Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Wednesday 8 July - 15:00-16:30 UPMC Jussieu - ROOM 103 - Block 24/34

1101 - From the Holocene to the Anthropocene: the history of human-environmental interactions

Parallel Session

Lead Convener(s): F. Sylvestre (Institut de Recherche pour le Développement, Aix-en-Provence, France)

Convener(s): T. Hoffmann (University of Bonn, Bonn, Germany)

15:00

Man versus Climate: what we learn from paleodata on the vulnerability of tropical ecosystems

A.-M. Lézine (LOCEAN, Paris, France), S. Ivory (Institute at Brown for the Study of Environment and Society, Brown University, Providence, United States of America), F. Bassinot (Laboratoire des Sciences du Climat et de l'Environnement/IPSL, CEA-CNRS-UVSQ – UMR8212, CEA-CNRS-UVSQ – UMR8212, France), C. Hély (Institut des Sciences de l'Evolution, Montpellier, France), P. Braconnot (LSCE-IPSL, Gif-sur-Yvette, France)

Abstract details
Man versus Climate: what we learn from paleodata on the vulnerability of tropical ecosystems

AM. Lézine (1) ; S. Ivory (2) ; F. Bassinot (3) ; C. Hély (4) ; P. Braconnot (5)
(1) LOCEAN, Paris, France; (2) Institute at Brown for the Study of Environment and Society, Brown University, Providence, United States of America; (3) Laboratoire des Sciences du Climat et de l'Environnement/IPSL, CEA-CNRS-UVSQ – UMR8212, CEA-CNRS-UVSQ – UMR8212, France; (4) Institut des Sciences de l'Evolution, Isem umr cnrs 5554, ird 226, université de montpellier, ephe cirad, Montpellier, France; (5) LSCE-IPSL, Gif-sur-Yvette, France

Abstract content

The timing and amplitude of the end of the Holocene humid period and the transition toward of the present day arid/semi-arid conditions in the northern tropics has been the subject of multiple debates involving many scientists from both model and data communities. Several scenarios have been developed to discuss the abrupt or gradual character of this period and to identify the forcings at work. These debates have mostly focused on regions under the Atlantic monsoon influence with a specific emphasis on the iconic “Green Sahara”. This region is well known to have hosted flourishing prehistoric cultures evidenced by widespread archaeological remains, rock paintings and carvings and abundant tropical faunas during the Holocene. Based on paleohydrological and archaeological evidence, it has been shown that the end of the “Green Sahara” period in northern tropical Africa and the initiation of present day arid conditions in the Sahara Desert were latitudinally time transgressive with the lake phase ending from 6.5 ka (between 26 and 28°N) to 3.5 ka between 20° and 16° N.

This late Holocene climate crisis was widely recorded across the tropics. Here we present a synthesis of paleohydrological and paleoenvironmental data in two specific areas: (1) the dry northern tropics from West Africa to East India (10-30°N) to compare the behavior of the Atlantic and Indian monsoon systems at the northern edge of the present day rain belt  and the mechanisms responsible for the dramatic regime shift (humid/arid) (2) West and Central Africa to discuss the impact of this crisis on the natural ecosystems (i.e., the equatorial forest) and the adaptation of human populations.

15:15

Abrupt African Quaternary Climate and Vegetation Change

M. Claussen (Max Planck Institute for Meteorology, Hamburg, Germany), S. Bathiany (Wageningen University, Wageningen, Netherlands), V. Brovking (Max Planck Institute for Meteorology, Hamburg, Germany), S. Egerer (Max Planck Institute for Meteorology, Hamburg, Germany), V. Groner (Max Planck Institute for Meteorology, Hamburg, Germany), C. Reick (Max Planck Institute for Meteorology, Hamburg, Germany)

Abstract details
Abrupt African Quaternary Climate and Vegetation Change

M. Claussen (1) ; S. Bathiany (2) ; V. Brovking (1) ; S. Egerer (1) ; V. Groner (1) ; C. Reick (1)
(1) Max Planck Institute for Meteorology, Hamburg, Germany; (2) Wageningen University, Wageningen, Netherlands

