PAGES Magazine articles

Masa Kageyama¹, A. Abe-Ouchi², J. Annan³, P. Braconnot¹, C. Brierley⁴, J. Fidel Gonzalez-Rouco⁵, J. Hargreaves³, S.P. Harrison⁶, S. Joussaume¹, D.J. Lunt⁷, B. Otto-Bliesner⁸ and M. Rojas Corradi⁹

PMIP contributed to the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports (ARs) by placing current climate change into a wider context, evaluating climate model performance in very different climatic states, and constraining climate sensitivity based on paleoclimates.

Before PMIP

Back in 1990 when the First Assessment Report (FAR) of the Intergovernmental Panel for Climate Change (IPCC; Houghton et al. 1990) was published, PMIP did not exist. However, in its fourth chapter, entitled "Validation of climate models", the report drew on the pioneering results from CLIMAP Project Members (1981), who produced the first set of boundary conditions for LGM experiments, and COHMAP Members (1988), who produced paleodata syntheses and model simulations for key periods between the LGM and present. It stated that "studies of paleoclimate changes are an important element in climate model validation for two reasons: (1) they improve our physical understanding of the causes and mechanisms of large climatic changes so that we can improve the representation of the appropriate processes in the models, and (2) they provide unique data sets for model validation."

This view has guided the contribution of PMIP results to subsequent assessment reports. The creation of PMIP was announced in the Second Assessment Report (Houghton et al. 1996) in Chapter 5 ("Climate models – evaluation"): "The earlier ice age SST (sea surface temperature) data sets […] are now being revised for use in the newly organized Paleoclimate Modelling Intercomparison Project (PMIP) which is focusing on simulations for the Last Glacial Maximum and for 6000 years BP using atmospheric models with both fixed SST and mixed-layer oceans".

PMIP in the Third Assessment Report: mid-Holocene and Last Glacial Maximum

PMIP studies on both topics outlined in the FAR, model evaluation and process understanding, have been included in every subsequent assessment report of the IPCC. In the Third Assessment Report (TAR; Houghton et al. 2001), PMIP results can be found in Chapter 8 ("Model evaluation"). The iconic figure for the mid-Holocene African monsoon (Joussaume and Taylor, this issue; Fig. 1, adapted from Joussaume et al. 1999) shows that models agree with precipitation reconstructions in simulating an increased monsoon, but that they underestimate the reconstructed northward displacement of the monsoon area. The text states that this is also the case for the northward displacement of the Arctic tree line, and highlights the inconsistency between the simulated drier Eurasia and reconstructed wetter climate there.

Figure 1: Summary of paleoclimate modeling mentions in the IPCC first and second assessment reports, and of the figures showing PMIP results in subsequent assessment reports.

Also in the TAR, PMIP results for the Last Glacial Maximum (LGM) are in terms of the potential link between the global mean cooling and climate sensitivity, and an estimate of the LGM radiative forcing is given. The text then evaluates model results in comparison to new reconstructions for the tropics (Joussaume and Taylor, this issue, Fig. 2) and the extratropics. The cooling over the tropics was a highly debated topic, in particular because the cooling over land was found to be much larger than over the oceans. This characteristic could only partly be explained by the "land–sea contrast" later found in observations of current climate change and projections for the future.

At the time of the third assessment, the main conclusion was that the CLIMAP reconstructions were probably too warm over the tropics. Results from slab-ocean models were in better agreement with reconstructions, despite the fact they used present-day meridional heat transport. The TAR also points to a good agreement between models and data over Europe, except for winter for which the models underestimate the reconstructed cooling. All these themes would be addressed in subsequent reports.

PMIP in the Fourth Assessment Report: addition of the Last Interglacial

In the Fourth Assessment report (AR4; Solomon et al. 2007), PMIP disappears from the evaluation chapter (apart from a citation on modeling abrupt climate change) and appears in Chapter 6, a new chapter entirely dedicated to paleoclimate, and in Chapter 9, on "Understanding and Attributing Climate Change". Figure 6.5 shows components of the radiative forcing for the LGM, together with the simulated cooling in terms of sea surface temperatures and the relationships between global and regional temperature changes from the LGM to pre-industrial. This figure thereby highlights processes leading to the temperature change, and simultaneously provides an evaluation of the results. The conclusion is that AOGCMs "are able to simulate the broad-scale spatial patterns of regional climate change recorded by paleodata in response to the radiative forcing and continental ice sheets of the LGM, and thus indicate that they adequately represent the primary feedbacks that determine the climate sensitivity of this past climate state to these changes."

The AR4 also introduces AOGCM simulations of the Last Interglacial and, for the first time, some simulations of the last millennium from AOGCMs and Earth system models of intermediate complexity, which announces subsequent coordinated work within PMIP. The AR4 quantifies the estimated global LGM cooling of 4–7°C, which makes this period very relevant to the warming projected for 2100. PMIP results are also highlighted in Chapter 9 in relation to future climate, and contribute to the estimated ranges of equilibrium climate sensitivity in Table 9.3.

PMIP in the Fifth Assessment Report: multi-period analyses

The Fifth Assessment Report (AR5; Stocker et al. 2013) contains the largest number of figures showing PMIP results; these appear in chapters 5 ("Information from paleoclimate archives"), 9 ("Evaluation of climate models"), and 10 ("Detection and attribution of climate change"). The results are based on the PMIP3 mid-Holocene, LGM, and last millennium simulations, and the chosen figures show updated process understanding for the LGM and data–model comparisons for the mid-Holocene and the Last Interglacial. For the last millennium, AR5 highlights the large increase in the number of available AOGCM simulations relative to AR4. Furthermore, the consistency of these simulations with reconstructions and external forcing changes is evaluated, showing our understanding of the processes involved in the unprecedented present warming at hemispheric and continental scales.

A novelty in AR5 is that results (specifically regarding polar amplification) are shown from multiple past periods (including for the mid-Pliocene Warm Period and the Eocene Climate Optimum), together with an idealized future scenario (2xCO2) in the same figure. Another new topic is the analysis of changes of ENSO variability for different periods. Several lines of evidence, including paleoclimate reconstructions and simulations are also combined to assess Equilibrium Climate Sensitivity in a comprehensive section on this topic in Chapter 10. Model evaluation (Chapter 9) focuses on the last millennium variability, large-scale and regional features of the LGM and mid-Holocene surface climate, as well as LGM large-scale deep ocean gradients in temperature and salinity. Model performance is also quantified in terms of metrics, similar to the approach used for evaluating present climate in comparison to observations. However, in the case of PMIP, the metrics are based on bioclimatic variables.

The Sixth Assessment report: PMIP distributed throughout the report

Simpler diagnostics have been chosen for the Sixth Assessment Report, in which most chapters are devoted to process understanding and provide a holistic assessment of broad topics, including paleoclimatic information. PMIP results, and results from paleoclimate studies more generally, are distributed throughout the report—with figures found in chapters 2 ("Changing state of the climate system"), 3 ("Human influence on the climate system"), 7 ("The Earth's energy budget, climate feedbacks, and climate sensitivity"), and 8 ("Water cycle changes"). One remarkable result is that within the combination of constraints on equilibrium climate sensitivity, paleoclimatic reconstructions, supported by modeling work associated with PMIP, were key to reducing the likely range of equilibrium climate sensitivity from the AR5 range of 1.5–4.5°C to 2.5–4.0°C. We are optimistic that this presentation may improve the public's awareness of PMIP results, and their potential for use by policymakers and other stakeholders.

affiliations

¹Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, UMR CEA-CNRS-UVSQ, Université Paris-Saclay, Gif sur Yvette, France

²Atmosphere and Ocean Research Institute, The University of Tokyo, Japan

³BlueSkiesResearch, Settle, UK

⁴University College London, UK

⁵Department of Earth Physics and Astrophysics, Geosciences Institute IGEO (UCM-CSIC), Complutense University of Madrid, Spain

