Human Impact On Air And Climate The importance of human influence on global climate change was again highlighted in a groundbreaking study of Earth's temperature over the past 600 years. Reconstructing the global temperature record, climatologists have determinined that three recent years were the warmest years since AD 1400 -- 1997, 1995, and 1990. The study, conducted by Michael Mann and Raymond Bradley of the University of Massachusetts geosciences department, along with University of Arizona colleague Malcolm Hughes, is detailed in the April 23 issue of the journal Nature. The researchers were able to estimate tempe