加州野火为什么越烧越猛？与气候有关系，但原因并不简单

森林大火正在摧毁加利福尼亚州。

多场大火正在加利福尼亚州肆虐，其中索诺玛县的金卡德大火（Kincade Fire）波及的范围达到了两个旧金山的面积。大约18万人被要求撤离，9万栋建筑遭到威胁，而加州最大的能源供应商太平洋煤气电力公司（Pacific Gas & Electric）近几周来第三次灯火管制，切断了超过94万用户的供电。

加利福尼亚州每年大火的严重程度似乎有上扬态势，尽管我们很容易将火灾的爆发与气候变化联系在一起，就像加利福尼亚州的前州长杰里·布朗所做的那样，但二者的关联并不总是那么简单。

哥伦比亚大学（Columbia University）的大气科学家和极端天气与气候倡议（Initiative on Extreme Weather and Climate）项目负责人亚当·索贝尔在《纽约时报》（New York Times）上写道，近年来大多数登上头条的火灾都发生在秋季，因此气温并非重要因素。索贝尔还指出，随着全球变暖的继续，加剧火灾的迪亚波罗和圣塔安娜的风力现象未来会越来越不常见。

然而，却有证据显示气候变化加剧了加利福尼亚州的干旱状况，尽管问题的矛头也可以指向规模高达500亿美元的农业市场，它们消耗了干旱州40%至80%的水资源。

无论如何，干旱导致了树木枯死，又抽干了落叶的水分，森林也就变成了干燥的易燃物。我们需要尽量缩小这些危险区域，然而根据美国林务局（U.S. Forest Service）的报告，联邦对于伐木的限制导致加利福尼亚州的林木采伐量从20世纪80年代至2012年减少了超过70%，密集的死亡森林面积在不断增长。

去年致命的加利福尼亚州大火发生之后，总统特朗普在推特上表示，火灾的原因是“森林的严重管理不善”。自然，这条推文引发了争议。州长布朗和州里的消防员很快表示特朗普的理论是“无知的”。不过布朗承认，森林管理由联邦政府而非州政府负责，是问题的“一大因素”。

基础设施管理是另一大因素：过去三年里，州能源供应商太平洋煤气电力公司的落地电线已经引发了多起火灾，而目前的金卡德大火可能也是因为类似事故导致。不过至少据我所知，更有趣的一点在于，人类的居住范围距离着火区域之近也是前所未有，这导致自然火灾成为了致命的威胁。

据Vox报道，随着城市开始向乡间扩张，加利福尼亚州有1,130万的居民住在“林野-城区交界”区域，占全州人口的30%。令人震惊的是，超过270万的加利福尼亚人住在“火灾隐患极高的区域”，这个数字预计还会增长。

波莫纳学院（Pomona College）环境分析教授、森林火灾政策专家查尔·米勒去年对《太平洋标准》（Pacific Standard）表示：“加利福尼亚州是火灾常发地，这很正常。现在的困境不在于火灾，也不在于它烧毁的东西，而在于人类如今大量居住在火灾隐患区，将自己陷于危险之中。”（财富中文网）

译者：严匡正

Wildfires are devastating California.

Multiple infernos are blazing across the state and one, the Kincade Fire in Sonoma County, has consumed an area twice the size of San Francisco. Some 180,000 people are under evacuation order, roughly 90,000 buildings are at risk and the state’s largest energy supplier, Pacific Gas & Electric (PG&E) has implemented blackouts for the third time in as many weeks, cutting power to over 940,000 customers.

The severity of California’s annual blazes appears to be on the rise and while it’s tempting to draw a line connecting the fire outbreaks with climate change—as former California Governor Jerry Brown does—the correlation is not always so simple.

Adam Sobel, an atmospheric scientist and director of the Initiative on Extreme Weather and Climate at Columbia University, writes in the New York Times that the most headline-catching blazes of recent years have come in fall when temperature is less of a factor. Sobel also notes that the Diablo and Santa Ana wind phenomena that have fanned those wildfires are expected to grow less common as global warming continues.

There is evidence, however, that climate change has increased drought in California—although the finger of blame could also be pointed at the $50 billion agricultural industry that consumes between 40% and 80% of the arid states water supply.

Either way, drought causes tree death and dries out the fallen, turning patches of forest into dried-out kindling. Those hotspots need to be thinned but, according to a U.S. Forest Service report, federal restrictions on logging caused timber harvesting in California to reduce over 70% between the 1980s and 2012, allowing dense, dead forest patches to grow.

After deadly wildfires in California last year President Trump took to Twitter and asserted that “gross mismanagement of the forests” was the cause of the blaze. Naturally, that was a controversial tweet. Governor Brown and state firefighters were quick to dismiss Trump’s theory as “uninformed” but Brown admitted forest management—a large swathe of which is handled by federal, not state, government—is “one element” of the problem.

Infrastructure management is another: fallen power lines managed by state energy provider PG&E have caused numerous fires in the past three years and the ongoing Kincade fire is suspected to have been caused by a similar mishap. But one of the more interesting issues, at least to my ears, is that humans are simply living closer to fire zones than ever before—turning natural fires into fatal threats.

According to reporting by Vox, some 11.3 million Californians, or 30% of the state population, live in “wildland-urban interface” areas where the city sprawls into the countryside. Shockingly, over 2.7 million Californians live in “very high fire hazard severity zones” and that number is expected to rise.

Char Miller, a professor of environmental analysis at Pomona College and an expert on wildfire policy told Pacific Standard last year, “California is one of those places where fire is normal and it should happen. The dilemma is not the fire, and it isn’t the stuff it burns—it’s the fact that human beings are now living in fire zones at an unhealthy rate and putting themselves in danger.”