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Forest could replace much of Alaska's tundra by 2100

Doug O'Harra

An arboreal invasion of the Far North is imminent, according to a new study, with vast swaths of Alaska tundra almost certainly yielding to trees and shrubs during coming decades, as human-triggered climate change slowly lengthens growing seasons across the region.

The findings, reported in a paper to be published soon in the journal Climate Dynamics, predict a dramatic reorganization of the ecology and plant cover throughout the Arctic, from Alaska's North Slope and the Canadian islands to Siberia and northern Europe.

"Imagine the vast, empty tundra in Alaska and Canada giving way to trees, shrubs and plants typical of more southerly climates," says a story describing the research, which has been posted by hundreds of web sites over the past week. "Imagine similar changes in large parts of Eastern Europe, northern Asia and Scandinavia, as needle-leaf and broadleaf forests push northward into areas once unable to support them. Imagine part of Greenland's ice cover, once thought permanent, receding and leaving new tundra in its wake."

Coniferous trees north of Fairbanks?

Over the next 90 years, Arctic tundra will shrink 33 to 44 percent, "while temperate climate types that support coniferous forests and needle-leaf trees (will) push northward into the breach," the study reported.

This shift in vegetation will in turn darken the surface of the Earth, absorbing far more solar energy than the reflective and grassy tundra. The result? The newly forested Arctic will grow warmer still.

"The expansion of forest may amplify global warming, because the newly forested areas can reduce the surface reflectivity, thereby further warming the Arctic," explained climate scientist Song Feng, research assistant professor in the University of Nebraska Lincoln's School of Natural Resources and the study's lead author. "The shrinkage of tundra and expansion of forest may also impact the habitat for wildlife and local residents."

In the study, Feng and his five Nebraskan and Korean co-authors analyzed 16 global climate models that cover 1950 to 2099 -- and then compared the results to 100 years of observational data. To express their predictions, they used the Koppen-Trewartha climate classification system, which divides Arctic ecology into ice fields, tundra, two types of subarctic boreal forests and two types of temperate forests.

Depending on which climate scenario prevails, changes will accelerate slowly over the coming decades, then begin to move even faster after mid-century.

"The response of vegetation usually lags changes in climate. The plants don't have legs, so it takes time for plant seed dispersal, germination and establishment of seedlings," Feng explained.

Climatic tipping point: Juneau's weather creeps north

The changes are well underway, according to the scientists, with impacts already spreading across an Arctic all too vulnerable to further disruption by climate shifts.

"Observations show that surface air temperatures in the Arctic have warmed at about twice the global rate over the past few decades," the authors wrote. "This Arctic warming also is expressed through widespread melting of glaciers and sea ice and rising permafrost temperatures. … A mounting body of evidence indicates that this recent, amplified warming in the Arctic is fueled by human-induced 'global warming'."

Rainfall has increased over the past 50 years -- a phenomenon consistent with higher temperatures that put more moisture into the air -- and this has in turn turbo-charged the flow in Arctic rivers.

Snow has been falling later and melting sooner. Combine these shorter snow seasons with the meltback of Arctic sea ice, and you end up with a region that's darker and, as a result, absorbs much more solar energy as heat.

Given the increasing warmth and rain, vegetation shifts are already well advanced, with leaf-out and blooming flowers occurring earlier, the authors point out. Some of the most dramatic changes have been reported in Alaska, where an estimated 2.3 percent of tundra has already transformed into forest during the past half century.

"The (extent) of tall shrubs in Alaska's North Slope tundra region has increased 1.2 percent per decade since 1950, also supported by indigenous observations in the same region," the authors wrote. "Throughout Alaska, a majority of the studied sites show a tree-line advance. White spruce has expanded into what was tundra and increased in density in western Alaska. … This widespread expansion of shrubs, and advancing treeline in Alaska and other Arctic regions is also supported by rapid greening and earlier start of the growing season."

And that's only the beginning.

"Tundra in Alaska and northern Canada would be reduced and replaced by boreal forests and shrubs by 2059," the study reported. "Within another 40 years, the tundra would be restricted to the northern coast and islands of the Arctic Ocean."

By the turn of the next century, a vast tundra prairie that once covered about one-third of Alaska will likely cover only 10 to 15 percent. Along the way, several estimates predict that Alaska's boreal forests and Taiga -- the forests that now dominate Interior Alaska -- may go into sharp decline about 2059, followed by a dramatic expansion of the temperate forests now seen in southern Alaska and the rain forests along the coasts. 

In the year 2100 

Other predictions for the region by 2100:

  • Average temperatures in the Arctic will increase by 5.6 to 9.5 degrees Fahrenheit.
  • The strongest warming in the winter will be up to 13 degrees Fahrenheit along the Arctic coast regions, with moderate warming along the North Atlantic rim.
  • The temperate forests will expand faster in northern Europe and Alaska than in other places.
  • Melting in Greenland will transform ice and snow into tundra.

"These results suggest that, though the temperature in the Arctic is projected to increase steadily under all scenarios, when a tipping point in temperature is reached, an abrupt shift can occur in regional climate types and vegetation," the authors wrote.

In the end, northern Alaska and the entire Arctic will be a much different place.

"The projected warming leads to large shifts in climate regimes in the Arctic regions," the paper concluded. "The areas occupied by polar climate types and subarctic continental climate type are projected to steadily decline, while the areas covered by temperate and boreal oceanic climate types are expected to steady expand."