Long-standing fears that permafrost melt could lead to “runaway” climate change have eased, just a bit and just tentatively, as new research reveals that warming temperatures are triggering explosive growth in carbon-sequestering woody vegetation.
Spring has always come rapidly to the Arctic, but the season of sudden flourishing is arriving even earlier as global temperatures rise, giving tundra plants a head start on turning atmospheric carbon into green growth, according to a study published last September in Nature Communications.
Lead researcher John Kimball, a University of Montana climate and remote sensing scholar, calls it “an earlier green wave” that, in tundra areas, is producing more woody vegetation cover than before, reports the Globe and Mail.
“Since around 1980, the Arctic tundra has actually become a much stronger carbon dioxide sink overall,” Kimball said. A shift took place around the year 2000, he added: Before that, the tundra was relatively carbon neutral, but now satellite data shows “much stronger carbon uptake.”
“Our study challenges the notion that these high northern latitude permafrost regions are becoming a net source of carbon dioxide to the atmosphere with global warming,” Kimball said.
But that effect is weakening, the Globe explains. Spring is arriving sooner, but autumn is also lingering longer, giving the swathes of boreal forest that grow atop permafrost more time to re-emit the carbon they absorbed earlier in the year.
And with the High Arctic warming three times faster than the global average, “the continued stability of northern forests as a carbon sink” is not certain—especially with the advent of late-season drought and Arctic wildfires, Kimball said.
David Olefeldt, a University of Alberta researcher who studies carbon cycles in Arctic landscapes, said the Earth’s current warming trajectory is likely to result in release of carbon emissions from permafrost equivalent to between five and 10% of current human-caused emissions. “It’s large enough that we would need to take it into account when negotiating emissions ceilings,” he added.
Still, worst-case scenarios of a sudden, uniform explosion of carbon from melting permafrost triggering “runaway climate change” are no longer expected, partly because permafrost is highly variable in its composition and behaviour, the Globe writes.
Researchers found that permafrost in northern Siberia decomposed rapidly and could create high carbon dioxide and methane emissions if it thaws. Permafrost in northern Canada “seems to be very hard to decompose after it thaws, and thus is unlikely to lead to large carbon dioxide emissions,” Olefeldt said.
A big takeaway from the recent research is that much remains to be understood. One study found that “northern lakes are becoming greater sinks for carbon dioxide” even as they become increasingly heavy emitters of climate-busting methane, the Globe says. That’s just one of several factors complicating projections of how permafrost melt will affect global temperatures.
