In 2019 and early 2020 alone, infernos in the Amazon rainforest, California wildfires, and Australia wildfires billowed smoke that traveled thousands of miles across entire oceans and continents.
In 2019 and early 2020 alone, infernos in the Amazon rainforest, California, and Australia sent smoke into the atmosphere for thousands of miles across entire oceans and continents.
It’s easy to think that wildfire smoke only affects those living closest to the blaze.
But research suggests that wildfire smoke has become a more pressing air quality issue as climate patterns create drier, hotter conditions. These conditions increase the possibility of wildfires by not only being more likely to ignite but also increasing the likelihood of longer burns.
More fire means more smoke – and over time, the combination of the changing global climate and air pollution from weeks-long wildfires may have dangerous consequences.
Wildfires have become more severe
If you thought you heard more breaking news than usual about wildfires in the past few years, your instincts are correct. As early as 2016, researchers were already noting stark patterns around the length and severity of wildfires.
A June 2016 report by Climate Central found that the average length of wildfire season in the western U.S. is 105 days longer today than in the 1970s – from under 150 days in 1970 to over 250 days in 2016.1
The report also found that the average size of fires in the western U.S. grew from just over 200,000 hectares in 1970 to nearly 810,000 hectares in 2016. In 2007 alone, nearly 1,620,000 hectares burned, and another 1,214,000 burned in 2012.
The average length of wildfire season in the western U.S. has gotten 105 days longer from 1970-2016. Also, the average of hectares burned has increased from just over 200,000 hectares to over 810,000.
According to a 2011 study, this is mainly due to warming trends in the global climate that are making peak wildfire seasons hotter and melting snowpack earlier.2
Researchers also found a correlation between how early snowpack melts and how severe wildfires are. But what exactly is a snowpack, and what does it have to do with wildfires?
Snowpacks are huge build-ups of snow that occur in cold climates and high altitudes and take months to thaw and melt. They’re also valuable sources of fresh water that turn into streams and rivers as they thaw when the weather warms up during spring and summer.
Some snowpacks last for months until they’ve fully melted, providing fresh water, humidity, and moisture to areas spanning hundreds of miles and immersing big pieces of land in streams, rivers, and reservoirs that would otherwise be dry and more vulnerable to ignition.
Once a snowpack is fully melted, this major water source disappears until the next big snowfall. This leaves the region around it drier and more susceptible to breakouts of wildfires from even the smallest ember from a discarded cigarette or lightning strike that sets a tree ablaze.
And increasing global temperatures that last longer and start earlier accelerate the melting of these snowpacks and reduce the amount of local rain and snowfall that create snowpacks in the first place – and less snow equals smaller, less potent snowpacks.
Increasing global temperatures accelerate the melting of snowpacks, reduce rain and snowfall, and leave regions drier and more susceptible to breakouts of wildfires from even the smallest ember from a cigarette or lightning strike.
There are two major consequences of this.
First, long months of snowpack melt typically allow high volumes of water to evaporate into the air and condense into humidity. Higher humidity means lower risk for wildfires because there’s more moisture in the air to keep areas damp and less susceptible to fire.
The smaller the snowpack and shorter the melt, the less humidity in the air to protect an area against wildfires. Second, moisture from snowpack melt helps form clouds that pour rain or snow onto the area. This provides another protective layer against wildfires. The less snowpack from drier winters and springs, the less water that can evaporate and rain back down.
This can multiply the risk of wildfires in dry regions that are already at high risk.
A 2018 study in Proceedings of the National Academy of Sciences (PNAS) confirmed this relationship between smaller snowpacks and higher wildfire risk by looking at decades worth of fire data across tens of millions of hectares of lands in the United States.3
In this study, researchers looked at the total amount of rain along with how many wildfires had burned from 1984 to 2015 across the entire western United States.
The researchers confirmed the vicious cycle of climate change, reduced rainfall, reduced snowpack melt, and wildfire severity. The less rain and the more wildfires that burn in these densely forested areas, the larger new wildfires become and the longer they burn. And the more and longer wildfires burn, the more the cycle begins anew - adding carbon pollutants and chemicals to the atmosphere that further contribute to warming global temperatures.
Research confirms the vicious cycle of climate change, reduced rainfall, reduced snowpack melt, and wildfire severity – the less rain and more wildfires that burn, the larger new wildfires become and the longer they burn.
The consequences of wildfires in the United States had an enormous impact on air quality in the western states, especially in smaller California suburbs where air quality is typically within safe air quality limits.
The IQAir AirVisual 2019 World Air Quality Report found that severe California wildfires caused California suburbs like Eastvale, Diamond Bar, Ontario, and Compton to occupy 25 of 30 spots in the most polluted regional cities for 2019.
Severe California wildfires caused California suburbs like Eastvale, Diamond Bar, Ontario, and Compton to occupy 25 of 30 spots in the most polluted regional cities for 2019.
This story holds true for other wildfires of unprecedented size in recent history.
