The primary objective of the proposed DFG Research Unit ‘Stratospheric Change and its Role for Climate Prediction’ (SHARP) is to improve our understanding of global climate change and the accuracy of climate change predictions. The emphasis is on the relevance of the stratosphere for climate change, particularly feedback processes with the troposphere. SHARP will provide answers to the question of how the stratosphere is likely to respond to climate change, and how the changed stratosphere will influence tropospheric climate and weather.

Climate change has been recognised to be one of the most serious problems for mankind. The global mean surface temperature has already increased by 0.7°C in the last 100 years (1906-2005) and 11 of the last 12 years were the warmest since observations exist. The troposphere is expected to warm significantly until 2100 (scenario calculations being in the range 1-6°C), accompanied by changes of regional climate patterns and an enhancement of extreme weather events (IPCC, 2007). As a consequence of enhanced greenhouse gas (GHG) concentrations and severe depletion of stratospheric ozone (O₃), a cooling of the stratosphere has been observed during the past two decades (WMO, 2007). Future increases of GHG concentrations will contribute to the average cooling in the stratosphere.

The climate models used for the IPCC climate projections are atmospheric General Circulation Models (GCM) which at their lower boundaries are coupled to ocean models (atmosphere-ocean GCMs, AOGCMs) to account for the interaction between the oceans and the atmosphere on multi-annual time scales. Future changes of atmospheric composition are considered by prescribing scenarios of GHGs, while stratospheric O₃ is either kept constant at present-day values or prescribed. However and very importantly, there are specific aspects that have been simplified in the IPCC climate projections and that are known to impact climate. These have been formulated by the international research programme Stratospheric Processes and their Role in Climate (SPARC), which is one of the core projects of the strategic framework for 2005-2015 of the World Meteorological Organisation (WMO) World Climate Research Programme (WCRP). The focus of SPARC is on the stratospheric aspects in the assessment of climate predictability. SPARC recommends research in three New SPARC Initiatives:

• Detection, Attribution, and Prediction of Stratospheric Change
• Climate-Chemistry Interactions
• Stratosphere-Troposphere Dynamical Coupling

 

In response to the open issues defined in the recent WMO Scientific Assessment of Ozone Depletion: 2006 (2007), motivated by the New SPARC Initiatives and based on its own analysis of research priorities and capabilities, the proposed Research Unit SHARP has selected key aspects to perform and coordinate research activities in Germany in the two leading themes:

• Theme 1:

The interaction between climate change and stratospheric dynamics and composition

• Theme 2:

The interaction between stratospheric change and tropospheric climate and weather

 

SHARP will make use of

• Measurements of stratospheric composition, in particular from satellite instruments, for the analysis of stratospheric change and the validation of results derived from model simulations. For the derivation of long-term trends, the data analysis will be supported by measurements from balloon platforms.
• mproved CCMs which simulate the complex interactions between chemical processes, dynamics and radiative forcing (including the interaction between chemistry and climate, and the troposphere and the stratosphere) for the attribution and prediction of climate change. The CCM studies will be supported by sensitivity studies with General Circulation Models (GCMs) and Atmosphere-Ocean GCMs (AOGCM) to investigate natural variability and separate the effects of specified climate forcings.

An innovative approach of SHARP will be the inclusion of ocean-atmosphere interactions in CCM simulations. First CCMs coupled with ocean models are currently under development. These models will include the vertical coupling from the middle atmosphere down to the oceans which will further improve the accuracy of climate predictions.

In addition to the key scientific issues for atmospheric physics and chemistry to be investigated, SHARP would enable German research groups to make significant contributions to the next WMO Scientific Assessment of Ozone Depletion: 2010. The establishment of the trends of O₃ and related key constituents over the last decade are key inputs for the WMO Assessment. Partners of SHARP are already involved in the preparation of the new CCM simulations for the WMO assessment, however additional funding from SHARP would be essential for the performance, evaluation and analysis of the new CCM simulations.

The goals of SHARP closely align with international activities and research programmes. The assessment of the new SHARP CCM simulations would be an integral part of the SPARC Chemistry-Climate-Model-Validation (CCMVal) activity. Results achieved within the DFG priority programme Climate and Weather of the Sun-Earth-System (CAWSES) would be accessible for SHARP and strongly support the interpretation of the CCM simulations by providing information on natural contributions to climate variability and trends. The goals of SHARP regarding the evolution of polar O₃ also meet scientific objectives in the framework of the International Polar Year (IPY). Results of SHARP will further contribute to the interpretation of the upcoming IPCC simulations.

The complex scientific issues and variety of disciplines involved in climate change (dynamics, radiative transfer, atmospheric chemistry, observations, modelling) necessitate the synergistic and complementary effort of experts from different fields. SHARP brings together the national excellence in universities completed by important contributions from three large research facilities in the relevant disciplines of atmospheric science.  To achieve the goals of SHARP, a coordinated use of numerical models and observational data is planned. The development of the Research Unit is an excellent opportunity and showcase for German contributions to international programmes. The German scientific community has a unique expertise in the exploration of global observational atmospheric chemistry data from the first generation of European based satellites and in the development of a new generation of atmospheric models. The development of state-of-the-art CCMs has made great progress in recent years. German CCMs based on the ECHAM model family provided important contributions to the recent WMO Scientific Assessment of Ozone Depletion: 2006 (WMO, 2007). Updated improved model versions currently being developed within European projects (e.g., SCOUT-O3), will be ready for use in SHARP. The success of MIPAS and SCIAMACHY instruments aboard the Envisat satellite, which have been providing data since 2002, represent an enormous progress in observational information about the stratosphere.