Valérie Masson-Delmotte Dr. Valérie Masson-Delmotte Laboratoire des Sciences du Climat et de l’Environnement IPSL/CEA-CNRS UMR 1571 France If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

I am 33 years old and the mother of two little girls. Since 1998, I am head of a research group at LSCE, France, reconstructing past climate changes over the continents. My favorite tools are the water stable isotopes measured from polar ice cores or tree rings that can be simulated by climate models. These studies cover a variety of timescales (from the last decades to glacial interglacial cycles) and are conducted within French, European or international research projects such as EPICA, NorthGRIP and ISONET. I am a member of several scientific committees (French Polar Institute, NorthGRIP, CLIVAR/PAGES Intersection, ICCL/IAMAS, HOLIVAR) and a lead author of the IPCC paleoclimate chapter. I think that climate history should be a part of basic education, together with human history, and I push for this through involvement in a variety of educational projects with children and adults.

Abstract:

Dynamics of climate and water cycle changes: interest of quantitative climate reconstructions

The awareness that climate has changed in the past has emerged from our capability to date past environmental changes and quantify the magnitude of climate change together with its consequences on local ecosystems. Instrumental records are too short—at best a few centuries—to capture the full spectrum of climate variability. They have to be complemented by a variety of proxies in a variety of archives. These indirect climate indicators have to be calibrated against climatic parameters and the various sources of biases have to be identified and quantified.

Most quantitative efforts have been dedicated to the reconstruction of past temperatures. Quantitative temperature reconstructions enable us to estimate not only local climatic changes but the aggregation of local records, to provide regional to hemispheric estimates that are critical for the comparison between observed and modeled past climate changes, and to understand the mechanisms of climatic changes. Water cycle changes are deeply involved in many feedback processes within the climate system, ranging from short spatial and temporal scales associated with cloud radiative properties, to large scales associated with snow and ice albedo feedbacks.

Polar regions represent the cold point of the climate system. They are both sensitive to climate change and actors of climate change due to polar amplification processes, contributions to sea level changes, and interactions with atmospheric and ocean circulations. Several methods enable us to reconstruct past temperature changes from polar ice cores. I will show the state-of-the-art to quantify polar temperature changes at various timescales and discuss past changes in the water cycle recorded in polar ice cores. As a result of these quantitative temperature reconstructions, the capacity of coupled climate models to capture past climate changes in polar regions will be discussed.

Paper:

Past changes in climate and water cycle: A polar ice core perspective

Why are polar ice cores precious paleoclimate archives?
Polar ice cores are unique continuous archives of past snowfall and atmospheric composition including changes in greenhouse gases trapped in the air bubbles. They offer temporal resolutions varying from a season at places where the annual snow accumulation rate is quite high (Greenland, coastal Antarctica) to a few decades in the dry areas of the East Antarctic Plateau.

New deep ice cores have enables to recover expanded climate records at both poles. The East Antarctic EPICA Dome C ice core covers more than 800,000 years, two times longer than the previous Vostok record, and enables to compare a variety of glacial and interglacial (warm) periods. The north Greenland NorthGRIP ice core includes one full climatic cycle back to the previous interglacial period (123,000 years ago), and enables to study in detail the onset of the last ice age.

How can past temperature changes be estimated at polar regions?
Several methods can be used. Since the 1960s, it has been observed that the proportion of heavy and light molecules of rainwater and snowfall depends on the local temperature. This spatial relationship between the isotopic composition of water and temperature (“isotopic thermometer”) has been applied on ice cores to reconstruct past changes in temperature using isotopic measurements conducted on the ice cores.

In the 1990s, extremely precise borehole temperature measurements have been performed in central Greenland, enabling to estimate the glacial interglacial temperature changes.

During the last decade, a new paleothermometry method has been developed for the study of rapid temperature changes. When transient temperature gradients occur between the surface of the porous snow and the bottom of the firn where the air is trapped into bubbles, they induce a molecular diffusion of the gases. The isotopic analysis of nitrogen and argon of the air trapped in ice cores therefore provides an alternative method to reconstruct past rapid temperature changes.

Why are polar regions important for climate change?
Polar regions represent the cold point of the climate system. They are both sensitive to climate change and actors of climate change due to polar amplification processes, contributions to sea level changes, and interactions with atmospheric and ocean circulations.

Owing to the quantitative temperature reconstructions from polar ice cores, it is possible to evaluate the capacity of state-of-the art climate models to capture the amplitude of past polar climate changes, and compare the future possible amplitudes of polar temperature changes to the observed past variations.

Figure 1. Eight climatic cycles recorded in EPICA Dome C ice core (central East Antarctica).
a) 65°N July insolation (blue, top) and 75°S annual insolation (black, bottom).
b) Vostok (red) and Dome C (blue) temperature changes recorded by the fluctuations of the ice isotopic composition (higher values reflect warmer temperatures; the glacial interglacial amplitude is estimated to be about 9°C).
c) Marine sediment isotopic records of past changes in global ice volume on a reversed scale (positive values downwards correspond to large ice volumes).
d) Dust concentration in Dome C ice, reflecting changes in aridity and dust transport to Antarctica. (EPICA community members, Nature, 2004)

Figure 2. From top to bottom (NorthGRIP community members, Nature, 2004):
1) A synthesis of the available estimates of rapid temperature (black bars, °C) and methane (grey bars, ppbv) increases during rapid events of the last glacial cycle.
2) Temperature changes in Greenland recorded in NorthGRIP ice isotopic composition.
3) Changes in south European vegetation recorded in marine sediments from the Alboran Sea (percentage of temperate pollen).
4) Changes in marine sea level reconstructed from marine sediment isotopic records.