In rural Suffolk， where I live， frost most commonly arrives in December. In Aviemore， October. In Penzance it might not happen at all. For gardeners and agriculturalists the phenomenon is a blessing and a curse： it breaks up heavy soils， kills weeds， reduces pest populations， and turns parsnips， carrots， kale and leeks so much sweeter. But at the other end of winter， unseasonably late frosts can wreak havoc1， leaving new plant-growth limp and blackened and dead.

我住在萨福克郡的乡下。一般而言，那儿一到十二月就开始起霜。在阿维莫尔是十月，在彭赞斯可能根本就不会有霜。对园丁和农夫而言，霜既是福音也是诅咒：它让硬土松软，杀死野草，减少害虫，萝卜、胡萝卜、甘蓝菜、韭葱因为它变得愈发甘甜。可如果霜在冬天将尽之时光顾，那迟到得可真不是时候。它会引发一场浩劫，打蔫新长出的嫩牙，让他们变黑，而后死去。

With the earlier springs of a warming world， late frosts are increasingly destructive and can devastate industries. Desperate not to lose entire vintages， French winemakers light bonfires and candles among the vines to keep the ice at bay2.

全球变暖，春天越来越早，晚霜的破坏性也越来越大，甚至会给相关产业酿成灾难。法国酿酒商为了不让葡萄园颗粒无收，只好在葡萄园中点起篝火和蜡烛防止霜冻。

Frost occurs because warm air is able to carry more moisture than cold air. When temperatures dip， water is lost from it. Should temperatures remain above freezing， this water is deposited as dew. If temperatures continue to fall， dew may freeze to a clear， glassy coat called rime ice. But with sufficient cold， water vapour lost from the air skips the liquid stage entirely and turns directly to crystalline ice： frost.

之所以会产生霜，是因为比起冷空气，暖空气携带的水分更多。温度下降，空气中的水分也随之流失。如果温度维持在冰点以上，析出的水分沉积在物体表面成为露水。而如果温度持续下降，露水会在物体表面形成清澈透明的雾凇。但如果足够冷，空气中析出的水蒸气就会完全跳过液态阶段，直接变为冰晶，也就是霜。

Like clouds， frosts have their own taxonomy. Wind frost occurs when a bitter wind blows over surfaces， forming tiny spikes that cluster along the edges of leaves， twigs or poles. The branching， feathered patterns on windscreens and the interior of windows in unheated rooms are known as fern frost or window frost， each curling frond3 seeded from an imperfection， a scratch or grain of dust or dirt that allows ice crystals their first purchase4 on an otherwise smooth surface.

霜和云一样，也分门别类。寒风吹过，沿叶面边缘、树枝或树干表面形成的细小尖刺状物叫做风霜。在挡风玻璃和没有暖气的房间窗户内侧形成的发散性羽毛状花纹叫做蕨纹霜或霜花。光滑的玻璃表面只要有瑕疵，一粒灰尘又或是灰尘留下的划痕，都会最先让冰晶紧紧附着在玻璃表面，形成一片片卷曲的蕨叶状花纹。

Hoar frost—spines and needles of white ice growing from frozen sur-faces—is often a consequence of freezing fog. And rarest of all is an exquisitely beautiful phenomenon called hair ice. Rotting wood of deciduous trees infected by the fungus Exidiopsis effusa5 can， under the right conditions， extrude a tangled， thick mop of long strands of white ice possessing the soft sheen of animal fur. The presence of the fungus and the chemicals it releases allow ice to grow in a form unlike any other manifestation： it looks like a tiny silver toupee or a patch of polar bear pelt discarded on the darkness of a forest floor.

白霜是形成于结冰物体表面的白色冰针和冰锥，往往是冻雾的产物。