As climate has warmed over recent years, a new pattern of more frequent and more intense weather events has unfolded across the globe. Climate models simulate such changes in extreme events, and some of the reasons for the changes are well understood. Warming increases the likelihood of extremely hot days and nights, favors increased atmospheric moisture that may result in more frequent heavy rainfall and snowfall, and leads to evaporation that can exacerbate droughts. Even with evidence of these broad trends, scientists cautioned in the past that individual weather events couldn't be attributed to climate change. Now, with advances in understanding the climate science behind extreme events and the science of extreme event attribution, such blanket statements may not be accurate. The relatively young science of extreme event attribution seeks to tease out the influence of human-cause climate change from other factors, such as natural sources of variability like El Niño, as contributors to individual extreme events. Event attribution can answer questions about how much climate change influenced the probability or intensity of a specific type of weather event. As event attribution capabilities improve, they could help inform choices about assessing and managing risk, and in guiding climate adaptation strategies. This report examines the current state of science of extreme weather attribution, and identifies ways to move the science forward to improve attribution capabilities.

We developed a high resolution global coupled modeling capability to perform breakthrough studies of the regional climate change. The atmospheric component in our simulation uses a 1{sup o} latitude x 1.25{sup o} longitude grid which is the finest resolution ever used for the NCAR coupled climate model CCSM3. Substantial testing and slight retuning was required to get an acceptable control simulation. The major accomplishment is the validation of this new high resolution configuration of CCSM3. There are major improvements in our simulation of the surface wind stress and sea ice thickness distribution in the Arctic. Surface wind stress and ocean circulation in the Antarctic Circumpolar Current are also improved. Our results demonstrate that the FV version of the CCSM coupled model is a state of the art climate model whose simulation capabilities are in the class of those used for IPCC assessments. We have also provided 1000 years of model data to Scripps Institution of Oceanography to estimate the natural variability of stream flow in California. In the future, our global model simulations will provide boundary data to high-resolution mesoscale model that will be used at LLNL. The mesoscale model would dynamically downscale the GCM climate to regional scale on climate time scales.

GKSS SCHOOL OF ENVIRONMENTAL RESEARCH The National Research Laboratory GKSS (member of the Hermann von Helmholtz-Association of German Reserach Centres) located in Geesthacht, near Hamburg, is engaged in environmental research. The main interest of the research center focuses on regional climatology and climate dynamics, interdecadal variations in the state of the Baltic and North Sea and related estuaries, and the flow ofheavy metals, nutrients, and other materials in river catchments to the coastal zones. This research aims at-developing an under standing ofchanges in the environment, both as a result ofinternal (natural) dynamics and as a result of anthropogenic interference. In an effort to dis seminate the results of these research activities, as well as to initiate a broad discussion among senior scientists in the field, and younger colleagues from all areas of the globe, the Institutes of Hydrophysics and Atmospheric Physics at GKSS have instituted the GKSS School of Environmental Research. Appliedenvironmental research has always containedanelement ofaware ness ofthe societal implications and boundary conditions associated with en vironmental concerns. Consequently, the School of Environmental Research adheres to the philosophy that all discussion regarding environmental change should incorporate a social component. This necessity has been well acknowl edged and is apparent by the incorporation ofsocial scientists into the series of lectures. Senior scientists from Europe and North America were invited to give lectures to "students" from all parts of the globe.

For the very first time, this book provides updated, integrated and organized, theoretical and methodological information on regional climate change and the associated environmental and socio-economic impacts on a regional scale. The most recent findings in the field of long-term climate change, which improve our understanding of the global climate puzzle, will be presented. Readers are introduced to state-of-the-art research in downscaling and GCMs, which involve the construction of reliable regional climate scenarios and the solution to key problems regarding the assessment of the impacts of climate change in the most important geographical areas of the world, from the Arctic to Antarctic regions, with special emphasis on the Northern Hemisphere.