As we continue to burn fossil fuels like there’s no tomorrow, an insidious transformation is taking place under our noses. Remote ecosystems in our planet’s far north are changing at a scale that’s hard to imagine.
A new study published in Global Change Biology is making that imagination part a bit easier. It estimates that 67,000 square miles of land—13 percent of the state of Alaska—has experienced “directional change” over the past 32 years, becoming greener, browner, wetter, or drier as permafrost thaws, glaciers retreat, treelines move north, and wildfires ravage landscapes.
Some of these changes are part of the natural course of ecological succession. But the fingerprints of human-induced climate change across this vast state are also impossible to ignore. So are the planet-wide consequences.
The study, led by scientists at the U.S. Geological Survey, analyzed high resolution satellite imagery acquired by Landsat from 1984 to 2015 to develop a mapping algorithm that estimated change across Alaska. Aerial and satellite imagery and field data were used to tie changes in specific satellite metrics, like landscape greenness, to specific drivers like wildfires. In total, 1.4 million square km (540,000 square miles) of land were analyzed for some sort of change.
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Those changes were widespread and diverse, but a few trends stuck out. For one, vast tracts of Alaska, especially in the far north where boreal forest gives way to tundra, are becoming greener as the growing season lengthens and the treeline advances. Meanwhile in the interior of the state, long-term drying and wildfires are causing vegetation to die back and landscapes to brown.
“What impressed me [was] how extensive and influential the fires were,” USGS scientist at study co-author Bruce Wylie told Earther, noting that statewide wildfires were the largest driver of change.
Alaska’s water resources are also changing profoundly. As the permafrost that forms a solid foundation beneath the ground thaws, landscapes are collapsing in on themselves, forming wetlands in forests or so-called thermokarst lakes on tundra. Alaska’s coastlines, where many Native villages are located, are eroding as thaw and a longer open water season causes shorelines to crumble.
Glaciers, as we already knew, are rapidly diminishing across the state.
Peter Griffith, a carbon cycle scientist at NASA’s Goddard Spaceflight Center, said that while the scale of transformation estimated in the new study is in line with prior work, this research took things an important step further by tying landscape-level changes to driving factors.
“Now with this study we have spatially explicit interpretations of the changes on the land, with specific drivers identified and attributed to the changes,” Griffith told Earther via email.
Teasing out how rising temperatures amplifies or alters the normal course of change remains an key challenge, noted Merritt Turetsky, an ecologist and permafrost expert at the University of Guleph. For instance while wildfires have long been part of the fabric of life in boreal forests, a growing pile of evidence points to climate change making them more frequent and severe.
“So I think what future studies need to do is characterize how ongoing warming and disturbance events are pushing ecosystems into new trajectories of change,” Turetksy said told Earther in an email.
Turetsky also said that the results of the new paper should be viewed as “quite conservative,” because some of the more fine-scale changes that we know are occurring up north can’t be captured via satellite.
“I think that these results represent a minimum estimate of change,” she said.