Impacts on Risk
One possible direct impact of climate change on cancer may be through increases in exposure to toxic chemicals that are known or suspected to cause cancer following heavy rainfall and by increased volatilization of chemicals under conditions of increased temperature. In the case of heavy rainfall or flooding, there may be an increase in leaching of toxic chemicals and heavy metals from storage sites and increased contamination of water with runoff containing persistent chemicals that are already in the environment. Marine animals, including mammals, also may suffer direct effects of cancer linked to sustained or chronic exposure to chemical contaminants in the marine environment, and thereby serve as indicators of similar risks to humans. Climate impact studies on such model cancer populations may provide added dimensions to our understanding of the human impacts. Another direct effect of climate change, depletion of stratospheric ozone, will result in increased ultraviolet (UV) radiation exposure. UV radiation exposure increases the risk of skin cancers and cataracts. The incidence of typically nonlethal basal cell and squamous cell skin cancers is directly correlated to the amount of exposure to UV radiation. This effect is compounded by several other variables including temperature and exposure to other compounds that can amplify the carcinogenic potential of UV radiation. Rising temperatures (such as occur at night versus day and in summer versus winter) are associated with increases in UV exposure. If increases in average or peak temperatures occur as a result of climate change, an increase in the incidence of non-melanoma skin cancers may occur. Previous studies have shown that increased UV radiation exposure combined with certain polycyclic aromatic hydrocarbons (PAHs) can enhance the phototoxicity of these compounds and damage DNA. However, it is also possible that increased exposure to UV radiation could elevate levels of circulating Vitamin D, which has been associated with a decreased risk for certain cancers such as colorectal cancer. Increased UV radiation also could impact the human immune system and alter the body’s ability to remove the earliest mutant cells that begin the cancer process, although it is unclear whether these changes would be beneficial or detrimental.