The K¿ppen climate classification system [K¿ppen, 1923> is a scheme that provides an objective numerical basis for defining regional climatic types based on temperature and precipitation. Through the years it has been used as a scientific and teaching tool for prescribing the general world pattern of climates. Here for the first time an evaluation of system is performed by employing coextensive temperature and precipitation data over the N. Hemisphere for the last 140 years. First the global pattern of climate type sensitivity is obtained. From this pattern it is discovered that several climate types exhibit a rather strong variability. Since all climate types depend on temperature we then tested whether or not the above variability is due to the fact that over the last 140 years the global climate system exhibits a well documented positive temperature trend known as global warming. We found that the K¿ppen system is rather insensitive to the observed global warming and concluded that overall the system performs rather poorly over Europe and Asia whereas it appears adequate over North America and North Africa. ¿ American Geophysical Union 1994