Vast carbon emissions from Canada's wildfires

Plus, May 2025 comes in a little bit cooler for the globe, an amazing wetlands map, and more.

The Shoe and Camp Fires in Saskatchewan, Canada, on May 10, 2025, as captured by Landsat 9. NASA Earth Observatory.

It’s happening again.

In 2023, amid extreme warmth and dryness, the wildfires burning through Canada’s vast northern forests were off the charts, consuming an astonishing 37 million acres of land. Here in the U.S., we mainly remember them because of the severely bad air quality days that resulted, even many hundreds of miles away or more, due to all the smoke that poured forth from these blazes.

But the planet also remembers them, because depending on how you count, the fires emitted an enormous amount of carbon dioxide and other greenhouse gases to the atmosphere. This study in Nature puts the total at 647 million tons of carbon (which, if converted into carbon dioxide gas, equates to more than 2.3 billion tons). That’s vastly more than Canada emits in a year from burning fossil fuels, and more comparable to the annual fossil fuel emissions of India.

“2023 was just so out of nowhere in terms of the emissions,” said Brendan Byrne, a scientist who led the Nature study while working at NASA’s Jet Propulsion Laboratory. “It was just so much higher than any previous year.”

And now, the blazes are back again, with over 8 million acres already burned by nearly 1,900 fires. These fires are again driving huge plumes of smoke that are dangerous to health, generating a haze that has reached as far as Europe. And based on data provided by the Copernicus Climate Change Service, they’re also on an emissions track that’s worryingly reminiscent of 2023. It’s early in the year, of course, so there’s no way of knowing if the trajectory will continue. But here’s what it currently looks like:

How do we know how many greenhouse gases the fires are emitting? Scientists with the Copernicus Climate Change Services and the European Centre for Medium-Range Weather Forecasts (ECMWF) use satellite imagery of the fires to infer how intense they are, and therefore, how many greenhouse gases result. It’s an estimate, of course, rather than a direct measurement. These are the data you’re seeing above.

Already, as of June 9, the 2025 emissions are higher than those during most full years in this dataset, which goes back to 2003. And the traditionally busiest part of the fire season hasn’t even arrived yet, typically falling later in the summer.

“For the time of year, it’s very comparable to 2023, and what that means is it’s quite distinct from all the other years in the dataset,” said Mark Parrington, a senior scientist at the Copernicus Atmospheric Monitoring Service within the ECMWF who manages the fire emissions data.

There have been thousands of evacuations so far due to these fires. But many of them, in regions such as Saskatchewan, upper Alberta and British Columbia, are burning far from large population centers, in Canada’s vast and remote boreal forest region.

Once megafires start up in this region, they often just continue on their way. “I expect many of these fires to burn through the summer, some might even burn through winter. Some of the fires burning today, as we speak, started in 2023,” said Mike Flannigan, a wildfire expert at Thompson Rivers University in British Columbia.

The evidence is pretty clear at this point that climate change is making things worse, Flannigan says. Things are warmer, and this in turn contributes to more dryness as well (through increased evaporation), and thus ideal fire conditions.

“It means more of that fuel on the forest floor has dried out, which leads to higher intensity fires that are difficult or impossible to extinguish,” Flannigan said.

There’s a twist, though, when it comes to wildfires and their emissions to the atmosphere. Yes, all the carbon dioxide emitted from burning trees makes global warming worse. But recent research suggests the fires are also kicking up so much smoke that the aerosols put into the atmosphere may have a countervailing cooling effect, by bouncing sunlight away and back into space.

This all gets complicated fast.

You would expect the carbon dioxide from the fires to stay in the atmosphere for much longer than aerosols, and thus to exert a more lasting effect. However, it’s important to remember that forests gradually grow back after these fires, sucking carbon back out of the atmosphere. However however, it is no longer clear whether boreal forests will entirely recover to their old state in what appears to be a new megafire regime. Meanwhile, these intense fires in northern forests could also expose more carbon-rich permafrost to thawing conditions, which also increases greenhouse gas emissions. But wait! — then there’s Arctic greening, as with more carbon dioxide in the air, tundras are growing more plants and …

Scientists are going to have to figure all how all of these tradeoffs ultimately work. It’s getting pretty urgent.

In the meantime, the entire planet clearly feels these large burning events, likely in multiple ways. And we can expect “more fire in the future, more smoke in the future, more greenhouse gases in the future,” said Flannigan.

Climate rundown, 6/11/2025:

Some other stuff that’s caught my attention in the past week or so:

An impressive dataset of inland waters. Anyone who cares about water should check out this new study in Earth System Science Data (one of my favorite journals). It’s led by McGill University’s Bernhard Lehner, who was behind the influential but 20 year old “Global Lakes and Wetland Database.” Lehner and his colleagues have now updated it with something of considerably higher resolution. And scientific accuracy, of course.

The study finds that the world contains 18.2 million square kilometers of wetlands. It also contains some cool maps. For instance, here’s a visualization of the distribution of global peatlands (and note that fires may be burning atop some of these at the moment):

From Lehner et al, “Mapping the world’s inland surface waters: an upgrade to the Global Lakes and Wetlands Database (GLWD v2),” Earth System Science Data, June 4, 2025. CC BY 4.0.

The Antarctic Tug-of-War, Continued. I’m continuing to closely monitor what’s happening in Antarctica. It is seeming lately like there is ever more research to keep an eye on. This new study suggests West Antarctica could collapse at current ocean temperatures or just slightly warmer, unleashing some 4 meters of sea level rise in the long term. This one says snowfall delivered through atmospheric rivers over Antarctica could increase by 2.5 times by 2100 under climate warming. It’s a which-wins-out-when kind of situation.

The Earth comes down from 1.5C territory. The Copernicus Climate Change Service, the source of the fire emissions data provided above, has also just released its global temperature estimate for May of 2025. While this was the second hottest May on record in the dataset, the month fell comfortably below the 1.5 C threshold. That’s something that hasn’t happened in a while.

So here’s how the data look now:

I discuss the data behind these estimates (including why they run a tad hotter than other global temperature datasets) more here.

Worse flooding on streets than at the coast. Last week, my former Post colleague Brady Dennis had a nice story about this study, by a team of researchers at the University of North Carolina at Chapel Hill and North Carolina State University, who are analyzing how the tides and other factors drive coastal flooding in the region.

The scientists find that flooding that actually gets onto roadways is much more common than flooding as measured at the coast by a tide gauge (the devices the National Oceanic and Atmospheric Administration uses to measure the sea level). This is for a variety of reasons, including very old drainage systems along much of the coast, and the fact that rainfall just makes everything worse.

At the same time, NOAA may just be setting a high bar for flooding that is generally accurate but understates what happens in some locations (something I saw often working on this series). The overall point is that a higher sea level can affect you in multiple, complex ways — and don’t ever bet against the ocean going where it wants to go.