⁶School of Archaeology, Geography and Environmental Science (SAGES), University of Reading, UK

⁷School of Geographical Sciences, University of Bristol, UK

⁸National Center for Atmospheric Research, Boulder, CO, USA

⁹Department of Geophysics, University of Chile, Santiago, Chile

contact

Masa Kageyama: masa.kageyamalsce.ipsl.fr

references

COHMAP Members (1988) Science 241: 1043-1052

CLIMAP Project Members (1981) Seasonal reconstruction of the Earth's surface at the last glacial maximum. Geol Soc Am, Map and Chart Series, pp 1-18

Houghton JT et al. (Eds; 1990) Climate Change: the IPCC Scientific Assessment. Cambridge University Press, 365 pp

Houghton JT et al. (Eds; 1996) Climate Change 1995: The Science of Climate Change. Cambridge University Press, 572 pp

Houghton JT et al. (Eds; 2001) Climate Change 2001: The Scientific Basis. Cambridge University Press, 881 pp

Joussaume S et al. (1999) Geophys Res Lett 26: 859-862

Masson-Delmotte V et al. (Eds; 2021) Climate Change 2021: The Physical Science Basis. Cambridge University Press, in press

Solomon S et al. (Eds; 2007) Climate Change 2007: The Physical Science Basis. Cambridge University Press, 1007 pp

Stocker TF et al. (Eds; 2013) Climate Change 2013: The Physical Science Basis. Cambridge University Press, 1535 pp

Pascale Braconnot¹, M. Kageyama¹, S.P. Harrison², B.L. Otto-Bliesner³, A. Abe-Ouchi⁴, M. Willé¹, J.-Y. Peterschmitt¹ and N. Caud¹

Over the last 30 years, PMIP has made significant progress in the development of Earth system models, climate reconstructions, and model–data comparisons. It has contributed greatly to our understanding of climate sensitivity, ocean circulation and abrupt events, the hydrological cycle, the linkages between climate and ecosystems, and climate variability.

From infancy to a mature project

During the last 30 years, the Paleoclimate Modelling Intercomparison Project (PMIP) has fostered synchronized model simulations, climate reconstructions, and model-model and model–data comparisons for key climate periods in the past (Fig. 1). The major objectives of the project developed for the first phase of PMIP are still valid today (see Joussaume and Taylor, this issue): to understand the mechanisms of climate change, test models in a climate context different from modern, and define evaluation criteria that are relevant to assess the credibility of future climate projections. However, the project has refined these objectives in four successive phases (Fig. 1 and 2).

The PMIP niche is to produce paleoclimate simulations with the same general circulation models (GCMs) used for future climate projections. During PMIP's lifetime, these models have evolved from atmosphere-only to Earth system models (Fig. 1), initially through the inclusion of either ocean or vegetation couplings with the atmosphere. The choice of the complexity of the model used, such as the inclusion of the carbon cycle or interactive aerosols, still varies across modeling groups. However, currently, the main focus is on full integration of the different components of the system. PMIP has provided a way both to test different climate feedbacks related to land surface, ocean, or ice sheets, and to improve understanding of the relationship between climate and variations in terrestrial and marine biogeochemistry. Because of its unique focus, PMIP has been endorsed from the beginning by PAGES and the World Climate Research Programme (WCRP) through its core project Climate Variability (CLIVAR) and subsequently the Working Group on Coupled Models (WGCM). These endorsements have allowed PMIP to maintain strong connections to the modeling and climate reconstruction communities throughout the last 30 years.

PMIP encourages growth in its activities while maintaining a focus on a limited number of key questions. It plays a key role by providing results in the open database for global climate simulations supported by WCRP (Peterschmitt et al. 2018). These results have been used for studies well beyond those originally envisaged by people outside the main PMIP community, including for impact studies, or to assess changes in biodiversity or ecological niches.

Evolution of the context and scientific questions

PMIP1 highlighted robust model responses to external forcings for the mid-Holocene and the Last Glacial Maximum (LGM) and discussed model uncertainties. The number of independent climate indicators from different natural archives has increased with time, allowing for tests of the modeled response to the forcings of the land, ocean, and ice sheets (see Bartlein et al. and Jonkers et al. this issue). The role of carbon cycle and other feedbacks has been considered since PMIP2. PMIP3 introduced a focus on analyses of interannual-to-centennial climate variability (Braconnot et al. 2012). New methodologies for model–data comparison have been continuously developed, from simple visual comparisons, to application of specific metrics, and finally to the use of forward modeling of the various climate indicators such as water or carbon isotopes. The importance of model–data comparison meant that there had to be a balance between the use of a strict experiment protocol to be able to understand model differences and more flexible protocols allowing different groups to sample uncertainties in boundary conditions.

Figure 1: PMIP phases highlighting major meetings (date, location, host, activities, and meeting report), together with the key periods, external forcings, and model complexity represented with small infographics either as core PMIP activities (green), small groups (orange), or as part of the wider network (blue). MH = Mid-Holocene, LGM = Last Glacial Maximum, EH = Early Holocene, LM = Last Millennium, PLIO = Pliocene, DEEP = deep time, LIG = Last Interglacial, and LD = Last Deglaciation. When a number is included (e.g. "115ka"), it refers to the exact period as discussed during PMIP meetings.

New periods and questions have been included progressively in PMIP to address a broader range of external forcings and climate issues. These choices were discussed and made at the regular PMIP meetings every 2–3 years (Fig. 1). A challenge has been to foster collaboration around key periods, with standardized simulations and associated databases, while also acting as a network to share new results and sensitivity experiments that improve our understanding of major climate feedbacks. The early Holocene and last glacial inception were included in PMIP2 to address questions about water cycle feedback from the ocean and vegetation, and the role of snow and ice sheets (PMIP 2000). Multi-model results were developed for the last interglacial in PMIP3. However, a common protocol for the last interglacial was only proposed in PMIP4 (Otto-Bliesner et al. 2017). Pre-Quaternary climates have also been included since PMIP3 because of their ability to provide constraints on climate sensitivity (Haywood et al. 2010). The Last Millennium in PMIP is associated with the PAGES 2k Network and the need to improve pre-industrial reference climates (Schmidt et al. 2011). Several fresh water flux experiments have also been regularly discussed, either for the Holocene 8.2 kyr event (see Gregoire and Morrill, this issue) or complementary experiments around the LGM. Recently the deglaciation has become one of the major flagships for PMIP simulations (Ivanovic et al. 2016).

The current organization into eight working groups (pmip.lsce.ipsl.fr/working_groups) favors exchanges on the different climatic periods, transverse analyses for model–data comparisons, and cross-period analyses. Five PMIP experiments have been included in CMIP6 (Fig. 1). More details of the PMIP journey are available online: www.tiki-toki.com/timeline/entry/1566548/HISTORY-OF-PMIP

What do PMIP iconic figures tell us about advances in modeling?

The two PMIP iconic figures presented in Joussaume and Taylor (this issue) are reproduced here to provide an overview of how simulated changes in mid-Holocene precipitation or in LGM land–sea contrast has been represented with increasing model complexity and resolution throughout the four phases of PMIP (Fig. 2). Figure 2 illustrates the 30-year quest to simulate sufficient precipitation in the Sahel-Sahara to support the reconstructed mid-Holocene vegetation cover, which has led to improved understanding of the role of global and regional feedbacks (soil, vegetation, albedo, etc.; Brierley et al. 2020). There has been a shift between PMIP phases such that models now produce more consistent representations of increased precipitation between 6°N and 16°N, but continue to struggle to reproduce the large observed changes from 16°N to 30°N.

