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闷烧中的北极:人类要如何面对环境浩劫

更新时间:2019/10/18 20:28:20 来源:纽约时报中文网 作者:佚名

Why the Arctic is smouldering
闷烧中的北极:人类要如何面对环境浩劫

The Arctic is transforming before our eyes: the ice caps are melting, the tree-line is shifting northwards, starving polar bears wander into cities. The region is warming twice as fast as the rest of the planet due to climate change, largely due to changes in albedo – the loss of sunlight-reflecting ice and snow, replaced by sunlight-absorbing ocean and soil. This is driving a dangerous positive feedback cycle where heating spirals into more heating.

北极就在我们眼前发生着变化:冰盖正在融化,林木线向北移动,饥饿的北极熊在城市里游荡。由于气候变化,该地区变暖的速度是其它地区的两倍。这主要是由于阳光反射率的变化——反射阳光的冰雪减少,取而代之的是吸收光照热量的海面和土壤。这就形成了一种正向循环机制,即热量螺旋上升,造成更多热量累积。这个现象十分危险。

And, now, the Arctic isn’t only losing its ice. It is being set ablaze.

现在,北极不仅冰雪渐融,它还出现了野火。

Gargantuan forest fires in Siberia, which burned for more than three months, created a cloud of soot and ash as large as the countries that make up the entire European Union. More than four million hectares of Siberian taiga forest went up in flames, the Russian military were deployed, people across the region were choked by the smoke, and the cloud spread to Alaska and beyond. Fires have also raged in the boreal forests of Greenland, Alaska and Canada.

西伯利亚大规模的森林火灾持续了三个多月,产生的烟尘云霾面积相当于整个欧盟。400多万公顷针叶林被大火吞噬,俄罗斯军队前往救灾。整个地区的人们都被浓烟呛得透不过气来,浓烟蔓延到了阿拉斯加乃至其它地方。就连格陵兰、阿拉斯加和加拿大的北方森林也发生了大火。

Though images of blazing infernos in the Arctic Circle might be shocking to many, they come as little surprise to Philip Higuera, a fire ecologist at the University of Montana, in the US, who has been studying blazes in the Arctic for more than 20 years.

尽管北极圈内熊熊大火的图片可能会让很多人感到震惊,但美国蒙大拿大学(University of Montana)火灾生态学家伊格拉(Philip Higuera)认为,这并不令人意外。

“I’m not surprised – these are all the things we have been predicting for decades,” he says.

“我并不感到意外——这些都是我们几十年来一直预测会发生的事情,”他说。

Higuera and his team predicted in 2016, based on sophisticated computer modeling, that fires in the boreal forests and Arctic tundra would increase by up to four times by 2100.

2016年,伊格拉团队便基于复杂的计算机模型预测到2100年北方森林和北极苔原的火灾将增加四倍。

A key tipping point, he says, is an average July temperature of 13.4C over a 30-year period. Much of the Alaskan tundra has been perilously close to this threshold between 1971 and 2000, making it particularly sensitive to a warming climate. The number of areas near to and exceeding this tipping point are likely to increase as the climate continues to warm in the coming decades, says Higuera.

他说,一个关键的临界点是30年来7月份的平均气温为13.4摄氏度。在1971年到2000年之间,阿拉斯加的大部分冻土带已经接近这一临界值,因此对气候变暖尤其敏感。伊格拉说,随着未来几十年气候继续变暖,接近或超过这个临界点的地区数量可能会增加。

“Across the circumpolar Arctic, the take-home message is that there are distinct thresholds above which you start to see the tundra burning – it’s like a binary switch,” says Higuera. “This threshold relationship is part of what makes the Arctic so sensitive: areas will stay below this threshold for years, off our radar for fire activity – and then all of a sudden with a change in temperature it will start to burn.”

伊格拉说;“在北极圈地区,我们得到的重要信息是,在你开始看到苔原燃烧的时候,会有不同的阈值,就像一个二元开关。这种阈值关系是北极对气温如此敏感的部分原因:在数年内该地区保持在这个阈值以下,在我们的火灾警戒线之下;然后,随着温度的变化,它突然开始燃烧。”

Though fires are a natural component of all ecosystems, including in the far north – they foster biodiversity and facilitate nutrient cycling – to see them on this scale in the Arctic is unprecedented and highly unusual.

