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Coordinator: M. Claussen

Overarching Questions

In the past, the various compartments of the climate system - encompassing atmosphere, oceans, cryosphere, marine and terrestrial biosphere, soils, and the lithosphere - and the components of the anthroposphere - the world of human activities - were subject to mainly disciplinary research. However, climate system and anthroposphere (often referred to as the Earth system) are now understood as one system controlled by a multitude of interactions and feedback mechanisms. Alterations in one compartment typically result in – sometimes unexpected – changes in other compartments, and these again have influence on the original compartment. Moreover, some processes have the potential to force this system out of a meta-stable state into transition. And most important, simulation of individual components or of various combinations of components of the system may yield different solutions than simulation of the entire system. There are various examples of synergy effects in the climate system and the anthroposphere where the response of the combined system differs from the sum of the responses of the individual components under identical forcing.

The climate system and the anthroposphere interact in many ways. Current research reflects this only to some limited extent. Here, we include economics and sociology as component of social science. Economics is most advanced among the social sciences in its experience with formal, mathematical models. Sociology provides a broader framework for analyzing interactions of the Earth system and social systems that is not limited to economies.

In the context of global change, the main questions to be addressed by an integrated climate or Earth system analysis include the resilience of the system. Will the system be driven out of its natural mode of operation by anthropogenic perturbation? Would it be possible for human society and economy to adapt to large climate change? Will the climate / Earth system be manageable or, in other words, is it possible to contain the ongoing uncontrolled experiment of greenhouse gas increase and land cover change?

 

Goals of RA-C

Accordingly, this research area will explore the dynamics of the climate system in response to natural and human-driven perturbations, with a focus on the feedbacks among the various components of this system and including the interactions of economics and sociology with climate.  The main goals of this RA are:

• Analysis of the feedbacks of the climate system during the current geological epoch, the Holocene, for example biogeochemical and biogeophysical feedbacks. In particular, natural changes in the carbon cycle, such as changes in boreal carbon pools, including carbon and methane stored in permafrost and wetlands, will be investigated.
• Analysis of critical thresholds or run-away feedbacks in the climate system and exploration of so-called hot spots, i.e., regions on Earth that sensitively respond to external (natural or anthropogenic) forcing and that, in turn, affect global-scale dynamics.
• Analysis of the role of deserts and dry lands, including their ecosystem services, in the recent past and in a changing climate.
• Analysis of the effects of human activities on natural feedbacks in the climate system. In particular, the biogeophysical and biogeochemical effects of land use, including its strongest form, urbanisation, will be investigated.
• Analysis of geo-engineering as a means to counteract the effects of greenhouse gas emissions on climate. This analysis includes exploration of the effects geo-engineering measures on the climate system as well as the economic and security aspects of their implementation.
• Analysis of new option type financial instruments such as weather derivatives that might allow to manage the exposure to climate change and to help managing growing weather risks.
• Analysis of the effectiveness of future regulation in international environmental treaties, including the Framework Convention on Climate Change (UNFCCC), and the Convention to Combat Desertification (UNCCD). How can these governance responses be assessed using recently developed theoretical power measures and evaluation methods?
• Analysis of the behaviour of institutional environments and alternative government policies under conditions of uncertainty.
• Analysis of the realisation of carbon mitigation potentials in national regulations (e.g. emissions trading systems).

 

Methods

The above goals will be achieved by using models of components of the climate system as well as coupled climate system models which have been developed or are available at the University of Hamburg ranging from Earth system models of intermediate complexity (EMICs) to comprehensive model systems. These include the Planet Simulator developed at the Meteorological Institute, and the comprehensive model systems developed at MPI-M. For deriving detailed description of processes, which are associated with subgrid processes of global models, meso-scale models systems will be used. Such a system, M-SYS, which includes meso-scale and micro-scale atmospheric models, chemical transport models and sea-ice models, has been developed at the University of Hamburg. The above questions mainly concern global-scale topics. If, however, a region – such as the North Atlantic or Northern Africa – appears to be a ‘hot spot’, then feedbacks among the various components of the climate system will be investigated at the regional scale. For tackling this problem, the regional climate system model, REMO, developed at MPI-M, is available.

The currently available model spectrum will be replaced by a new unified model system whose development has already started. Future computer generations will enable model resolutions simulating processes on a scale that, today, can only be represented in parameterised form. New mathematical formulations of the next high resolution model generation and parameterisations of the remaining subgrid-scales are being developed. A promising option is a unifying approach comprising meso to micro-scales and large to global systems with similar or identical physics representing the key processes in the climate system.

To tackle the questions related to economy and sociology, analytical and numerical modelling techniques that have been developed and applied to model various inter-temporal decision and optimisation problems in the past can be used. The existing and proven research expertise in Hamburg also includes the application of stochastic calculus and optimal control techniques. The research strategy is to increase the number of couplings between the natural and social science modelling approaches. This approach is interesting from an interdisciplinary perspective. Time will tell how important these interactions are – and hence how tightly models of the natural and social systems need (and will) be coupled. Many of the questions are also interesting from a disciplinary perspective, which increases the prospect of high quality people working on this endeavour.

A number of steps have already been taken at ZMAW to couple components of the climate system and the economy, e.g., conceptual global economy and society models and models of biospheric and economic aspects of land use and land-cover change. These are the starting point for the development of new coupling strategies.

Relations with other RA's

The central question of natural science is conditional prediction (what would happen if?). In the context of global change, such conditional prediction is often referred to as climate projection or climate scenario. The theory of predictability will be explored in RA-B; in RA-C, only the feedbacks within the climate system and between climate and anthroposphere will be addressed. Social science contributes to climate projections (a) by developing scenarios of human activities that drive change in the natural system, such as greenhouse gas emissions and land and water use and (b) by exploring the impacts of global change on human activities. While the former will be dealt with in RA-B, the latter will be tackled in RA-D. Here, social science will address two further central questions: evaluation (so what?) and policy analysis (what should be done?). The analyses undertaken here will rely on data of the present and past state of the system obtained in RA-A.

 

Participating Scientists

1. UniHH: M. Claussen, K Fraedrich, H. Schlünzen (Meteorological Institute), J. Backhaus, I. Harms, L. Kaleschke, D. Quadfasel (Institute for Oceanography), M. Funke, M. Holler, B. Lucke, S. Napel (Institute for Macroeconomics and Economy), A. Engels (CGG), M. Köhl (Centre for Forestry and Forest Products), E.-M. Pfeiffer, T. Streck (Institute of Soil Science), N. Jürgens (Biozentrum Flottbek), M. Kalinowski (ZNF)
2. MPI-M: A. Chlond, D. Jacob, S. Hagemann, E. Maier-Reimer, J. Marotzke, Ch. Reick