its alone owo orsodnemyb drse.Eal [email protected] Email: addressed. be may correspondence whom To ue,hglgtn h motneo nenlvraiiyin variability internal budget. energy of energy radiative importance Earth’s the the affect highlighting that fluxes, circulation ocean to in the due that possibly changes time, show this We during period. the significantly warm varied from Holocene imbalance system the into climate age the ice last brought which several for , maintained thousand was imbalance positive a deglaciation, global for deglaciation, imbalance last drives radiative The the the system. reconstructs imbalance study ocean–atmosphere This positive the warming. is of anthropogenic, energy out present, whether or into determines flowing imbalance radiative Earth’s Significance h ca stedmnn nryrsrori h climate the in reservoir energy dominant the is ocean The a,b . 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EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES is reflected by a change in ocean mass and volume, and thus slight cooling from 14.6 to 12.8 ka, coinciding with the Antarctic global mean (GMSL), which has been reconstructed for Cold Reversal (ACR) observed in Antarctic records (23) the last deglaciation with sufficient accuracy (21, 22). All other and the Bølling–Allerød warm stage in the North Atlantic (24). terms in the global energy budget are at least an order of magni- After the OHC maximum at ∼10 ka, there is little change tude smaller (SI Appendix). Thus, the sum of OHC change and or, if at all, a slight cooling up to historic times. There is GMSL-derived latent heat storage of land ice is a good first- an ongoing discussion about surface-temperature trends during order representation of the total energy change in the climate the Holocene warm period, with proxy reconstructions showing system, the temporal slope of which can be used to derive PRI in warmer temperatures from 10 to 6 ka followed by a clear (mostly the past. high latitude) cooling through the mid- dle to late Holocene, while model simulations estimate a gradual Results warming (25, 26). The most likely culprits for this disparity are OHC Record. To reconstruct the OHC evolution during the seasonal (summer) biases on the proxy data side, as well as insuf- deglaciation, we used the recent mean ocean temperature ficient sensitivity (e.g., on sea ice) and additional feedbacks on (MOT) assessment from the West Antarctic Divide the model side (27). During times of relatively stable ocean cir- (WD) ice core (20) alongside a new dataset from the European culation, such as the Holocene, MOT/OHC should be mainly Project for Ice Coring in (EPICA) Dome C (EDC) ice coupled to high-latitude sea-surface temperatures (SSTs), likely core presented here (Fig. 1). Both records are based on noble with a bias toward winter temperature since deep-water forma- gas thermometry, which uses the ratio of heavy noble gases in tion is most sensitive to winter conditions (28). Our MOT data the paleo atmosphere to infer past MOTs via the gas-specific, do not show a pronounced Holocene cooling found in many high- temperature-dependent solubilities of atmospheric gases in the latitude proxies, but, in contrast to SST in models, MOT reaches ocean (Materials and Methods). The paleo atmospheric signal Holocene values much earlier (∼11 ka) and remains flat through- should be identical at WD and EDC, but site-specific firn frac- out the Holocene. Our data thus point to the high-latitude early tionation corrections and storage effects could cause differences Holocene warmth in ref. 25 not being restricted to the summer between the two records. The generally good agreement of WD season. and EDC OHC proves the soundness of the principles underly- The main systematic difference between the WD and EDC ing noble gas mean ocean thermometry, even though the two ice records in Fig. 1 is the magnitude of the glacial/interglacial cores represent two end members of site conditions for Antarc- change, with 19.0 × 1024 J for EDC and 14.0 × 1024 J for WD tic drill sites. The ocean warming from the LGM to the early (equivalent to 3.5- and 2.6-K temperature changes, calculated at Holocene is achieved in two stages, interrupted by a period of 20 ± 1 ka for the LGM and 10 ± 1 ka for the early Holocene). Both are consistent with estimates of deep-ocean deglacial tem- perature change (29–31), keeping in mind that the noble gas thermometry results encompass the integrated global ocean, whereas sediment-based reconstructions are local by . The discrepancy between EDC and WD can likely be attributed to an imperfect correction for gas-fractionating processes in the firn column by using high-precision noble gas isotope analy- ses. The reconstructed glacial/interglacial OHC difference is sensitive to systematic uncertainties in our understanding of firn gas-transport processes. For example, including a correc- tion term for differential kinetic fractionation (32) reduces the EDC glacial/interglacial MOT difference to 2.7 K (SI Appendix). Accordingly, based on our current knowledge of the firn col- umn at EDC and WD, we cannot determine the absolute net glacial/interglacial heat uptake by the ocean to better than 20%. The amplitude of our derived PRI estimate scales with this glacial/interglacial net energy uptake and is, therefore, also sub- ject to an uncertainty of 20%. However, the relative temporal changes in the imbalance are largely independent of the absolute level. Our conclusions on ocean heat-uptake anomalies during the deglaciation are therefore not affected by the use of a specific MOT record. To avoid erroneous variability in the PRI due to the mea- surement noise in the MOT reconstruction, we used a low-pass filtered version of each OHC record (spline approximation with 2,500-y cutoff period). Thus, we reconstructed only the aver- age PRI that is typical for these long time scales, whereas higher-frequency variation in PRI could be significantly larger.

