When Trees Aren't Great For Climate Change

A spruce tree growing in the Alaskan Arctic in a place
where it had been too cold for trees for many millennia. 
Photo by Roman Dial via Outside Magazine.

 Trees are usually heroes when it comes to climate change mitigation. 

They suck up carbon dioxide and spit out nice fresh oxygen. What's not to love? 

The only thing not to love is when climate change makes trees grow in the wrong place.  

The tundra in northern Alaska and other areas way up there, not far from the North Pole, aren't supposed to support trees. It's too cold. The summer growing season was always too short to allow trees. You just got low shrubs, grasses and sedges.

But as scientists are discovering, actual trees, mostly white spruce, are spreading north to places where no tree could have grown for the past 20 millennia or so

Roman Dial, an ecologist at Alaska Pacific University, has been working on this phenomenon. In 2019, he'd seen satellite imagery that showed odd shadows on parts of the tundra.  He flew out there, then hiked around, and what he saw confirmed what he suspected from the satellite pictures. There were trees growing in places where it used to be impossible for them to do so. 

As Wired reports:

"The journey confirmed what Dial suspected: That the shadows in the satellite images were in fact out-of-place trees that are part of a phenomenon known as Arctic greening. As the Arctic warms more than four times faster than the rest of the planet, that's bringing down ecological barriers for plants in the far north, and more vegetation is marching toward the pole."

The white spruce are marching north across the tundra at a rate of 2.5 miles per decade, faster than any conifer tree line that scientists have measured, says Wired.  

Scientists had not expected to see spruce trees this far north until many decades from now. The trees have been spotted in northern Alaska, north of the Brooks Range growing in a spot where trees have until now not grown for at least 20,000 years, before the last glacial maximum, notes Outside magazine. 

Researchers had also expected to find these Alaskan trees struggling at the outer edges of where they can grow, but many seem to be thriving. They're not big but still, they're healthy.  For example, they found one spruce that was about five feet tall and had been there for about 20 years. But its growth is accelerating. The spruce they examined, for instance, had tripled its height in the last five years. 

Here's why all this is bad, as Wired reports: 

"The white spruce colonists are likely warming the Arctic landscape, too. Normally snow cover makes these northern lands reflect the sun's energy back into space - in scientific parlance, the land's 'albedo' is high. But trees are darker, so they have a lower albedo and absorb heat, which warms the area. 'The albedo effect is the the big thing,' says Goetz. 'They absorb a lot more energy.'"

The trees also trap snow beneath them, out of the reach of the sun.  But that snow beneath the trees protects the winter frost and freezes from penetrating as far into the ground as they should. That makes melting permafrost more likely when it warms up in the summer. Melting permafrost releases carbon dioxide and methane, an even more powerful greenhouse gas. 

Which means the spruce trees are technically also aiding and abetting climate change in the winter, too.

This is yet another example of how climate change works in surprising ways, usually not good ways. I'm sure there's a lot of other oddball effects of the climate crisis I'm not aware of. I imagine scientists are aware of a lot of these, but probably not all of the scary effects of this global change. 

It's probably what keeps climate scientists up at night.