尽管火灾是整个生态系统的自然组成现象,包括在遥远的北方——它们促进生物多样性和营养循环,但北极发生如此大规模的火灾是前所未有的,也是极不寻常的。

“It’s an indication of how much we humans are kicking the system,” says Higuera. “And changing [the] global climate is a very big kick to the system.”

伊格拉说:“这表明我们人类正在干扰这个系统。改变全球气候对生态系统是非常大的冲击。”

Part of the reason for the explosion in fires is that this increased heat is drying the soil and melting the permafrost. But there are more surprising reasons, too – such as that the warming climate is leading to more lightning strikes, which are causing more forest fires.

火灾爆发的部分原因是累积的热量使土壤干燥,并使永久冻土融化。但也有更令人惊讶的原因,比如气候变暖导致更多的雷击,引发更多的森林火灾。

Slow burn

缓慢燃烧

“Working in the field in Alaska this summer in a hot and smoky environment, you could literally feel the impacts of a number of fires that were happening in different places all over the landscape,” says Sue Natali, associate scientist with the Woods Hole Research Center, a Massachusetts-based organisation that researches climate change science and solutions. “You could also see the long-term impacts of fires that had happened years beforehand. We were walking on ground that was literally collapsing as a result of permafrost thaw brought on by previous fires.”

“在阿拉斯加今夏炎热和烟雾缭绕的环境中做实地考察,你可以感受到不同地方受火灾的影响。”娜塔莉(Sue Natali)说。娜塔莉是伍兹霍尔研究中心(Woods Hole Research Center)的副研究员。这家机构位于马萨诸塞州,专门研究气候变化和解决方案。“你还可以看到多年前发生的火灾所造成的长期影响。由于之前的火灾导致冻土融化,我们正在行走的地面发生了坍塌。”

If simmering permafrost isn’t surprising enough, this summer she saw something even more shocking.

如果说烧焦的永久冻土还不算什么,今年夏天她看到了更令人震惊的事情。

“I worked in a wetland that had burned,” says Natali.

“我在一个被烧毁的湿地工作,”娜塔莉说。

The fires are impacting entire ecosystems in the north. The air is polluted, droughts are endemic, and in response new assemblages of plants and trees are growing in unexpected places. A report last year found, for example, that warming in the Arctic, and attendant vegetation changes, have caused caribou populations to plummet by half – due to the animals being unable to locate their normal food sources of lichen.

大火正影响整个北部的生态系统。空气被污染,地方性的干旱;而生态系统的一个反应是,在意想不到的地方,植被和树木的新组合正在生长。例如,去年的一份报告发现,北极地区气候变暖,以及随之而来的植被变化,已经导致北美驯鹿的数量锐减了一半,原因是无法找到正常的食物来源——苔藓地衣。

Fires in the Arctic also have huge implications for the global climate. Boreal forests and Arctic tundra cover 33% of the global land surface, and hold an estimated 50% of the world’s soil carbon – more carbon than is stored in all the world’s vegetation, and equal in size to the amount of carbon in the atmosphere.

北极大火对全球气候也有巨大影响。北方森林和北极苔原占全球陆地表面的33%,并保有全球土壤碳含量的50%左右,比地球所有植被中储存的碳还要多,其大小与大气中的碳含量相当。

Because conditions in the north are so cold, microbial growth and decomposition are much slower than in the tropics, so carbon is stored in layers of permafrost rather than recycled back into the nutrient cycle through vegetation growth.

因为北方气候非常寒冷,微生物的生长和分解速度比热带要慢得多,所以碳被储存在永久冻土层中,而不是通过植被生长返回到营养循环中。

In other words, if the forests burn and tundra melts, we could dramatically increase the amount of carbon in our atmosphere – essentially rendering useless even the most coordinated global attempts to cut global emissions.

