California and Climate Changes: An Update

Most epidemiologic research on temperature and health in California has been conducted over the past two decades. Studies initially focused on mortality followed by morbidity outcomes such as hospitalizations and emergency room visits and, most recently, adverse birth outcomes, such as preterm delivery, low birth weight, and stillbirth. The evidence to date suggests positive associations between apparent temperature, a combination of temperature and relative humidity, and mortality and morbidity from several health outcomes, such as cardiovascular diseases including ischemic heart disease, myocardial infarction, and congestive heart failure; diabetes; gastrointestinal illnesses; respiratory outcomes such as pneumonia; kidney diseases; mental health–related outcomes; as well as the more typical causes including dehydration and heat-related deaths and illnesses. These associations have been observed during the warm season (April/May through September/October) in California at background ambient levels. These associations are mostly independent of air pollutants. Several vulnerable subgroups have been identified, including infants, young children, pregnant women, the elderly, and racial/ethnic minorities. During heat waves, health effects have been more pronounced, raising public health concern in the future with more intense, frequent, and longer heat waves predicted.