We've all seen the heartbreaking TV reports of communities devastated by wildfires, returning to pick through the smoldering ruins of their homes.
But there are other, less visible wildfire tragedies, like the asthmatic child choking for breath in the ER, and the elderly man with emphysema hastened to his grave.
These insidious effects of wildfire smoke are hard to disentangle from illnesses worsened by traffic fumes and other forms of air pollution. But wildfires are thought to be claiming thousands of lives across North America — and the toll will likely rise as climate change intensifies.
Already, wildfires cause "some of the worst air quality that populations in North America will ever experience," Sarah Henderson of the British Columbia Centre for Disease Control in Vancouver, Canada, told BuzzFeed News.
And as the West Coast gets hotter and drier, fires are expected to become more frequent and burn more intensely. Indeed, a Harvard team has estimated that by 2050, smoke from these fires will cause the summertime air above the western United States to contain up to 27% more soot than it does today, and up to 70% more of the other types of fine particles that are contained in smoke.
That's worrying, because this will boost levels of airborne "PM2.5" — airborne particles less than 2.5 micrometers across that can cause lung and heart disease.
The worst affected areas include cities on the Pacific coast, which can be hit by smoke plumes from major wildfires.
On this map, the largest estimated death tolls are where large populations can find themselves downwind of major fires. In 2003 and 2007, for instance, catastrophic wildfires sent smoke billowing across Southern California, including Los Angeles and San Diego.
By analyzing more than 40,000 records of people admitted to the hospital with breathing or circulatory problems, researchers led by epidemiologist Ralph Delfino of the University of California, Irvine, painted a picture of the health effects of the 2003 fires.
Delfino's team related PM2.5 measurements by zip code to patients' addresses. The researchers found that wildfire smoke increased admissions for conditions including bronchitis and pneumonia. The biggest effect was on asthma, with heavy smoke exposure boosting hospital admissions by 34%. Worst affected were the elderly and children age 4 or younger.
Wildfire smoke can even reach into the womb: Pregnant women who were exposed to smoke from the 2003 fires gave birth to smaller babies. It was a small effect — reducing the babies' birth weight, on average, by less than half an ounce.
"Some people might say that's not a huge deal," Rachel Morello-Frosch of the University of California, Berkeley, who led the study, told BuzzFeed News. But for some vulnerable babies, even small reductions in birthweight could be dangerous, she said.
Bad as Southern California’s fires can be, Southeast Asian cities have it much worse.
Thankfully, wildfires as intense as those that hit Southern California in 2003 and 2007 are still relatively rare and brief events. But across much of Southeast Asia, including the city state of Singapore, prolonged and intense hazes from wildfire smoke happen every year.
The blame for Singapore's smoke problem lies mostly to the south and west, in Indonesia, where forests are being cleared by burning for agriculture. Swamp forests have also been destroyed and drained, exposing peaty soil that can itself ignite.
Globally, wildfire smoke is already estimated to kill 339,000 people each year.
The data behind these maps comes from a 2012 study led by Fay Johnston of the University of Tasmania in Australia. Her team estimated exposure of populations across the world to wildfire smoke, based on satellite observations and a computer simulation of how PM2.5 circulates through the atmosphere.
Johnston's team then converted exposure estimates of PM2.5 into approximate death counts, based on the known health effects of these tiny particles.
The researchers' best estimate of global deaths from wildfire smoke — 339,000 — compares to some 800,000 people thought to be killed each year by traffic fumes and other forms of urban air pollution, and an estimated 183,000 people who die from illegal drug use.
Henderson, who worked on the study, told BuzzFeed News that the researchers decided not to publish estimated death tolls for individual countries — given the large margins of error, they were uncomfortable quoting numbers for U.S. or Canadian residents killed each year by inhaling smoke from wildfires.
The American West isn't in immediate danger of going the way of Southeast Asia. But given the threat from climate change, air quality officials are ramping up their forecasts and warnings to help people protect themselves from the worst effects of wildfire pollution.
The path of smoke plumes can be predicted using computer models similar to those used by weather forecasters, and many state and local agencies are now incorporating these predictions into air quality forecasts.
When smoke from wildfires threatens the Los Angeles Basin, for instance, the South Coast Air Quality Management District starts using smoke plume forecasts — and issues alerts if any of the 38 zones in its forecast area is likely to to be affected.
These typically tell vulnerable people to stay indoors and run an air conditioner with a filter, and urge everyone to avoid vigorous exertion. Schools are also told to avoid outdoor activities.
"I've canceled homecoming football games," the district's planning and rules manager, Joe Cassmassi, told BuzzFeed News. "That made me very unpopular."
We can expect more of these disruptions with climate change, Cassmassi added, as smoke plumes threaten the cities of the American West more regularly. "As conditions become more arid, we're going to see more and more wildfires."
Peter Aldhous is a Science Reporter for BuzzFeed News and is based in San Francisco. His secure PGP fingerprint is 225F B2AF 4B8E 6E3D B1EA 7F9A B96E BF7D 9CB2 9B16
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