换句话说,如果森林被烧毁,冻土带融化,我们大气中碳的含量就会急剧增加,即使是全球最齐心协力的减少碳排放的努力也会无济于事。

“The north is a vast, global refrigerator for carbon that has been stockpiled from the atmosphere,” explains biologist Merritt Turetsky of the University of Guelph, in Ontario, Canada. She specialises in studying how permafrost thaws – when solid land turns into a “big soupy mess”, as she describes it. Communities in the north have for years been documenting lopsided homes and crumbling roads.

加拿大安大略省圭尔夫大学(University of Guelph)的生物学家图雷斯基(Merritt Turetsky)解释说:“北方相当于全球的一个巨大冰箱,储存着来自大气的碳。”她专门研究永久冻土层是如何融化的。正如她所描述的,固态土地变成一坨“大汤团”。多年来,北方地区一直在发生房屋倾斜和道路坍塌。

Now, we are seeing that once solid ground itself burn. Fires on the peatland are dominated by flameless smouldering combustion, which move overland through the leaf litter at the snail’s pace of half a metre a week, rather than the speedy rate of 10km per hour in a forest fire.

现在,我们看到曾经坚实的土地正在燃烧。泥炭地的火灾的特点主要是无焰闷烧,这种燃烧在地表的落叶淤积层蔓延开来,速度缓慢,大约每周半米,而不是像森林火灾每小时10公里的速度。

“These aren’t flames licking up into the trees like in Bambi,” says Turetsky. “These are slow-moving edges of ignition that move through the moss, the leaf biomass, and everything else that has fallen onto the forest floor.”

“不是窜上树的那种火焰,”图雷斯基说。“这些是缓慢移动的无焰之火,它们穿过苔藓、树叶淤泥和其他所有沉积在森林浅层地表的东西。”

These smouldering fires not only are ignited much more easily than fiery flames by lightning strikes – they also can persist through cold and wet conditions much longer, largely because the peat holds vast stores of the combustible gas methane. As the climate warms, northern soils and peat dry out, making smouldering fires much more likely.

这些火不仅比雷击更容易被引燃,而且在寒冷和潮湿的环境中能持续更长时间,这主要是因为泥炭中含有大量的可燃气体甲烷。随着气候变暖,北方的土壤和泥炭变干,潜在的火灾便更有可能发生。

In a research paper from 2015, Turetsky explains how smouldering fires are actually a much greater threat to the global climate. They burn for much longer, so they can transfer heat much deeper into the soil and permafrost, overall consuming twice as much carbon-rich fuel as normal fires.

在2015年的一篇论文中,图雷斯基解释了闷烧的火灾如何对全球气候造成更大威胁。它们燃烧的时间要长得多,因此能将热量更深地传递到土壤和永久冻土中,总体上消耗的含碳燃料是普通火灾的两倍。

“Unfortunately, there’s just no way you can send out a bomber plane with a belly full of water or fire retardant to put these out – the tools that fire managers have at their disposal to tackle these huge scale fire events are just ineffective when it comes to smouldering,” she says.

“不幸的是,你根本没有办法派出一架灭火飞机,装满水或灭火剂,来扑灭火灾——灭火专家现有的工具只能应对这些大规模的明火火灾,对付闷烧火灾根本无效,”图雷斯基说。

Even more disconcerting, rainfall doesn’t always help.

更令人不安的是,降雨对于灭火也无助益。

“You need a huge amount of precipitation to fall to put these out – but if you get just a moderate amount of rain, that often comes with lightning, which can just blow things up thanks to the methane in the peat, and just make it worse,” she says.

她说:“你需要大量的降水才能把火扑灭,但是如果雨量仅仅适中,根本无益。而且那往往伴随着闪电,引爆泥炭中的甲烷,会把东西炸飞,情况变得更糟。”

Sink to source

沉在地底的碳源

In a new study, Turetsky and others report that the boreal forests will switch from absorbing carbon from the atmosphere through photosynthesis and growth, and so acting as a carbon sink, to releasing their carbon through drying and burning, making them a carbon source.