Figure 2: Iconic PMIP graphics to show how well models represent the increase and northward extent of the mid-Holocene West African monsoon and the Last Glacial Maximum land–sea contrast through the different phases of PMIP. (Top) Summary of the data constraints. Temperature anomalies compiled from MARGO Project Members (2009) and Bartlein et al. (2011); biome reconstruction from Joussaume et al. (1999).

For the LGM, PMIP results have consolidated the understanding of the ratio between temperature over land and over the ocean, which is relevant for discussions about future climate (Stocker et al. 2013). Independent reconstructions over land and ocean support this ratio, and can be used to define which of the results better fits with past conditions. The current generation of climate models and new proxy reconstructions produce a large range of results, however, suggesting that the debate on the LGM land–sea ratio has not yet been resolved (Kageyama et al. 2021).

Paleoclimate modeling and systematic benchmarking within PMIP have demonstrated that feedbacks from ocean and vegetation are needed to reproduce climate changes at global or regional scales. PMIP has also demonstrated that models that produce good simulations of present-day climate do not necessarily have good skill in simulating past changes. This raises questions about how to pre-select models only looking at modern conditions when considering future climate projections, for example for impact studies. The current phase of PMIP should provide a wider range of past constraints from the combination of the different climate periods to isolate missing mechanisms or the impact of model biases on the seasonal, annual, or interannual-to-centennial scale characteristics of climate changes.

In conclusion

During the last 30 years PMIP has provided a scientific basis to define the level of model complexity needed to understand climate change processes and interactions between the different timescales fully. This is one of the reasons why PMIP results serve as reference in IPCC assessment reports (Kageyama et al. this issue, p. 68). Little by little, paleoclimate simulations are no longer being considered just to check confidence in the models, but also as a necessary step for identifying model deficiencies and contributing to the improvement of the physical and biogeochemical content of the models. Paleoclimate simulations represent an essential element in understanding climatic events with a high impact on ecosystems or societies.

affiliations

¹Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, UMR CEA-CNRS-UVSQ, Université Paris-Saclay, Gif sur Yvette, France

²School of Archaeology, Geography and Environmental Science (SAGES), University of Reading, UK

³National Center for Atmospheric Research, Boulder, CO, USA

⁴Atmosphere and Ocean Research Institute, The University of Tokyo, Japan

contact

Pascale Braconnot: pascale.braconnotlsce.ipsl.fr

references

Bartlein PJ et al. (2011) Clim Dyn 37: 775-802

Braconnot P et al. (2003) CLIVAR Exchanges 28: 19-20

Braconnot P et al. (2007) Clim Past 3: 261-277

Braconnot P et al. (2010) CLIVAR Exchanges 56: 15-19

Braconnot P et al. (2012) Nat Clim Chang 2: 417-424

Brierley CM et al. (2020) Clim Past 16: 1847-1872

Crucifix M et al. (2005) Eos 86: 264-264

Crucifix M et al. (2012) Eos 93: 539-539

Crucifix M et al. (2014) PAGES Mag 22: 103

Harrison SP et al. (2002) Eos 83: 447-447

Haywood AM et al. (2010) Geosci Model Dev 3: 227-242

Haywood AM et al. (2011) Eos 92: 180-180

Ivanovic RF et al. (2016) Geosci Model Dev 9: 2563-2587

Joussaume S, Taylor KE (1995) Status of the paleoclimate modeling intercomparison project, Proceedings of the first international AMIP scientific conference, WCRP Report, 425-430

Joussaume S et al. (1999) Geophys Res Lett 26: 859-862

Kageyama M et al. (2018) Geosci Model Dev 11: 1033-1057

Kageyama M et al. (2021) Clim Past 17: 1065-1089

Liu J et al. (2021) PAGES Mag 29: 57

MARGO Project Members (2009) Nat Geosci 2: 127-132

Otto-Bliesner BL et al. (2009a) Eos 90: 93-93

Otto-Bliesner BL et al. (2009b) PAGES news 17: 42-43

Otto-Bliesner BL et al. (2017) Geosci Model Dev 10: 3979-4003

Peterschmitt J-Y et al. (2018) PAGES Mag 26: 60-61

Schmidt GA et al. (2011) Geosci Model Dev 4: 33-45

Schmittner A et al. (2011) PAGES news 19: 83-84

Stocker TF at al. (Eds; 2013) Climate Change 2013: The Physical Science Basis. Cambridge University Press, 1535 pp

Zhang Q et al. (2017) PAGES Mag 25: 160

Sylvie Joussaume¹ and Karl E. Taylor²

The Paleoclimate Modelling Intercomparison Project celebrates its 30th anniversary in 2021. The first phase initiated systematic model-model and model–data comparisons for the Last Glacial Maximum and Mid-Holocene. Here, we describe the historical context of PMIP, the experiment design, and the project's early impacts.

PMIP Launch

The Paleoclimate Modelling Intercomparison Project (PMIP) was launched 30 years ago at an international North Atlantic Treaty Organization (NATO; nato.int) workshop in Saclay, France, in 1991. Its main objectives were to investigate the mechanisms of climate change and to evaluate model capabilities in simulating past climates. At this workshop, the first PMIP experiments were conceived, which focused on two very different climatic periods: the Last Glacial Maximum (LGM; 21,000 years before present (BP)) with extremely cold conditions and the mid-Holocene (6,000 years BP) with an orbitally-forced change in seasonal cycle.

PMIP built on ground-breaking paleoclimate experiments performed with earlier models and capitalized on well-documented data syntheses for these periods, notably the extensive work of the Cooperative Holocene Mapping Project (COHMAP) group led by John Kutzbach. In the initial phase of the project, the main features of the selected paleoclimates were investigated by offering an experimental protocol where all models would be run with the same prescribed boundary conditions. From the start, PMIP was endorsed by both the International Geosphere Biosphere Program through PAGES and the World Climate Research Programme (WCRP; wcrp-climate.org), first through the Working Group on Numerical Experimentation and later by the Working Group on Coupled Modelling as part of Climate and Ocean – Variability, Predictability, and Change (CLIVAR; clivar.org).

Figure 1: PMIP1 simulations of annual mean precipitation changes (6 kyr BP minus present; mm/year) in the African monsoon region (20ºW–30ºE). (A) Biome distribution (desert, steppe, xerophytic and dry tropical forest/savannah; DTF/S) as a function of latitude for 6 kyr BP (green triangles) and present-day (red circles). The limit of desert-steppe at 6 kyr BP around 23ºN (blue vertical dashed line) provides a range of precipitation excess above model results shown in (B). (B) Model results with hatched lines showing estimated upper and lower bounds excess precipitation needed to support grasslands based on present climatic limits. Figure reproduced from McAvaney et al. (2001); redrawn from Joussaume et al. (1999).

During its first phase (1991–2001), PMIP focused only on atmospheric general circulation models (AGCMs), which at that time were the standard climate models. The final design of the PMIP experiments was only arrived at following intense discussions that began with the initial 1991 NATO workshop with a focus on the experimental design for the LGM. A major point of contention was whether to constrain the PMIP simulations of the LGM by prescribing sea surface temperatures (SSTs) as reconstructed by the Climate: Long range Investigation, Mapping, and Prediction (CLIMAP) project in 1981, with the prospect that the resulting climate would be more realistic, or to use AGCMs coupled to slab oceans, allowing for some surface ocean interactions, but with ocean horizontal heat transport fixed as present-day and, therefore, inconsistent with paleoclimate data. Each of these approaches had its proponents and its merits, and in the end, both were endorsed as options for the LGM.

For the mid-Holocene experiment, the choice of surface boundary conditions was easier since SSTs are nearer to present-day conditions. In this case, to help isolate the impact of orbital changes, the SSTs were simply prescribed to be the same as in the Atmospheric Modelling Intercomparison Project (AMIP) experiments. In the few years following the first workshop, consensus was reached concerning the LGM ice-sheet boundary conditions; the Peltier ice-sheet reconstruction was adopted in 1992 following discussions at a workshop at Lamont–Doherty Earth Observatory, USA, organized by Bill Ruddiman. Considerable work was required to iron out details concerning definition of the insolation forcing for the mid-Holocene and the proper way to compare seasonal cycles from past and present climates when statistics are based on civil calendar months, but climate responds to astronomically-determined seasons.

