Climate Change, Plant Biology and Public Health Impacts of elevated temperature and CO2 on agriculture and beyond

In addition to being the principle greenhouse gas, carbon dioxide (CO2) is also the principle source of carbon for photosynthesis. Although the stimulation of plant growth by rising CO2 is usually viewed as a positive aspect of climate change, the rise in CO2 is indiscriminate with respect to the stimulation of both anthropogenically important and deleterious plant species. Here we present laboratory and in situ data from studies that have examined the response of undesirable plants to CO2 increases during the 20th century (from 290 to 375 parts per million by volume, ppmv), as well as that projected for the mid-21st century (500-l000 ppmv). Data from these studies indicate a number of potential indirect effects (changes in nutritional content of foods, increased use of herbicides) as well as potential direct effects (increased ragweed pollen) on public health. These initial results regarding CO2 and/or temperature-induced changes in plant biology suggest a number of potentially unfavorable and some favorable consequences in human systems. Introduction Documented and projected changes in the concentration of atmospheric carbon dioxide (CO2) and other gases suggest potential changes in temperature and global climate that could negatively impact human health. Public health concerns related to climate stability include changes in the range of insector rodent-borne diseases (malaria, yellow fever, dengue); changes in waterborne and seafood-borne disease outbreaks; increasing ground-level ozone and respiratory ailments; contamination of drinking water due to increased flooding; and, heat-related deaths (stroke). At present, there is a concerted effort among academic and government institutions to both recognize the degree of health risk and to formulate strategies to minimize adverse impacts. The implications of a changing climate with respect to floods, storms, range of disease vectors, etc. are well recognized. However, less attention has been given to potential associations between climate, plant biology and human health. Plant biology is directly affected by rising CO2, since CO2 is the sole supplier of carbon for photosynthesis. Because 96% of all plant species are deficient in the amount of CO2 needed to operate at maximum efficiency, recent increases in CO2 and future projections have already, and will continue, to stimulate plant growth, with the degree of stimulation being at least, potentially, temperature dependent. Critics of the role of carbon dioxide as a greenhouse warming gas have stressed that