在一项新的研究中,图雷斯基和她的同伴认为,北方森林通过光合作用从大气中吸收碳,并形成碳沉积,再通过干燥和燃烧释放碳,从而成为碳源。

In other words, rather than acting as a brake on climate change, by burning, the northern forests will dramatically exacerbate global heating.

换句话说,北方森林不仅没有起到遏制气候暖化的作用,引发的火灾反而会极大地加剧全球变暖。

Rather than acting as a brake on climate change, by burning, the northern forests will dramatically exacerbate global heating
Not all of the soil carbon is burned during a forest fire. Over time, “legacy carbon” builds up in the soil after repeated fires. But as fires in the boreal increase in size and severity in a warming climate, the likelihood of this “legacy carbon” being released to the atmosphere increases.

并不是所有的土壤碳都能在森林大火中燃烧。随着时间的推移,在反复的火灾后“遗留碳”在土壤中积累。但在气候变暖的情况下,北方森林大火的规模和程度增加,这种“遗留碳”被释放到大气中的可能性也在增加。

“The really bad news is that big fires can move through a landscape and tap into old carbon layers that had been removed from the atmosphere thousands of years ago,” explains Turetsky. “When 100,000-year-old carbon is released back to the atmosphere, that’s the stuff of true positive feedback. And while occasional fires are a natural part of the boreal forest, it’s not a regular feature of the Arctic further north – but it may be in the future. We’re dialling up the volume.”

图雷斯基解释说:“真正的坏消息是,大火可以穿透地表,深入数千年前从大气层转化至地下的旧碳层。10万年前的碳被释放回大气,这才是真正的正向反馈和加速循环。虽然偶尔的火灾是北方森林的自然调节机制,但这并不是北极地区的常规特征。它可能会在未来发生,人类正在加剧这种可能。”

If conceiving of fires in the Arctic wasn’t enough of a paradigm shift, an even greater psychological hurdle is understanding that much of the fire in the Arctic is actually underground.

如果说,想象北极地区都可以发生火灾,还不足以带来思维的转变,那么更大的心理突破,是要理解北极地区的大部分火灾实际上是在地下发生的。

“A better understanding of what is actually on fire in these ecosystems – the peat and the muck and the soil beneath the surface – might change the way people understand how the Arctic can go up in flames,” says Carly Philips, Kendall Fellow for Protecting Carbon in Alaska’s Boreal Forests at the Union of Concerned Scientists, a non-profit founded 50 years ago with the aim of using science to improve the health of people and the planet.

阿拉斯加关注北方森林科学家联盟(Alaska's Boreal Forests at the Union of Concerned Scientists)的肯德尔碳保护研究员(Kendall Fellow for Protecting Carbon)菲利浦(Carly Philips)说:“更好的是要理解,是生态系统中什么物质着了火——泥炭、淤泥和土壤表层下的物质在燃烧,可能改变人们对北极火灾的理解。”该联盟是一个50年前创立非盈利的机构,旨在利用科学改善人类健康和保护地球。

Capable of smouldering beneath the surface, these subterranean fires can persist through the winter and pop up in spring in completely unexpected locations. Hence their nickname: “zombie fires”. They’re neither dead nor alive.

这些火灾在地表下闷烧,能够持续整个冬天,并在春季突然出现在完全意想不到的地方。因此它们的绰号是“僵尸火灾”。他们既不明显,却也没有熄灭。

Taken together, melting permafrost, methane release, drying peat, vanishing ice, simmering zombie fires and of course a warming climate are all combining into an unprecedented setting for dramatic changes in the Arctic.

这些因素叠加在一起,融化的冻土、甲烷的释放、干燥的泥炭、正在消失的冰层、悄无声息的闷烧火灾,当然还有气候变暖,这些因素综合在一起,使北极发生了前所未有的巨大变化。

In a 2018 study, Woods Hole’s Natali describes a field experiment that lasted from 2012 to 2016 in Siberia, where she and her colleagues scorched patches of earth to varying degrees and waited to see how easily larch seedlings would grow. By 2017, there were five times more larch seedlings in the moderately and highly scorched earth compared to other plots – implicating that in a landscape razed by forest fires, new species would increasingly flourish.

