Not good for climate (Image: NASA)

ON A July afternoon in the eastern Siberian town of Cherskiy, 220 kilometres north of the Arctic circle, it is a warm 27 °C. The vista features silver-blue rivers bisecting green swathes of boreal forest – Earth’s biggest ecosystem. But drive a metal rod into the soil and roughly 75 centimetres below the surface you hit a layer that’s as hard as steel – and perhaps as dangerous as dynamite.

Arctic permafrost holds more than in its frozen soil as Earth’s atmosphere. Which is what brings me here, accompanying seven US scientists from various labs, led by the Woods Hole Research Center in Falmouth, Massachusetts. We have travelled 7000 kilometres and 15 time zones to Cherskiy to study a phenomenon that might hasten the release of that carbon: the rise of Arctic wildfires.

“Welcome to Cherskiy,” our host Nikita Zimov says minutes after we disembark the Antonov-24 propeller plane that brought us here. Zimov directs the . “I understand you want me to take you to that hellhole,” he says as he points to a ghost of a forest that will soon enchant the scientists, despite its bugs, muck and fallen trees.

The trees at Hellhole – the moniker sticks – were burned a decade ago and could provide an important clue in the debate over the impact of Arctic fire (see diagram). There is no question that warmer temperatures, drier conditions and, possibly, an uptick in lightning are catalysing a rise in blazes across the Arctic. This summer over 9 million hectares of forest in have burnt – a record – drawing thousands of firefighters to help.

Fires devour the organic layer of leaf litter and shrubs on the floor of boreal forests and tundra alike. As this layer offers insulation during the summer, burned sites could see an increase in the depth of the soil that thaws in summer, before refreezing in winter. More thawed soil could mean more microbial respiration of ancient Arctic carbon into the atmosphere, eventually turning the boreal forest from a carbon sink into a source.

“Arctic fires may be creating new methane sources that could be the new fuse on the Arctic carbon bomb”

The science on this is far from settled, however. For example, some research suggests that the uptick in fires could actually reinforce the permafrost by helping regenerate trees, which insulate the soil and prevent erosion. Larch, the dominant tree species, is fire-tolerant and its seedlings benefit from underbrush-burning blazes.

This is where Hellhole comes in. To reach the forest we take a skiff across the Kolyma river. Trees lean left and right, forming crosses one must traverse. Most are lifeless, but the place is hardly dead: thick mosses and tussock grasses are thriving.

The most striking thing is how bumpy and wet the ground is. Unlike the smooth floors one finds in normal boreal forests, the fire thawed the permafrost in a wild zigzag pattern. The low areas are where the permafrost was mostly ice, while the segments comprised of actual soil now form the high ground surrounding endless pools, each maybe a metre deep.

McKenzie Kuhn, a recent college graduate, checks one of a series of funnel-shaped bubble traps she set in the pools days ago. In the anoxic conditions found in the soil beneath the ponds, microbes can create methane, a potent greenhouse gas. The team is now trying to measure emissions from the ponds and determine if they come from the carbon locked in the permafrost.

Back in Cherskiy, preliminary lab tests of the gases emitted by the soils below Hellhole’s ponds show surprisingly high amounts of methane. So by destabilising the soil and creating microponds, the scientists hypothesise, fire may be creating a new fuse on the Arctic carbon bomb.

This article appeared in print under the headline “On the trail of the Arctic’s time bomb”

An unusual threat is looming off the Pacific coast of North America from Juneau in Alaska to Baja California. Now roughly 2000 kilometres wide and 100 metres deep, a mass of warm water that scientists are calling “the blob” has lingered off the coast for a year and a half and has set temperature records, with waters between 1 °C and 4 °C warmer than normal.

Fresh research published in Geophysical Research Letters has examined the causes and impacts of this area of water, which has grown more recently.

The blob has changed water-circulation patterns, affected inland weather and reshuffled ecosystems at sea. Although scientists say the planet’s warming oceans may not be responsible for the mysterious and long-lived anomaly, some see it as an early warning of changes that might be coming to the Pacific in the next few decades.

Satellite imagery first alerted scientists to the strange formation in August 2013, when the roundish blob was seen over the Gulf of Alaska. Researchers think that a long-lasting weather pattern called a high-pressure “ridge” deflected winds that stir up cool waters from the deep and bring cool air and water from high latitudes.

Unusually warm sea-surface temperatures are being observed in the North Pacific. The darker the red colouring, the more above average the temperature (Image: NOAA)

Months later, fishermen and officials around Alaska reported sightings of species found in more temperate or even tropical waters, including skipjack tuna, thresher sharks and sunfish. Other marine species showed up thousands of kilometres north of their normal ranges, including pygmy killer whales and tropical species of copepods – tiny crustaceans that are key to marine food webs.

“I’ve never seen some of these species here before,” says plankton expert of the Northwest Fisheries Science Center in Seattle, Washington – part of the National Oceanic and Atmospheric Administration.

Spreading warmth

The anomaly has spread out over the last 12 months, with warm water showing up all the way from Alaska to the central Mexican coast. Physical oceanographers have speculated that the blob is influenced by a major climate pattern known as the Pacific Decadal Oscillation (PDO), a combination of several phenomena that have the effect of warming water across the eastern Pacific for periods of 4 to 20 years.

Yet the patterns of warming seem to be different this time round, says oceanographer of Scripps Institution of Oceanography in San Diego, California. “This is a phenomenon beyond the typical PDO-like oscillations we’ve seen for the recent decades,” he adds. “I’m in a state of confusion.”

Inland, the blob contributed to a number of unusual weather events along the Pacific Northwest last summer, including an uptick in thunderstorms and lightning – and the resulting forest fires.

But the biggest impacts so far have concerned marine species. Peterson fears that a big drop in copepod populations in waters off the Pacific Northwest could doom harvests of various species of salmon – a multibillion-dollar industry – for years to come. “They had nothing to eat,” he says of juveniles that ventured out from rivers into the blob last year.

Thousands of seabirds called Cassin’s auklets have been found dead along the Pacific shore, and conservationists have had to rescue scores of starving sea lions on beaches in southern California.

Journal reference: Geophysical Research Letters, DOI: