Even though severe wildfires can warm the planet over time, right now the smoke floating down from Quebec to the United States is actually making temperatures cooler.
Robert Field, a scientist at NASA and Columbia University, told me that by his rough estimation the smoke earlier in June reduced temperatures by around 5 degrees Celsius — or 9 degrees Fahrenheit — in New York City.
Field came to this figure by comparing weather forecasts, which are produced by models that do not account for smoke, and the actual observed temperature on the given smokey day.
This effect was also observed on the East Coast by electric grid operators, who noted that lower than expected temperatures led to less usage of air conditioning and demand on the grid (although the smoke also meant less generation from solar panels).
This is hardly a surprising or counterintuitive finding: Smoke essentially works as a cloud, blocking energy from the sun from reaching the surface.
A team of scientists looking at the climate effects from COVID-19 and the attendant lockdowns actually found that the larger influence on climate came from the Australian wildfires of 2019 and 2020, which caused “a strong and abrupt climate cooling.” Some of the most dramatic climatic events have been cooling associated with pumping aerosols into the atmosphere, either from volcanic eruptions or, uhhh, wildfires in Canada.
And then there’s the long-term effect on the climate. These wildfires have pumped a massive amount of carbon into the air, but an exact accounting for forest fires in high latitude, boreal forests is tricky, Field explained, because there’s a natural fire cycle. “The starting point is that fire is a necessary ecological process in those forests. Those forests are meant to burn every 70 to 80 years. And over that time period the CO2 emissions that we’re seeing now will be offset over time by regenerating forests,” Field said.
But, he cautioned, in a warming world, these cycles could be disrupted. “Higher intensity fires can be harder to recover from and that carbon offsetting can take longer,” Field told me.
There are also worries about how in some northern forests, the soil’s so-called “legacy carbon” — old leaves, branches, and roots that have been long-buried — could be released by recent forest fires.
The exact effect of fire on greenhouse gas concentrations remains an active area of research. What’s well established is that when fire leads to changes in land use — like clearing rainforests for agriculture — carbon emissions will go up and stay up.
In short, what clearly matters for emissions is not so much forests burning, but forests turning into something else after they burn, whether it be pasture or crops or degraded forests that absorb less carbon. One paper found that about a fifth of fire emissions “represent a source of CO2 that can be termed as irreversible … because it cannot be recovered by vegetation regrowth or soil carbon rebuild.”
Climate change is almost certainly making wildfires more likely and more severe with all sorts of horrible impacts on our health. But what's truly scary is that these wildfires may also be making climate change itself worse.