在2018年的一项研究中,伍兹霍尔的娜塔莉描述了2012年至2016年在西伯利亚进行的一项实地实验。她和同事们在西伯利亚不同程度地烧灼一片片土地,等待观察落叶松幼苗生长的难易程度。到2017年,在中度和高度焦化的土地上,落叶松幼苗的数量是其它地块的五倍,这意味着在被森林大火夷为平地的土地上,新物种将会越来越多。

It could mean that the Arctic landscape shifts away from coniferous forests to become more dominated by leafy deciduous trees that are found further south.

这可能意味着北极的景观从针叶林转变为更低纬度常见的落叶乔木。

“In the boreal zone, we are already seeing a proliferation of deciduous forest across the landscape as coniferous forest fails to return post fire,” says Turetsky. “The iconic structure of how we define the boreal itself might be changing.”

图雷斯基说:“在北方地区,由于针叶林在火灾后无法恢复,我们已经看到落叶林在那里大量生长。定义里北方标志性的生态结构可能正在改变。”

Global influence

全球影响

Dramatic changes in the boreal and the Arctic will affect the entire planet in more ways than one.

寒带和北极地区的剧烈变化,将以不止一种方式影响整个地球。

“This is a global problem: fires in one region affect air quality in other parts of the world,” says Mark Parrington, a senior scientist at the Copernicus Atmosphere Monitoring Service (Cams) at the European Forest Fire Information System. Their monitoring has tracked plumes of smoke from Alaska reaching the Great Lakes; fires in Alberta causing red skies in Europe; a smoke plume from the Canadian Arctic reaching the European Arctic, and more.

“这是一个全球性的问题:一个地区的火灾会影响世界其它地区的空气质量,”欧洲森林火灾信息系统(European Forest Fire Information System)哥白尼大气监测局(Copernicus Atmosphere Monitoring Service)的资深科学家帕林顿(Mark Parrington)说。他们的监测跟踪了从阿拉斯加到五大湖的烟尘云团;阿尔伯塔省的大火导致欧洲天空发红;加拿大北极圈飘来的烟雾到达欧洲的北极地区,甚至更远。

Parrington says we need look at where black particulates – soot – from these fires is falling back to earth to understand the impact on the global climate. If it is deposited onto snow and ice, this would decrease the albedo and lead to more sunlight and heat being absorbed – increasing warming. Cams have some data to address this question, but urgently need more, he says.

帕林顿说,我们需要观察这些火灾产生的黑色颗粒,即碳灰,落回地球的位置,以了解它们对全球气候的影响。如果它们沉积在冰雪上,将减少反照率,导致更多的阳光和热量被吸收,加速全球变暖。他说,哥白尼大气监测局有一些数据是关于这个问题的,但迫切需要更多数据。

Beyond more research, what can be done? Is there any chance of stopping these fires from spreading? Higuera, for one, isn’t optimistic. “It’s just not in the realm of possibility to say we will stop fires like this from happening in the future,” he says. “It’s like trying to stop a hurricane.”

除了做更多的研究,我们还能做些什么?有可能阻止这些火灾蔓延吗?很多人并不乐观,伊格拉就是其中之一。他说:“我们不可能在未来阻止这样的火灾发生。这就像我们无法阻止飓风来袭。”

Even fighting individual fires is extremely challenging, thanks to the remote, vast nature of the area and its lack of infrastructure. But not every fire should be fought, experts say: instead, we need to turn our attention elsewhere.

由于该地区偏远,幅员辽阔,缺乏基础设施,即使扑灭零星火灾都极其困难。但专家表示,并非每一场火灾都应该被扑灭;取而代之的是,我们需要将解决问题的焦点转向别处。

“It’s not an effective use of funds to go out and put out every northern fire – it’s just not feasible,” says Turetsky. “The most important thing we can do is overall climate mitigation – and our chance to do that is not in 15 or 10 years’ time.

图雷斯基说:“消耗资金去扑灭北方的每一场火灾,这并非有效方法,也不可行。我们能做的最重要的事情是全面减缓气候变化,不是10年或15年后才开始做。”

 “It’s now.”

“而是现在就开始做。”

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