The record wildfires of 2023 (compliments of our neighbor to the North) started gaining momentum in March of that year. Their intensity increased, starting in June, but Canada had been affected by an ongoing, record-setting series of wildfires. As the worst wildfire season in recorded Canadian and North American history, Big Burn 2023 surpassed the record held by the 2020 California wildfires.
On June 6 of that year, I was traveling through southern Madison County in New York during what was later officially declared by climatologists to be the peak of the Canadian wildfire smog inundation for the Northeast region. Listening to news reports that night, I learned that a lot of other things besides timber were being incinerated in Canada. Some of those things’ emissions were serious pollutants which medical professionals advised babies and old folks not to inhale.
On June 25, the Canadian Interagency Forest Fire Centre declared 2023’s wildfire season to be the worst in Canada’s recorded history. As of July 16, over 4,000 fires had torched almost 39,000 square miles of forest in Canada – an area approximately equal to that of the state of Virginia. International aid reduced the impact of those fires.
Smoke emitted from them caused air quality alerts and evacuations in Canada and the U.S. In late June 2023, the smoke crossed the Atlantic, reaching Europe. According to Canada’s climate experts, due to these weather-related anomalies, average temperature readings had been warmer and drier. This occurrence raised wildfire risk, since vegetation can become tinder under these conditions. Wind from a passing cold front during the week of May 18 intensified the problems, fanning existing flames.
The big question, agriculturally, was how this type of climate misbehavior affected crop production. Crop researchers at Indiana’s Purdue University discussed how Canadian wildfire smoke could impact corn growth. These agronomists explained that such smoke resulted in noticeable haze and reduced direct sunlight, caused many farmers to ask how this uninvited smoke could harm crops. They were told that wildfire smoke, with its reduced air quality, can impact crops both negatively and positively. The first negative impact is a reduction in light availability, which reduces crop photosynthesis.
During the week of June 26 – when local air quality concerns were the greatest – average weekly solar radiation was decreased by 32% compared to the week prior (June 12) and the week after (June 30) at their main campus at West Lafayette, IN.
Atmospheric wildfire smoke reflected portions of incoming sunlight, reducing the total amount available to plants. Reductions in light availability from wildfire smoke more likely impact corn than soybean. This is due to corn being a C4 photosynthetic crop, having a higher light saturation point – at which further ultraviolet light increases do not benefit photosynthesis.
C4 plants store their energy in four-carbon modules. But soybean is more susceptible to changes in carbon dioxide.
The second negative impact from wildfire smoke is increased ground-level ozone, which can be harmful to both human health and crop growth. Wildfires can emit various air pollutants which can form ozone when reacting with sunlight. Ozone can harm both corn and soybean by entering the plant through the stomates, causing harm to plant tissue during respiration. Both sunlight reductions and ozone increases can undermine photosynthesis. Thus, corn may tend to liberate carbohydrates from the stalks later in the season to satisfy grain fill requirements. This carbohydrate relocation increased the potential for weak stalks and lodging prior to harvest.
Despite reduced sunlight and increased ozone, wildfire smoke in the atmosphere also has positive effects on crop growth. For instance, not only can wildfire smoke reflect sunlight, it can also scatter sunlight, allowing it to penetrate deeper into the crop canopy, increasing photosynthesis. When light is scattered and direct sunlight is reduced, it can also lower leaf surface temperatures, which benefits crops under drought stress. Lower leaf temperatures reduce the amount of transpiration (water movement and evaporation from the plant) needed to cool the plant, reducing overall water stress.
Corn is more susceptible to the negative effects of wildfire smoke during the grain fill stages; the good news is that the majority of corn in Indiana and the Northeast was in the vegetative stages during the smoke barrage in June and July 2023. Thus, no major yield loss was expected in these regions. However, deflected solar radiation delayed corn maturity in the Great Lakes states by two to three weeks. That same delay in solar radiation retarded maturity in perennial forages which in turn markedly improved average forage quality, according to lab analyses – many June 15 cut hays boasted quality normally common in June 1 hays.
However, much is still needed to be learned about the impacts of wildfire smoke on crop growth. As these events are unfortunately expected to become more frequent, it will be important to pay attention to them in the future. Thinking that climate change aggravation might become even more commonplace, some crop researchers recommend that plant breeders develop corn varieties that are less susceptible to reduced solar radiation.
Fast-forward to January 2025 in Los Angeles. Conditions similar to those predisposing to Canadian conflagrations in 2023 hit California, torching almost 90 square miles. Then jump to July 15, 2025, when the New York State Departments of Environmental Conservation and Health posted air quality health advisories for most of New York State due to the impact of smoke from Canadian wildfires. The primary reasons that smoke reached New York were prevailing wind patterns at different atmospheric levels. These carried the smoke southward from the wildfire locations in central and western Canada.
Hitching a ride with that smoke is ozone, whose production can be enhanced by wildfire smoke. This surface pollutant should not be confused with the protective layer of ozone in the upper atmosphere.
