During the last decade, more than 300 civilian workers died on the job due to environmental heat exposure. In addition, heat could be a contributing factor to many other severe or fatal injuries or illnesses.

A number of worker populations may be particularly vulnerable to threats from climate change, including outdoor workers, emergency responders, commercial fishermen, healthcare workers, firefighters, farmers, transportation workers, and workers in hot indoor environments such as warehouses and factories. It is also likely that the variety of occupations and number of workers exposed will increase. The effect of climate change on workers is of particular concern because workers may be exposed to conditions that the general public can elect to avoid (a situation not unique to climate change) and because employment increases are predicted for the most at-risk workers (for example, wildland firefighters). Potential health consequences to workers who may be affected by a changing climate include asthma, respiratory allergies, and airway diseases; cancer; cardiovascular disease and stroke; heat-related morbidity and mortality; mental health and stress-related disorders; neurological diseases and disorders; waterborne diseases; weather-related morbidity and mortality; and vector-borne, zoonotic, and other infectious diseases such as Lyme disease, Valley Fever (coccidioidomycosis), chikungunya, and dengue. Climate change directly affects workers through hazards such as increased ambient temperatures, air pollution, extreme weather, and increased prevalence and geographic range of vector-borne and other infectious diseases. Occupational hazards resulting from the indirect effects of climate change are likely to occur from industrial transitions, emerging “green” industries (renewable energy, recycling, and carbon sequestration, for example), increased use of pesticides, changes to the work force resulting from altered economic activities, and changes in the built environment. Higher temperatures or longer, more frequent periods of heat may result in greater occupational heat stress, potentially leading to more cases of heat-related illnesses (heat stroke, heat exhaustion, and so on), decreased chemical tolerance, and fatigue. Exposure to increased temperature can also result in reduced vigilance and increased risk of injury or lapses in safety. Thousands of heat-related illnesses occur each year in the United States. During the last decade, more than 300 civilian workers died on the job due to environmental heat exposure. In addition, heat could be a contributing factor to many other severe or fatal injuries or illnesses, such as those caused by falls or myocardial infarctions. With a warming climate and more frequent extreme weather events predicted, heat exposure and heat stress are becoming a prominent employee safety issue. Even small changes in average temperature can potentially translate into a substantial increase in the number of deaths and cases of severe illness. Air pollution is affected by climate change, and outdoor workers have longer exposure to air pollutants, which may be linked to chronic health effects such as respiratory diseases and allergic disorders. For example, elevated temperatures can increase levels of air pollution (including ground-level ozone) and wildfire smoke, which contains particulate matter, carbon monoxide, nitrogen oxides, and various volatile organic compounds and can significantly reduce air quality, both locally and in areas downwind of fires. Extreme weather events or natural disasters such as floods, landslides, storms, lightning, droughts, and wildfires are becoming more frequent and intense. As the frequency and intensity of these events increases, there will be a need for more emergency responders. Workers involved in rescue and cleanup will have more exposure to the risky conditions created by weather disasters. For example, climate change is currently increasing the vulnerability of many forests to wildfire. Since 1983, the National Interagency Fire Center (NIFC) has documented an average of 72,000 wildfires per year. The data do not show an obvious trend during this time, but the extent of area burned by wildfires each year appears to have increased since the 1980s. According to NIFC data, of the 10 years with the largest acreage burned, nine have occurred since 2000. This period coincides with many of the warmest years on record. And there is something of a synergistic effect: climate change influences fire, and fire activity can influence climate. The fire season varies depending on location but has historically been from mid-April through October in the U.S. In the last 25 years, the fire season has increased by an average of 78 days. Thus firefighters will have longer durations of exposures and less recovery time between fire seasons. The increase in wildfires will require response from an ever-increasing number of firefighters, including volunteers. Statistics from the Federal Emergency Management Agency indicate that from 2000 to 2013, almost 300 wildland firefighters died while on duty. Common hazards faced by wildland firefighters can include burns, heat-related illnesses, smoke inhalation, and injuries from slips, trips, and falls. In addition, due to prolonged intense physical exertion, wildland firefighters are at risk for rhabdomyolysis, a condition resulting from an increase in core body temperature and subsequent breakdown of muscle cells and the release of their contents into the bloodstream. Extreme weather events may also cause damage to infrastructure (power lines, roads, and transportation) and buildings. Workers could be put in new or unfamiliar circumstances leading to a high risk of traumatic injury. Some workers may be at increased risk of violence if mobility, electricity, communication, food, and shelter become compromised. In summary, extreme weather events and weather disasters are expected to lead to an increased risk for occupational fatalities, injuries, diseases, and mental stress. Changing temperatures and shifting rainfall can affect habitats of vectors, pathogens, hosts, and allergens. Increased prevalence and distribution of water-borne and food-borne pathogens could affect outdoor, emergency response, and healthcare workers. Pollen may increase from earlier flowering and longer pollen seasons. Increasing numbers of hurricanes and floods could lead to more houses with mold and more remediation and construction workers exposed. Increasing temperatures and atmospheric carbon dioxide may increase the growth and spread of poison ivy and other poisonous plants.

Figure 1. Longer, more frequent periods of heat may result in greater occupational heat stress.

Figure 2. Global temperature change: decade averages (source: National Oceanic and Atmospheric Administration).

Temperature changes affect insect vectors, increasing their populations, extending their transmission seasons, and expanding their distribution seasonally and spatially. Outdoor workers may be at increased risk for mosquito-borne diseases (such as West Nile) and tick-borne diseases (such as Lyme disease). Previous research has found that outdoor workers were five times more likely to acquire Lyme disease than indoor workers. Vector ranges will continue to expand, and new diseases not previously prevalent in the U.S. (dengue and chikungunya Virus are examples) will be introduced. Valley Fever has increasingly been found to be an occupational hazard—archeologists are among the exposed worker populations—and its endemic range could increase with a changing climate. THE IH RESPONSE As our society responds to climate change, “green” industries such as renewable energy production and recycling are projected to grow, and some traditional industries are expected to transition toward activities such as retrofitting buildings for energy conservation. These changes present opportunities for industrial hygieni​sts to apply their knowledge of well-understood hazards such as slips, trips, and falls; musculoskeletal disorders; and chemical exposures in new environments. Vigilance is required to identify unanticipated hazards resulting from new work practices, or use of alternative chemicals and materials. What can we do as industrial hygienists? Staying informed about emerging issues and hazards associated with climate change will help us to respond and implement effective prevention strategies. There is much we can do using established tools and strategies for hazards that we routinely deal with (temperature extremes, pesticide use, and so on) that may be exacerbated as our climate changes. As we identify emerging issues we can alert researchers, regulators, and PPE manufacturers of specific worker safety and health needs. We can also educate others, including company executives and safety professionals, about how to prepare and respond. Industrial hygienists have the skills and knowledge needed to develop specific company-level plans to address this emerging threat to worker safety and health. Please check the NIOSH climate change topic page for additional information and to stay informed of climate change and work-related issues. MAX KIEFER, MS, CIH, is the interim associate director for science in the NIOSH Western States Division. He can be reached at myk3@cdc.gov. JOANNA WATSON, MSC, DPHIL, is an epidemiologist in the NIOSH Western States Division and project officer for the NIOSH Climate Change Initiative. She can be reached at wgq6@cdc.gov.