ICCC Terms of Reference

The growing data record from numerous geodetic observation techniques (GNSS station observations, satellite radio occultation and reflectometry, satellite gravimetry, satellite altimetry, InSAR, VLBI, GNSS-controlled tide gauges, etc.) provides a new quantitative view on various variables that are relevant for climate research, such as tropospheric water vapor, thermospheric neutral density, terrestrial water storage, ice sheet and mountain glacier mass , steric and barystatic sea level, sea surface winds, ocean waves, subsurface and surface currents, or sea ice extent and -thickness. Many of these are listed as Essential Climate Variables (ECV) according to the definition by the Global Climate Observing System (GCOS).

Geodetic methods provide unique information on the Earth's surface geometry, its large-scale mass transports such as fluctuations in Earth’s water cycle, and the global energy imbalance. Time series of geodetic data start to reveal a complex picture of natural climate variability, long-term climate change and anthropogenic modifications. Combined with other observations by means of, e.g., global or regional Earth system simulations or reanalyses, they provide excellent tools to improve our understanding of climate-related processes. Furthermore, due to their advantage of being independent of other data commonly used to drive and evaluate coupled climate models, geodetic observations have strong potential for either being used as input for numerical models as constraints (e.g. water budget, sea level budget) or for a posteriori model assessment. While it is generally recognized that geodetic data provide invaluable information for studying the planet’s changing climate, programmatic obstacles, technical limitations such as the length of time series, and scientifically open questions have been identified that hamper the broader recognition of geodesy as an important source of information for climate research. In order to better promote and facilitate the use of genuinely geodetic data in the climate community, and to better explore the synergies between the different geodetic branches with respect to observing climate signals, we propose to establish an Inter-Commission Committee on “Geodesy for Climate Research”. It will be based on the work started in the 2015-2019 IAG period’s Joint Working groups 2.6.1 “Geodetic Observations for Climate Model Evaluation” and 4.3.8 “GNSS Tropospheric Products for Climate”. It will continue the roadmap initiated at the workshop “Satellite Geodesy for Climate Studies” (Bonn 2017), which brought together geodesists representing all different observation techniques and climate scientists in a dedicated framework.

The topic of the suggested ICC is positioned at the interface between geodesy and climate science and is of high relevance for the entire scientific discipline geodesy. Various geodetic observables provide complementary information on climate change processes. Examples include (but are not limited to) the following: climate change related mass transport (e.g. ice melting, sea level rise, changes in the continental and oceanic water cycle as well as their impact on water resources) are among the primary signals derived from (satellite) gravity observations and can also be detected directly by geometrical measurements of volume change (satellite altimetry for water bodies/ice, InSAR over aquifers) or indirectly via crustal deformations induced by surface loads (terrestrial GNSS, InSAR, VLBI). Furthermore, by changing the Earth’s moments of inertia and relative momentum term, mass transports also lead to measurable variations in Earth orientation parameters. Climate change related variations of the atmosphere affect the propagation of geodetic signals and thus can be inferred from long time series of VLBI and ground and satellite based GNSS observations. Finally, a stable global geodetic reference frame (GGRF) is an indispensable requirement for providing a uniform reference for monitoring global change processes, as has recently been recognized by the corresponding UN resolution1. However, synergies between the different geodetic observing systems for monitoring climate change have not yet been fully exploited and the interaction with the climate communities needs to be intensified in order to achieve a broader – and better recognized – use of geodetic data for climate research.

Objectives:

• To deepen the understanding of the potential (and limitations) of geodetic measurements for the observation, analysis and identification of climate signals
• To advance the development of geodetic observing systems, analysis techniques and data products regarding their sensitivity to and impact on Essential Climate Variables
• To advance the improvement of numerical climate models, climate monitoring systems, and climate reanalysis efforts through incorporating geodetic observations
• To stimulate scientific exchange and collaboration between the geodetic and the climate science communities
• To make geodetic variables more user-friendly by sharing them publicly and explaining their usefulness

Program of Activities (tentative):

• The ICC will establish a workshop series to intensify the exchange between different geodetic communities and the climate monitoring and modeling communities.
• The ICC will create opportunities for communication and discussion through suggesting/organizing sessions at international scientific meetings and conferences.
• The ICC will develop reference (best-practice) methods for evaluating/improving climate models with geodetic data and publish these methods (e.g. in a ‘white paper’).
• The ICC will seek to organize special issues on its topic in appropriate international journals.
• The ICC will work towards a better recognition of geodesy as an essential provider of precise information about long-term changes in the Earth system.
• The ICC will establish links to other climate science related bodies, e.g. the IUGG Union Commission on Climatic and Environmental Change (CCEC) or the IAMAS International Commission on Climate (ICCL).
• The ICC will maintain a website for dissemination of ICC related information