Abstract content

Pronounced changes in African climate, specifically during the transitions between glacials and interglacials, have been found in palaeo climatic archives. Some geological records suggest abrupt climate shifts others, more gradual transitions. Here, we discuss data and simulations aiming at understanding these changes. African climate and vegetation shifts were likely induced by large changes in ice masses, ocean circulation and monsoon dynamics which, in turn, were triggered by variations in the Earth orbit around the sun and subsequent alteration of meridional insolation gradients. It is shown that abrupt change, or ‘tipping, could result from a strong feedback between vegetation and climate at different times at different locations. Moreover, strong feedback in one region can lead to ‘induced tipping’ in other, seemingly stable regions. However, the diversity of plants can affect the strength of biogeophysical feedback. Regions rich in plant diversity may stabilize the system leading to more gradual transitions. As alternative hypothesis, abrupt changes may also emerge from intrinsic threshold behaviour of hydrological systems and ecosystems. Finally, an assessment is made to which extent abrupt climate and vegetation changes in this region are likely to happen in the future.

15:30

High-resolution paleolimnology opens new management perspectives for lakes adaptation to climate warming

M. Perga (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), V. Frossard (UMR CARRTEL, University of Savoie-Mont Blanc, Chambéry, France), J.-P. Jenny (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), B. Alric (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), F. Arnaud (EDYTEM, University of Savoie-Mont Blanc, Chambéry, France), V. Berthon (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), L. Domaizon (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), C. Giguet-Covex (EDYTEM, University of Savoie-Mont Blanc, Chambéry, France), M. Magny (UMR CHRONO-ENVIRONNEMENT, Besançon, France), M. Manca (CNR-ISE, Verbania-Pallanza, Italy), A. Marchetto (CNR-ISE, Verbania-Pallanza, Italy), L. Millet (UMR CHRONO-ENVIRONNEMENT, Besançon, France), C. Paillès (Aix-Marseille Université, CNRS, IRD, UM34 CEREGE, Europôle de l’Arbois, Aix en Provence, France), C. Pignol (EDYTEM, University of Savoie-Mont Blanc, Chambéry, France), J. Poulenard (EDYTEM, University of Savoie-Mont Blanc, Chambéry, France), J.-L. Reyss (LSCE, Gif sur Yvette, France), F. Rimet (INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France), F. Sylvestre (Institut de Recherche pour le Développement, Aix-en-Provence, France), P. Sabatier (EDYTEM, University of Savoie-Mont Blanc, Chambéry, France), V. Verneaux (UMR CHRONO-ENVIRONNEMENT, Besançon, France)

Abstract details
High-resolution paleolimnology opens new management perspectives for lakes adaptation to climate warming

M. Perga (1) ; V. Frossard (2) ; JP. Jenny (1) ; B. Alric (1) ; F. Arnaud (3) ; V. Berthon (1) ; L. Domaizon (1) ; C. Giguet-Covex (3) ; M. Magny (4) ; M. Manca (5) ; A. Marchetto (5) ; L. Millet (4) ; C. Paillès (6) ; C. Pignol (3) ; J. Poulenard (3) ; JL. Reyss (7) ; F. Rimet (1) ; F. Sylvestre (8) ; P. Sabatier (3) ; V. Verneaux (4)
(1) INRA, UMR CARRTEL, Université Savoie-Mont-Blanc, Thonon les Bains, France; (2) UMR CARRTEL, University of Savoie-Mont Blanc, Chambéry, France; (3) EDYTEM, University of Savoie-Mont Blanc, Chambéry, France; (4) UMR CHRONO-ENVIRONNEMENT, Besançon, France; (5) CNR-ISE, Verbania-Pallanza, Italy; (6) Aix-Marseille Université, CNRS, IRD, UM34 CEREGE, Europôle de l’Arbois, Aix en Provence, France; (7) LSCE, Gif sur Yvette, France; (8) Institut de Recherche pour le Développement, CEREGE, Aix-en-Provence, France

Abstract content

Varved lake sediments provide opportunities for high-resolution paleolimnological investigations that may extend monitoring surveys in order to target priority management actions under climate warming. This paper provides the synthesis of an international research program relying on >150 years-long, varved records for three managed perialpine lakes in Europe (Lakes Geneva, Annecy and Bourget). The dynamics of the dominant, local human pressures, as well as the ecological responses in the pelagic, benthic and littoral habitats were reconstructed using classical and newly developed paleo-proxies. Statistical modelling achieved the hierarchization of the drivers of their ecological trajectories.

