Heat exhaustion is marked by excessive dehydration and electrolyte depletion. Early hypotheses included excess concentrations of CO2 and oxygen depletion. Both chlorine and bromine contribute significantly to overall ozone depletion. Halothane also contributes to ozone depletion. The EPA also researched the implications of stratospheric ozone depletion. It would not cause ozone depletion or climate change. NOAA data is also relevant to the issues of global warming and ozone depletion. This cancer connection is one reason for concern about ozone depletion and the ozone hole. The mechanism of CD4 T cell depletion differs in the acute and chronic phases. These include the chlorofluorocarbons (CFCs) that cause ozone depletion and HCFCs (such as chlorodifluoromethane). It was replaced with R-134a refrigerant, which has no ozone depletion potential. It also lowers energy costs by preventing future resource depletion. Problems also have arisen as groundwater supplies used for irrigation face depletion. Public misconceptions and misunderstandings of complex issues like the ozone depletion are common. They were not aware of the ozone layer depletion at the time.