Climate inherent variability

Instrument-based and reconstructed climatic records indicate that climate is inherently variable over a broad spectrum of time scales, ranging from years to millennia. 

The inherent temporal variability of climate thus obscures the search for long-term climatic signals. In addition, the search is plagued by the great spatial variability of climatic change. 

Environmental conditions in the Arctic, as elsewhere, are not static. Indeed, environments change over a large range of ecologically relevant scales diumally, seasonally, annually, decadally, and over centuries. The patterns and scales of variability of the physical environment set the framework conditions of species existence and community interactions. Arctic organisms, communities and ecosystems are thus adapted to the patterns of their respective local climates and the inherent environmental variability. Under such conditions, natural systems can be in quasi-equilibrium with the climate forcing mechanisms. 

In general, the excavations in urban environment have small width, depth, and opening time. These works are done for installation or maintenance of urban infrastructures. Usually do not have too much complexity what, in many cases, decreases the prevention actions causing mortal accidents. The nature of work is variable from severe physical tasks to full mechanize ones, often performed under extreme climate conditions and in isolated areas or on the other hand in very crowded areas. The specifics of the work on construction industry entail that uncertainties are inherent in every condition (Tam et al. 2004). 

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