Marie-France Loutre - Academia.edu (original) (raw)

Papers by Marie-France Loutre

Encyclopedia of Quaternary Science, 2007

Current Opinion in Environmental Sustainability, 2021

An increasing number of voices highlight the need for science itself to transform and to engage i... more An increasing number of voices highlight the need for science itself to transform and to engage in the co-production of knowledge and action, in order to enable the fundamental transformations needed to advance towards sustainable futures. But how can global sustainability-oriented research networks engage in co-production of knowledge and action? The present article introduces a strategic tool called the 'network compass' which highlights four generic, interrelated fields of action through which networks can strive to foster coproduction. It is based on the networks' particular functions and how these can be engaged for co-production processes. This tool aims to foster self-reflection and learning within and between networks in the process of (re)developing strategies and activity plans and effectively contributing to sustainability transformations.

Climate of the Past, 2019

This PAGES (Past Global Changes) 2k (climate of the past 2000 years working group) special issue ... more This PAGES (Past Global Changes) 2k (climate of the past 2000 years working group) special issue of Climate of the Past brings together the latest understanding of regional change and impacts from PAGES 2k groups across a range of proxies and regions. The special issue has emerged from a need to determine the magnitude and rate of change of regional and global climate beyond the timescales accessible within the observational record. This knowledge also plays an important role in attribution studies and is fundamental to understanding the mechanisms and environmental and societal impacts of recent climate change. The scientific studies in the special issue reflect the urgent need to better understand regional differences from a truly global view around the PAGES themes of "Climate Variability, Modes and Mechanisms", "Methods and Uncertainties", and "Proxy and Model Understanding".

ABSTRACT The Last Interglacial warm period (LIG, ~130 to 114 kyr BP), for which increasingly bett... more ABSTRACT The Last Interglacial warm period (LIG, ~130 to 114 kyr BP), for which increasingly better proxy data have recently become available, is the most recent analogue for future warming in the climate history of the Earth. It represents a real-world test case for the stability of the Greenland and Antarctic ice sheets, both thought to have lost considerable amounts of ice compared to their present-day configuration. We use the Earth system model of intermediate complexity LOVECLIM version 1.3 to perform transient simulations over the LIG forced with changes in orbital parameters and greenhouse gases. The model includes thermomechanically coupled models of the Greenland and Antarctic ice sheets, which are interactively coupled with the atmosphere and ocean component. We present modelling results with focus on the evolution of the polar ice sheets and their sea-level contribution, ice-climate interactions and inter-hemispheric coupling. In preliminary experiments LOVECLIM simulates annual mean temperature and summer temperature anomalies over the present-day ice covered area on Greenland relative to the present day that peak at 2.5 °C and 4 °C, respectively. The Greenland ice sheet sea-level contribution peaks at 3 m mainly in response to increased summer temperatures and to a smaller extent due to reduced precipitation. The evolution of the Antarctic ice sheet over the LIG with a peak sea-level contribution of 3.8 m is governed by changes in global sea-level stand and melting below the ice shelves that control the grounding-line position, while changes in surface melting have a negligible effect.

Earth's Climate and Orbital Eccentricity: The Marine Isotope Stage 11 Question, 2003

ABSTRACT

Developments in Quaternary Sciences, 2007

Tellus A, 2002

Seventy-one sensitivity experiments have been performed using a two-dimensional sectoraveraged gl... more Seventy-one sensitivity experiments have been performed using a two-dimensional sectoraveraged global climate model to assess the potential impact of six different factors on the last millennium climate and in particular on the surface air temperature evolution. Both natural (i.e, solar and volcanism) and anthropogenically-induced (i.e. deforestation, additional greenhouse gases, and tropospheric aerosol burden) climate forcings have been considered. Comparisons of climate reconstructions with model results indicate that all the investigated forcings are needed to simulate the surface air temperature evolution. Due to uncertainties in historical climate forcings and temperature reconstructions, the relative importance of a particular forcing in the explanation of the recorded temperature variance is largely function of the forcing time series used. Nevertheless, our results indicate that whatever the historical solar and volcanic reconstructions may be, these externally driven natural climate forcings are unable to give climate responses comparable in magnitude and time to the late-20th-century temperature warming while for earlier periods combination of solar and volcanic forcings can explain the Little Ice Age and the Medieval Warm Period. Only the greenhouse gas forcing allows the model to simulate an accelerated warming rate during the last three decades. The best guess simulation (largest similarity with the reconstruction) for the period starting 1850 AD requires however to include anthropogenic sulphate forcing as well as the impact of deforestation to constrain the magnitude of the greenhouse gas twentieth century warming to better fit the observation. On the contrary, prior to 1850 AD mid-latitude land clearance tends to reinforce the Little Ice age in our simulations.

