science activities

cct 2 - proxy development, calibration and validation
rationale

Widespread, reliable instrumental records are available only for the past 150 years. Climatic variations in the more distant past can be estimated by analyzing proxy evidence from sources such as tree rings, corals, ocean and lake sediments, cave deposits, ice cores, boreholes, glaciers, and historical documents. These multiple types of proxy data can be used to infer past climate variations from single sites to large geographic regions.

Considerable advances have been made over recent decades on the quality of proxy-based reconstructions. However, the demand on accuracy, precision, resolution, and quantitative interpretation is increasing as the questions asked in Global Change research are becoming more and more detailed, including seasonal to interannual variability, climatic parameters other than temperature, or local to regional environmental variability.

To meet these demands and maximize the value of paleoscience in complementation to observational and projection studies, we need to constantly improve the analytics, calibration, and interpretation of the proxies and the validity of synoptic reconstruction methods.


goals

The goal of this CCT is to support improvement of the precision and accuracy of paleoenvironmental proxies as a basis for high-quality records of past global change (see Focus 2), which are able to complement instrumental data and modeling efforts. Activities include improvements in proxy interpretation and development, refinements in analysis and calibration and inter-laboratory comparisons. Several issues along the path from the site selection to reconstruction provide specific opportunities to improve the quality of proxy records:

Discovery of new proxies: Despite a growing array of proxies, for some environmental parameters we have basically no or only poor proxies at hand. The search for new proxies is therefore desirable in order to arrive at a comprehensive reconstruction of Earth’s environmental history.

Development of proxies: Past-present cross-disciplinary efforts improve our understanding of the biological, physical and chemical controls on the formation of proxies and proxy-archives and of their post-depositional history. Such deeper understanding is necessary to reliably and quantitatively interpret the proxy data with respect to their representation of environmental parameters. A complementary approach to increase confidence in reconstructions is to combine multiple independent lines of evidence, e.g. multi-proxy reconstructions or with data-modeling comparisons.

Site selection: Observational data (e.g. results from IGBP sister projects and WCRP) and model runs with incorporated proxies help identification of the best sites for sampling. PAGES provides a platform for communication with these groups and supports campaigns to study key locations and undersampled regions.

Data collection: The field and laboratory observations are continuously becoming more accurate and precise. Progress usually results from innovations, often of technical nature, by specialist scientists. PAGES can contribute to analytical improvement by organizing group efforts such as interlab comparison/calibration studies.

Calibration: The calibration of proxy data requires large sets of samples or proxy-datasets from the (quasi-modern) calibration period as well as optimal datasets of instrumental measurements. Collaboration with sister projects of PAGES in IGBP, WCRP, and beyond can help to identify and provide these datasets.

Proxy-data uncertainties: Beyond efforts to reduce uncertainties in general, the coherent and quantitative expression of uncertainties is a major task within CCT2. This is addressed according to the requirements of the modeling community and in close collaboration with modelers, statisticians, and with working groups of the Foci 1 and 2.



PLEASE NOTE: This is draft text pending publication of PAGES Science Plan and Implementation Strategy.