POLARISO · A new isotope-enabled climate model dedicated to polar studies, to reconstruct Antarctic climate variability and improve sea level rise projections

A new isotope-enabled climate model dedicated to polar studies, to reconstruct Antarctic climate variability and improve sea level rise projections

The rate of Antarctic ice loss reached 20% of the global sea level rise in 2012–2017. This acceleration of ice fluxes toward the ocean is attributed to the coupling between large scale atmospheric patterns, ocean circulation and ice sheet dynamics. Intensive research efforts are in place to better understanding and modelling of this complex coupled climate system. However, the extremely sparse instrumental deployment preceding the most recent 40 years is a major limitation for the evaluation of global climate models used for climate projections, as several 30-year observational windows are required for a proper evaluation of circulation patterns, climate modes variability, and coupled ocean-atmosphere dynamics. Consequently, the greatest uncertainty in simulating the future of the Antarctic ice sheet is due to the lack of observational constraints that are required to evaluate and improve large scale climate variability in global climate models. While the remoteness and harsh climate of the Antarctic region hampered instrumental deployment, the cold climate and large ice sheet make Antarctica a unique site for reconstructing past climates from ice cores. In addition to reconstruction of large temperature changes from temperature-isotope relationships, isotopic signals also reflect dynamics of the whole water cycle (e.g. moisture sources, trajectory of the moist air, polar processes, see Figure). For the last few centuries, ice cores extracted at high-accumulation margin sites have high potential to contain records of large scale climate modes from annual to seasonal temporal resolutions over the recent centuries, but this richness comes with high complexity, as it involves the whole water cycle pathway. This makes the use of climate models equipped with water stable isotopes a necessary step for linking the isotopic signal at the ice sheet surface to local polar processes and large scale circulation patterns. Consequently, the key for reconstructing past climate circulation patterns from ice cores and for evaluating their representation in global climate models is to use a back-and-forth method between models and data: (1) use isotopic and other instrumental data to evaluate isotope-enabled models; (2) use isotope-enabled models to relate the isotopic signal to climate modes; (3) use climate modes derived from ice cores to evaluate global climate models. The POLARISO main objective is to relate the isotopic signal recorded in the Antarctic snow to large scale climate modes. This is a fundamental step toward new reconstructions from ice cores of the Antarctic climate variability over the recent centuries which can be used to evaluate global climate models. For this we combine modelling and experimental advances to remove the two main limitations of state-of-the-art approaches: A) we significantly reduce the uncertainties related to unresolved polar processes in climate models by implementing water stable isotopes in a polar-oriented regional climate model, and B) we evaluate this model with new observations of the isotopic composition of atmospheric water vapor and snowfall measured in Antarctica before deposition in the snowpack. The methodology proposed for achieving the above-mentioned objectives is: Step 1: implement water stable isotopes in a polar-oriented regional climate model; Step 2: evaluate the model with new continuous isotopic measurements in the water vapor and snow; Step 3: identify the large scale drivers of the isotope variability at the Antarctic surface in the model. At the end of the POLARISO project, I advanced on Steps 1 and 2, while Step 3 is planed to be achieved in the forthcoming years.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз