science activities

cct 3 - modeling
rationale

Over the past years Earth System (ES) modeling has become increasingly important in paleoclimatic research. Specifically, physically based ES models provide a valuable tool to assess conceptual models of past climate changes derived from paleoclimatic data. On the other hand, data-based reconstructions of past climate variations provide critical test grounds for ES models that are usually tuned to capture present-day climate. Thus, combining data-based reconstructions and paleoclimate modeling offers a promising path to fully comprehend past climate dynamics.

Specific benefits that can result from the joint utilization of paleoclimatic reconstructions and paleoclimate modeling include a means for formulating and testing hypothesis, e.g., by quantifying the response of the ES to different forcings. Moreover, ES models provide a comprehensive framework for exploring couplings and feedbacks between the various components of the system. This type of analysis is of particular in detecting ES thresholds. Finally, ES models provide a powerful link between past climate changes and projections of future climate, which are both assessed by the same types of models.

Models can also be used for interpreting proxies at a local scale (e.g., lake-level models) as well as human-climate interaction models. These models are frequently developed outside the paleoclimate research community and are therefore optimized for capturing modern processes. Accordingly, a number of issues that are important to paleo-modeling are not dealt with. Specific issues include:

- forward modeling of proxies,
- objective comparison of proxy data and modeling results (including upscaling/downscaling techniques; assimilation of sparse data),
- optimizing selection of sampling locations,
- requirement for modules of reduced complexity allowing for longer integration times (in additions to the physical climate system also ecosystem and biogeochemistry modules),
- modules for Earth system components relevant at geological timescales (e.g. weathering-carbonate burial cycle).

These topics are best addressed in a paleo-framework that includes modelers and data researchers.


goals

The specific goals for CCT 3 are threefold:

(1) Fostering the development of strategies for proxy-modeling

To maximize synergy, the focus should be on those proxies with wide spatial coverage and large existing data collections (e.g., stable isotopes reflecting the physical and biogeochemical processes in the ES). Strategies for including proxies such as aerosols or pollen will also be considered.

(2) Devising methods for the objective comparison of proxy data and modeling results

In present-day climatology, data assimilation has become an important tool for quantifying the state of the climate system based on observations. However, these methods are sparsely distributed for paleo-data. Successfully strategies for assimilation of paleo-data could also help scientists working on proxy-based reconstructions to optimize the selection of sampling locations. Another issue arises from the fact that proxy-based reconstructions are often associated with uncertainties that are not well constrained and are sparsely spaced. There is a lack of suitable statistical methods for comparing such data with model output. Finally, strategies for downscaling the output of global models to regional scales (e.g., for lake-level, ice sheet, fire, coastal upwelling, or aerosol transport models) are still immature.

(3) Promoting the development of comprehensive Earth System model families

The long timescales associated with geological processes often require integration times that are significantly longer than those used for generating, say, future climate scenarios. To meet this requirement and at the same time rely on the same type of models used in the IPCC community, it seems appropriate to offer these models with a range of resolutions and system components suitable for long paleoclimate experiments.