Permafrost regions constitute about a quarter of the northern hemisphere land area, and about two thirds of Earth’s terrestrial surface are subject to seasonal ground freezing. Profound and often rapid changes in frozen ground conditions can be observed and are expected to increase in the context of future climate change. The effects that frozen ground and its changes have on human and natural systems span a wide range from local engineering problems to important feedback mechanisms affecting global climate. As a consequence, the quantitative understanding and anticipation of changes in frozen ground conditions are of great scientific interest societal relevance. In this context, computer models are becoming increasingly important but the reliability and value of results is often unknown or even unquestioned. More or less obviously, this brings about many new research questions and technical challenges. With this session and the associated activities, we aim to bring together and exchange expertise with respect to these questions:

• How do we connect measurements and models at and across diverse scales?

• How do we interface with differing fields of science, their models and theoretical frameworks?

• How can we quantify and communicate error and uncertainty?

• What is the importance of sub-grid variability? How do we consider this in models and communicate corresponding results?

• How can we balance model complexity and the ability to cover diverse conditions in space and time? (parameterization vs. process model)

• How and how much do we calibrate models? (local goodness-of-fit vs. reliable simulation of large areas)

• How do we initialize and spin-up models and what are the associated uncertainties?

• Are present measurement and monitoring efforts sufficient for the support of modeling?

• Are established mapping legends and terminology still suitable? How are model uncertainty and spatial abundance represented (e.g., temperature and permafrost presence/absence)? How are inactive, degrading permafrost bodies represented?

We look forward to a high-quality session with contributions that present major advance in one or several of these topics, provide in-depth reviews and guidance for important future research, or show modeling case studies related to the questions above.

This session and a twinned session at the AGU Fall Meeting in 2009 in San Francisco, USA are initiated as part of a working group of the International Permafrost Association (IPA). During both conferences – AGU 2009 in San Francisco and EGU 2010 in Vienna – we aim to provide an occasion for in-depth discussion between interested parties in a separate splinter meeting. A special issue of The Cryosphere (www.the-cryosphere.net) will be announced shortly before AGU 2009 and will serve as a vehicle for combining and integrating contributions from both sessions.

We cordially invite you to participate and look forward to seeing you and your presentations in Vienna.