From the beginning, PMIP modelers and the paleoclimate data community forged a strong working relationship, as this had been key to the success of COHMAP. Thus, one of PMIP's many objectives was to encourage data syntheses for the two paleoclimate periods that would enable model–data comparisons. A model–data sub-committee organized this work, led by Sandy Harrison, Joël Guiot and Pat Bartlein. At a workshop in Aussois, France, in 1993, participants discussed both inverse and forward approaches for evaluating models using paleoclimate observations. These discussions highlighted the importance of fostering close interactions between the two communities.

Figure 2: Annual mean simulated tropical cooling over ocean and land from PMIP1 LGM simulations, compared to estimates of terrestrial cooling from pollen (Farrera et al. 1999) and from ocean SSTs estimated from alkenones (Rosell-Melé et al. 1998). Figure reproduced from McAvaney et al. (2001; adapted from Pinot et al. 1999).

By 1994, all experimental conditions were fixed and described in a foundational paper by Joussaume and Taylor (1995). This first phase of PMIP attracted the participation of 18 modeling groups, from Europe, the USA, Canada, Australia, Russia, Korea, and Japan. Following the lead of its slightly older sibling AMIP, PMIP relied on infrastructure support from the Program for Climate Model Diagnosis & Intercomparison (PCMDI; pcmdi.llnl.gov) and its director, Larry Gates. In PMIP's first phase, data were collected and stored at PCMDI in a restricted-access database, as was the practice for AMIP as well. Several papers were published (see pmip1.lsce.ipsl.fr), and the major findings were emphasized in the third IPCC Assessment Report (McAvaney et al. 2001). Two key PMIP figures are reproduced here in Figures 1 and 2.

PMIP results became the focus of several community workshops that included both paleoclimate modelers and specialists in paleoclimate data. At the first workshop in 1995 in Collonges-la-Rouge, France, initial analyses were shared. Then in 1997 at San Damiano, USA, subprojects were organized and papers planned. Subsequently, in 1999 at La Huardière, Canada, a synthesis of the results was prepared and then published in a WCRP special report (Braconnot 2000). These workshops have been essential to PMIP's success. They were instrumental in developing the close working relationship between modelers and data specialists that led to a better appreciation of the limitations of both models and observations and to development of improved understanding of the climate system. The PMIP workshops have all been intensive, interactive, and lively; and we will not forget the "PMIP song" introduced in the Collonges-la-Rouge workshop (pmip1.lsce.ipsl.fr/goodies/song.html), and revised in San Damiano; and the dancing and revelry in La Huardière!

Main highlights from the first PMIP phase

In what became known as the "Big Picture Paper", Joussaume et al. (1999) showed that as a result of increased summer insolation, all the models simulated an increase in the summer monsoon precipitation over Africa and Asia during the mid-Holocene (Fig. 1). A quantitative comparison over Africa using results from BIOME 6000 (Jolly et al. 1998) showed that all the models underestimated the northward displacement of the desert-steppe transition, which was also confirmed by vegetation simulations using PMIP outputs (Harrison et al. 1998). This is a modeling problem that continues to challenge state-of-the-art models.

The model–data comparisons over Europe led to the establishment of new bioclimatic variables such as temperature of the coldest month and growing degree-days, rather than the commonly-used January and July temperature estimates (Cheddadi et al. 1996). These more robust variables enhance confidence in model–data comparisons (Masson et al. 1999).

For the LGM, models simulated a global cooling of about 4ºC when forced with CLIMAP SST reconstructions, whereas AGCMs coupled to slab oceans produced a global cooling between 2º and 6ºC. Following the issue raised by Rind and Peteet (1985) about the underestimation of the simulated terrestrial tropical cooling at LGM, a detailed model–data comparison study was conducted for the tropics that relied on a new data synthesis effort fostered by PMIP (Farrera et al. 1999). In the tropics, models forced by the relatively warm CLIMAP SSTs confirmed an underestimated terrestrial cooling, whereas models that computed SSTs obtained estimates in better agreement with the observed tropical cooling (Fig. 2), compensating for their relatively weak cooling over land with excessive ocean cooling (Pinot et al. 1999). In addition, an extensive comparison over Europe (Kageyama et al. 2001) concluded that according to pollen data (Peyron et al. 1998), models tended to underestimate winter cooling, at least over western Europe.

Looking forward

When launching PMIP in 1991, we did not expect the project would still be relevant, let alone vibrant, 30 years later. During this time, younger scientists have brought new energy and ideas to the project, and have reinvigorated the quest to understand paleoclimates. We believe that PMIP will continue to attract a community of researchers who enjoy working together and who will seize opportunities to expand our knowledge of our climate system by looking at the past.

affiliations

¹Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, UMR CEA-CNRS-UVSQ, Université Paris-Saclay, Gif sur Yvette, France

²PCMDI, Lawrence Livermore National Laboratory, Livermore, CA, USA

contact

Sylvie Joussaume: sylvie.joussaumelsce.ipsl.fr

references

Braconnot P. (Ed; 2000) Paleoclimate Modelling Intercomparison Project: proceedings of the third PMIP Workshop. WCRP-111, WMO/TD-1007, 271 pp.

Cheddadi R et al. (1996) Clim Dyn 13: 1-9

Farrera I et al. (1999) Clim Dyn 15: 823-856

Harrison SP et al. (1998) J Clim 11: 2721-2742

Jolly D et al. (1998) J Biogeogr 25: 1007-1027

Joussaume S, Taylor KE (1995) Status of the paleoclimate modeling intercomparison project, Proceedings of the first international AMIP scientific conference, WCRP Report, 425-430

Joussaume S et al. (1999) Geophys Res Lett 26: 859-862

Kageyama M et al. (2001) Clim Dyn 17: 23-43

Masson V et al. (1999) Clim Dyn 15: 163-182

McAvaney BJ et al. (2001) In: J. Houghton (Ed) Climate Change 2001: The Scientific Basis. Cambridge University Press, 471-523

Peyron O et al. (1998) Quat Res 49: 183-196

Pinot S et al. (1999) Clim Dyn 15: 857-874

Rind D, Peteet D (1985) Quat Sci Rev 24: 1-22

Rosell-Melé A (1998) EOS 79: 393-394

Paul J. Valdes¹, P. Braconnot² and K.J. Meissner³

Thirty years is a long time in science. New data leads to revisions of old theories, and new theories challenge interpretations. Thirty years is a particularly long time in climate research, with huge advances in our understanding and ability to predict climate change and its impacts. Throughout this time, the Paleoclimate Modelling Intercomparison Project (PMIP) has been at the forefront of testing the latest generation of climate and Earth system models against paleoclimate data, acting as an important conduit between the paleodata community and the climate modelers involved in future projections. It has also acted as an important motivator of paleodatabase development, which is so essential for rigorous model–data comparisons.

Figure 1: Participants at the PMIP workshop in Collonges-la-Rouge, France. Many are still involved in the PMIP community, though some are looking a lot older! Front row: Pat Bartlein, Robin Webb (?), John Kutzbach, Dave Pollard, Bob Oglesby. Second row: Pascale Braconnot, Karl Taylor, Sandy Harrison, Gerhard Krinner, Klaus Herterich, Sylvie Joussaume, Norman MacFarlane, Jozef Sytkus. Third row: (?), Ayako Abe-Ouchi, Bette Otto-Bliesner, Lisa Sloan, Natalie de Noblet, Michael Lautenschlager (?), Marie-France Loutre, Masa Kageyama, Valerie Masson, Gilles Ramstein, Akio Kitoh, Tony Broccoli. Back row: Buwen Dong, Jai-Oh Oh (?), John Mitchell, Paul Valdes, Michael Schlesinger, Chris Hewitt, David Rind, Christophe Genthon (?), Alex Kislov, Dominique Jolly (?), Joel Guiot, Mikhail Verbitsky. Corrections and additions sent to pagespages.unibe.ch are very welcome!

