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CAFFEINE IS ONE of the world’s most popular drugs, and coffee one of its best-loved delivery mechanisms. It is grown in more than 70 countries; more than 2bn cups are drunk each day. It helps support the livelihoods of an estimated 125m people. It indirectly supports many more, including your Californian corre­spondent (though not his tea-drinking British editor), by supplying them with a jump-start every morning.

咖啡因是世界上最受欢迎的药物之一，而咖啡是其最受欢迎的传递方式之一。咖啡在70多个国家种植，每天饮用超过20亿杯。它支持着估计有1.25亿人的生计。它还间接支持着更多人，包括你的加利福尼亚通讯员（尽管不包括他的喝茶的英国编辑），为他们每天早上提供一种启动。

But global warming threatens the world’s coffee supply. Temperatures are rising and rainfall patterns shifting across South America, central Africa and South­ East Asia, where most of the world’s coffee is grown. By the end of the century be­tween 35% and 75% of the coffee-growing land in Brazil, the world’s biggest producer, could be unusable, according to a recent paper published in Science of the Total Envi­ronment by Cassia Gabriele Dias, an agri­cultural engineer at the Federal University of Itajuba, in Brazil. Another paper, published in 2015, con­cluded that by 2050 between43% and 58% of the world’s coffee-growing land would be rendered unsuitable, depending on how high greenhouse-gas levels rise (see map). Some of that loss will be off­set as other bits of land, presently too cold for coffee, warm up. New plantations might take root in southern China, for in­stance, or on the northern coast of the Gulf of Mexico.But they are unlikely to make up for the shortfall.

但全球变暖威胁着世界的咖啡供应。南美洲、中非和东南亚，这是全球大部分咖啡产地，温度升高，降雨模式发生变化。根据巴西伊塔乌班巴联邦大学的农业工程师卡西娅·加布里埃尔·迪亚斯（Cassia Gabriele Dias）最近在《科学总环境科学》杂志上发表的一篇论文，到本世纪末，巴西这个世界最大的咖啡生产国，35%到75%的咖啡种植地可能无法使用。另一篇于2015年发表的论文得出结论，到2050年，全球43%到58%的咖啡种植地将因温室气体水平的升高而变得不适用。其中一些损失将被其他目前对咖啡来说太冷的土地弥补。新的种植园可能会在中国南部或墨西哥湾北部沿海扎根。但它们不太可能弥补供应不足。

The problem is that coffee is a fussy plant-and Coffea arabica, the beans of which account for 70% of the world’s pro­duction, is especially so. Its best yields come when temperatures remain between 18°C and 23°C throughout the year. Many of the places in which it is grown are already near the top of that range.It is susceptible to diseases such as coffee rust (a fungal in­fection) and the depredations of berry-bor­er beetles, which lay eggs inside growing beans. Both are expected to spread more readily in a warmer world. Farmers growing Robusta (Coffea ca­nephora) , Arabica’s tough, bitter cousin, have a bit less to worry about. Robusta prefers warmer temperatures. But coffee snobs dislike the taste. Robusta beans fetch a lower price than Arabica ones, and are mostly used in instant coffee. For cof­fee-lovers, therefore, the solution is not to shift to Robusta but to save Arabica.

问题在于咖啡是一种挑剔的植物，而阿拉比卡咖啡的豆子占据了全球产量的70%。阿拉比卡咖啡尤其挑剔，最佳产量要求全年温度保持在18°C到23°C之间。许多种植咖啡的地方已经接近这个温度范围的顶端。咖啡容易受到疾病的影响，比如咖啡锈病（一种真菌感染）和果蠹虫的危害，后者在生长中的豆子内产卵。在更温暖的世界中，这两者预计会更容易传播。种植罗布斯塔咖啡（Coffea canephora）的农民要少担心一些，因为罗布斯塔更喜欢较暖的温度。但是对于咖啡狂热者来说，他们不喜欢罗布斯塔的味道。罗布斯塔豆的价格较阿拉比卡豆低，主要用于速溶咖啡。因此，对于咖啡爱好者来说，解决方案不是转向罗布斯塔，而是拯救阿拉比卡。

Onwards and upwards

One option is simply to move uphill. Other things being equal, temperatures fall by about 0.7°C for every 100 metres above sea level. Tanzania, for example, has signifi­cant areas of land 150 to 200 metres above where Arabica is currently grown that ought to work well for coffee-farming as temperatures rise. In Ethiopia, some farm­ers have already moved their plantations as much as 600 metres higher.

一个选择是简单地向山上移动。其他条件相同，海拔每升高100米，温度约下降0.7°C。例如，坦桑尼亚有相当多的土地位于比阿拉比卡目前种植的地方高出150到200米的地方，这对咖啡种植来说应该是合适的，因为温度上升。在埃塞俄比亚，一些农民已经将他们的种植园移动到高出600米的地方。

But higher altitude usually means steeper slopes and shallower soils, which increase the rate at which nutrients are washed out by rain. Replacing them with artificial fertiliser is expensive. Higher slopes are also often covered in dense, spe­cies-rich forests. Cutting them down to make room for coffee plants might not be compatible with a country’s climate pledg­es. And moving cannot be done overnight. New plantations require five years or more to produce a good harvest. For many small­ holders, such delays are not an option.

但是较高的海拔通常意味着更陡峭的坡度和更浅的土壤，这会增加养分被雨水冲走的速度。用人工肥料替代它们是昂贵的。较高的坡度通常也被密集的、物种丰富的森林覆盖。砍伐它们以腾出空间种植咖啡植株可能与一个国家的气候承诺不相容。并且迁移不是一夜之间可以完成的。新的种植园需要五年或更长时间才能产生丰收。对于许多小农户来说，这样的延迟是不可行的。

Another option is to change the way in which existing plantations are managed. Coffee plants are relatively short, and evolved to live in the shade beneath a for­est canopy. Indeed, that is how they were originally cultivated. But as demand grew in the 20th century, farmers removed the taller trees in order to fit more coffee plants on their land. Now some are giving these old techniques a second look.

另一种选择是改变现有种植园的管理方式。咖啡植株相对较短，并且进化为在森林树冠下生长。事实上，这就是它们最初被培植的方式。但随着20世纪需求的增长，农民们移除了更高的树木，以在他们的土地上容纳更多的咖啡植株。现在，一些人正在重新审视这些古老的技术。