Rapid tundra ‘greening’ on Alaska’s North Slope linked to retreating sea ice

NOME -- Biologists say early-retreating sea ice is potentially causing vegetation productivity changes on the tundra across Alaska and the Arctic.

Uma Bhatt, a climate variability expert with the University of Alaska Fairbanks, says the land warms more quickly when sea ice recedes earlier than usual.

“The tundra is temperature-limited, and if it has more warmth available during the course of the summer, things can grow more. That’s the first-order effect.

"But what I think has happened is as the sea ice has gone away even further each year from the coast, there’s more time for open water and that has led, I think, to increased cloudiness.”

Bhatt says more cloudiness can cool temperatures and potentially reduce plants’ photosynthetic activity or “greening.”

According to a publication recently released by UAF and the International Arctic Research Center, the tundra on the North Slope has shown more “greening” over the last five years than any other region in the state.

“If you look at the Arctic as a whole, it’s greening, and the productivity is increasing," Bhatt says. "But there’s a lot of spatial variability, and we think it has to do with what the permafrost is doing locally. If things are drying out locally, or if the snow patterns are changing, that’s going to affect what the vegetation is able to do.”

On the North Slope, increased shrub growth, general warming of the tundra and more available moisture are possible contributors.

According to climatologist Rick Thoman, sea ice extent in the Chukchi and Beaufort seas is still shrinking, now 37% of what used to be the average seasonal minimum.

In stark contrast to the North Slope, the Yukon-Kuskokwim Delta has seen a decreasing Normalized Difference Vegetation Index, or measured greening.

According to Skip Walker with UAF’s Institute of Arctic Biology, the lack of greening in the Y-K Delta doesn’t necessarily mean that the vegetation is “browning.”

“What is the actual cause of that is a mystery right now. I don’t think we really understand it fully. And so that seems to be an area that really needs some research."

Walker has been working with Bhatt for more than a decade to study tundra greening in the Arctic. Even though they are focusing on a larger area, Bhatt says the Seward Peninsula seems to be transitioning between the “greening” North Slope and the potential browning in the Y-K Delta.

In areas that Walker refers to as the low Arctic, satellite imagery shows an increasing number of shrubs popping up on the landscape. He says in the near future he expects to see shrubs growing in areas where they weren’t seen before.

“I think overall the increase in shrubs will eliminate a lot of the species’ what we could call diversity. The species diversity tends to go down when you have a lot of shrubs in the landscape, and that seems to be happening.”

If shrub growth continues to increase eventually, Walker says, the Alaska tundra will totally transform, but through a gradual process that may not finish during his lifetime.

According to Walker, these landscape changes, such as more shrubs and increased greening, will affect everything in Alaska. To see how wildlife, vegetation and humans living on the tundra could be affected down the line, Walker suggests keeping an eye out for the yet-to-be-released 2019 Arctic Report Card.

This article originally appeared at KNOM.org and is republished here with permission.