All three lakes underwent different levels of eutrophication in the first half of the XXth century, followed by re-oligotrophication. Climate warming came along with a 2°C increase in air temperature over the last century, to which lakes were unequally thermally vulnerable. Unsurprisingly, phosphorous concentration has been the dominant ecological driver over the last century. Yet, other human-influenced, local environmental drivers (fisheries management practices, river regulations) have also significantly inflected ecological trajectories. Climate change has been impacting all habitats at rates that, in some cases, exceeded those of local factors. The amplitude and ecological responses to similar climate change varied between lakes, but, at least for pelagic habitats, rather depended on the intensity of local human pressures than on the thermal effect of climate change. Deep habitats yet showed higher sensitivity to climate change but substantial influence of river flows. As a consequence, adapted local management strategies, fully integrating nutrient inputs, fisheries management and hydrological regulations, may enable mitigating the deleterious consequences of ongoing climate change on these ecosystems.

15:45

The Mediterranean Basin in a warmer and drier world: what can we learn from the past?

J. Guiot (CNRS, Aix-en-Provence, France), D. Kaniewski (University of Toulouse 3, Toulouse, France)

Abstract details
The Mediterranean Basin in a warmer and drier world: what can we learn from the past?

J. Guiot (1) ; D. Kaniewski (2)
(1) CNRS, CEREGE, Aix-en-Provence, France; (2) University of Toulouse 3, Ecolab, Toulouse, France

Abstract content

 

Since the late-nineteenth century, surface temperatures have non-uniformly increased worldwide. The repercussion of the global warming in drylands, such as in the Mediterranean, may become a main source of concern in a near future, as it is often accompanied by increased droughts, that will severely degrade water supply and quality. History shows that access to water resources has always presented a challenge for societies around the Mediterranean throughout the Holocene (roughly the last 10,000 years). Repeatedly, adverse climate shifts seem to have interacted with social, economic and political variables, exacerbating vulnerabilities in drier regions. We present a reconstruction of the Holocene climate in the Mediterranean Basin using an innovative method based on pollen data and vegetation modeling.

The method consistsin calculating the inputs of the vegetation model so that the outputs fit the pollen data, using a Bayesian framework. This model inversion is particularly suited to deal with increasing dissimilarities between past millennia and the last century, especially due to a direct effect of CO2 on vegetation. The comparison of far past and last century shows that the intensity of century-scale precipitation fall, amplified by higher temperatures and then evapotranspiration, is unmatched over the last 10,000 years. The recent climatic change is then unprecedented during the last 10,000 years in the Mediterranean Basin. We show also that adverse climate shifts are often correlated with the decline or collapse of Mediterranean civilizations, particularly in the eastern Basin. The main consequence is that, over the next few decades, Mediterranean societies are likely to be much more critically vulnerable to climate change, than at any dry period of the past.

16:00

Long-term ecological dynamics of an alpine lacustrine ecosystem during the Holocene in the French Alps (Lake Petit, 2200 m a.s.l): regime shift and resilience of algal communities

E. Brisset (Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France), C. Paillès (Aix-Marseille Université, CNRS, IRD, UM34 CEREGE, Europôle de l’Arbois, Aix en Provence, France), F. Guiter (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), F. Sylvestre (Institut de Recherche pour le Développement, Aix-en-Provence, France), F. Ruaudel (Aix-Marseille University, CNRS , Aix-en-Provence, France), C. Miramont (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), R. Cartier (Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France)

Abstract details
Long-term ecological dynamics of an alpine lacustrine ecosystem during the Holocene in the French Alps (Lake Petit, 2200 m a.s.l): regime shift and resilience of algal communities