Fig. 1. OHC change relative to the late Holocene average, derived from Ice Sheets. Fig. 1 also shows the energy required to melt WD (blue) and EDC (pink and orange) ice core noble gas records, includ- land ice equivalent in volume to 130 m of GMSL rise. This ice- ing a 1-σ confidence band based on Monte Carlo smoothing splines with sheet contribution to the energy budget (latent heat of melting; 2,500-y cutoff period. The orange band shows the EDC OHC record if a LHM) is assessed with the sea level record of Lambeck et al. (ref. correction for differential kinetic fractionation (SI Appendix) is applied. The 21; Materials and Methods). As we are interested in the millennial green line shows the heat anomaly associated with the continental glacia- tion derived from the sea-level record (21), also splined with a 2,500-y cutoff averaged PRI, we again used a spline approximation of the sea- period. In black, the deep ocean temperature reconstruction from ref. 31 is level record with a cutoff period of 2,500 y. This also implies that shown. The gray bar on top indicates specific climate periods discussed in the short-term events such as Meltwater Pulse 1A at 14.6 ka are not main text: (LGM), Heinrich 1 (HS-1), Antarctic resolved in this record. Curiously, the total amount of heat taken Cold Reversal (ACR), (YD), and the Holocene. up by the ocean over the entire deglacial transition is very similar

2 of 6 | www.pnas.org/cgi/doi/10.1073/pnas.1905447116 Baggenstos et al. Downloaded by guest on September 26, 2021 Downloaded by guest on September 26, 2021 agntse al. et specific Baggenstos indicates top on sum bar the text. gray as main The forcing the Total in (11). (i) discussed reconstruction area. periods climate sheet GST ice by (j) ICE-6G estimated e–h. (70) as changes of the to forc- from scaled (GHG) forcing 46, gas Radiative ref. Greenhouse (h) 45. (g) ref. (47). from glacial ing the in forcing radiative nulislto ocn 6) f lblds ue rmrf 8sae to scaled 48 ref. from fluxes Global W·m (f) 1 overturning (69). meridional forcing the insolation for annual proxy a higher (51), subtropical with core a from sediment complexity record Atlantic protactinium/thorium intermediate North The LOVECLIM (d) the (52). OHC fitting. model from spline (b) climate the strength of WD AMOC effects and edge Modeled are (a) reconstructions (c) PRI EDC the the of end using and PRI ning present: 1-σ the with to records LGM the from GST 2. Fig. amount the on depends of it magnitude since The constrained Dryas OHC. well Younger not in is increases the peaks strong and in the to peaks (HS-1) linked two 1 are the Stadial (YD) Further, Heinrich was S1). melting Fig. during ice-sheet Appendix, PRI by (SI dur- sink maximum release heat heat a latent slight at the ACR. a while even ACR, the or by the uptake during ing separated heat global no the ka, fluxes to with points 12.5 radiative exchange ocean heat and balanced of 15.5 contribution more reconstructed at The of peaks two period exhibits a b) and a PRI. has volume ice modern approximately once sta- reached. ka, and land-ice been 7 later the slightly at than increase only to quickly bilizes begins more latter equilibrium The faster new contribution. reacts a component oceanic reaches the and however, LHM; total the to h eosrce R ae nOCadLM(i.2 (Fig. LHM and OHC on based PRI reconstructed The − eosrce R,oetrigcruain siae ocns and forcings, estimated circulation, overturning PRI, Reconstructed 2 nteLM hc sa vrg ftesree ieaueon literature surveyed the of average an is which LGM, the in 231 Pa/ ofiec ad h nacducranya h begin- the at uncertainty enhanced The band. confidence 230 hipyn ekndcruain e lblmean Global (e) circulation. weakened implying Th 6.FloigMrh ta.() h o-famshr (TOA) as top-of-atmosphere written be the can (5), balance al. energy et system to Earth Murphy long of forcing Following the components to (6). the many due of adjust, of scales to time part time reequilibration had the hasn’t forcing reflects temperature the such atmo- imbalance which to the energy response in The surface-temperature gases (34). a greenhouse the through of and (e.g., concentration sphere) irradiance the net in the change of perturbation Deglacia- (external) the a over Forcing Radiative tion. Global in Changes Long-Term Discussion records. two anomalously the be reconcile may would WD the on which that based high, suggests