Oliver Bothe1, K. Rehfeld2, B. Konecky3 and L. Jonkers4

Data is an important foundation of scientific progress. It allows us to contrast hypotheses with observational evidence. Sharing and providing data openly have a long tradition in paleoenvironmental research, supported by repositories such as WDS-Paleo1, PANGAEA2,and Neotoma.3

The 2018 Past Global Changes Magazine issue (Williams et al. 2018) "Building and Harnessing Open Paleodata" touches on all the questions from the production of individual records to the reuse of compilations. Common themes were conventions for reporting, for metadata, and for data structures; crediting mechanisms, community as well as external support in data curation and infrastructure; automating processes; and making data more widely usable.

Today, with many new published data compilations (e.g. Iso2k4, Konecky et al. 2020; SISAL5, Comas-Bru et al. 2020; PalMod, Jonkers et al. 20206, Cao et al. 20207; PlioVAR8, McClymont et al. 2020), the need for improving reusability and interoperability of data is becoming more pressing. Each of those compilations adheres, to some extent, to the principles of Findability, Accessibility, Interoperability, and Reusability (FAIR; Wilkinson et al. 2016). The creation of such compilations, which includes quality controlling large numbers of original data records, improves the interoperability of available data records and increases the amount of usable data for understanding past environments and assessing uncertainty. But are the syntheses themselves interoperable enough?

Interoperability benefits from common standards about what is reported, using which vocabularies, and in which storage structures (see e.g. Khider et al. 2019). The highlighted compilations still use a variety of vocabularies and metadata elements. They are provided in a number of different formats including LiPD files, a SQL database, and tab-limited text files. Working with multiple compilations requires becoming fluent enough in each of them to write code to harmonize data formats, interact with files, or produce new files.

A harmonized workflow would allow data from different compilations to be used together more efficiently. This in turn would mean that findings could rely on a larger amount of data and better account for uncertainties. In short, we could more reliably establish agreement and disagreement between data sources (including simulation output), and we could obtain more complete pictures of past environments. Standardization of data synthesis products would therefore be a valuable step towards standardization of all paleoenvironmental observation data and towards using all paleoenvironmental data to their fullest, which certainly motivates many PAGES working group activities.

A number of recent initiatives provide key elements of such a toolchain. Curated repositories assist in harmonizing reporting standards, vocabularies, as well as data formats. These repositories cater to a number of research fields with different conventions. Requirements may also differ between the data producers and the data users. Of particular interest for interoperability are the storage conventions and the vocabularies.

Figure 1: The diverse formats of paleoenvironmental datasets resemble an assortment of gear wheels that do not necessarily work together (Image credit: Laura Ockel, Unsplash11).

In contrast to paleo-observational data, established sharing and access channels as well as utilities provide standardized workflows and a high degree of FAIRness for simulation output. Paleo-observational data standardization efforts can benefit from the experiences of the wider Earth system modeling community. However, harmonizing climate simulation output with tools like the Climate Model Output Rewriter (CMOR9) may be more straightforward than harmonizing paleoenvironmental observations. For the latter, we have yet to finish coordinating vocabularies among research communities and may still have to optimize multiple ways of organizing and storing research data before a standard emerges. Finally, we might find that we cannot use one common format but rather that we need a well-designed, automatable, and well-documented set of tools for interacting with multiple community specific standards to create, modify, and update (parts of) files, as well as read files from different formats.

Community engagement is necessary for tools to be adopted for community specific-use cases. Development and maintenance of tools must not depend on individuals and short funding cycles. Community governance as well as technical solutions can ensure sustainable long-term support for standards for reusable and interoperable paleoenvironmental data that maximally serve our understanding of past and future environmental changes. The paleoenvironmental community, as a community of many research communities, has to provide guidance. For this to be established and adhered to, communities as represented, for example, by the PAGES working groups, have to talk to each other, the repositories for paleoenvironmental data, and providers of technological infrastructure. Then, we can tailor standards, formats, and tools to community needs.

PAGES has taken up data stewardship as an integrative activity with relevant structures and cooperations. Thus, PAGES and comparable efforts are in an ideal position to assist sustainable solutions with a long-term commitment, for which the new Data Stewardship Scholarship10 offered to PAGES working groups may be a valuable stepping stone. Another step can be for PAGES working groups and PAGES governance to instigate and moderate the necessary conversations, e.g. in the form of a virtual data roundtable bringing together all interested parties.

affiliationS

1Helmholtz-Zentrum Hereon, Geesthacht, Germany
2Institute of Environmental Physics, Ruprecht-Karls-Universität Heidelberg, Germany
3Department of Earth and Planetary Sciences, Washington University, St. Louis, MO, USA<
4MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany

contact

Oliver Bothe: oliver.bothehereon.de

references

Cao X et al. (2020) Earth Syst Sci Data 12: 119-135

Comas-Bru L et al. (2020) Earth Syst Sci Data 12: 2579-2606

Jonkers L et al. (2020) Earth Syst Sci Data 12: 1053-1081

Khider D et al. (2019) Paleoceanogr Paleoclimatol 34: 1570-1596

Konecky BL et al. (2020) Earth Syst Sci Data 12: 2261-2288

McClymont EL et al. (2020) Clim Past 16: 1599-1615

Wilkinson MD et al. (2016) Sci Data 3: 160018

Williams JW (Eds) (2018) PAGES Mag 2(26), 52 pp

LINKS

1https://www.ncdc.noaa.gov/data-access/paleoclimatology-data

2https://www.pangaea.de/

3https://www.neotomadb.org/

4https://doi.org/10.25921/57j8-vs18

5https://doi.org/10.17864/1947.256

6https://doi.org/10.1594/PANGAEA.908831

7https://doi.org/10.1594/PANGAEA.898616

8https://doi.org/10.1594/PANGAEA.911847

9https://cmor.llnl.gov/

10http://pastglobalchanges.org/science/wg/data-stewardship-scholarship

11https://unsplash.com/photos/e_hQZ2EM-Qg

PASES workshop organizers*

Online, 9-11 November 2020

Effective interdisciplinary collaboration requires trustful interactions and several iteration cycles throughout the scientific process, from the formulation of research questions to the conclusions. Collaborative research is especially challenging among early-career researchers (ECRs), who usually face cultural and geographical barriers among peers, as well as having less experience of networking. In the paleosciences, although the interpretation of historical and paleoenvironmental records requires cross-fertilization of knowledge, this is usually undertaken within the framework of monodisciplinary investigations. As a consequence, conclusions are often drawn as simple, deterministic (either environmental or human) interpretations. This reductive approach minimizes the complexity of the causal relationships involved in human-environmental systems, especially over longer timescales (Fig. 1). Understanding the interplay between past human societies and the natural systems they inhabited may provide us with sustainability strategies for current and future socio-environmental challenges.

Figure 1: Diagram of an idealized past socio-environmental system showing the coupling between natural and human systems.

The Past Socio-Environmental Systems (PASES; https://www.pases2020.com; vPASES) workshop was designed as a joint venture between PAGES ECN (pastglobalchanges.org/ecn) and INQUA ECRs (https://inqua.org/ecr) to foster cross-disciplinary collaborations among the next generation of paleoscientists. This workshop was especially designed for those conducting research at the interface of the climate-culture-environment nexus, with experience in proxy-based and modeling records of paleoclimate, archaeology, paleoecology, and human paleodemography.

