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Climatic change and in particular the notion of “global warming” is a theme of scientific concern that has come into the realm of public awareness since the early 1990s. The severity of the potential impacts of climatic change, in particular in the developing world, has prompted international action at the level of governments to address the problem. The United Nations Framework Convention on Climate Change (UN-FCCC) was negotiated at the 1992 United Nations Conference on Environment and Development (UNCED, Rio de Janeiro, Brazil) despite the large range of uncertainties that are inherent to current understanding of the intricacies of mechanisms within the system that lead to its complex behavior. Although subsequent international meetings aimed at implementing the governing articles of the UN-FCCC have made very slow progress, as for example the 1997 Kyoto Protocol that set a calendar for reducing greenhouse-gas emissions, there is nevertheless an unprecedented level of concern among the community of nations that climatic change is a genuine problem with potentially far-reaching consequences for environmental and socio-economic systems.

The Sun provides the overwhelming share of energy available for the Earth and its various physical, chemical, and biological components; close to 99.7% of the energy supplied to the Earth is of solar origin, while the remaining 0.3% is related to tectonic and geothermal processes.

The climate system is in perpetual evolution as it responds to a range of forcing factors. It is possible to distinguish between and forcings of the system. External forcings are essentially linked to changes in the orbital parameters of the Earth that control the intensity and location of incident solar radiation, and fluctuations in solar energy.

Human activity, through industry, agriculture, energy generation and transportation, has released significant amounts of greenhouse gases into the atmosphere since the beginning of the industrial era that began in the first half of the 19 century. Today, there is concern that this may be inadvertently modifying the global climate through an enhancement of the natural greenhouse effect. According to the IPCC (2001), global mean temperatures could increase by 1.5 to 5.8°C by the end of the 21 century in response to the enhancement of radiative forcing in the atmosphere. While this may appear to be a minor amount of warming when compared to diurnal or seasonal amplitudes of the temperature cycle, it should be emphasized that the projected global-mean temperature rise is unprecedented in the last 10,000 years. It is not only the amplitude of change but also the rate of warming that is generating concern in the scientific community, especially in terms of the vulnerability and response of environmental and socioeconomic systems to climatic change.

Models are mathematical, computer-based, or conceptual tools that allow a synthesis of the current understanding of particular systems in the realms of physics, chemistry, biology, or economics. In climate research, numerical models attempt to take into account numerous elements of the system that are important for its evolution, in particular the oceans, the cryosphere, and the biosphere. Advanced models enable investigations of certain mechanisms that may ultimately be relevant to a system’s evolution, such as feedbacks between its different constitutive elements, and the sensitivity of climate to disturbance. Models also have some measure of predictability for complex non-linear processes, which are the rule in the physical, biological or economic sciences.

In view of the observational evidence regarding changes in atmospheric chemistry that are related to human activities, it is of interest here to provide a brief summary of changes in climate that have been observed in the past that may be related to the increased radiative forcing in the atmosphere.

This section will investigate aspects of climate during the 20 century that are specific to the European Alps, and will provide an insight into the manner in which climate may change in the latter part of the 21 century in response to global warming.

The more recent work conducted within the context of EU Framework Program 5 projects alluded to in Chapter 6 has served to confirm earlier simulations of climatic change in the alpine region conducted by Marinucci et al. (1995) and Rotach et al. (1997). These studies concluded that the Alps would within decades experience a shift towards a Mediterranean-type climate, i.e., one that is characterized by a wet winter season and a long, dry and warm summer season. The northward progression of climatic zones that are currently located to the south is, as seen in Chapter 6, expected to be of the order of 500 km within 100 years. The climate of the western part of the Alps may therefore resemble, in terms of its temperature and precipitation characteristics, a type of climate that is currently found in the Mediterranean Alps of southern France.

This book has attempted to provide in the first section an up-to-date overview of the physics of the climate system and its observation and modeling of. In the second section, issues related to regional climate change and impacts on Switzerland, as a particularly interesting case-study region, have been addressed.