YD the (33) during al. increase WD. et in OHC Shackleton peak by YD work sharper recent a is However, WD and EDC PRI the using climate between reconstruction within difference these notable well of most agree The close stability generally uncertainties. their is S2 ). PRI relative EDC-derived flux Fig. the and radiative from WD- Appendix, periods. net expected (SI the as data Holocene, zero, to and raw LGM the the to During applied smoothing of n lu oe de otepaeayabd hne These change. lowering, albedo level planetary sea the to to cov- added due ice cover area sea cloud cover, land other and , addition, seasonal global In in erage, changes (38). as changes by such albedo largest elements, replaced to the were represents contributing forests which factor sheets, boreal ice LGM, continental the high-albedo In shortwave the fluxes. on and influence radiative considerable biogeochemical a has reflectivity the surface total in the a comprising in changes W·m (41–44), 2.9 maximum them of a control that to result processes LGM physical a the as in minimum Holocene a from increased forcing radiative in jump hypothetical F A (36). water- the feedback to due vapor (35) temperature surface but with theory, linearly Stefan–Boltzmann lin- increases classical The follow not time. does radiation equilibration Eq. long in sufficiently earization time-scale-dependent a 1/α the after and sensitivity describes (5), best imbalance energy that parameter tion change and forcing, with nesod(0.Cnetain of outgoing been Concentrations reduce long has to (40). radiation atmosphere understood infrared capac- trapping the by The in radiation insolation unchanged. gases longwave average greenhouse essentially global of remains and ity Earth annual by the substantial scales, received are time budget radiation While these the (39). on to changes the incoming seasonal for or accuracy in local high orbits with changes planetary solved governing be The equations param- the can as orbital 38): known, varying well ref. are continuously eters to e–i; due 2 radiation cli- shortwave using (Fig. by models estimated been mate have scales time glacial/interglacial disequilibrium explained. lower be of to period needs a and by unexpected pattern separated is observed peaks the PRI but two deglaciation, in of anomaly entire radiation the changes global for long-term positive predicted biogeo- a or is line, the warming In albedo. of initial planetary increasing feedbacks the the continuously sev- positive to 2, for as cycles Fig. unbalanced such chemical in needed, budget seen are the as forcings keep years, To are thousand (37). records eral our resolve than (3). faster to again is reachieved able se is per budget process balanced reequilibration a This until surplus PRI the y1W·m 1 by eea niiulcnrbtost h aitv ocn on forcing radiative the to contributions individual Several PRI h R safnto fbt h aitv ocn u to due forcing radiative the both of function a is PRI The ∆ − T 2 stenteeg o oadEarth, toward flow energy net the as nraei h O aitv aac 4) Planetary (45). balance radiative TOA the in increase ntepaeaysraetemperature. surface planetary the in − α∆T 2 illa ogoa ufc amn htreduces that warming surface global to lead will 1 h hnei ugigrdaincue ya by caused radiation outgoing in change the sjsie,a at’ ugiglongwave outgoing Earth’s as justified, is PRI = F − hudapoc Earth-system approach should α∆T CO NSLts Articles Latest PNAS , 2 , CH 4 F α and , salineariza- a is h radiative the N | 2 all O f6 of 3 [1]

EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES are less certain and are not included in Fig. 2, but may be rele- in the models during an AMOC recovery. This implies that, dur- vant for variability in the global radiative budget on top of these ing the ACR, the radiative response is dominated by the local long-term changes (see below). The impacts of the LGM ice North Atlantic warming, even though the GST decreases. Thus, sheet and the implied changes in land–sea distribution on the the impacts of circulation changes during the deglaciation [char- radiative budget are assessed by Abe-Ouchi et al. (46) with 11 acterized by a back-and-forth in overturning circulation strength climate models of intermediate complexity, which yield an aver- (51) with a weak AMOC during HS-1 and the YD and a strong age radiative forcing of 3.9 W·m−2 (spread 2.7 to 5.2 W·m−2). AMOC