Without the possibility of meeting in La Serena, Chile, for an in-person workshop due to the COVID-19 global pandemic, the objectives of the virtual PASES workshop were to bring together ECRs who are open to interdisciplinarity, as well as to promote equal opportunities for participants around the world. The online workshop involved 16 presenters and more than 200 attendees from 26 different countries. The workshop included two three-hour sessions on human paleoecology and synthesis of paleorecords. The last day consisted of an open-table discussion with senior researchers reflecting on community-driven paleoscience questions, and a breakout activity to catalyze scientific collaborations among ECRs.

The virtual workshop began with the Human Paleoecology session, introduced by César Méndez's (Patagonian Ecosystems Investigation Research Center, Chile) keynote presentation. Méndez explained the importance of comparative archaeological studies in semiarid regions for understanding human-environmental interactions during the Pleistocene-Holocene transition. Subsequent talks by ECRs gave insights into land-use changes and agricultural practices, the importance of robust chronologies for island colonization processes, and how climate and human pressures can be revealed using sedimentary records in coastal and mountain regions. On day two, keynote speaker Yoshi Maezumi (University of Amsterdam, The Netherlands) spoke about human legacies in the Amazonia through the application of multiproxy evidence from paleoclimatology, archaeobotany, and paleoecology. The following talks by ECRs highlighted the usage of various records (pollen, charcoal, historical archives, bat guano, and ancient eDNA) to tease apart the human and climate drivers explaining past environmental responses. The talks were followed by a lively and interactive Q&A discussion. For attendees who either couldn't attend or wanted to re-watch the presentations, we shared links privately following the workshop.

The final day was dedicated to interactive and collaborative activities. First, attendees participated in the open discussion "ECRs ask, mentors respond", guided by a panel of four senior scientists. These experienced researchers addressed some of the most pressing questions in the field of past socio-environmental systems, which were posed by ECRs during the PASES workshop pre-registration process. Finally, the breakout activity "Pillars of collaboration" had a strong focus on team science, aiming to initiate conversations for genuine interdisciplinary collaboration revolving around boundary objects – elements that any research collaboration should be built upon (question/hypothesis, region, field of study, and methodology) to define a joint problem for past socio-environmental systems' research.

Organizing an international virtual workshop was a significant challenge for the Local Organizing Committee – especially in the midst of a pandemic – and particularly in terms of adapting to different time zones and exploring the myriad of different technical options available to maximize attendance. Altogether, the range of expertise from presenters and attendees led to inspiring discussions that provided scientific foci to build new partnerships and plant the seed for the postponed in-person workshop in La Serena, Chile (planned for November 2022; PASES 2022). For the immediate future, there are virtual PASES networking channels available to encourage active participation and we invite interested ECRs to become involved through the website forum and breakout groups. These virtual workspaces can be a platform for advancement of the PASES outputs, including short articles in the PAGES ECR-led special issue of the Past Global Changes Magazine, and a global database comprising well-known case studies characterized by datasets measuring paleoecological proxies, human population and paleoclimatic changes, as well as integrative methodologies.

Authors and affiliations

X. Benito (National Socio-Environmental Synthesis Center (SESYNC), University of Maryland, College Park, USA)

I.A. Jara (Center for Advanced Studies in Arid Zones (CEAZA), La Serena, Chile)

G. Camperio (Department of Earth Science, ETH Zürich, Switzerland & Department of Surface Waters, Research & Management, Eawag, Kastanienbaum, Switzerland)

F. Charqueño (CENAC-PNNH-CONICET, Bariloche, Argentina)

K. Davies (Institute for Modelling Socio-Environmental Transitions (IMSET), Bournemouth University, UK)

A. Adamu Isa (Department of Archaeology and Heritage Studies, Ahmadu Bello University, Zaria, Nigeria)

F. Ferrario (Università dell’Insubria, Como, Italy)

A.-M. Klamt (Yunnan Normal University, Kunming, China)

M. Mariani (School of Geography, University of Nottingham, UK); V. Merino (Department of Biology, Universidad Nacional de Mar del Plata, Argentina)

E. Orijemie (Department of Archaeology and Anthropology, University of Ibadan, Nigeria)

contact

Xavier Benito: xavier.benito.granellgmail.com

Jian Liu1, M. Yan1, L. Ning1, P. Braconnot2 and S.P. Harrison3

Nanjing, China, 26-30 October 2020

The Paleoclimate Modelling Intercomparison Project 2020 Conference (pastglobalchanges.org/calendar/26947), conducted in a hybrid format at Nanjing Normal University and by Zoom, was the 11th event of the PMIP workshop series initiated in 1991 in Collonges-la-Rouge, France. The major aim of the PMIP2020 Conference was to bring the whole community together once again to discuss progress during the fourth phase of PMIP (PMIP4) since the last meeting in Stockholm in 2017.

Major foci of this meeting were the first results from PMIP4/CMIP6 model evaluations, new ideas on the use of proxy system modeling in PMIP, and reviewing new approaches to reconstruct climate quantitatively for comparison with model simulations. Time was also allotted to other PMIP4 activities, including but not limited to climate transitions, abrupt events, climate variability, and their linkages with changes in climate mean states.

About 300 participants from more than 20 countries attended the conference, with more than 130 presentations (for a selection of results, see Fig. 1). A PMIP overview highlighted new results from PMIP working groups on climate sensitivity, monsoons, sea ice, and ENSO. These studies used results from the Pliocene Model Intercomparison Project (PlioMIP), the Last Interglacial (LIG), the Last Glacial Maximum (LGM), the mid-Holocene, and model-data comparisons.

Figure 1: Example of new results from some of the PMIP4-CMIP6 publications for PlioMIP (Haywood et al. 2020; Brierley et al 2020). For more examples, see the PMIP special issue (GMD topical editors 2021).

Four scientific sessions were organized to provide complementary views from all PMIP activities on monsoons, climate sensitivity, transient experiments, and ocean and internal variability. Online discussions of posters and comments on different analyses were designed to identify new results that could fuel new collaborations and feed into the PMIP joint special issue of Global Model Development and Climate of the Past (pmip.lsce.ipsl.fr/outcome/special_issue). Three keynote speakers (Dr. Yongjin Wang from Nanjing Normal University, China; Dr. Steven Sherwood from University of New South Wales, Australia; and Dr. Marie Kapsch from Max Planck Institute for Meteorology, Germany) gave talks in the monsoon session, climate sensitivity and feedbacks session, and transient session, respectively. The keynote speakers highlighted new scientific advances that should be considered as part of the PMIP4 analysis plan. A discussion of new paleoclimate results that would be relevant to consider in the ongoing IPCC report was also organized with some of the IPCC WG1 lead and contributing authors.

On the final day of discussions, the eight PMIP working group leaders summarized the progress, major findings, and potential future research topics based on the presentations and discussions from the four sessions. Several grand challenges were also proposed by the Chinese paleoclimate modeling community, including (1) glacial ocean tracer modeling, (2) possible changes in equilibrium climate sensitivity with different background climate, (3) evolution of glaciers over the Tibetan Plateau during the glaciation, (4) global climate responses to land-use and cover change (LUCC) since 21 kyr BP, and (5) multiscale climate variability driven by different forcings during the Holocene.

It was suggested that a new working group (named paleo-monsoon) should be initiated, based on wide research interests on paleo-monsoon variability and new research directions made possible by long transient simulations. Some of the scientific goals of the paleo-monsoon working group would be to: improve the understanding of physical processes within global and regional monsoon systems during the past periods (e.g. the last 2 kyr, Holocene, LGM, LIG); differentiate between the contributions from internal variability and external forcings on multi-timescale variabilities of global monsoon systems; and strengthen model-data comparisons on paleo-monsoon systems. This paleo-monsoon working group would be led by Jian Liu, and will help to facilitate collaborations with other MIPs, especially the Global Monsoons Model Intercomparison Project (GMMIP), which focuses on modern and future monsoon variability. Also, the paleo-monsoon working group will help to improve communications between the modeling and observational communities.

