SCIENTIFIC AMERICAN
El deshielo del Ártico está liberando grandes cantidades de metano. ¿Cuán grande es la amenaza de efecto invernadero? ¿Qué puede hacerse?
Por Sarah SimpsonA young scientist with curly, reddish hair tucked beneath a knit cap stepped gingerly onto the three-day-old ice of a remote lake in northeastern Siberia. Coating the black depths like cellophane, the thin film held no promise to bear her weight, but a sudden dunk in the frigid water was a risk she had to take. Searching the lake by rickety rowboat all summer had failed, and any day winter’s first big snow would engulf the region, obscuring the lake’s surface until spring. She could not afford to wait that long.
The woman shivered in her worn, blue down jacket and glanced up at the overcast sky. After one more cautious step, she spotted her quarry: a cluster of platter-size bubbles frozen into the ice. Those pockets of gas, which had risen from thawing permafrost—formerly frozen soil—at the lake’s bottom, were the aim of her doctoral research. Long elusive, they suddenly stood out like white stars against a night sky, though less serenely. With a small pick she cracked the icy skin of one of the bubbles and remained unfazed when it hissed back like a punctured gas pipe. Leaning forward, she apprehensively struck a match just above the broken bubble and flames as high as her head burst skyward. The flammable substance was methane, a greenhouse gas that could cause more global warming than carbon dioxide (CO2).
Today, nearly seven years after igniting that first bubble, Katey Walter finds herself center stage in an environmental drama playing out across the frozen north. Now a 33-year-old assistant professor at her alma mater, the University of Alaska–Fairbanks, Walter was the first to explain the mysterious methane emissions from Arctic lakes. She isn’t shy about touting their significance as a ticking time bomb. In a complete Arctic thaw, these lakes could discharge a whopping 50 billion tons of methane: 10 times the amount already helping to heat the planet.
Whether a total or more moderate release is in store is still anyone’s guess. But pound for pound, methane in the atmosphere traps 25 times more of the sun’s heat than CO2 does. Consequently, even a modest thaw of the perennially frozen soil that lies under these ephemeral lakes and caps the dry land around them could trigger a vicious cycle: warming releases methane and creates lakes, which thaw permafrost and liberate more gas, which intensifies warming, which creates more lakes, and so on. Some Arctic lakes are growing larger, and researchers are eyeing them suspiciously as a reason why global methane concentrations shot up in 2007 and have stayed high ever since. Other signs indicate that permafrost thawing on the Arctic seafloor may be loosening the cap on large pockets of methane stored deeper down.
Walter is sounding the alarm even louder than before because global warming is taking a special toll across the far north. The region is heating up twice as quickly as the rest of the globe, rapidly melting sea ice in the Arctic Ocean as well as the permafrost, which underlies 8.8 million square miles of the Northern Hemisphere. Leading climate models already suggest greenhouse warming as a result of most of the Arctic’s permafrost thawing by 2100—and the estimates do not yet include the potentially vast additional warming imparted by methane bubbling up out of chilly waters. Walter and others are trying to determine just how much methane could be released into the atmosphere, how soon, how aggressively that release would accelerate the earth’s warming and whether anything can be done to temper the escalating threat.
Burps and Belches
Scientists know with great certainty how much methane is in the earth’s atmosphere at any given time from sampling its concentration weekly at dozens of sites worldwide. By plugging these measurements into global climate models, they know methane is responsible for a third of the current warming trend. Exactly how much gas comes from where is harder to say, which is why the Arctic lake bubbles were so long overlooked.
Scientists know with great certainty how much methane is in the earth’s atmosphere at any given time from sampling its concentration weekly at dozens of sites worldwide. By plugging these measurements into global climate models, they know methane is responsible for a third of the current warming trend. Exactly how much gas comes from where is harder to say, which is why the Arctic lake bubbles were so long overlooked.
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