Space Science Reviews, 2007

Links between climate and Earth's orbit have been proposed for about 160 years. Two decisive adva... more Links between climate and Earth's orbit have been proposed for about 160 years. Two decisive advances towards an astronomical theory of palaeoclimates were Milankovitch's theory of insolation (1941) and independent findings, in 1976, of a double precession frequency peak in marine sediment data and from celestial mechanics calculations. The present chapter reviews three essential elements of any astronomical theory of climate: (1) to calculate the orbital elements, (2) to infer insolation changes from climatic precession, obliquity and eccentricity, and (3) to estimate the impact of these variations on climate. The Louvain-la-Neuve climate-ice sheet model has been an important instrument for confirming the relevance of Milankovitch's theory, but it also evidences the critical role played by greenhouse gases during periods of low eccentricity. It is recognised today that climatic interactions at the global scale were involved in the processes of glacial inception and deglaciation. Three examples are given, related to the responses of the carbon cycle, hydrological cycle, and the terrestrial biosphere, respectively. The chapter concludes on an outlook on future research directions on this topic.

Quaternary Science Reviews, 2010

The calculation of the total solar energy received during a given interval of time over the year ... more The calculation of the total solar energy received during a given interval of time over the year requires more attention than the calculation of the daily incoming solar radiation (daily insolation). It depends indeed upon whether the time interval is defined in terms of the true longitude or of the calendar date. The details of such a calculation based on elliptic integrals and on the sum of the daily irradiations are given in this paper. Numerical examples show the very high accuracy of both methods. The analytical expression and the spectral analysis of the long-term variations of such irradiation received during any time interval over the year show that they depend almost exclusively upon obliquity with a very small contribution of eccentricity, not at all upon precession. The eccentricity signal comes from the variation of the so-called solar constant through the variation of the mean distance from the Earth to the Sun. The precession signal is eliminated through the second law by Kepler. The correlation between total irradiation and obliquity reverses its sign at a specific latitude of the summer hemisphere which is a function of the selected time interval. At this latitude the obliquity signal disappears and only a pure eccentricity signal is left in the total irradiation, but with a very weak amplitude. Amplitude of the continuous wavelet transforrm shows that the amplitude variation of both the daily irradiance (mostly precession) and of the total irradiation (obliquity) vanishes around the Mid-Pleistocene Transition.

Paleoceanography, 2005

Investigations during the last 25 years have demonstrated that the astronomically related 19‐, 23... more Investigations during the last 25 years have demonstrated that the astronomically related 19‐, 23‐, and 41‐kyr quasiperiodicities actually occur in long records of the Quaternary climate. However, the same investigations also identified the largest climatic cycle as being about 100 kyr long. As the 100‐kyr variations in standing insolation due to eccentricity change are too small, they cannot be the direct cause of the ice ages. This is the reason why most of the modeling studies attempting to explain the relation between the astronomical forcing and climatic change have focused on this 100‐kyr cycle. In this paper, we will show the astronomical origin of the periods at about 100 kyr that characterize the long‐term variations of eccentricity, of its first derivative, of the frequency modulation of obliquity, and of the inclination of the Earth's orbit on the invariable plane of reference. Five independent values are found between 95 and 107 kyr, and a wavelet signature is sugges...

Nature, 2001

Celestial mechanics has long been used as an aid for interpreting geological records. The complim... more Celestial mechanics has long been used as an aid for interpreting geological records. The compliment is being repaid through analysis of Mediterranean sediments.

Journal of Paleolimnology, 2007

This paper introduces the background and main results of a research project aimed at unravelling ... more This paper introduces the background and main results of a research project aimed at unravelling the paleolimnological and paleoclimatological history of Lago Puyehue (408 S, Lake District, Chile) since the Last Glacial Maximum (LGM), based on the study of several sediment cores from the lake and on extensive fieldwork in the lake catchment. The longest record was obtained in an 11-m-long piston core. An age-depth model was established by AMS 14 C dating, 210 Pb and 237 Cs measurements, identification of event-deposits, and varve-counting for the past 600 years. The core extends back to 17,915 cal. yr. BP, and the seismic data indicate that an open-lake sedimentary environment already existed several thousands of years before that. The core was submitted to a multi-proxy analysis, including sedimentology, mineralogy, grain-size, major geochemistry and organic geochemistry (C/N ratio, d 13 C), loss-on-ignition, magnetic susceptibility, diatom analysis and palynology. Along-core variations in sediment composition reveal that the area of Lago Puyehue was characterized since the LGM by a series of rapid climate fluctuations superimposed on a long-term warming trend. Identified climate fluctuations confirm a.o. the existence of a Late-Glacial cold reversal predating the northern-hemisphere Younger Dryas cold period by 500-1,000 years, as well as the existence of an early southern-hemisphere Holocene climatic optimum. Varve-thickness analyses over the past 600 years reveal periodicities similar to those associated with the El Niño Southern Oscillation and the Pacific Decadal Oscillation, as well as intervals with increased precipitation, related to an intensification of the El Niño impact during the southern-hemisphere equivalent of the Little Ice Age.