during the ACR] on the energy imbalance at the top of The temporal evolution of this forcing from the LGM to the the atmosphere are consistent with our PRI results. preindustrial era has not been studied in detail, but should to Low-Level Clouds. An additional effect leading to the reduction first-order scale with the amount of ice-covered land area. The of PRI during the ACR could be a change due to the net cloud final radiative forcing contribution considered here is due to radiative forcing, in particular at low latitudes. With the recovery changes in the atmospheric dust load. There is a broad consen- of the AMOC during the ACR, the Intertropical Convergence sus that the global dust cycle was more active in the LGM than Zone (ITCZ) most likely migrated to a more northerly position today, but the radiative impact of the evolving dust load ranges (42, 53) following Earth’s thermal equator. This rearrangement from −2.0 to +0.1 W·m−2 in various studies (47) because the of the atmospheric circulation could affect the cloud regime in dust shortwave radiative effect depends strongly on the size and the subtropical subsidence regions. Low-level clouds have an type of the dust particles. Furthermore, the spatiotemporal evo- especially strong negative effect on the energy balance because lution of the dust load during the deglaciation is poorly known, they reflect solar radiation efficiently, and yet their emission although there have been attempts to quantify it using models temperature is similar to that of the underlying ocean surface. (48). Other aspects that could affect the TOA radiative fluxes, Furthermore, the radiative energy fluxes in low latitudes are sub- such as changes in cloud coverage or atmospheric chemistry, stantially larger than in the mid or high latitudes, allowing for are highly uncertain (49), and thus cannot be included in this a relatively small change in cloud distribution to have a large compilation. impact on Earth’s energy balance. Also of note is the timing of the PRI peak at 15.5 ka, which Additional Short-Term Changes in the Radiative Forcing. Our PRI occurs in the latter part of HS-1, even though ocean-sediment reconstruction over the transition shows typical values of proxies indicate that the overturning circulation in the North +0.2 W·m−2, implying that the warming is sustained due to slow Atlantic was reduced throughout the entire Heinrich stadial. positive feedbacks, which keep the system out of radiative equi- This discrepancy may be related to an extreme southern position librium throughout the multimillennial climate changes during of the ITCZ with a switch in the hydrologic cycle and expansion the glacial termination. This is to be expected, given the long of sea ice in the north starting at 16.2 ka (refs. 42 and 54 and equilibration times of the large continental ice sheets and the references therein). ocean. However, the described forcings and the latest recon- Conclusion structed global surface temperature (GST) change (11) are not always consistent with the PRI as predicted by Eq. 1. In partic- Our study presents an attempt to investigate past changes in ular, the highest rate of change of the total forcing in Fig. 2 is OHC and land-ice volume in the framework of global radiative found at the end of HS-1 and the YD. At the same time, the flux and energy considerations. Our PRI reconstruction suggests increase in GST is enhanced, whereas the radiative imbalance that internal variability in the is critical to under- shows maxima during HS-1 and the YD. During the ACR, the standing the global energy fluxes on millennial time scales. In total forcing shows a continuing increase, but GST is increas- particular, as deep ocean circulation is expected to slow in the ing less or even decreasing (11), which implies, according to Eq. future (34), Earth may accelerate its rate of heat uptake. To 1, a large radiative imbalance, contrary to our reconstruction. further evaluate an AMOC influence on the radiative balance, The apparent decoupling of the record in radiative imbalance it would be valuable to determine OHC changes across major at the top of the atmosphere on the one hand and the forcings Dansgaard–Oeschger events (12), which are thought to repre- and GST on the other during these intervals indicates that there sent disruptions in the global overturning circulation (50, 55) but must be