R. Cartier (1)
(1) Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France

Abstract content

Multidisciplinary investigations on lake sediments in the Mediterranean Alps enable tracking back the dynamics of lacustrine ecosystems as well as their response to human activities and climate change. Such external forcing may lead to a variety of lake responses, ranging from gradual changes to sudden regime shifts. Sediments from Lake Petit (2200 m a.s.l., Southern French Alps) were particularly relevant for a coupled palaeoecology of landscape and palaeolimnology study providing (1) exceptional richness in preserved bio-indicators and (2) a well-studied context with archaeological, palynological and geochemical data (Brisset et al., 2013).

The lacustrine ecosystem has been reconstructed for the last 5000 years using microfossil analysis (diatoms and Pediastrum) and organic matter composition of sediments (TOC, TN) (Cartier et al., in press):

  • From 4800 to 4300 cal. BP, Lake Petit was a stable diatom productive water body dominated by alkaliphilous diatoms. Nutrients were supplied by the chemical weathering of podzols that developed under conifer woodlands. This overall stability was suddenly interrupted at 4200 cal. BP by a major detrital pulse that triggered a drop in diatom productivity and diversity probably climate-linked with the “4.2 ka event”;
  • From 4100 to 2400 cal. BP, diatom productivity decreased whereas the algae Pediastrum developed. Diatom assemblages subjected to terrigenous inputs from continuous erosion of pasture soils, were more diversified;
  • Finally, from 2400 cal. BP to the present day, diatom assemblages reveal a slight acidification and nutrient enrichment of waters concomitant with increasing human pressure in the catchment.

Results obtained at Lake Petit provide a good example of abrupt regime shift in mountain systems in response to rapid climatic event, and further by incremental change triggered by human activities beyond critical threshold.

16:10

How humans feed flood: lessons from the past

E. Brisset (Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France), F. Guiter (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), C. Miramont (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), T. Troussier (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), Y. Poher (Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France), E. Anthony (Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France)

Abstract details
How humans feed flood: lessons from the past

E. Brisset (1) ; F. Guiter (2) ; C. Miramont (2) ; T. Troussier (2) ; Y. Poher (2) ; E. Anthony (1)
(1) Aix-Marseille Université, CNRS, IRD, Collège de France, UM 34 CEREGE, Aix-en-Provence, France; (2) Aix-Marseille Université, CNRS, IRD, UMR 7263 IMBE, Aix-en-Provence, France

Abstract content

Future projections on alpine climate changes suggest that more hydrological extreme can be expected to increase the river flood risk in this region. During mountain-river floods, the amount of sediment rushing down slopes constitutes a threat for society, burring floodplains and devastating people and infrastructures. This hydro-geological phenomenon poses hazards in mountainous areas of the world because they occur on steep slopes having abundant sediment available. By promoting land degradation, human are susceptible to modify the sensitivity of landscapes to natural hazard. As a result, it is crucial to investigate how humans have transformed geomorphic response to river flood on historic timescale, and what this means for our present and future. Here we explore since when mountain-river flood are linked to human agencies and to what extent man influence nature.

To address these issues, we examined the geomorphic response during flood events to vegetation cover and land-use changes over the last 7400 years for a large mountain lake of the European Alps, the Lake Allos (44°14’N, 6°42’35’’E, 2230 m a.s.l.). Indeed, the sediments of the Lake Allos are a reliable geological archive to reconstruct flood deposits calendar over long time scale as their suspension load produce a distinct detrital layer contrasting to background sedimentation allowing their identification, counting and dating.

Our results show that the progressive increase in human activities (domestic livestock grazing) was not followed by a progressive increase in erosion at Allos. At 2000 cal. BP, the flood record shows an abrupt transition in sediment load and in event frequency which have been multiplied by a factor of four. Since this date, precipitations of higher intensity were able to mobilise and transport larger amount of sediment and precipitations of lesser intensity were more frequently able to trigger sediment inputs.

These results indicate that a threshold in the sensitivity to erosion in the source area were attaint due to several millennia of human pressure. These results also argue that humans, by changing sensitivity of landscapes for their activities, have considerably amplified geomorphic responses to natural hazards.