Journal of Geophysical Research, 1990

The earth&amp;#39;s orbital elements involved in the astronomical theory of paleoclimates... more The earth&amp;#39;s orbital elements involved in the astronomical theory of paleoclimates are the eccentricity, the obliquity, and the climate precession. The sensitivity of their frequencies to the dynamical ellipticity of the earth is investigated for the Quaternary period. According to the model used, the modification of the distribution of the masses on and inside the earth during full glacial conditions

Journal of Geophysical Research: Atmospheres, 1993

Solar irradiance received on a horizontal surface depends on the solar output, the semimajor axis... more Solar irradiance received on a horizontal surface depends on the solar output, the semimajor axis of the elliptical orbit of the Earth around the sun (a), the distance from the Earth to the sun (r), and the zenith distance (z). The spectrum of the distance, r, for a given value of the true longitude, λ, displays mainly the precessional periods and, with much less power, half precession periods, eccentricity periods, and some combination tones. The zenith distance or its equivalent, the elevation angle (E), is only a function of obliquity (ϵ) for a given latitude, ϕ, true longitude, and hour angle, H. Therefore the insolation at a given constant value of z is only a function of precession and eccentricity. On the other hand, the value of the hour angle, H, corresponding to this fixed value of z varies with ε, except for the equinoxes, where H corresponding to a constant z also remains constant through time. Three kinds of insolation have been computed both analytically and numericall...

Geophysical Research Letters, 1998

The Roda Nilometer (Cairo, Egypt) has recorded more than 2,000 gauge readings, i.e. annual low-wa... more The Roda Nilometer (Cairo, Egypt) has recorded more than 2,000 gauge readings, i.e. annual low-water and flood levels, from A.D. 622 to the beginning of this century. Spectral analysis of the A.D622-1470 data set yields several statistically significant periodicities, for both low-water (256; 75.9; 52.6; 38; 28.9; 20.9; 18.5 and 13.4 yr) and flood levels (75.9; 33.6; 21.4; 14.7; 13.7; 9.7 and 8.1 yr). Evolutionary Multi Taper Method analysis suggests that shifts or disappearances of spectral peaks occur in sub-intervals of the studied time span. This is noticeable for the low frequency peaks in the sub-interval A.D.-950-1250 which corresponds to the Medieval Warm Period in Europe. By contrast, a remarkable time stability is observed for the 5 yr period, that could confirm the existence of a robust ENSO-like forcing during the studied period.

Earth and Planetary Science Letters, 2003

Climatic variability of the last 3 millennia in NW Iberia has been documented using high-resoluti... more Climatic variability of the last 3 millennia in NW Iberia has been documented using high-resolution pollen analysis of Vir-18 core, retrieved from the R| ¤a de Vigo (42 ‡14.07PN, 8 ‡47.37PW). The depth^age model is based on two accelerator mass spectrometry 14 C dates and three historically dated botanical events in Galicia: the expansion of Juglans and Pinus, as well as the introduction of Eucalyptus. During the last 3000 years, the relative pollen record demonstrates the occurrence of an open deciduous oak forest, indicating a humid and temperate climate in northwestern Iberia. Two-step forest reduction since 975 cal BC suggests climate as the main cause rather than major socioeconomic changes documented in historical archives. Absolute pollen influx has been compared with instrumental summer and winter temperatures and tentatively used as a proxy of short (decadal-scale) and lowamplitude (V1 ‡C) temperature variations. This new approach allows us to detect for the first time in NW Iberia the millennial-scale climatic cyclicity suggested by North Atlantic records, challenging the apparent climatic stability reflected by the relative pollen record. The Little Ice Age is recorded as low pollen influx values between 1400 and 1860 cal AD, with a cold maximum at 1700 cal AD (Maunder Minimum). The Roman and Medieval Warm Periods are detected through high pollen influx values at 250 cal BC^450 cal AD and 950^1400 cal AD, respectively.

Earth and Planetary Science Letters, 2004

Long-term climatic changes, such as glacial^interglacial cycles, are usually explained in term of... more Long-term climatic changes, such as glacial^interglacial cycles, are usually explained in term of changes in solar energy received at the top of the atmosphere. In particular, daily insolation in the high Northern Hemisphere latitudes during summer is widely used in interpreting palaeoclimate records. This insolation forcing is strongly marked by changes in precession. However, some climate variations are much more imprinted by changes in obliquity. This was the case for sea surface temperature in the North Atlantic during the Eemian period, as well as for the Vostok ice core deuterium excess history over the last 250 ka. Therefore, we investigate the insolation forcing in order to identify characteristics that could explain the observed climate response. This is mainly the case for annual mean insolation variations. Simple hypotheses for how this forcing could act on climate are also suggested, these being mainly related to changes in the moisture transport induced by the annual insolation gradient between low and high latitudes. Along these lines, a simple conceptual model of annual mean temperature variations illustrates the role of annual mean insolation on climate.