The Canadian wildfire season in 2015 began early and ended late. Over the year almost 5000 fires burned through 3.25 million hectares of woodland—four times the 25-year average. In British Colombia, the months of May and June were close to being the driest months on record, and this weather was clearly thought to drive the rampant fires. The thick and pungent smoke from the flames left thousands of residents gasping for air through surgical masks. Further east across the prairies in Saskatchewan, uncontrollable fires prompted what was up to that time the largest evacuation in Canada’s history—more than 13,000 people fled the flames .
But 2015 was merely a prelude to the 2016 fire the Canadians called the Beast.
The spring of 2016 was the driest ever recorded at Fort McMurray and the second warmest on record. Weeks of warm dry weather created a bone-dry forest floor—the perfect conditions for a firestorm. On May 1 the fire ignited, and blustery winds quickly blew it out of control. Within two days the fire had doubled in size, jumped highways and the Athabasca River and was burning its way towards downtown Fort McMurray. The town’s 88,000 residents scrambled to leave—a mass exodus of unprecedented scale for Canada.
By May 4, the wild fire was so large it could be seen from space. It burned through an area the size of Prince Edward Island, destroyed 2400 homes and other buildings, scorched 18,600 vehicles and left the town a smoldering ash-covered ruin. It was the costliest catastrophe in Canadian history: total damages reached $4 billion in insured losses and billions more in lost business, infrastructure and uninsured losses .
What made the wildfire so dramatic was the speed with which it spread into the town of Fort McMurray. Many residents were caught by surprise and had to flee the city driving through a wall of flame. The photo below taken from inside a car approaching what looks like a raging inferno, captures the terrifying experience many residents endured as they fled the city to escape the encircling flames.
If anything the year 2017 was worse. By the month of August, the province of British Columbia was in a state of emergency as 138 wildfires burned across the province, and metro Vancouver was covered in a thick layer of smoke. This was British Columbia’s worst fire season in history .
At the same time in California, wildfires burned across thousands of hectares of land fueled by scorching temperatures that were breaking heat and fire records across the region. At least 15 cities registered record-breaking heat and the state experienced its hottest summer on record. San Francisco hit 41°C the first week of September 2017, breaking its previous record by 1.7°C.
At one point, over 80 large fires were blazing across 600,000 hectares along the west coast from Colorado to California and north to Washington. Seattle and Vancouver were shrouded in a smoky fog .
Then in early December yet another fire ignited–60 miles northwest of Los Angeles. Dubbed the Thomas Fire and whipped up by Santa Ana winds, it burned for a month and became the largest fire in California history—scorching 281, 893 acres and destroying 1063 structures. Fifty thousand people were evacuated from in and around Ventura county.
In October of the same year, wild fires burned across Portugal. At least 37 people died in the wildfires—fueled by temperatures of 34°C and strong winds. The image gives an idea of the huge scale and intensity of the fires.
The Mendocino complex
In 2018, the California fire season was even worse. The Mendocino complex fire consisted of two conflagrations — the River Fire and the Ranch Fire. The flames ravaged more than 280 structures, 157 of which were homes, and scorched an area bigger than Los Angeles. The fire burned for weeks and became the largest wildfire in California history. It consumed close to 459,000 acres and killed a firefighter who was among hundreds who came in from across the country to combat the flames.
The years since 2015 have been the hottest on record across the globe, and the extremely hot summers were certainly a factor in these years of record wildfires. But in the forests along the western US, fires have been increasing in intensity since the mid 1980s.
The graph below shows that the frequency of large forest wildfires has continued to increase with each decade since the 1970s. The area burned in these fires has also continued to increase—so the fires are getting larger. Most of the increase in large wildfires is due to lightning-ignited wildfires. Less than 12% of the trend in large forest fires is due to human-ignited wildfires .
There are two things to notice about the numbers shown in these graphs : first, although there is a large degree of variability, the ten-year averages show a steady and unmistakable upward trend. Second, lightning is becoming the dominant source of ignition for these wildfire in the western US. This was not the case in the 1970s, but lightning-ignited wildfires have become increasingly predominant over the last 30 years. This is a worrying trend: there is evidence that the frequency of lightning strikes increases as the climate gets warmer .
Lightning-caused fires have risen 2 to 5 percent per year for the last four decades according to a paper published in June in Nature Climate Change. As thunderstorms intensify and become more frequent fires are increasingly occurring in the boreal forests and even on the permafrost tundra. Warmer temperatures encourage more thunderstorms which in turn bring more lightning and greater fire risk .
In August 2017, a large wildfire was burning in Greenland only 40 miles from the Greenland ice sheet and in a place so remote that no-one noticed it until satellites spotted the smoke at the end of July. Small fires are not unknown in Greenland during the summer, but for such a large blaze to burn for so long was unusual. Scientists at the University of Technology in Delft in the Netherlands said that 2017 was by far the worst year for wildfires in Greenland since records began in 2000 . It is not known what caused the fire in the tundra of western Greenland, but the summer of 2017 was a particularly dry summer.
Are wildfires growing in number and intensity across the world? The data are mixed, but for most regions the trend is actually downward. A 2017 research article that examined multiple satellite data sets found that global burned area has declined by about 24 % over the last 18 years. But these data cover all fires, not just wildfires, including those deliberately set by farmers to burn crop residues or to clear away forests to open up the land for agriculture. The global trend for wildfires, as opposed to fires deliberately set for agriculture, is unclear. 
But in boreal forests of western North America–the trend is unmistakably upwards.
For more information check out these sources:
 The website of the Canadian Metorological and Oceanographic Society
 The Canadian Meteorological and Oceanographic Society (CMOS) website for the year 2016 //www.cmos.ca/site/top_ten?a=2015#Forest
 Check out the article : B.C. wildfires map 2017: Current location of wildfires around the province.
 See the article : Potent Mix of Record Heat and Dryness Fuels Wildfires Across the West.
 The figure is from the article by Leroy Westerling. Cited as : Westerling ALR 2016 Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring. Phil. Trans. R. Soc. B 371:20150178.
 One study asserts that for every degree Celsius of warming, lightning strikes are estimated to increase 12 percent according to research published in the journal Science in 2014. See Lightning-caused fire rise in Arctic as the region warms. The trend could worsen significantly in the future if tree cover spreads northward. Accessed at //www.scientificamerican.com/article/lightning-caused-fires-rise-in-arctic-as-the-region-warms/
 See the article in Science: Fires rise in Arctic as ‘lightning follows the warming. Accessed at //www.eenews.net/stories/1060056631
 See the article : Ice and fire: large blaze burns in Greenland for two weeks, accessed at //www.theguardian.com/world/2017/aug/20/ice-and-fire-large-blaze-burns-in-greenland-for-two-weeks/
 See the article published in Science cited as : Andela N, Morton D.C., Giglio L., Chen Y. et al. A human-driven decline in global burned area. Science 356, 1356-1362 (2017). [