The paper concerns influences of global warming on health of the population. We consider an important parameter of global warming - a heat index - that is a characteristics of a human thermal comfort and represents a combination of air temperature and relative humidity. Based on the heat indexes, we propose a new approach - the fuzzy methods - to investigate heat waves which, if defined properly, can be used to assess the potential impacts of climate change on human health, e.g., in the heat-health warning systems. We find typical characteristics of heat indexes during different time periods, using most typical fuzzy expected values. We use these typical characteristics to process heat waves. Our results are applied on the data collected in the Ministry of Preservation of the Environment of Georgia during 1955-1970 and 1990-2007 years as well as free accessible meteorological data of air temperature and relative humidity during August 2003 in Paris (France) and Tbilisi (Georgia). (C) 2014 Elsevier B.V. All rights reserved.