Introduction

As temperatures warm, sunny days multiply, and the last remnants of winter melt away, dreams of long summer days spent outside come to fruition. Unfortunately, this also signals the inevitable beginning of wildfire season. Wildfires can be massively destructive and dangerous, while also being a natural and vital process that rejuvenates our natural landscapes. Wildfires remove brush and debris from the forest floor, helping prevent the debris from later acting as fuel to ignite large, uncontrollable fires. Larger, healthier trees can subsequently access more nutrients, therefore allowing our forests to thrive. However, in recent years fires have become increasingly severe, destructive to property, and threatening to human life and health. Current climate change predictions only predict longer and more severe wildfire seasons. And, as the population grows, developments continue to move closer to the urban-wildland interface with more people now living in the path of these deadly blazes. With more people estimated to be exposed to longer and more destructive wildfire seasons, the effects of smoke exposure on our health is a growing public health concern.

Climate Change

Climate change has led to higher temperatures, drier conditions, earlier snowmelt and a changing snowpack. Combined with the previous history of U.S. fire suppression, this has created dry, hot conditions with forest floors full of debris and primed to ignite uncontrollable, destructive wildfires. In 1983, 18,000 fires burned a little more than 1 million acres. Since then, there has been a steady, yet variable increase. The National Interagency Fire Center reports 71,499 wildfires burned approximately 10 million acres in 2017. According to NASA's Goddard Institute for Space Studies, global temperature on earth increased by 1 degree Celsius (1.9 degrees Fahrenheit) since 1880. However, 2/3 of the warming has increased since 1975. The correlation between global warming and increased extreme weather events, including wildfire severity, continues to increase.

Burning trees release massive amounts of carbon into the atmosphere further contributing to the vicious cycle of climate change. In the United States, the western forests are a vital source of carbon sequestration; they capture 20-40 % of U.S. carbon emissions. It is imperative to protect our forests if we want to slow the destructive forces of climate change. Many different models exist to estimate future wildfire potential with our current rate of climate change and population growth. Liu et al. estimate a 160% increase in exposure to wildfire smoke under moderate climate change predictions by 2046-2051. With this interactive map used by Lui, anyone can select a county in the Western United States and view present and future (2050) fire risk index, length of seasons, and intensity.

High temperatures and drought have not only directly increased the length and severity of wildfire season, but have also provided ideal conditions for invasive species to proliferate and threaten our forests. Bark beetle infestations have occurred across the U.S. as their physiological processes are temperature dependent and prosper in warmer climates. According to the U.S. Forest Service, 66 million trees in the South and Central Sierra Nevada have died from bark beetles since 2010.

Wildfire Smoke Composition

We know that without major changes to human activity, global warming will continue and wildfires will burn with more fury and devastation. Thus, it's essential to understand how increased smoke exposure will affect our health. Wildfire smoke is composed of fine and coarse particulate matter, carbon monoxide, carbon dioxide, methane, nitrous oxide, and volatile organic compounds along with numerous other gases. PM2.5 (fine particulate matter under 2.5 microns) is the most concerning pollutant to human health because of its ability to penetrate deeply into the lung. Fine particulate constitutes a substantial proportion of wildfire-generated particulate. However, particulate size can vary depending on the intensity of the fire, type of fuel, and whether the fire is flaming or smoldering. Therefore, the composition of smoke particulate from natural wildfires burning in the dry season versus a prescribed fire intentionally set during the wet season may vary substantially. The two different types of wildfires could have markedly different effects on health, however this has not yet been studied.

Health Effects

In Cascio’s 2018 Systemic review, the authors found multiple studies reporting strong associations between wildfire smoke PM2.5 and respiratory exacerbations. They found increased ER visits and admissions for COPD, asthma, bronchitis and pneumonia. In the same review, the data on cardiovascular disease was inconclusive with mixed results of associations between wildfire smoke and CHF, MI and cardiac arrests.

Reid and colleagues modeled daily wildfire PM2.5 exposure from a large 2008 northern California wildfire. They found that for each 5µg/m3increase in PM2.5, the risk of emergency department visits for asthma and COPD increased. They also found that effects were more prominent in women, in people living in low socioeconomic regions, and in elderly adults. A study by Liu and colleagues confirmed these results.

Studies of wildfire firefighters pre-and post-season demonstrate a decrease in pulmonary function. The most significant and consistent finding in Black’s review of six studies was a decline in forced expiratory capacity in 1 second (FEV1). Two of the six studies were able to follow up and noted that after several months FEV1 returned to baseline. When pre-and post-shift FEV1 were compared, there was no difference in FEV, suggesting the decline is due to continual exposure instead of an acute event. However, the long term health effect of repeated wildfire smoke injury is not yet known. Similarly, it is hypothesized that children are susceptible to long term effects from wildfire smoke exposure. Prior research demonstrates when children are exposed to chronic air pollution (non-wildfire sources) during susceptible periods of childhood they develop significantly decreased FEV1.

Take Action

As a healthcare provider, there are numerous ways to help your patients. You can help counsel patients who live in areas or travel to areas at risk of wildfire smoke exposure to check daily air quality and PM2.5 levels, by checking proximity of fires and air quality measurements with a tool such as this interactive map. If conditions are dangerous, advise patients, particularly those at risk, to stay indoors, close windows and doors, and use HEPA filters if available. For patients living in fire prone areas, advise them to clear their property of brush and vegetation in order to create a barrier against spreading fires. Advise those patients to have emergency plans and to be ready to evacuate. In addition to these recommendations, you can advocate for climate change and land use policies. Lead by example and decrease your own carbon footprint. Be thoughtful of your consumerism, how much you travel, your method of travel, the food you eat and the food you waste. Vote for local and state politicians and policies that will decrease carbon emissions. As a healthcare provider, your voice is respected; seize the opportunity to be heard. Call your elected leaders or write to your local congresswomen and congressmen. Encourage your hospitals and workplaces to become more sustainable and energy efficient. As summer temperatures rise, and wildfires begin to blaze, be mindful of you and your patients’ respiratory health. And, seek opportunities to advocate and protect our wild spaces so we can all enjoy the beautiful outdoors without compromising our health.