A 2020 study in Natural Hazards and Earth System Sciences found that this cycle was responsible for one of the largest and deadliest fires in recent history: the Australian wildfires in 2019 and 2020.4
To make this conclusion, researchers looked at a huge amount of data from the Fire Weather Index, heat and drought patterns, and eleven cutting-edge climate data models, finding that:
- Average global 7-day temperature highs in June/July (one of the key wildfire seasons and period of extreme dryness) have risen from about 30°C (86°F) in the 1980s to nearly 35°C (95°F) in 2020
- warming global temperatures made extreme heat waves twice as likely to happen
- highly irregular temperature changes in the southern hemisphere during 2019 resulted in record heatwaves and extreme droughts in Australia
All of these factors made late 2019 and early 2020 ripe for the ignition and spread of the Australian wildfires, which burned nearly 5 million hectares of land and burned for nearly five months straight before being fully contained.
And the air quality impact was noticeable – the 2019 World Air Quality Report also found that Australian cities affected by the wildfires exceeded the “safe” limit for average annual PM2.5 (10 µg/m3) by up to 78%.
Australian cities affected by the 2019/2020 wildfires exceeded the “safe” limit for average annual PM2.5 (10 µg/m3) by up to 78%.
Why are wildfires getting longer?
Just as the cycle of climate change worsens wildfires over time, other major events in the world’s ecosystem contribute to increased risk for wildfires.
A 2016 study that looked at climate and wildfire data from 1984 to 2015 proposed that human activity is the leading cause of worsening wildfires.5
This study found that climate change caused by industry, vehicle, and fuel pollution sped up global temperature increases and made natural climate patterns more drastic. Naturally warm and dry seasons were made even warmer and drier by human pollution sources.
Another big contributor to wildfires is deforestation.
Forests are often burned or cut down on purpose to clear land for agriculture or economic development, which can cause even bigger wildfires that burn out of control and send many thousands of tons of smoke into the atmosphere.
Furthermore, even just half a hectare of trees and plants normally help absorb over 2 billion metric tonnes of carbon dioxide from the air each year and produces about one-third of the world’s total supply of oxygen in its place.6,7
Even just half a hectare of trees helps absorb over 2 billion metric tonnes of CO2 from the air each year and produces one-third of the world’s oxygen. Less trees means less oxygen and more CO2, increasing global temperatures and the risk of wildfires.
Fewer trees leads to less oxygen being produced and more carbon dioxide lingering in the atmosphere. Both contribute to rising global temperatures and an increased risk of wildfires.
Other researchers have also found less obvious causes of longer, more severe wildfires thousands of miles from where wildfires burn.
Two 2012 research articles both found a possible correlation by crunching the numbers from data around the shrinking of sea ice in the Arctic and increasing global temperatures as well as reduced rain and snow around the world.
The first article noted that the thinning of ice in the Arctic from global warming made it harder for ice to form again during each cold winter season.8 Typically, thick Arctic ice helps cool temperatures around the world and contributes significantly to global rainfall, even in countries as far away as the equator.
But over time, as Arctic ice becomes thinner from warming temperatures, the reduced amount of ice ironically makes temperatures even warmer year-round and contributes less moisture to the air that can turn into rainfall – another vicious cycle of warming and drying trends.
Over time, as Arctic ice becomes thinner from warming temperatures, the reduced amount of ice ironically makes temperatures even warmer year-round and contributes less moisture to the air that can turn into rainfall – another vicious cycle of warming and drying trends.
The other 2012 article looked at atmospheric patterns around the Arctic from 1970 to 2010, paying special attention to Rossby waves that bring cool air and water from the Arctic to other parts of the world.9
The researchers observed that warming temperatures and thinning ice have both reduced the amount of cold air and water that spreads downward from the Arctic into regions as far south as Central and South America, Africa, South Asia, and northern Australia.
This may not seem like a big deal at first. But cool air and water from Rossby waves are critical to keeping the global climate in check, especially by cooling areas near the equator that are more affected by harsh UV light from the sun.
So the less cool air and water from the Arctic that’s available to keep global temperatures regular year-round, the more extreme that weather events become.
The less cool air and water from the Arctic, the more extreme that weather events like droughts, floods, cold snaps, and heat waves become – all of which can make wildfires worse.
Here, the researchers found a direct relationship between thinning Arctic ice as well as weakening Rossby waves and the increasing intensity of droughts, floods, cold snaps, and heat waves – all of which can make wildfires worse.
Wildfires have always been a natural part of the global ecosystem – but human contributions to rising global temperatures have made wildfires more severe and longer-lasting.
One way to reverse this trend is to address human causes of climate change like industrial and traffic pollution by switching to renewable energy sources that drastically reduce carbon emissions and help stabilize global temperature fluctuations that can lead to wildfires.
There must also be a reversal of deforestation and controlled wildfires that disrupt natural cycles of burning and regrowth – if left unchecked, the world may one day lose all of its forests and grasslands permanently.
Until then, wildfires and wildfire smoke will continue to worsen. Be ready to protect yourself from smoke pollution with outdoor masks and safe indoor air.