Synthesis of transient climate evolution of the last 21 ka (SynTRaCE-21) workshop

Zhengyu Liu1, B. Otto-Bliesner2 and P. Clark3

1Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, USA; zliu3@wisc.edu
2Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, USA
3Department of Geosciences, Oregon State University, Corvallis, USA

Mount Hood, Oregon, 10-13 October 2010

Figure 1: SynTraCE-21 meeting participants in the foreground, Mount Hood in the background.

Climate reconstructions covering the last 21 ka provide critical observational data for testing state-of-the-art climate models for the simulation of climate evolution and abrupt climate changes. New proxy evidences and modeling activities have led to rapid advances in our understanding of climate change for this period. Therefore, a new PAGES Working Group, SynTraCE-21, was initiated in 2009 to synthesize the transient climate evolution of the last 21 ka. The overarching goals of the Working Group and the associated workshop series are (i) to facilitate an international synthesis effort of proxy climate records to better describe the major features of global climate during the last 21 ka, and (ii) to compare these data to transient model simulations. The first international SynTraCE-21k workshop was supported by PAGES, NOAA, and the US Department of Energy, and attracted more than 40 participants from around the world with expertise from terrestrial and marine paleoclimatology to climate modeling.

The first day began with a review of two previously held pilot workshops, which focused on marine and terrestrial records (held in Madison August 2008, and Boulder August 2009). Following this, the focus turned to an update of the meltwater history, which is the most uncertain component of climate forcing in the last deglaciation. The rest of the day was devoted to preliminary model-data comparisons in three models, two coupled general circulation models (CCSM3 and HadCM3) and a climate model of intermediate complexity (ECBilt). These transient simulations mark a new era beyond the “snapshot” studies on “time-slice” climate in paleoclimate model-data comparison because they allow for a direct comparison of time series between the model and data. The studies presented ranged from the evolution of monsoons and global surface climate to regional abyssal circulation variability, showing the great potential of these transient simulations for model-data comparison.

Transient simulations provide an unprecedented opportunity to the paleoclimatology community for model-data comparison and for improved understanding of climate evolution and abrupt climate change. As a result, it has become critical to develop a major data synthesis to better characterize the global climate variability and to compare with the new generation of transient model simulations.

The second day focused on the terrestrial proxies, with synthesis discussions of lake sediment records, including pollen and charcoal data, ice cores and speleothems. A special session was also arranged to discuss several model-data comparison strategies, including both forward and inverse modeling. The third day was devoted to marine proxies. Reconstructions of the character of the deep and intermediate waters with sedimentary isotopes studies were described. Finally, surface ocean proxies for sea surface temperature and salinity were discussed. Each day ended with an open discussion on the major topics of the day.

The presentations on each major proxy provided a great learning opportunity to all the participants, greatly promoting the interdisciplinary approach towards a multi-proxy data synthesis. To examine model robustness, the meeting participants also recommended coordinated modeling activities among the different research groups. To better assess model-model differences and climate sensitivities to external forcing, notably to meltwater forcing, while allowing for flexibility for such long simulations, one strategy proposed was to design common standard sensitivity experiments for different models. Finally, given the large amount of model data, a coordinated model data distribution was also discussed. The workshop participants agreed that the next meeting would be held in the summer of 2012. This workshop will focus on several key topics using an interdisciplinary synthesis approach. Notably, the topics will include the meltwater history and sea level reconstructions for the deglaciation, climate and terrestrial ecosystem in the North American region, and tropical hydrology.