One study shows that the frost-free season in the Northeast began 11 days earlier in the 1990s than it did in the 1950s. At the high end of the scale, those summer days when temperature and humidity conspire to become killers have been increasing since the 1940s. Despite the hundreds of deaths caused by a brief Midwestern heat wave in 1995, the records don't reveal any significant increase in hot days between 1931 and 1997. The culprit is likely to be humidity. There appears to be more water vapor in the atmosphere because warmer temperatures are stepping up the rate of evaporation, say climatologists.
Records also show that the amount of rain falling over large regions of the world is increasing.
But the effects on weather are not more misty mornings and drizzly days. And that translates to more flash floods. Quite simply, more people are living in the paths of storms. The rate mirrors the population growth in flood-prone areas. According to the Census Dept., coastal habitation in Florida grew from 1 million in 1940 to 10 million in 1990.