The news on climate change unfortunately keeps getting worse. The latest is that CO2 levels are now higher than they’ve been in about three million years, when oceans were also about 20 meters higher. There is still time to change course, but the challenge is enormous. The Intergovernmental Panel on Climate Change issued a report last year indicating that to stay below 1.5°C of average global warming, the threshold for catastrophic climate impacts, we need to peak carbon dioxide emissions by next year, bring emissions to net- zero by mid-century, and then start generating “negative emissions.” In other words, by mid-century we actually need to be drawing down CO2 from the atmosphere!

What to do? We need to eliminate fossil fuel emissions as fast as possible. But we also need help from Mother Nature, because as of now, the most effective technology for taking carbon out of the atmosphere is a tree. You might conclude that, given the current climate emergency, we should be planting trees everywhere. But planting trees isn’t the top priority — in fact it’s at the bottom of the list. The top priority is protecting the carbon that has already been stored in forests, especially in “primary” forests. Here’s why.

Forests store vast amounts of carbon. Researchers estimate that global forests store at least 862 gigatons of carbon, and that’s a conservative estimate. That means there is more carbon in forests than there is in the atmosphere, and more than in oil and coal reserves combined. So we have to keep those enormous carbon stocks where they are: safely stored in trees and soil and out of the atmosphere. If we release even a fraction of those carbon stocks, we have no chance of staying below 1.5°C, even if we eliminate all fossil fuel emissions.

Still, that’s not the whole story. Forests aren’t all the same. “Primary” or “old growth” forests store far more carbon than logged forests: about 30 to 70 percent more. And not only do they store much more carbon, old growth forest carbon stocks are also more secure. This is because old growth forests still retain all of their native plant and animal species, which makes them more stable than degraded forests. What’s more, old growth forests are also carbon “sinks” — they continue to absorb carbon every year.

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In addition to maximizing forest carbon benefits, old growth forests provide many other benefits. They are the richest forests in terms of biodiversity, they generate the highest quality freshwater, they can drive precipitation, and they prevent erosion. They are also the homelands of Indigenous peoples and protect some of the last uncontacted tribes on the planet. Old growth is truly irreplaceable.

Of course, restoring degraded forests is also important. Allowing a degraded forest to recover rebuilds the forest’s carbon stocks so that they eventually reach old growth forest levels, though that can take a long time. Regenerating forests where they’ve been cleared can also absorb a huge amount of carbon. So in fact we need a holistic approach: protect old growth to secure their huge carbon stocks, restore degraded forests, and let forests come back where they have been cleared. When we’ve done all that, then we can talk about planting trees as well.

I started Wild Heritage because we need to do much more to prioritize old growth forest protection around the world. We simply can’t solve global environmental crises without old growth. We need these forests to stem species loss and to capture and store carbon. In a way, the close links between the biodiversity and climate change crisis is good news. We can solve these problems, and we can solve them together.