additional processes not yet considered to explain the are unaffected by the long-term dynamics of a deglacial transi- discrepancies. tion. A caveat to our analysis concerns the uncertainty in internal Ocean Circulation. The most likely candidate for such a process climate feedbacks. A better understanding of aerosol and cloud is the radiative impact of changes in the global ocean overturn- radiative effects as well as reconstruction of past aerosol loading ing circulation (13). Several models have shown that a reduction and cloud cover are needed to make progress in closing Earth’s of the AMOC leads to an accumulation of heat in the ocean radiation budget. In addition, continuing work on understanding interior (13, 15, 50), while an AMOC recovery lowers OHC. In firn gas processes are paramount to reduce the uncertainties in the , heat diffusing into the interior at low lati- noble gas-based OHC reconstructions. tudes is in constant competition with the southward advection of Materials and Methods cold subsurface water from North Atlantic deep-water formation sites. Thus, a reduced AMOC leads to increased subsurface tem- Ice Core Measurements. A total of 39 ice samples spanning 40 ka BP to present in ∼1,000-y resolution from the EDC ice core were analyzed at peratures in the Atlantic and, consecutively, the interior ocean, the University of Bern for elemental and isotopic composition of nitrogen, and vice versa. From a planetary point of view, the energy to heat argon, krypton, and xenon. The gas extraction and processing followed the ocean has to be provided via a TOA radiative imbalance. In broadly the method (1) of Bereiter et al. (19) with a few notable differences: this case, the radiative response is a result of the surface cooling Sample size was only ∼600 g; cryogenic trapping of the gases was achieved centered in the North Atlantic region. During an AMOC reduc- with a cryostat instead of liquid helium; no water bath was used in the tion, as implied during HS-1 and the YD (51, 52), the decrease overnight equilibration; and we were able to report xenon isotopic ratios of outgoing longwave radiation from the locally cooler ocean sur- at similar precision as for krypton. All gas data are presented with respect face is larger than the reduction of incoming shortwave radiation, to the modern atmosphere, consisting of regular measurements of ambi- ent air collected in Bern, Switzerland. The long-term reproducibility of the due to higher surface albedo via increased sea-ice concentration, system (given as the SD of 28 measurements of “ambient air” over 10 mo) is −2 causing a net positive global radiation anomaly of ∼0.5 W·m shown in SI Appendix, Table S2. Interlaboratory comparisons of selected ice in the models (13), very similar to the magnitude of the vari- samples have shown excellent agreement between the Bern and San Diego ability in our reconstruction. The opposite process is observed laboratories. Of the 39 measurements, one was rejected due to a procedural

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Box application. this smaller Antarctica for have preferred cores in ice are Antarctic gradual and from uncertainties derived more MOTs Thus, are . in which than change, surface-temperature results our with on thermal in fractionation explored and kinetic representing of is gravitational term influence to a possible include addition The to fractionation. in need fractionation the the calibrate gradi- kinetic to to point differential temperature measurements data firn temperature isotopic firn The resulting modern model. the diagnosed to was scaled and gradient) was enrichment, thermal ent model the isotopic ice-flow (for the column thick- 1D The firn from calibrated (63). diffusive model the a diffusion of and of advection ness heat runs and dynamic derived transient a was to on connected gradient col- based thermal firn This for the diffusion. corrected with throughout thermal ratios gradient to is elemental temperature leading site raw umn, permanent EDC the a low-accumulation corrected The (32, to we settling. air subjected (20), gravitational of convective for al. advection isotopes et a downward argon Bereiter net to in and As due pumping, 62). thermal fractionation barometric 58), disequilibrium (61), (57, zone 60), settling gravitational (59, by fractionation atmosphere contemporary the Corrections. Fractionation Firn all for used was scale age (56). 