THE fires are blazing. The west of the United States has endured some 50,000 wildfires this year, and over 8.5m acres (3.4m hectares) have burned. 大火如荼。美国西部今年已经经历了50000次火灾，火灾波及面积850万英亩（340万公顷）。
Northern California has suffered in particular recently as flames have swept through parts of the landscape, killing at least 23 people and devastating wineries. 加州北部遭遇了尤其大的一场火。大火扫过部分区域，造成至少23人死亡，瘫痪了本地酿酒业。
In Canada, as of August 30th, 7.4m acres had burned. The Canadian fires extended eastwards, but the main concentration was in the west, with British Columbia enduring its worst year, in terms of land burned, since 1958. 在加拿大，到8月底为止，740万公顷被大火夷为焦土。加拿大的火向东烧，但是集中爆发在西部。根据过火面积算，不列颠哥伦比亚经历了1958年来的最坏的一年。
Why have so many fires burned in North America this year? 为什么北美今年有这么多场大火爆发？
Wildfires are particularly common in places with higher densities of dry woods or grasslands. 野火在有高密度的干燥树木或者草地的地方实属平常。
They can be started by a lightning strike or a careless campfire—even firecrackers. 引起野火的原因是多样的，比如闪电，无心的篝火，甚至点燃的爆竹。
Ernesto Alvarado of the University of Washington, who specialises in large fires, says that historically portions of the forests of America’s north-west would burn every five to 20 years. 华盛顿大学的Ernesto Alvarado 专门研究大型火灾，他说历史上美国东北的森林按区域每二十年烧一遍。
In many areas, however, these fires have been suppressed for over a century by the needs of loggers and residents. Over time, undergrowth, saplings and dead trees accumulate, creating conditions in which a fire can spread very rapidly. 尽管如此，在很多区域，这些火灾由于伐木工人和居民对木材的需求被压制了。经年累月的灌木、树苗和死树的累积，造成了一旦火灾发生便可迅速蔓延的局面。
Furthermore, a recent reduction in logging has led to an even closer packing together of trees. “To maintain good forest health in many of these forests, you need fire,” says Dr Alvarado. 此外，伐木的减少导致了树木密度的增加。Ernesto Alvarado 说：“要保持森林的健康，我们需要野火”。
While some burns are prescribed, they are a fraction of what is required. In Washington, for instance, between 2001 and 2014 the Forest Service burned just 2% of the state’s 9.3m acres of forest. 有些大火是刻意安排的，他们只是森林保护措施的一部分。例如，在华盛顿州，从2001到2014年，森林管理部门本州的930万公顷森林烧了2%。
In terms of scale, 2017 is not actually an outlier. In the past decade, wildfires have burned an average of 6.6m acres each year in the United States and 6.2m acres in Canada. 在规模上，2017年并不特殊。过去十年，在美国平均每年有660万公顷森林毁于野火，在加拿大是620万公顷。
The particular problem this year is the dispersed nature of the blazes. In other years, the fires have clustered in a single state or province. 今年的特殊问题是野火的分散性。在其他年头，野火是集中在一个州烧的。
This year, not only have the wildfires burned on more fronts, but they have done so closer to heavily populated areas. 而今年，野火不但在多个地方开烧，而且有些地方和人类居住区很贴近。
Prevailing winds have deposited ash in cities like Portland, and kept a red sun glaring in a smoky sky for weeks at a time in Seattle. 盛行风已经把灰吹到了波特兰等城市，还让西雅图变成红日下烟雾漫天的魔幻之城。
The current state of the north-western forests, combined with the effects of climate change, increase the likelihood that wildfires will be worse in future. 西北地区森林的现在形势，加上气象变化的影响，增加了在未来野火变大的可能。
Higher ambient temperatures cause snow to melt earlier, leading to drier, more flammable biomass in forests. More extreme weather means more severe storms, more lightning and thus more fires. 更高的温度让雪更容易融化，导致了森林中生物量更干更容易着火。更多的极端天气意味着更严重的风暴，更多的闪电，从而更多野火。
The opening up of forests to the public does not help, either, with more backpackers increasing the likelihood that fires will be started accidentally. 把森林对公众开放并不能有所帮助。背包客的增多只能让事故性的人为火灾的概率增加。
Researchers also believe that larger, hotter, longer-burning fires can lead to deforestation as they prevent some species of trees from recovering as robustly as they do with smaller outbreaks. 研究者们也相信，更大、更热和时间更长的野火会造成去森林化，因为他们导致某些物种无法像小火灾后那样蓬勃的再生。
Little can be done to reduce the danger without a dramatic increase in prescribed burns, and these are unlikely as people continue to move into forested areas. 除了人为得制造更多的可控小火灾，没有任何办法能降低这个风险。可是，随着居民往森林地区的迁移，人为制造小火灾也不再适宜。
One further consequence: the smoke and ash that drift across densely inhabited areas affect human health, too. 一个附带的后果：飘向人类高密度聚居区的烟灰，也会影响人类健康。
A study by the universities of Harvard and Columbia of slash-and-burn fires in Indonesia in 2015 blamed the fires for 100,000 additional deaths and 500,000 injuries in Indonesia, Singapore and Malaysia. 哈佛和哥伦比亚大学的一项研究显示，印尼对森林的刀耕火种造成的火灾在2015年造成了印尼、新加坡和马来西亚50万例附加死亡。
Where there’s smoke, there’s fire: this year’s haze presages years of potentially more ferocious burns. 有烟的地方，就有火。今年的雾霾预示着火荼之年。
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