比尔·盖茨：我们应像谈论煤炭一样多地讨论土壤

我对牛屁真算是够了。

我已经在过去六个月里写过几篇关于牛放屁的文章，而且我本不应该在礼貌的交谈中多次提到这件事。我为自己辩护，因为我有一个正当的理由：如果想找一个与发电无关却能导致气候变化的例子，牛放屁就是个好例子。

大多数关于应对气候变化的讨论，都集中在电力和对可再生能源的需求上。消除发电过程中的碳足迹会是一个巨大的进步，但如果我们不能在50年内让各经济部门的净排放降为零（并在未来10年内实现大幅消减），那么这一进步也远远不够。在这些经济部门中，农林和土地利用部门贡献了24%的温室气体排放总量——只比电力部门少一个百分点。

 “牛胀气”是一个难忘且显著的排放例子，但它并不是农林和土地利用部门碳排放的唯一贡献因素。如果你正在寻找气候变化的元凶，看看土壤你也能有不小收获。

有一个令人震惊的事实：土壤中的二氧化碳比大气和所有植物中的总和还要多。在自然状态下这并没什么大不了。但是当土壤被扰乱（比如把森林变成农田），所有贮存在土壤里的二氧化碳便会被释放到大气中。这就是为什么仅森林砍伐一项就产生了全球温室气体排放的11%。(另一个原因是，森林和草原是天然碳汇，去掉它们会降低地球从空气中清除二氧化碳的能力。)

土壤中的微生物与肥料接触时也会产生温室气体。化肥彻底改变了世界粮食供给的方式，但化肥在被微生物分解时会释放一种叫做一氧化二氮的强大温室气体。而像粪肥这样的天然肥料也好不到哪里去，因为它们在分解时同样会释放温室气体。

那我们该如何抗击农业导致的气候变化呢？我们不能简单地清除掉土壤，抑或停止种庄稼、使用化肥和饲养牲畜。虽然有一些社会能做出的改变（例如第三层级和第四层级国家的人可以减少肉类消费），但到头来人还是需要吃饭的。

这就是为什么对于农业来说，目标不是减少总产量，而是减少每件产品的排放量。由于每个国家、每种文化所采用的食物生产方式都不一样，所以达成这项目标的方法有很多种（我所参与的“突破能源基金”正在为这个问题提供一些创造性的解决方案）。下面是一些我觉得最有趣的：

• 替代化肥的微型氮工厂：如果我们既能给植物施肥，又能不向空气中释放那么多有害的一氧化二氮，情况将会怎样？突破能源基金投资了一家名为Pivot Bio的公司，该公司利用经基因改造的微生物为植物提供其所需的氮，且不会像化肥那样产生过多的温室气体。你可以通过下面这段视频了解它是如何起作用的。    

• 用更长的根从土壤中吸收碳：Kernza培育出了一种新的小麦品种，它的根更长、更浓密，可以从土壤中吸收更多的二氧化碳。由于传统小麦是一年生植物且只能持续一个生长季，它的根既短又相对脆弱。Kernza的种子能长成多年生小麦，而且根的长度是传统小麦的两倍。此外，它更具抗逆性的结构让农民收获更高的产量，其结果是用水更少、对气候的耐受力更大、土壤更健康。

• 用微生物酿造的实验室棕榈油：棕榈油有着破坏环境的坏名声：为建造新的棕榈油种植园而毁掉婆罗洲森林的这一做法，导致了200多年来最大的单年排放量增长。但棕榈油已成为现代社会的固定产品，存在于从食物到洗发水的任何东西里。C16生物科学公司（C16 Biosciences）创造出了一种天然棕榈油的替代品，用发酵技术来酿造一个合成的版本。

• 帮助食物保鲜的隐形保护层：每年约有三分之一的食物被丢弃或浪费。这对没有足够食物的人来说是坏事，对农民来说是坏事，对环境来说也是坏事。两家公司——阿佩尔公司（Apeel）和剑桥作物公司（Cambridge Crops）正在研究一种能使食物保鲜更久的保护层。这种保护层是隐形的，且完全不会影响味道。

• 集体作物贮藏：并非所有的创新都是技术型的：巴班戈纳（Babban Gona）是尼日利亚的一种新型商业模式，它帮助农民更久地保存农作物。许多尼日利亚的农民没有贮藏农作物的设施，只能在收获季节之后——也就是当市场上供应着大量商品的时候——出售他们的产品，因此他们只能卖最低价，或者有时根本卖不出去（在尼日利亚，食物在到达消费者之前就已损失了50%至60%）。巴班戈纳的农民们合力购买一个谷仓。这意味着他们可以等到更有利的时候再出售他们的作物——在减少废物排放的同时增加了收入。

我们永远不会有一个阻止气候变化的所谓妙招，但我希望这些和其他的创新将能足够地减少农业排放，来防止最糟糕的情况发生。(不幸的是，撒哈拉以南非洲地区的农民已经受到气候变化的影响，因此我们也必须帮助他们适应气候变化。)

我希望农业创新能像电力对气候变化的影响一样受到重视，因为农业创新的成功对阻止气候变化同样至关重要。未来人口和收入的变化可能会让粮食系统对环境的影响翻倍。我相信，针对这一挑战的具有创造性和可扩展性的解决方案已经存在，现在正是投资它们研发的时候。

We should discuss soil as much as we talk about coal

I’m done with cow farts.

