Letter from the Editor

Susan Cutter

Climate, in particular climate change, climate impact and climate policy, and the perspectives they provide have occupied front seats in the global arena for over two decades. “Climate change” in particular has become a household term, and needs little explanation.

Climate change also represents a complex of societal issues. Our scientific knowledge is laden with inherent uncertainties, decisions about “solutions” are urgent while stakes are high, and social values are involved. This complexity is typified by the term “post-normal”: that is, we often expect science to determine “solutions” rather than providing assessments of possible solutions. The leading, UN-mandated, Intergovernmental Panel on Climate Change (IPCC) seeks to be policy-relevant but not policy-prescriptive. At the same time policymakers often present their efforts as facilitating purportedly scientific necessities without alternatives.

But what, in fact, is climate? One definition is simple: climate is short-hand for “statistics of weather” (not only in the atmosphere), such as a temperature mean in a certain region and in a certain season; the distribution of storm surge heights on a coast; the spectra of variations, and so on. Another definition refers to the climate system, which the atmosphere, oceans, cryosphere, hydrology and other components comprise, and which form climate. In this definition, the climate system is open, as it is influenced by different factors and drivers, among them human activities, but also by variable solar outputs. At the same time, the climate system has very many, often chaotic degrees of freedom, so that the system may be described as mostly stochastic. Macro-chaotic elements also may prevail (such as tipping points). Spatial scales are mostly linked to each other in a downscaling cascade; that is, larger scale dynamics together with smaller scale physiography condition smaller scales dynamics. Here, regional and local climate appear mostly as manifestations of global (continental) scale climate. And mitigation of climate change, for example, refers to reductions in the global drivers of such change, with positive effects spreading to all regions on Earth in a downscaling cascade.

A very different approach was used in earlier times; namely, as global climate is the sum of all regional climates, the latter have a direct bearing on human welfare and ecosystems. In his 1845 book, “Cosmos, A Sketch of a Physical Description of the Universe,” Alexander von Humboldt wrote: “The term climate, taken in its most general sense, indicates all the changes in the atmosphere, which sensibly affect our organs, as temperature, humidity, variations in the barometrical pressure, the calm state of the air or the action of varying winds, the amount of electric tension, the purity of the atmosphere or its admixture with more or less noxious gaseous exhalations, and, finally, the degree of ordinary transparency and clearness of the sky, which is not only important with respect to the increased radiation from the earth, the organic development of plants, and the ripening of fruits, but also with reference to its influence on the feelings and mental condition of men”. In this view, adaptation to the risks and opportunities in different regions appears as a more obvious route of response. Although this does not obviate the necessity of dealing with the causes of climate change, it does allow society and ecosystems to react to specific changing conditions. After our first decade of debate focusing almost entirely on global mitigation schemes, it has become clear that anthropogenic climate change cannot completely be avoided by such measures. Significant challenges at regional and local scales must be confronted.

This encyclopedia engages both the global and the regional view. It structures the issues that “climate” presents into three threads, namely: (1) our understanding of, and response to, the geophysical and biogeochemical system, including the sensitivity of the system to external drivers and its natural variability. (2) The ubiquitous presence of communication and policymaking leads us to deal with different cultural framings of climate, as well as with the social process of climate science. (3) Finally economic and climate policy issues at the international and at the local level are considered.

A special feature is our plan to cover many regions of the world by interdisciplinary analyses of what climate, climate impacts, and perspectives on climate are as well as the options for, and the conditions and meaning of, societal response to climate.

Dr. Hans von Storch
Institute for Coastal Research, Helmholtz Zentrum Geesthacht, Germany
Editor in Chief