杏吧原创

DEVASTATING wildfires across the world have made front-page news in recent times, from last year鈥檚 deadly blazes in Greece to the widespread property destruction in Canada three years ago. One place you might not expect to be burning, however, is the Arctic. While fires in the region have begun to calm down this week, millions of hectares have been burned this summer.

Fire is a natural part of the ecology of the vast boreal forests that girdle Earth in northern latitudes. But the amount of vegetation that has been on fire across Alaska, Canada and Russia since June is highly unusual. Even Greenland, four-fifths of which is covered in ice, has seen fires. The impacts on human health and the environment are coming into focus 鈥� and they are worrying. Is there anything we can do?

This year has already seen striking fires around the world, including in places not usually known for them, such as the UK (see 鈥�Fires in February鈥�). In Indonesia, where fires are often started to clear areas for oil-palm plantations, the fire season may prove to be as bad as that of 2015, when blazes there created a plume of smoke that extended halfway around the planet. Brazil鈥檚 space agency has reported more than 75,000 fires in the Amazon this year, a record number. A surprising number of crop fires have hit the Netherlands, Germany and Luxembourg, says Cathelijne Stoof at Wageningen University in the Netherlands.

You would be forgiven for thinking that fires are on the rise globally. In fact, the evidence doesn鈥檛 bear that out. For example, a 2017 study led by Niels Andela at NASA used satellite images to show that the amount of land being burned worldwide has actually decreased in recent decades. This is probably because of the way we are managing forests to reduce the risk of fire.

Surprising as it may seem, this year isn鈥檛 that special when it comes to fire, either, globally speaking. The European Union鈥檚 (CAMS) says that some 3500 megatonnes of carbon dioxide were emitted from wildfires in the first half of this year. At a global level, that makes 2019 distinctly middling compared with the past 16 years.

The fires in the north, however, are exceptional. 鈥淭his year has been unprecedented for wildfires in the Arctic,鈥� says Carly Phillips at the Union of Concerned 杏吧原创s and Woods Hole Research Centre in Massachusetts. About 173 megatonnes of CO2聽have been emitted from Arctic fires so far this year, according to CAMS, which is a record amount (see 鈥�Chart鈥�). Russia has been hit hardest, with more than 13 million hectares affected and smoke hazes reported in cities.

So why the surge in Arctic fires? The region is effectively stuffed with fuel: huge swathes of forest and peat. Most of this doesn鈥檛 normally burn because it is cold and wet. But this year, maximum temperature records have tumbled, making it warm and dry enough for blazes. 鈥淭he north is a big tinder box, but it鈥檚 been limited from burning by the climate,鈥� says at the University of Guelph in Canada. 鈥淚f you remove those climatic constraints, all those fuels are ready to go.鈥�

Climate change could also be contributing to the lightning strikes that usually ignite the fires. More lightning is linked to rising surface temperatures. 鈥淗ot weather is making the Arctic more thunderstormy than normal,鈥� says Rod Taylor of the World Resources Institute in Washington DC.

Most of the fires are in remote regions, but that doesn鈥檛 mean people are escaping the effects. 鈥淲hat happens in the Arctic doesn鈥檛 stay in the Arctic. Pollution can carry thousands of miles away,鈥� says Elizabeth Hoy at NASA. The agency has . That pollution can combine with a city鈥檚 local fumes to turn air quality from average to poor, potentially causing respiratory problems for young, old and other vulnerable people.

The health costs aren鈥檛 just physical. Turetsky says that in Yellowknife, the capital of the Northwest Territories in Canada, doctors have reported increasing rates of hospital admissions for post-traumatic stress disorder during and following wildfires. At a workshop she ran in the city, many people reported what they called eco anxiety. 鈥淎 lot of these people didn鈥檛 experience the fires directly, but they know it鈥檚 going to come back,鈥� says Turetsky.

The effect on the climate could be more serious still. The problem isn鈥檛 simply that fires release a lot of CO2. This will exacerbate global warming, and Arctic wildfires have released about the same amount of CO2聽this year as the Netherlands does in a year.

鈥淔or me what is far more insidious is the long-term climate impact,鈥� says Phillips. Her worry is the prospect of a harmful positive feedback loop. Fires burn off vegetation, stripping away an insulating layer that helps maintain permafrost 鈥� ground that is normally frozen. This makes it more likely that the permafrost could thaw and release even more CO2. Permafrost thaws discharge not just CO2, but also the more powerful greenhouse gas methane.

The potential positive feedback doesn鈥檛 end there. Researchers at CAMS have already used satellites to track soot from this year鈥檚 northern Russia fires. Some landed on ice in Greenland. That matters because studies have shown that , making it absorb more of the sun鈥檚 energy and heat up.

The remote nature and sheer scale of the Arctic means there isn鈥檛 a lot that firefighters can do about these fires. Russia had to send in the army, planes and helicopters to tackle flames in some areas. 鈥淟arge-scale intervention is very costly and not very effective for large and remote fires,鈥� says Cristina Sant铆n at Swansea University, UK.

Russian authorities have tried seeding clouds to induce rain. The idea is that planes spray chemicals such as silver iodide in an effort to enhance the rate of ice crystal formation in the atmosphere, producing more clouds, but there is no evidence this is effective.

Today, firefighters鈥� priority is to protect life and property. Turetsky says that could in future be extended to protecting rich stores of carbon in the Arctic. 鈥淚t might be governments come together to protect certain areas where we understand where the old carbon is,鈥� she says. The other thing we can do is to reduce CO2聽emissions.

In the future, hotter, drier conditions in the Arctic will set the stage for more blazes. A recent by the UN鈥檚 climate science panel warned as much. Stephen Pyne, who studies the history of fire at Arizona State University, says we are entering the 鈥渁ge of the pyrocene鈥�.

One crumb of comfort is that the feedback loop can鈥檛 continue forever. Once forest is burned, it can鈥檛 keep burning. And smoke from northern fires has a modest cooling effect, reflecting some of the sun鈥檚 energy. In the meantime, however, the Arctic is still on fire.