Figure 2: Participants of the hybrid PMIP2020 Conference.

Acknowledgements

The PMIP2020 Conference was co-sponsored by National Natural Science Foundation of China (Grant No. 41942033); School of Geography, Nanjing Normal University; Institute of Earth Environment, Chinese Academy of Sciences; Institute of Atmospheric Physics, Chinese Academy of Sciences; and the Pilot National Laboratory for Marine Science and Technology (Qingdao). Support was also provided by Laboratoire des Sciences du Climat et de l'Environnement (France) for the online meetings and technical solutions to promote interactive tools for poster sessions and online comments. The local organizing committee thank the scientific committee, the PMIP working group leaders, as well as the early-career scientists for their involvement in the preparation and smooth running of this challenging conference.

affiliations

1School of Geography, Nanjing Normal University, China

2LSCE/IPSL, CEA-CNRS-UVSQ, University Paris-Saclay, France

3School of Archaeology, Geography and Environmental Science, University of Reading, UK

contact

Jian Liu: jliunjnu.edu.cn

references

Brierley et al (2020) Clim Past 16: 1847-1872

Haywood et al. (2020) Clim Past 16: 2095-2123

GMD topical editors (eds) (2021) Paleoclimate Modelling Intercomparison Project phase 4 (PMIP4) (CP/GMD inter-journal SI), Geosci Model Dev

Laurie Menviel1, E. Capron2 and R. Ivanovic3

Online, 10 and 12 November 2020

The PAGES-PMIP working group on Quaternary Interglacials (QUIGS; pastglobalchanges.org/quigs) and INQUA PALCOM project (https://inqua.org/commissions/palcom) on Terminations Five to Zero (TV-T0) held a virtual meeting on "Glacial terminations: processes and feedbacks" on 10 and 12 November 2020 (pastglobalchanges.org/calendar/2020/127-pages/2054). The meeting focused on the latest data and modeling results on the largest global climate changes of the Quaternary: the glacial-interglacial transitions, also referred to as terminations (Fig. 1).

Figure 1: (A) Marine benthic foraminifera δ18O representing ice-sheet volume (Lisiecki and Raymo 2005); (B) Antarctic surface temperature reconstruction from the EPICA Dome C ice core (Jouzel et al. 2007); (C) composite atmospheric CO2 record from Antarctic ice cores (Bereiter et al. 2015). Vertical yellow bars highlight TV-TI.

This first QUIGS-PALCOM virtual meeting, which featured 33 talks, was attended by 70 scientists during both three-hour sessions. The sessions were scheduled so that scientists from across the world could attend at least one session at a convenient time, and the full meeting was recorded. Early-career researchers presented 75% of the talks, thus giving them a great opportunity to present their research to a large group of international experts.

Talks were mainly presented within breakout sessions focusing on (1) deglacial changes in the carbon cycle, (2) deglacial climate and ice-sheet dynamics, and (3) deglacial vegetation dynamics. Most presentations focused on TI (~18–10 thousand years before present; kyr BP) but some also presented results on TII (~140–129 kyr BP) and on older terminations. A few presentations took the broader perspective of the last few million years.

Terminations V to I were interrupted by millennial-scale variability, with a weakening of the Atlantic Meridional Overturning Circulation (AMOC; e.g. McManus et al. 2004; Cheng et al. 2016). New paleo proxy records from the Atlantic Ocean were presented, confirming the occurrence of significant AMOC weakening during TI and TII, while Southern Ocean ventilation was enhanced.

Latest modeling work on Termination I showed that coupled climate models, forced by deglacial ice-sheet evolution and associated meltwater routing, simulate the millennial-scale variability identified in paleorecords, but the simulated timing of these events is not correct. Hence, work remains to better understand the processes involved in the deglacial millennial-scale variability. In addition, some processes currently not taken into account in ice-sheet modeling, such as tidal amplitude and its impact on glacier drainage, could lead to rapid ice-stream deglaciation driven by instability processes.

Talks on deglacial changes in the carbon cycle highlighted the lack of consensus regarding the contribution of the different processes governing the deglacial atmospheric CO2 concentration increase, i.e. temperature, sea ice, iron fertilization, ocean circulation, and the terrestrial biosphere. Additional proxy records and modeling are still needed.

Discussions mainly focused on (1) the importance of feedbacks during terminations, and particularly the processes leading to the CO2 rise, given the role of the atmospheric CO2 increase in the deglacial temperature rise; and (2) the potential misrepresentation of deglacial ice-sheet history, including retention and routing of the meltwater into the appropriate coastal regions, or inappropriate sensitivity of climate models to external forcings.

The meeting highlighted the need to improve our understanding of the deglacial sequence of events, including better constraints on the demise of glacial ice sheets and the associated meltwater routing, the drivers and role of millennial-scale variability, and the processes driving the measured atmospheric CO2 concentration increase. Additional paleorecords and modeling studies on TII-TV are needed, as they present additional case studies with different climate background and forcing and could thus provide constraints on deglacial processes and feedbacks. TIII (~250 kyr BP) is a particularly interesting case, as changes during this interval are among the fastest over the past 800 kyr, and the millennial-scale dynamics appear to be different compared to other terminations (Cheng et al. 2016; Obrochta et al. 2014).

Robust chronologies for paleoclimatic records are essential in order to decipher the sequence of changes in climate, ice sheets, and the carbon cycle with respect to orbital forcing during glacial terminations. Although more challenging, this is especially true for TII-TV, where radiocarbon dating is not available. Such accurate chronologies are also crucial for robust model-data comparisons.

The joint in-person PAGES QUIGS-INQUA PALCOM TV-T0 workshop "Glacial terminations: processes and feedbacks" is currently scheduled for 21-23 September 2021 in Cassis, France (pastglobalchanges.org/calendar/2021/127-pages/1992). It will focus on understanding whether the deglacial sequence of events influence the following interglacial. The causes for the observed differences between TI and TII will also be discussed in detail.

affiliationS

1Climate Change Research Centre, University of New South Wales, Sydney, Australia

2Université Grenoble Alpes, CNRS, IRD, IGE, France

3School of Earth and Environment, University of Leeds, UK

contact

Laurie Menviel: l.menvielunsw.edu.au

references

Bereiter B et al. (2015) Geophys Res Lett 42: 542-549

Cheng H et al. (2016) Nature 534: 640-645

Jouzel J et al. (2007) Science 317: 793-796

Lisiecki LE, Raymo ME (2005) Paleoceanography 20: PA1003

McManus JF et al. (2004) Nature 428: 834-837

Obrochta SP et al. (2014) Earth Planet Sci Lett 406: 198-212

Émilie Saulnier-Talbot1, N. Dubois2 and J. Boyle3

The recently launched Human Traces working group (pastglobalchanges.org/human-traces) aims to bring together scientists from various fields whose work examines archives of anthropogenic activity in the environment. The main goal of the working group is to assemble a shared community resource of Holocene stratigraphic archives optimized to assess drivers and responses to human impacts on the environment and to identify periods of stability and change leading up to the Anthropocene epoch.

In 2019, the Subcommission on Quaternary Stratigraphy voted that the Anthropocene should be treated as a formal chronostratigraphic unit defined by a Global Boundary Stratotype Section and Point (GSSP), to be placed within the 20th century. This vote ended the "Anthropocene" debate, but left the long legacy of pre-Anthropocene human impacts unchanged. Although defining a global "golden spike" has chronostratigraphic value, it may lead to the assumption that all major environmental impacts by human activities are recent. A mid-20th century start to the Anthropocene does not represent the varied history of human activity with regionally asynchronous impacts on the environment that manifested dissimilarly in different parts of the world. Substantial pre-Anthropocene impacts, which can be traced back several thousands of years, and a quantitative understanding of them is essential to managing the planet's resources with the goal of moving towards sustainability.

