For centuries, long before the basics of infectious diseases were understood, humans realized that climate change had an effect on epidemic diseases (Patz et al. ). The Roman aristocracy retreated to the hills each summer to avoid malaria, and South Asians learned that in early summer, heavily curried foods were less likely to cause diarrheal illness (Patz et al.) . Patz et al. stated that there were three distinct transition periods that altered the relationship between man and microbe. These three transitional periods are: 1) the first human settlements allowed enzootic infectious species to enter the human population, 2) the first civilizations of Eurasion exchanged dominant infections through military and trade contacts, and finally, 3) European expansionism over the last five centuries caused the spread. infectious diseases that are often fatal. They also argue that we may be in the fourth transition, with climate change having a wide range of impacts on the occurrence of infectious diseases in human populations. Most climate scientists agree that the primary cause of global climate change is human expansion of the greenhouse effect. effect. This is global warming, which occurs when the atmosphere traps heat radiating from Earth to space (climate.nasa.gov). The main gases contributing to the greenhouse effect are water vapor, carbon dioxide, methane, nitrous oxide and chlorofluorocarbons (climate.nasa.gov). Human activities modify the natural greenhouse effect. The burning of fossil fuels like coal and oil has increased the amount of carbon dioxide in the atmosphere (climate.nasa.gov). Carbon dioxide levels have increased from 280 parts per million to 379 parts per million over the past 150 years due to human action... middle of paper ...... more disease-friendly conditions in regions that did not previously host diseases or disease carriers (climate.org). Climate change accelerates the spread of diseases largely because warmer temperatures increase the geographic area in which disease-carrying animals and insects can survive (climate.org). Climate change contributes to more extreme events such as floods, storms, droughts and uncontrolled fires, which can also have a negative effect on human health (climate.org). Flooding can spread bacteria and viruses and can also contribute to insect breeding (climate.org). All of these together will have enormous implications for human health. We could expect a higher infection rate as well as a higher mortality rate in some areas. We could also expect children and the elderly to get sick and even die more often..