Explaining wildfires

Meteorologists aren’t yet able to forecast wildfire outbreaks, but there are three conditions that must be present in order for a wildfire to burn. Firefighters refer to it as the fire triangle: fuel, oxygen, and a heat source. Four out of five wildfires are started by people, but dry weather, drought, and strong winds can create a recipe for the perfect disaster—which can transform a spark into a weeks- or months-long blaze that consumes tens of thousands of acres.

Another possible cause of forest fires is lightning. Scientists have found that every degree of global warming sets off a 12 percent bump in lightning activity. Since 1975 the number of fires ignited by lightning has increased between two and five percent.

Historically, wildfires are actually supposed to be beneficial to certain natural landscapes, clearing underbrush in forests and triggering the release of seeds in some plant species, such as the Jack pine.

Unfortunately, the suppression of naturally occurring, low-intensity forest fires has actually aided in the ability for high-intensity wildfires to run rampant.

In the first half of the 20th century, the U.S. Forest Service suffered from what historian Stephen Pyne calls “pyrophobia,” or the desire to suppress all wildfires (even the good ones). Since the science of forestry first took root in temperate Europe, which is home to a vastly different forest ecosystem than those found in the United States, fire was seen by early U.S. foresters as a problem caused by people.

In some places, the path toward a safer, more ecologically sound relationship with fire is being blazed with prescribed fire, and what’s being called by officials as “managed wildfire.” Fire crews put their efforts to suppress wildfires around the most fire-prone areas, such as communities, municipal watersheds, and sequoia groves. Otherwise they are learning to let some fires burn themselves out, as nature intended.

Forest fires actually have the ability to heat up the entire planet, a NASA study from 2016 revealed. In ecosystems such as boreal forests, which store more carbon than any other terrestrial ecosystem on the planet, the effects of climate change are playing out twice as fast.

Fires ravaged the boreal forests of Canada’s vast north woods in May 2016 and continued for months, consuming millions of acres of trees, and scorching the rich organic soil on the forest floor, which serves as a large reservoir for carbon. For every degree that our planet warms, the forest needs a 15 percent increase in precipitation to compensate for increased dryness.

Worldwide, wildfire smoke kills 339,000 people a year, mostly in Asia and sub-Saharan Africa, according to estimates. Tenfold increases in asthma attacks, emergency room visits, and hospital admissions have also been reported when smoke blankets the places where people live.

National Geographic