2012 samples Chronology EDC Core Ice Antarctic The problem. h epoen h o oe rdcssprt Osbsdon based MOTs (64, separate in produces ocean Water model Bottom the Antarctic box δ in of 20) The gases fraction ocean. (19, noble the deep in heavy the al. possi- expansion the potential a et of the for or state Bereiter made 65) saturation were in in assumptions described change No ble model modifications: following four-box the the with used we MOT, agntse al. et Baggenstos neglect- ocean, the of mass the and water sea of heat specific the with change and effects Calculation. firn PRI for correction after is sample model box single the a using calibration for by MOT reached derived be would the conclusions same somewhat at The the proxy. looking by MOT unaffected of largely choice are sin- from arbitrary results noise our the the but reduce used to measurements, ratios we gle elemental analysis, individual the our three all with For of reconcile observed. average to we hard offset be increasing would firn this systematically likely the However, in offset. is this fractionation offset brittle explain diagnosed the The could insufficiently into than S5). depth an Alternatively, with older Fig. clathratization zone. ice Appendix, increasing ice for and (SI loss proxies age gas MOT with to three related increases the which between ka, offset 25 small a note we .D .Murphy imbalance. M. radiation D. Earth’s and content 5. heat Ocean Knox, S. R. Douglass, H. D. 4. Hansen J. 3. Loeb G. N. 2. Schuckmann von K. 1. .J .Els .H .Ha,S eiu,A .Or,Teana aito ntegoa heat global the in variation annual The Loeb Oort, G. H. N. A. Levitus, 9. S. Haar, V. H. T. Ellis, S. J. 8. and imbalance energy Earth’s Roemmich Schuckmann, D. von K. 7. Kharecha, P. Sato, M. Hansen, J. 6. Xe/N 1950. A Lett. (2005). 1431–1435 308, uncertainty. within consistent (2012). heating upper-ocean Change Clim. rmstlieobservations. satellite from Earth. the of balance Change Clim. Nat. implications. cd c.U.S.A. Sci. Acad. deglaciation. last the during concentrations (2014). 3129–3144 ieipc fAlni eiinloetrigcruaindisruptions. circulation overturning Lett. meridional Atlantic of impact tive period. interglacial last the into extending 2 and , 2482 (2016). 8214–8221 43, .Gohs e.Atmos. Res. Geophys. J. 2630 (2009). 3296–3300 373, δ otasaeatmospheric translate To at’ nryiblne ofimto n implications. and Confirmation imbalance: energy Earth’s al., et dacsi nesadn o-famshr aito variability radiation top-of-atmosphere understanding in Advances al., et δ lblciaeeouindrn h atdeglaciation. last the during evolution climate Global al., et Kr/N Kr/N bevdcagsi o-fteamshr aito and radiation top-of-the-atmosphere in changes Observed al., et to.Ce.Phys. Chem. Atmos. IAppendix SI 3–4 (2016). 138–144 6, nbtdpaeaywrigadisoensrcuesne2006. since structure ocean its and warming planetary Unabated al., et lblwrigpeee yicesn abndioxide carbon increasing by preceded warming Global al., et nosrainlybsdeeg aac o h at since Earth the for balance energy based observationally An al., et O a ovre oOCb utpyn h temperature the multiplying by OHC to converted was MOT 2 13–14 (2012). E1134–E1142 109, , 2 4–4 (2015). 240–245 5, δ htsol ofr ihnterucranis o EDC, For uncertainties. their within conform should that niprtv omntrErhseeg imbalance. energy Earth’s monitor to imperative An al. , et eK,or Xe/Kr, .Gohs e.Oceans Res. Geophys. J. orcin o h hra rcinto scale fractionation thermal the for Corrections . uv Geophys. Surv. 117(2009). D17107 114, δ rpe i niecrsi rcintdfrom fractionated is cores ice in air Trapped Xe/N 32–34 (2011). 13421–13449 11, . K. ±0.4 2 δ niiuly h oa netit of uncertainty total The individually. Xe/Kr, Nature 5–8 (2012). 359–385 33, Nature 9816 (1978). 1958–1962 83, δ 4–5 (2004). 147–151 431, Xe/N 95 (2012). 49–54 484, 2 and , a.Geosci. Nat. δ Kr/N 2 epy.Res. Geophys. aisinto ratios 110–113 5, .Clim. J. rc Natl. Proc. δ Science Xe/Kr, Phys. Nat. 27, 2 .U lr,L aao,Coigtesalvlbde ttels lca maximum. glacial last the at budget level sea the Closing Tarasov, L. vol- Clark, ice U. P. global and 22. level Sea Sambridge, M. , Y. Mean Purcell, A. Severinghaus, Rouby, H. J. Lambeck, K. Kawamura, K. 21. Baggenstos, D. Shackleton, S. atmo- measuring Bereiter, for B. methods 20. New Severinghaus, P. J. Kawamura, K. Kr/N Bereiter, measure B. to 19. method A Severinghaus, P. J. Headly, A. M. 18. Church A. J. 17. Levitus tem- ocean S. mean of 16. proxies as gases Noble Severinghaus, P. J. Stocker, F. T. Ritz, P. S. 15. 