Climate change refers to any of the dynamics of the climate system (in terms of both mean and variance on temporal and spatial scales), which is based on the interactions between the atmosphere, the biosphere, the cryosphere, the hydrosphere, and land surface activities. Climate system dynamics may be distinguished into internal and external forces with respect to the climate system. Furthermore, they can be respectively associated with the human activity, and the natural variability or other components that are able to intensify or reduce the initial variation effect. Examples of natural components are solar fluctuations, volcanic activity, etc.
Only recently human activity (both direct and indirect) has been taken into account as one of the main sources that are able to alter the global atmosphere composition. The most influential human actions are related to the emissions of greenhouse gases (GHGs) resulting from the exploitation of natural resources and the land use change and management (such as agricultural activity, deforestation, and forest degradation), and the use of fossil fuel for the industry and transportation development. The increase in GHG concentration in the atmosphere driven by the growing trend of GHG emissions leads to higher values of the mean world surface temperature, causing the so called "global warming" problem, which is one consequence of climate change. The Intergovernmental Panel on Climate Change (IPCC) states that the mean global surface temperature has increased by about 0.74 °C in the last 100 years only (IPCC, 2007).
The interaction between natural variability and human activity results in the variation of different meteorological parameters such as maximum and minimum global surface temperatures, ocean temperature, precipitation levels, etc.
Research on climate change focuses mainly on the development of models to analyse how climatic and physical values change over time and what are the interactions between climate change and climate change drivers. Climate models are often used to simulate the response of the climate system to greenhouse gas (GHG) and aerosol emission or concentration scenarios, or radiative forcing scenarios. Climate-economic models, as e.g. the ICES (Bosello et al., 2007) and the WITCH (Bosetti et al.,2006) models, translate climate changes into their socio-economic impacts.
One of the most important international steps in the research on climate change was the creation in 1998 of the IPCC by the United Nation Environmental Programme (UNEP) along with the World Meteorological Organization (WMO). The aim of this organisation is to collect and spread the scientific and technical information produced worldwide, which is relevant for the understanding of the climate change risk. The 1995 IPCC Second Assessment Report provided a great contribution to the negotiations of the Protocol adopted in Japan on 11 December 1997.

Bibliography
BOSELLO F., DE CIAN E. and ROSON R., (2007). Climate Change, Energy Demand and Market Power in a General Equilibrium Model of the World Economy. Fondazione Eni Enrico Mattei Working Paper N.71.2007.
BOSETTI  V., CARRARO C., GALEOTTI M., MASSETTI E. and TAVONI M. (2006). WITCH: A World Induced Technical Change Hybrid Model. The Energy Journal, Special Issue "Hybrid Modelling of Energy Environment Policies: Reconciling Bottom-up and Top-down", pp. 13-38.
IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I, to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Synthesis Report.

Editor: Melania MICHETTI
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