At the present stage of environment knowledge development special attention is given to the research of anthropogenic climate change impact on various spheres of social activity and natural systems. One of the basic objects of such research is urban areas. In the modern world the rate of urbanization is unprecedented: beginning from 1950 till 2012 the urban population has increased almost by five times. According to the National Climatic Doctrine signed by the President of the Russian Federation, when working out the programs of sustainable development, including the municipal level, it is necessary to insure the solution of such tasks as the development of legislation acts concerning the future development of territories taking into consideration the consequences of climatic factor impact, realization of adapting measures to expected climate changes, substantiation and installation of a responding system on dangerous weather and climatic phenomena, energy conserving technologies and the other measures. This paper is focused on large cities, and its authors being St. Petersburg inhabitants, have addressed to the analysis of some features of general adaptation strategy of megacities to climate changes giving as an example of their study St. Petersburg, the largest city of northern Europe. In the paper the examples of the most vulnerable components of St.-Petersburg infrastructure influenced by expected climate changes are presented. In developing global warming amplified by local climatic features of large cities, it is possible to say that such most «vulnerable components» are meteorological and hydrological standards for a long time fixed in legal-standard and technical standard certificates. Epidemic situations and human health, modern building designs, transport infrastructure, industrial manufacture, green plantations, especially protected natural areas and objects as well as historical-cultural memorials are exposed to more and more intensive impacts of climatic factors, whose estimation accuracy depends on adequate representation of their modern and expected changes in the appropriate normative documents. So, one of major hydrological standards in St. Petersburg, which in many respects regulated St. Petersburg town-planning is maximum water level increase during the Neva river flooding. Besides the other things, the importance of this problem is also discussed in this paper. In the list of the possible consequences, which are extremely necessary for understanding global warming in megalopolises, including St.-Petersburg, there is an issue of climate change influence on human health which is analyzed using the data of extreme temperature anomaly of the hot 2010 summer. The examples, discussed in this paper testify that the change of meteorological and hydrological norms when expecting climate changes can practically affect all components of megacities infrastructure and life. Already now these changes became rather appreciable and undoubtedly should be included in norm-legal documents used for planning and maintenance of sustainable urban system development.