来源：《新科学家》
原文见刊日期：2022年6月25日
Eat locally to reduce food miles and your carbon footprint. That is the message promoted by some environmentalists and businesses, but it has long been clear that often this isn’t true – foods that travel thousands of kilometres can have a lower carbon footprint than local produce.
食用本地食品可以减少食物里程和碳足迹。这是一些环保人士和企业所宣扬的信息，但长期以来，人们一直清楚地知道，这往往不是真的——食品经过数千公里的运输，其碳足迹可能比本地农产品更低。
At least, that is what many studies have found. But research published last week claimed that global food miles account for 20 percent of food-related emissions – a much higher proportion than reported in earlier work. So, do food miles matter more than we thought? Spoiler: no, they don’t.
至少，这是许多研究发现的。但上周发表的一项研究称，全球食物里程占与食物相关排放的20%——这一比例比之前的研究报告要高得多。那么，食物里程比我们认为的更事关紧要吗？剧透：不。
The production of the food we eat is responsible for more than a third of global greenhouse gas emissions, so reducing food-related emissions is crucial to limiting further global heating. The question is, what should consumers do to help reduce these emissions?
我们吃的食物的生产造成了全球三分之一以上的温室气体排放，因此减少与食物相关的排放对于限制全球进一步升温至关重要。问题是，消费者应该做些什么来帮助减少这些排放？
Previous studies have found that the emissions from food miles – measured in kilometres food has to be transported multiplied by the tonnage – are tiny compared with those from growing that food. A 2008 study of US diets concluded that transporting food from farms to shops produces just 4 percent of food-related emissions, while a 2018 study of European diets put it at 6 percent.
先前的研究发现，食物里程(以运输食物的公里数乘以吨位计算)的排放与种植食物的排放相比微不足道。2008年一项关于美国饮食的研究得出的结论是，从农场到商店运输食品只产生了4%的食品相关排放，而2018年一项关于欧洲饮食的研究则认为这一比例为6%。
What this means is that if you want to reduce the carbon footprint of your diet, you should focus on buying foods with lower overall carbon footprints rather than those that don’t have to travel far. This basically means eating less meat and dairy. For example, producing 1 kilogram of beef can emit as much as 99 kg of carbon dioxide while making a kilogram of cheese emits up to 24 kg. The figure for bananas is just 0.9 kg, and for apples it is even less: 0.4 kg.
这意味着，如果你想减少你饮食中的碳足迹，你应该专注于购买总体碳足迹较低的食物，而不是那些不用远距离运输的食物。这基本上意味着少吃肉类和奶制品。例如，生产1公斤牛肉会排放99公斤的二氧化碳，而生产1公斤奶酪会排放24公斤的二氧化碳。香蕉的这一数字仅为0.9公斤，而苹果则更少：0.4公斤。
What’s more, even with the same food types, local isn’t always better. For instance, if you live in a nation with a cooler climate where tomatoes can be grown only using heated greenhouses, these local tomatoes will typically have a higher carbon footprint than those shipped in from a warmer country.
更重要的是，即使是同样的食物类型，本地的并不总是更好的。例如，如果你生活在一个气候较凉爽的国家，西红柿只能通过加热的温室种植，这些本地的西红柿通常会比那些从较温暖的国家运来的西红柿有更高的碳足迹。
The latest study doesn’t overturn any of this. The main reason why it concludes that food miles account for such a high proportion of food-related emissions is that the 20 percent figure includes all the transport involved, including that of fertilisers and farm equipment, not just the transport of food.
最新的研究并没有推翻这一切。该报告的结论中，食品里程在食品相关排放中所占比例如此之高的主要原因是，这20%的数字包括了所有涉及的运输，包括化肥和农业设备，而不仅仅是食品的运输。
“Our study looks at the entire supply chain for food consumption, and naturally non-food commodities are part of it,” says one team member of the study.
“我们的研究着眼于食品消费的整个供应链，当然非食品商品也是其中的一部分，”该研究团队的一名成员表示。
It is worthwhile to estimate this, but the team should use a term other than “food miles” to avoid confusion, says Hannah Ritchie at the University of Oxford.
牛津大学的汉娜•里奇表示，这样的估计是有价值的，但研究团队应该使用“食物里程”以外的术语，以避免混淆。
If the standard definition were applied to the numbers in the study, food miles would account for only 9 percent of food-related emissions, says Ritchie. That is much closer to previous research. “The bottom line is still that what you eat has a much bigger impact on emissions than the distance that food has to travel to reach you,” says Ritchie.
里奇说，如果将标准定义应用于研究中的数字，食品里程将仅占食品相关排放量的9%。这与之前的研究更为接近。里奇说：“归根结底，你吃的东西对排放的影响要比食物到达你身边的距离大得多。”