5 .A act,J .Sau,P .Cak .C i,Arcntuto frgoa and regional of reconstruction A Mix, C. A. Clark, U. P. Shakun, D. J. Marcott, A. S. 25. Rasmussen O. S. 24. Stenni B. 23. 6 .Liu Z. 26. with rgam ainl iRcrh nAtriea oeC hsi EPICA is This C. Dome at Antartide in 311. logis- and no. Ricerche Victor main publication Emile di Franc¸ais–Paule The Polaire Nazionale contri- Institut Kingdom. by Programma United national provided , was the and the support and Italy, tic Union Germany, Switzerland, France, European Sweden, , Norway, the Belgium, Commission by from contribu- Foundation/European butions a funded Science Ice is European program work Polar joint This scientific a in Foundation. EPICA, Science Reconstructions to National tion Temperature Swiss the to and Sev- Advanced supported Cores) Union’s Approaches (ERC European 226172 was Modern Grant the results ERC Grant under FP7/2007-2013 these (ERC) Program Council Framework to for enth Research leading reviewers the European anonymous research the on two by The discussions and transport; comments. helpful and helpful for Gregory cutting and Pedro sample Eicher, Olivier for Joel Nehrbass-Ahles, Teste Christoph and budget; Galbraith heat oceanic Eric data; ature than larger ACKNOWLEDGMENTS. likely are and for accounted loss error. be gas measurement not quoted of the could influence way records, the the MOT or model, our for, box on corrected the is of fractionation evaluation setup gravitational the entire the as the such struc- uncertainties, through However, gradient. systematic fashion thermal tural firn Carlo the in Monte uncertainties including a routine, in errors surement Estimation. Uncertainty Appendix, (SI peaks the lower periods shows cutoff experiment large S2). very sensitivity Fig. of while A periods PRI, series. of cutoff time of tions LHM with period and cutoff smoothing a OHC with that the Low-pass (68) results. for spline robust y smoothing get a 2,500 by to performed desirable was instru- is filtering intrinsic smoothing includes which some series, noise, time mental energy total the Records. of derivative LHM the and OHC the of Smoothing h lblrdaieiblnePIi hncluae as calculated then is PRI in imbalance presented radiative is global energy components The the system of climate assessment different thorough in more change the A during 67). they increase (66, OHC as period the neglected, warming than smaller current both magnitude of were order components one least land at are the content and heat the atmosphere in the Changes of estimate. nature temperature speculative ice-sheet the of average reflective the error of be large a to including of estimated LHM, temperature the was ice to average added point an freezing (assuming heat the latent to the of ice energy the additional The warm freshwater. for to change fusion required mass of heat equivalent latent GMSL specific reconstruction. as the the times calculated an in was is uncertainties contribution which other ice-sheet capacity, than The heat smaller specific magnitude the of of order dependence temperature the ing msfo h atgailmxmmt h Holocene. the (2014). to 15296–15303 maximum glacial last the from umes transition. glacial last the during samples. (2018). temperatures core ocean ice global in ratios elemental and ocean isotope Spectrom. mean Mass gas Commun. past noble reconstructing heavy in spheric application its and cores ice temperature. in trapped bles (2013). 2008. 1955–2010. m), (0–2000 complexity. reduced of model climate Rev. a using studies Sensitivity perature: lbltmeauefrteps 130years. 11,300 past the for temperature global termination. (2001). 2074–2077 U.S.A. Sci. Acad. Natl. 30–30 (2014). E3501–E3505 A sfc 7834 (2011). 3728–3741 30, epy.Rs Lett. Res. Geophys. h ooeetmeaueconundrum. temperature Holocene The al., et en h ufc rao Earth. of area surface the being noenccl eesldrn h atdeglaciation. last the during reversal cold oceanic An al., et ol ca etcnetadtemsei e ee change level sea thermosteric and content heat ocean World al., et eiiigteErhssalvladeeg ugt rm16 to 1961 from budgets energy and sea-level Earth’s the Revisiting al., et .Gohs e.Atmos. Res. Geophys. J. .Gohs e.Atmos. Res. Geophys. 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