DICE scientific goals

Aerosols-climate interaction constitute one of the major sources of uncertainty in assessing radiative forcing – the energy imbalance at the top of the atmosphere caused by agents capable of affecting climate. In its AR5, the IPCC-WG1 listed similar uncertainties in aerosol forcing (somewhere in the order of 100%) as it had in its AR4.

In the AR5 paleoclimate chapter, the IPCC stated that "the spatial and temporal fluctuations in atmospheric mineral dust aerosol [MDA] concentrations make it difficult to assess the global radiative forcing linked with past MDA changes". Therefore, not surprisingly, climate and aerosol interactions were recognized as one of the major uncertainties in climate projections; reducing those uncertainties is a fundamental goal of present and future climate studies.

DICE aimed to address some of the existing knowledge gaps around the climate impacts of dust and aerosols, specifically to:

1. Strengthen the links between paleo data observations and paleoclimate modeling

DICE aimed to provide a collaborative platform to build a much tighter and better coordinated link from paleo data observations to paleoclimate modeling by fostering direct interaction between the observations and theory i.e. the climate/dust modeling community and paloeclimatologists/geochemists. An enhanced exchange between these two communities helped define future 'data needs' and requirements.

An example of a vital interchange could be the issue of dust size, which is widely used to interpret either changes in sources or changes in wind strength (both at the source and during transport). Both hypotheses can be examined within models. As Earth System models lean towards implementing aerosol modules and towards multi-centennial to multi-millennial transient model runs, the data/proxy community needs to be prepared to provide relevant data sets for model calibration and validation. As part of this effort, DICE aimed to improve the communication and exchange between the extensive modern aerosol community and scientists who focus on paleo processes. This allowed time scales to be linked, and the gap between paleo observations and modern instrumental observations to be filled.

2. Create a new generation data compilation

DICE facilitated the compilation of a next-generation global observational dataset for dust deposition from sedimentary archives for the Late Quaternary. It synthesized spatially and temporally resolved data sets from different climate archives: marine sediments, sediment traps, corals, ice cores, terrestrial deposits, and lake sediments.

The compilation (DUSTSPEC) built on, and significantly extended, the success of the DIRTMAP (Dust Indicators and Records of Terrestrial and Marine Paleoenvironments) project. While DIRTMAP was limited to a time-slice approach, the new data compilation provided time-series data, and therefore allowed researchers to go beyond a time-slice approach to look, for example, at abrupt climate changes imprinted in dust records.

Even more importantly, the availability of a dataset with fully resolved records serves as a reference for transient studies which look at millennial scale variability or variability associated with abrupt climate change, for example features such as Dansgaard/Oeschger events, Heinrich Stadials, or processes such as the Bølling-Allerød/Younger Dryas transition occurring at the last glacial termination.

The development of such a database is not a trivial activity because of the many issues associated with different proxies and different media (e.g. ice cores vs. marine sediment cores). The resolution and the uncertainties in the age models can be very different for different cores, and yet a consistent framework is needed. Thus, this effort must go beyond just single-data contributors; it requires a centralized coordinating effort.

3. Explore new proxies and processes

DICE was keen to explore novel proxy applications and interpretations of dust records and improve our understanding of dust-related feedback processes. This included, for example:

(i) Exploring the impact of mineral dust on the albedo. While modern climate studies investigate the change in albedo as a function of dust/aerosol load, this is a process that has so far been largely neglected in the paleoclimate community. This example highlights potential mutual benefits and synergies to be gained.

(ii) Researching mineral dust as an indicator of droughts and changes in the hydrological cycle.

(iii) Integrating novel organic proxies (e.g., n-alkanes) with traditional inorganic dust proxies.