16:20

Interdisciplinary and transboundary work to rebuilt extreme hydrological events in the Rhine Graben (France – Germany - Switzerland) during the last six centuries (TRANSRISK and TRANSRISK² Programs)

B. Martin (CRESAT, mulhouse, France), R. Glaser (Institut fur Physische Geographie, Freiburg, Germany), F. Giacona (CRESAT, mulhouse, France), N. Holleville (CRESAT, mulhouse, France), I. Himmelsbach (Institut fur Physische Geographie, Freiburg, Germany), B. Furst (CRESAT, mulhouse, France), J. Schönbein (Institut fur Physische Geographie, Freiburg, Germany), L. With (CRESAT, mulhouse, France), P. Wassmer (Laboratoire de Géographie Physique, paris, France), M.-C. Vitoux (CRESAT, mulhouse, France)

Abstract details
Interdisciplinary and transboundary work to rebuilt extreme hydrological events in the Rhine Graben (France – Germany - Switzerland) during the last six centuries (TRANSRISK and TRANSRISK² Programs)

B. Martin (1) ; R. Glaser (2) ; F. Giacona (1) ; N. Holleville (1) ; I. Himmelsbach (2) ; B. Furst (1) ; J. Schönbein (2) ; L. With (1) ; P. Wassmer (3) ; MC. Vitoux (1)
(1) CRESAT, Université de haute - alsace, mulhouse, France; (2) Institut fur Physische Geographie, Albert ludwig university, Freiburg, Germany; (3) Laboratoire de Géographie Physique, Université paris 1 panthéon-sorbonne, paris, France

Abstract content

The franco - german projects TRANSRISK (2008 – 2011) and TRANSRISK² (2014 – 2017) have made it possible to elaborate a comparative chronology of the floods in the area of the Upper Rhine over a long period (1480 – 2015), paying attention to the description of the events (characteristics, climatic and human causes, consequences) as well as to the management by those in charge at the local scenes of the risk. The objective was to understand the evolutions and to make comparisons at all scales, particularly between France and Germany. This interdisciplinary work (historians, geographers, anthropologists, sociologists, linguists) has been done by researchers from Germany and France on both side of the Rhine between Basel and Strasbourg. The interest of that research is twofold:

  • It is carried out on a territory which is limited and relatively homogeneous, but divided by borders between three nations, Switzerland, France and Germany, and these two last countries have been three times at war between 1870 and 1945.
  • It is really concerning a major stake of territorial management: the prevention of floods, a hazard not well known in its spatio-temporal characteristics on account of the wars and of the many political and administrative changes that this territory has gone through.

The researches in the archives have thus made it possible to establish a database including over 3.000 events related to the floods between 1480 and nowadays, involving the Rhine, and 13 tributaries on both side on the border. The most important of those floods have been mapped, classed and compared, revealing at the end a real underestimation of flood risk and the necessity of building new flood scenarios for the future. That’s why these research programs are involved into many actions of flood risk management, concerning, for example, memory and risk culture, as well as modelling of extreme events in a historic – progressive approach.

About scenarios, if no pattern of coherent and synchronized evolution appears for all the rivers, the reconstruction of the underlying climatic conditions permits to determine 4 broad types of situations favourable to flooding in that area. And, facing an extreme situation that has already occurred yet in a past not so far away, neither the actors of prevention, nor the people are really prepared. That’s also the reason why we have developed a website (linked to social networks) to share information on historical floods (www.orrion.fr), even if floods need a real contextualization to try to make them comparable over time and space. But the chronologies demonstrate, on the one hand, the importance of conditions on a local scale, and, on the other hand, all the aggravating or lessening role of human factors. They generate variations in time and space of the vulnerability to floods, which are manifest on different scales, revealing in particular a real “borderline effect” between France and Germany.

What those studies also point out, however, is that the fight against floods has been at all times the manifestation of political will, mostly a reaction to disaster, and thus has been constantly re-defined in any context of important changes in the political structures. This is of course a lesson for the future.