Canada’s managed forest is one of the largest living reservoirs of carbon on the planet. For centuries it slowly filled, as billions of growing trees pulled carbon dioxide (CO2) from the air and stored it away in their wood. This ancient, continent-spanning "carbon sink" now locks away more than 100 billion tonnes of CO2, helping keep the climate calm and cool. 

But the flow of CO2 has completely reversed in the last couple of decades. What started as a trickle has turned into a growing flood of CO2. And that flood surged right off the charts in both 2023 and 2024.

The amount of Canadian forest carbon pouring into the atmosphere now dwarfs the fossil fuel emissions of most nations. And this crisis is accelerating.

That’s the sobering story told by Canada’s recently released National Inventory Report (NIR) which covers our nation’s managed forest carbon from 1990 through 2024. 

More than four billion tonnes, so far

Unlike most forms of pollution that dissipate quickly, CO2 can persist for centuries, building up in the atmosphere and oceans. As a result, it is our cumulative emissions of CO2 that determine how extreme the climate emergency will become for ourselves and for generations to come.

My first chart focuses on the cumulative CO2 emitted by Canada’s managed forest carbon since 1990.

All this CO2 used to be stored away in wood and soils. Now it is in the atmosphere.

Three critical things jump out at me from this chart. 

The first is the massive scale of these emissions — 4,200 million tonnes of CO2 (MtCO2) by the end of 2024. For comparison, most of the world’s nations emitted far less CO2 during those years. 

A second key thing to note is that Canada’s managed forest used to be a helpful CO2 sink (green line). During the 1990s, the forest was removing more CO2 from the air than it was losing — and locking that extra CO2 away in wood and soils. 

But starting in the early 2000s, more forest carbon has been turned back into CO2 than the forest replaced. This shift from CO2 sink to CO2 source has pumped billions of tonnes of CO2 into the atmosphere, as shown by the rising red line.

And the third critical takeaway from this chart is that the red line isn’t rising steadily; it’s accelerating.

An accelerating crisis

My next chart lets you see the acceleration more clearly. It focuses on annual changes, with each year having its own bar. 

Years when more managed forest carbon was turned into CO2 than the forest recaptured are shown in red. Green shows the opposite.

During the 1990s, most years were green. 

Starting in 2002, however, every year has been red. That’s 22 straight years of adding CO2 to the atmosphere. 

And notice how the red bars keep growing more extreme. This shows that the crisis is accelerating — much like a boulder rolling downhill. 

In 2023 and 2024, this acceleration jumped to a new level. With record-smashing emissions of 1,000 MtCO2 and 430 MtCO2, these years were many times more extreme than the worst years just a decade ago. The rolling boulder is gaining speed as it careens through our forests.

Those red bars vary a lot from year to year. When climate scientists want to more clearly understand the underlying trend in “noisy” data like this, they often look at decade averages. I’ve shown decade averages as black horizontal lines on the chart. 

During the 1990s decade, the forest removed an average of 10 MtCO2 from the atmosphere each year. It was a small, net carbon sink. By the middle decade, however, carbon losses dominated and 110 MtCO2 was emitted each year on average. And then, during the most recent decade, the average leaped to nearly 300 MtCO2 emitted per year. If we allow this trend to continue, the decades ahead will be overwhelmingly worse.

Where is all the CO2 coming from?

Canada’s NIR reports managed forest carbon in six main categories. My next chart shows the cumulative CO2 impact for each one since 1990.

Four categories have been net CO2 sources (red bars), while two have been net CO2 sinks (green bars). As we saw above, all of them combined resulted in net emissions of 4,200 MtCO2 since 1990. That total is shown by the red bar on the right.

The first two sources come from logging.

Harvested wood has emitted more than four and a half billion tonnes of CO2 since 1990. That’s from the burning and decay of wood hauled out of the forest. The dashed box shows that another billion tonnes of CO2 waits in wood still in use. 

Forest areas that have been logged emitted an additional three billion tonnes. 

The remaining two sources come from insects and wildfire. These were formerly low-level impacts. In the last couple of decades, however, they’ve been turbocharged by our fossil-fueled climate shifts. Canada’s forests have drawn the short climate straw because they are overheating and drying out much faster than southern ones. 

Native insects, such as bark beetles, have been helped by our fossil-fueled warming and drought, while the giant trees they feed have been weakened. Explosive insect outbreaks have resulted in a billion tonnes of CO2 since 1990.

Wildfire has also been turbocharged by our fossil-fueled warming and drought. Wildfires continue to explode in increasing scale and ferocity. Nearly five billion tonnes of CO2 have been directly emitted by wildfires since 1990. 

Those four CO2 sources — harvested wood, logged areas, insects and wildfire — have collectively emitted 13 billion tonnes of CO2 since 1990.

The forest’s two sinks have pulled nine billion tonnes of CO2 back out of the air and stored it away in wood. These are shown by the green bars on the chart. 

The largest sink is unlogged forest areas with mature trees. These areas, which humans have mostly left alone, removed six billion tonnes of CO2 from the air since 1990. 

The smaller sink is forest areas recovering from wildfire. Regrowth after wildfires has removed three billion tonnes of CO2. This has partly offset the five billion tonnes directly emitted by wildfire. Unfortunately, the data shows that this post-wildfire sink has stopped growing. The annual amount of CO2 recaptured by it has dropped to zero.

As the chart above illustrates, billions of tonnes of CO2 that were locked away in forest carbon have drained back out on the backs of logging trucks and in the swirling smoke of fossil-fueled wildfires. This flood of CO2 is far larger than Canada’s managed forest has been able to recapture. 

If we want to rein in this metastasizing climate threat while we still can, we need to bring our managed forest back into carbon balance with the atmosphere.

There is plenty more CO2 where that came from

The 4,200 MtCO2 of Canada’s managed forest carbon that has already been lost to the atmosphere is a tiny fraction of what remains.

A study by Natural Resources Canada pegs the "wood volume" in Canada’s forests at 50 billion cubic metres. That much wood stores around 60,000 MtCO2. A similar amount is held in roots and soil. This suggests at least 100,000 MtCO2 remains stored in our forest. 

If we are foolish enough to keep cranking open the floodgates on this massive carbon reservoir, there is more than enough CO2 remaining to overwhelm any climate progress Canadians make elsewhere. 

And there’s more than enough to fill our lives with chaotic megafires and choking smoke for centuries to come.

In her classic 2006 climate book, Field Notes from a Catastrophe, Elizabeth Kolbert relates a FAFO warning from climate scientist Donald Perovich: 

“You’ve got a big boulder sitting there on this rolling hill … you start rocking it, and you get a bunch of friends, and they start rocking it, and finally it starts moving. And then you realize, maybe this wasn’t the best idea. That’s what we’re doing as a society.” 

We, and the great ecosystems we rely on, would be in a much safer place today if we’d acted decades ago. The next best time is now.