Right now Indonesian farmers are burning hundreds of thousands of hectares of the oldest rainforests on earth to clear land for plantation crops. The resulting smoke has covered Southeast Asia in a thick haze, affecting the health of hundreds of millions of people. This happens every year, which is incredibly frustrating because the Indonesian government made slash-and-burn agriculture largely illegal in 2001, following the severe regional haze it generated 1997-1998. On paper those laws were strengthened in 2009 and again 2014, but in actuality the 2015-2016 season is likely to be the worst on record.
Humans and landscape fire are inextricably intertwined
Although landscape fire is a natural part of the global ecosystem, humans have been influencing fire regimes for millennia. We employ fire as a tool to clear previously forested areas, to change the properties of underlying soils, and to lessen the risk of catastrophic wildfire. We also employ fire suppression as a tool to protect our lives, our assets, and our natural resources.
This complex relationship with fire is further complicated by its complex role within the global climate system. Briefly put, a changing climate leads to more fire-prone conditions for many forests due to warmer temperatures and less precipitation. The resulting fires tend to be larger and more intense, which leads to more greenhouses gases being released to the atmosphere, and less global vegetation to act as a carbon sink. Indonesian farmers are currently putting this feedback cycle to their advantage by using the dryer-than-normal conditions created by a particularly strong El Niño.
Tiny particles, huge health implications
Smoke is composed of particulate matter measuring less than 2.5 micrometers in diameter (PM2.5), which is about 5% of the width of a human hair. Particles of this size can be inhaled deep into the lungs, where they elicit the same kind of immunological response as other other foreign invaders, such as viruses or bacteria. The resulting inflammation can then affect the entire body, not just the respiratory system.
We know that long-term exposure to PM2.5 leads to increased chronic disease and decreased life expectancy within urban populations, and we assume that PM2.5 from landscape fire smoke has a similar effect based on the available evidence. In addition, we know that short-term exposure to PM2.5 from landscape fire smoke and other sources can trigger acute exacerbations of those chronic diseases. On days with more PM2.5 we expect more people to have respiratory symptoms, to need rescue medications, to be admitted to hospital, and to die. We also know that women who are exposed to PM2.5 during their pregnancy are more likely to have pre-term births and/or smaller babies, which can have lifelong health implications for those children.
Landscape fire smoke causes hundreds of thousands of deaths each year
We know that landscape fires are a globally important source of PM2.5, though their contribution to short- and long-term exposures varies from place to place and year to year. In areas such as Southeast Asia, sub-Saharan Africa, and South America, smoke from annual landscape fires contributes a significant and increasing proportion of lifetime PM2.5 exposures. It follows that landscape fire smoke is responsible for a significant and growing burden of chronic disease and reduced life expectancy in the affected populations.
We first attempted to quantify these global impacts by estimating the number of annual deaths attributable to landscape fire smoke from 1997 to 2006. The estimate for the strong El Niño year of 1997-1998 was 532,000 deaths, of which 296,000 were in Southeast Asia. While these numbers are based purely on statistical models, they help us to contextualize the issue and to better understand how landscape fire smoke affects the health of different populations during different periods.
We use effective policy to protect populations from PM2.5 from other sources
The health effects of PM2.5 in urban environments have been studied for decades, and results from those studies have been used as part of the global impetus for policies that control emissions from sources such as vehicles, power generation, and industry. Furthermore, ambient concentrations of PM2.5 are now measured around the world to help governments and citizens understand trends in short- and long-term population exposures. These data have been combined with satellite measurements and air pollution models to estimate that exposure to PM2.5 is one of the top ten risk factors for global death and disability, following risk factors such as smoking, obesity, and diets low in fruits and vegetables. However, exposure to PM2.5 is different from these other risk factors because it affects the entire population and it cannot be easily modified by individual behavioral changes. We rely on policies and technologies that control PM2.5 emissions at their source to improve and protect public health.
Southeast Asia needs effective policy to protect its population from landscape fire smoke
The fires creating the haze in Southeast Asia are not episodic and unpredictable like wildfires in many parts of the world. They are deliberately set, year after year, to clear forested land for agricultural purposes. The socioeconomic motivations underlying the need to clear land are complex, but the argument against using fire is simple. The only way to reduce the burden of haze-related death and disability in the entire population of Southeast Asia is to effectively restrict or prohibit the use of fire for land clearing, preferably long before the next strong El Niño year.