More and more signs of ongoing climate changes are recorded all over the world. There is a high likelihood that these changes are generated by greenhouse gases emissions of anthropogenic origin. Human health, ecologic systems and socio-economic sectors are significantly affected by weather and climate related changes. Human civilization has been developed in the last several thousand years and there are indications that the climate conditions had important influences on it. While variable climate conditions affect the lives of millions of people, a natural goal is to predict (if possible) the future climatic evolutions. However, due to the high complexity of the climate system, this is not a trivial task.
Including components with very different properties (atmosphere, hydrosphere, cryosphere, biosphere and lithosphere), the climate system is characterized by a continuously changing state, under the permanent influence of the energy coming from Sun. The most general method which allows an as exact as possible climate prediction should be based on a comprehensive understanding of the whole set of processes within the Earth system. Possible approaches toward such an understanding may be based on conceptual decompositions of climatic variability, based on specific criteria.
The hypotheses formulated to explain specific aspects of climate variability may be validated using observational data and numerical experiments (e.g. general circulation models). Observational datasets containing systematic measurements with quasi-global coverage are available only for the last 150 years. However, different techniques have been developed to construct proxy records which may provide useful information for past climate (e.g. corals, tree rings, sediments, ice-cores, speleothems).
Such considerations created my personal subjective opinion that the process of investigating and understanding the climate changes is a challenging but wonderful task.