I’ve written about them several times over the last six months, and I bring them up in polite conversation more than I should. In my defense, I have a legitimate reason: cow farts are a good example of something that contributes to climate change but isn’t related to generating electricity.

Most discussions about fighting climate change focus on electricity and the need for renewable energy. De-carbonizing the way we generate electricity would be a huge step, but it won’t be enough if we don’t reach zero net emissions from every sector of the economy within 50 years (and make a serious dent in the next ten). That includes the agriculture, forestry, and land use sector, which is responsible for 24 percent of all greenhouse gas emissions – just one percentage point less than electricity.

Bovine flatulence is a memorable and significant example of emissions – but it’s not the only major contributor to agriculture, forestry, and land use’s slice of the emissions pie. If you’re looking for a climate change boogeyman, you’re just as well-off picking on soil.

Here’s a mind-blowing fact: there’s more carbon dioxide in soil than in the atmosphere and all plant life combined. That’s not a big deal when left to its own devices. But when soil gets disturbed – like it does when you convert a forest into cropland – all that stored CO2 gets released into the atmosphere. That’s one reason why deforestation alone is responsible for 11 percent of all global greenhouse gas emissions. (Another reason is that forests and grasslands are natural carbon sinks. Clearing them reduces the planet’s capacity to remove carbon dioxide from the air.)

The microbes in soil can also create greenhouse gases when they come into contact with fertilizer. Synthetic fertilizers revolutionized how we feed the world, but they release a powerful greenhouse gas called nitrous oxide when broken down by those microbes. Natural fertilizers like manure aren’t any better, because they release greenhouse gases as they decompose.

So how do we fight climate change caused by agriculture? We can’t simply get rid of soil – or stop growing crops, using fertilizer, and raising livestock. There are some changes that societies can make – people in level 3 and 4 countries could consume less meat, for example – but at the end of the day, people need to eat.

That’s why the goal with agriculture is not to reduce the amount created, but to reduce emissions per product. Because every country and every culture approaches food production differently, there are a lot of different ways to do that (I’m involved with a group called Breakthrough Energy Ventures that is backing a number of creative solutions to tackle the problem). Here are some of the ones I find most interesting:

• Microscopic nitrogen factories that replace fertilizer: What if we could fertilize plants without releasing so much harmful nitrous oxide into the air? BEV is invested in a company called Pivot Bio that has genetically modified microbes to provide plants with the nitrogen they need without the excess greenhouse gases that synthetic alternatives produce. Watch the video above to learn more about how it works.

• Longer roots that suck carbon out of soil: Kernza has developed a new strain of wheat with  longer and denser roots, so it can absorb more carbon dioxide from soil. Since traditional wheat is an annual plant and only lasts for one growing season, it has short and relatively fragile roots. Kernza’s seeds produce a perennial wheat with roots that are twice as long as traditional wheat. Plus, its hardier structure creates higher yields for farmers -- which in turns leads to less water use, greater climate resiliency, and healthier soils.

• Lab-grown palm oil brewed from microbes: Palm oil has earned its bad environmental reputation: the destruction of Borneo’s forests to build new palm oil plantations resulted in the largest single-year increase in emissions in over two hundred years. But it’s a fixture of modern society, found in everything from food to shampoo. C16 Biosciences has created an alternative to natural palm oil by using fermentation to brew a synthetic version.

• An invisible barrier that helps food stay fresh longer: Approximately one-third of all food produced gets lost or wasted every year. That’s bad for people who don’t have enough to eat, bad for farmers, and bad for the environment. Two companies – Apeel and Cambridge Crops – are working on protective skins that keep food fresh longer. The coating is invisible and doesn’t affect the taste at all.

• Collective crop storage: Not all innovations are technological: Babban Gona is a novel business model in Nigeria that helps farmers hold onto their crops longer. Many Nigerian farmers don’t have facilities to store their crops. They can only move their products right after harvest when the market is flooded with goods, so they sell for a rock-bottom price, or sometimes not at all (Nigeria loses 50 to 60 percent of its food before it even gets to the consumers). Babban Gona farmers go in together to purchase a grain silo. This means they can wait to sell their crops at a more advantageous time – reducing emissions from waste, and increasing income at the same time.

There will never be one silver bullet that stops climate change – but I’m hopeful that these innovations and others will chip away at agricultural emissions enough to prevent the worst from happening. (Unfortunately, farmers in places like sub-Saharan Africa are already experiencing the effects of climate change, so we also have to help them adapt.)

I wish agricultural innovation got as much attention as the impact on climate change from electricity, because its success is just as critical to stopping climate change. Future changes in income and population may come close to doubling the current environmental impacts of the food system. I believe creative, scalable solutions to this challenge are out there, and now is the time to invest in their R&D.