Basic results of IPCC Working Group II, derived in the process of the work at the Fourth Assessment Report, are considered in brief. The results are given in conformity with the Summary for Policymakers adopted at the Plenary Meeting of Working Group II in Brussels on April 6, 2007. The authors' comments on some results connected with the key vulnerable elements of natural and socioeconomic systems are given in the conclusion.Key impacts: Dependence on increasing global mean air temperature (they also depend on adaptation, rate of temperature change, the way of socioeconomic development). Two asterisks denote high reliability impacts. Changes in global mean temperature are given relative to the level of 1980-1999. "Significant" means > 40%. An asterisk denotes the impact based on the assessment of the rate of the sea level rise of 4.2 mm/year in 2000-2080.

Results of a field experiment on studying solar radiation passing in the visible wavelength range are described with the model aerosol media created in the surface atmosphere. High-efficiency thermocondensation generators were used for creating model aerosol media. The index of refraction and an average size of the aerosol particles formed are close to those characteristic of the natural stratospheric aerosol. The composition and technical characteristics of the equipment complex used in the experiments to control aerosol optical and microphysical parameters and meteorological conditions of the experiment are considered. The Gaussian model of impurity dispersion in the boundary layer is used for the analysis and interpretation of measurement results. It is found that with a number concentration of aerosol particles of~10 2 -10 3 cm -3 (which corresponds to the aerosol density in the deposited layer of about 1-10 mg/m 2 with the layer thickness along the ray path of about 100 m) the solar radiation attenuation with artificial aerosol layers accounts for 1 to 10%. Model estimates are in satisfactory agreement with the measurement results.

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