Lake sediments and other stratigraphic archives such as ice cores serve as long-term records of natural variability and human-induced changes (Fig. 1), making it possible to assess environmental responses to change on various timescales and to link them with either climatic or anthropogenic drivers (Mills et al. 2017). They also allow us to define targets and reference conditions for ecosystem management and conservation, providing a longer-term perspective for recent global changes in the context of the Anthropocene. However, there is still a paucity of long-term environmental regional data, and a global synthesis of human impacts recorded in stratigraphic archives is also lacking.

Figure 1: Human traces in sediment archives reflect the history of anthropogenic activities.

Scientific goals and activities

Human Traces will focus its scientific activities on collecting and analyzing evidence of the long legacy and build-up of pre-Anthropocene human impacts on the environment with the overarching goal of addressing knowledge gaps about spatial and temporal variations in early human impacts (Dubois et al. 2018). Integral to this work will be the creation of a suitable database of long-term evidence of human impacts from the paleorecord, developed following wide consultation with interested parties.

Activities of the working group will include regular online meetings (every three months) in order to ensure the progress of activities and exchange of information in preparation for in-person workshops. These yearly, if possible, workshops will allow for online participation as well. Meetings and workshops will focus on the identification of the most desirable data types, the collection and quality control of data, database creation, as well as working on crafting of manuscripts based on specific questions relating to various pre-Anthropocene environmental impacts around the world. Summer schools will also be held to foster networking for graduate students, postdocs, and early-career scientists interested in investigating anthropogenic environmental impacts in natural archives at various spatial and temporal scales.

Upcoming meetings and workshops

Our first meeting will be held online in May 2021 (pastglobalchanges.org/calendar/2021/127-pages/2118). An ongoing survey regarding population of the database will be developed and sent out to the PAGES community. The second meeting, focused on the theme: "What is a human impact/trace in a record of broad interest?" and planned for September 2021 (pastglobalchanges.org/calendar/2021/127-pages/2123), will initiate exchanges with other PAGES working groups that also focus on human dimensions: LandCover6k (pastglobalchanges.org/landcover6k), Paleoclimate and the Peopling of the Earth (PEOPLE 3000; pastglobalchanges.org/people3000), and Integrating diverse knowledge systems for environmental policy (DiverseK; pastglobalchanges.org/diversek).

An in-person workshop, specific to lake- and coastal-sediment records, is planned in March 2022, in association with the International Paleolimnology Congress in Bariloche, Argentina, and an interdisciplinary workshop will be held in association with the PAGES Open Science Meeting in Agadir, Morocco, in May 2022. Visit our webpage for more information and to stay up to date: pastglobalchanges.org/science/wg/human-traces/meetings

You can also follow the Human Traces working group on social media!

Twitter: @HTraces

Facebook: facebook.com/HTraces

affiliationS

1Départements de biologie et de géographie, Université Laval, Québec, Canada

2Oberflächengewässer, SURF, EAWAG, Kastanienbaum, Switzerland

3Department of Geography and Planning, University of Liverpool, UK

contact

Nathalie Dubois: nathalie.duboiseawag.ch

references

Dubois N et al. (2018) Anthr Rev 5: 28-68

Mills K et al. (2017) WIREs Water 4: e1404

Daniele Colombaroli1, M. Coughlan2, Q. Cui3, C. Kulkarni4, J. Mistry1 and E. Razanatsoa5

There is a growing need for more sustainable approaches to tackle future environmental and human livelihood challenges, including biodiversity losses following land-use intensification, and climate impacts under future warmer conditions (Fischer et al. 2018). Conservation plans often lack the full knowledge base to address such challenges (Fig. 1), resulting in conflicts between restoration targets and people's needs. For example, management policies such as fire suppression often contrast with traditional fire-use practices to sustain local livelihoods, or they undermine the key role of disturbance regimes for long-term ecological succession (Coughlan 2013; Kulkarni et al. 2021).

The goal of PAGES' new DiverseK working group is to merge diverse types of local and regional knowledge from science and stakeholders, and to build a more integrative, cross-disciplinary evidence base for better decision-making on environmental and social justice issues. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) only recently adopted a specific framework for Indigenous knowledge (IPBES-5/1), but the role of past legacies and long-term ecological processes are still overlooked in ecosystem management, despite their relevance (e.g. Gillson and Marchant 2014). Synergies between long-term ecology and local/Indigenous knowledge can better support conservation policies to meet landscape conservation targets, for example, by addressing the social-ecological consequences of traditional land management, or identifying the natural and anthropogenic (biocultural heritage) components that maximize biodiversity and resilience in ecosystems (Colombaroli et al. 2019). Such synergies can also help support local communities and other stakeholders as they face the most pressing environmental issues, in ways that are more socially just (Mistry and Berardi 2016).

Figure 1: Under warmer conditions and rapid land-use changes predicted for the future, tropical peatlands will require new conservation measures to mitigate the impacts of catastrophic fires (Image credit: Ibnu Fikri).

Scientific objectives

The objectives of DiverseK include methodological advancements, resolution of regional stakeholder-led challenges, and global-scale analyses. We will engage stakeholders in selected areas to foster dialog locally and use our integrated framework to discuss best practices for integration of local knowledge with other disciplines, including fire ecology, paleoecology, and dendroecology. This will provide the ground for a clearer methodological basis for diverse knowledge inclusion, which takes into account ethics and impacts of engagement with local people. Finally, we will focus on areas where conservation targets contrast with the traditional use by local communities and/or the paleoevidence (in terms of baselines, species turnover, community responses, etc.) and identify best management approaches that can be effective in local planning, drawing upon the new integrative knowledge in co-production with stakeholders.

Opportunities for using diverse knowledge systems

The mutual exchange between the scientific and stakeholder communities can provide new opportunities for conservation-based research. For paleoecologists, knowledge of contemporary local practices can aid the interpretation of paleorecords. For local people, in the context of ongoing loss of traditional knowledge, paleoevidence can support local social and environmental-justice struggles. Together, the combination of paleoecology-informed, community-owned and stakeholder-driven knowledge developed from previous collaborations within the former Global Paleofire Working Group 2 (Vannière et al. this issue) can foster dialog between the different disciplines, promoting the inclusion of ecological and socio-cultural disciplines (traditionally separated in academia) and Indigenous knowledge, which represents a key challenge for the science-policy interface (Colombaroli et al. 2019).

Upcoming activities

In the coming year, we plan a series of webinars to involve local communities, academics, and other stakeholders such as protected-area managers, in a process of intercultural exchange to inform environmental management. We welcome participants working at the interface between paleoecology and local knowledge to discuss existing approaches and develop guidelines for best practices.

Visit our website at pastglobalchanges.org/diversek and register for our mailing list to keep up to date with our activities. The working group is also supported by the Leverhulme Wildfires Centre (https://centreforwildfires.org/) and the International Paleofire Network (https://ipn.paleofire.org)

affiliations

1Department of Geography, Royal Holloway University of London, UK

2Institute for a Sustainable Environment, University of Oregon, Eugene, USA

3Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China

4Independent researcher, ckulkarnigradcenter.cuny.edu

5Plant Conservation Unit, Department of Biological Sciences, University of Cape Town, South Africa

contact

Daniele Colombaroli: Daniele.colombarolirhul.ac.uk

references

Colombaroli D et al. (2019) Policy Brief. Royal Holloway University of London, 8 pp

Coughlan MR (2013) J Ethnobiol 33: 86-104

Fischer H et al. (2018) Nat Geosci 11: 474-485

Gillson L, Marchant R (2014) Trends Ecol Evol 29: 317-25

Kulkarni C et al. (2021) J Environ Manag 283: 111957

Mistry J, Berardi A (2016) Science 352: 1274-1275