The Arctic is getting greener, and it’s about as pretty as you might expect—vast stretches of coastal land positively glowing against cobalt seas. But all that green is in fact an alarm: Vegetation is growing more abundant as this region warms twice as fast as the rest of the planet. Northern landscapes are undergoing massive change, with potential consequences not just for the Arctic itself, but the world as a whole.
One group of researchers has been on a multiyear quest to understand that change on a fine scale. They’re combining satellite data, quadcopter measurements, and good old boots-on-the-frigid-ground fieldwork. We’re talking about labor like measuring individual leaves on plants to determine how much they’re growing, year after year. “So it kind of scales up from all of these little dramas of individual plants playing out, that then influence which plants exist on the landscape,” says Jeffrey Kerby, an ecologist at Aarhus University in Denmark and coauthor of a new paper from the team. “And when you spread that out over a huge area, it can have very consequential impacts on the carbon cycle.”
That’s because perhaps a third of the carbon stored in the soils of the world is in the Arctic permafrost—essentially frozen dirt. Growing in that soil are mostly grasses and shrubs, none of which grow above knee height. But these scientists are finding that as the Arctic warms, the period between when the snow melts and when it returns is getting longer, so plants are greening up earlier in the year. Some are also growing taller.
Normally, the shrubs and grasses of the tundra trap snow in the winter, and keep it from blowing around the landscape. But as temperatures rise, taller shrub species are becoming more abundant, trapping thicker layers of snow. That might seem great—all that snow keeps the permafrost from warming up—but in fact it prevents the chill of winter from penetrating the soil enough to keep it frozen. And that’s a problem, because if the permafrost doesn’t get cold enough to stay frozen—well, permanently—it will start to release that trapped carbon dioxide and methane, an extremely potent greenhouse gas.
“In other instances, shrubs are darker than grasses, so that changes the albedo,” says Kerby, referring to the way that the landscape reflects light back into space. The white snow reflects light, while darker bare earth and green plants absorb it. “It's kind of like wearing a black T-shirt on a summer day versus a white T-shirt: You're just going to feel hotter, because black is absorbing more heat,” Kerby continues. “And so that will melt the snow faster, or it can thaw permafrost faster.”
To make the Arctic carbon cycle even more complicated, all that vegetation of course sequesters carbon: Plants suck in CO2 and spit out oxygen. “So one of the big questions is, will this greening signal, these increases in plants, offset the losses of carbon from the systems as permafrost thaws?” says Isla Myers-Smith, an ecologist at the University of Edinburgh, who supervises the research and coauthored the paper.
The team is beginning to answer that question and a slew of others with fancy drones. Being able to point a satellite at vegetation in the Arctic is great for collecting data about a large area, but the resolution is usually not super; it’s on the scale of 30 meters if you’re lucky, but usually more like 250 meters. That’s like a microbiologist only being able to study bacteria with a magnifying glass. With off-the-shelf quadcopters, like the DJI Phantom, the team can now fly over a hectare of Arctic vegetation and scan it in fine detail. In a way, they’ve now got themselves a microscope.
These drones are equipped with cameras that see into the near-infrared, rather than the visible world you and I see. “The way a leaf reflects near-infrared—and red—light is dependent on both the chlorophyll content in there, as well as the structure of the cell layers on the leaf,” says Aarhus University ecologist Jakob Assmann, who led the work and coauthored the paper. “People have been using this to estimate vegetation productivity, the amount of photosynthetic activity.” That activity is an indicator of growth and the extent to which the Arctic is greening.
This data is much richer and more reliable than just pointing a regular old camera at a plant and determining how green it is, given that lighting can change dramatically out in the field. By looking at the ratio between the red and near-infrared light, the team can more accurately show how plant productivity may be changing as the Arctic warms.
These drones are what the team needed to fully characterize how the region is changing. Not that satellite data is now worthless—in fact, that data combined with the drone work and the on-the-ground measurements of plants provides a more holistic picture of the landscape. “So even though we can't cover the whole landscape with the drones, we can still cover a large enough section that we can then statistically relate to the changes that we see in the satellite data and make sense of that,” Assmann says.
With this font of new data, the team has set out to answer a bevy of questions. For instance, what are the consequences of plants greening up earlier in the year? “One of the big questions that we have is whether this means that the plants are going to grow longer across the summer season, or whether they're just going to move their growth to earlier in the season,” says Myers-Smith. How might this in turn affect the carbon cycle? Will an increasingly green Arctic release that locked-up carbon, or will it at the same time sequester more carbon in the new vegetation? And how will this affect herbivores like musk oxen and caribou—surely their feeding habits will change as plant communities do?
A greening Arctic is at once a beautiful and alarming sight, climate change visualized on a massive scale. And this new work is one of our first looks that combines both minute close-ups and a large-scale portrait of the landscape from above. “Plants are kind of books that you can read, because they experience environments all year round, and then reflect that in themselves,” says Kerby. “And so if you want to see what's changing with the climate, and you can just visualize that in the plants.”
UPDATE, 11/30/20, 1:15 pm ET: This story has been updated to clarify that the researchers are looking at the ratio between red and near-infrared light, as opposed to looking at just near-infrared light.
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