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As we saw in the last lecture,
在上一堂課我們已經看到了，
a major cause of climate change is the rapid rise in the level of carbon dioxide in the atmosphere over the last century.
導致氣候變化的一個主要原因就是自上個世紀以來，大氣中二氧化碳含量迅速增加。
If we could reduce the amount of CO2, perhaps the rate of climate change could also be slowed down.
如果我們能減少CO2的含量，也許氣候變化的速度就也能有所減緩。
One potential method involves enhancing the role of the soil that plants grow in, with regard to absorbing CO2.
一個可能的措施是加強培育植物的土壤在吸收二氧化碳方面的作用。
Rattan Lal, a soil scientist from Ohio State University, in the USA,
來自美國俄亥俄州立大學的土壤學家Rattan Lal聲稱，
claims that the world's agricultural soils could potentially absorb 13 per cent of the carbon dioxide in the atmosphere
全世界的農業土壤可能一共能夠吸收大氣中百分之十三的二氧化碳，
the equivalent of the amount released in the last 30 years.
這一數字相當於過去三十年裡釋放的二氧化碳總量。
And research is going on into how this might be achieved.
研究還在繼續進行，以探究怎樣才能做到這一點。
Lal first came to the idea that soil might be valuable in this way not through an interest in climate change,
Lal最初產生土壤也許在方面非常重要這個想法，並不是通過對氣候變化的興趣，
but rather out of concern for the land itself and the people dependent on it.
而是出於對土壤本身以及靠它生存的人們的關心。
Carbon-rich soil is dark, crumbly and fertile, and retains some water.
碳質豐富的土壤顏色很深，易碎且肥沃，而且還能留住一些水分。
But erosion can occur if soil is dry, which is a likely effect if it contains inadequate amounts of carbon.
但是如果土壤中所含碳質不足，可能就會很乾，而這也許會導致侵蝕。
Erosion is of course bad for people trying to grow crops or breed animals on that terrain.
對想要在那塊地上種植莊稼或者放牧動物的人來說，土壤侵蝕當然是件壞事。
In the 1970s and 80s, LaI was studying soils in Africa so devoid of organic matter
二十世紀七八十年代時，Lal正在非洲研究土壤，那裡的土壤有機物質十分匱乏，
that the ground had become extremely hard, like cement.
以至於地面變得極其堅硬，就像水泥一樣。
There he met a pioneer in the study of global warming,
他在那兒遇見了一位研究全球變暖的先驅，
who suggested that carbon from the soil had moved into the atmosphere.
這位研究人員提出，土壤中的碳質都揮發進大氣裡了。
This is now looking increasingly likely.
現在看來這一說法越來越可信。
Let me explain. For millions of years, carbon dioxide levels in the atmosphere have been regulated,
我來解釋一下，數百萬年以來，大氣中的二氧化碳水平都被控制著，
in part, by a natural partnership between plants and microbes — tiny organisms in the soil.
部分是由植物和土壤中的微小生物——細菌之間的天然合作關係控制的。
Plans absorb CO2 from the air and transform it into sugars and other carbon-based substances.
植物從空氣中吸收CO2，並把它轉化成糖分和其他碳基物質。
While a proportion of these carbon products remain in the plant,
這些碳產品中一部分會留在植物中，
some transfer from the roots to fungi and soil microbes, which store the carbon in the soil.
另一些會從植物根部轉移到真菌和土壤細菌中，它們會將碳保留在土壤裡。
The invention of agriculture some 10,000 years ago
大約一萬年前，農業的發明
disrupted these ancient soil-building processes and led to the loss of carbon from the soil.
打亂了這些古老的土壤構成程式，導致了碳質從泥土中流失。
When humans started draining the natural topsoil,
當人類耗盡自然表層土並開始為了耕種而犁田時，
and ploughing it up for planting, they exposed the buried carbon to oxygen.
他們就把土壤中掩藏的碳質暴露在了氧氣中。
This created carbon dioxide and released it into the air.
這一行為製造了二氧化碳並將其釋放進了空氣中。
And in some places, grazing by domesticated animals has removed all vegetation, releasing carbon into the air.
在某些地方，家養牲畜將地表所有的植被都啃噬殆盡了，碳質也因此進入了空氣裡。
Tons of carbon have been stripped from the world's soils — where it's needed — and pumped into the atmosphere.
大量的碳都被從地球土壤中剝離了出來，灌進了大氣中，但是土壤才是需要碳質的地方。
So what can be done?
那麼我們能做些什麼呢?
Researchers are now coming up with evidence
研究人員現在正在拿出證據證明，
that even modest changes to farming can significantly help to reduce the amount of carbon in the atmosphere.
即使是耕種方法中的`微小變化，也能在很大程度上幫助減少大氣中的碳含量。
Some growers have already started using an approach known as regenerative agriculture.
一些農民已經開始使用一種叫做再生農業的方法。
This aims to boost the fertility of soil and keep it moist through established practices.
這種方法目的在於通過既有的慣常做法，增加土壤的肥力，保持土壤溼度。
These include keeping fields planted all year round, and increasing the variety of plants being grown.
包括保證土地上全年都有植物生長，並且增加種植的植物的多樣性。
Strategies like these can significantly increase the amount of carbon stored in the soil,
像這樣的策略能夠大量增加土壤中保留的碳含量，
so agricultural researchers are now building a case for their use in combating climate change.
所以農業研究人員現在正在建立一個他們能用來對抗氣候變化的案例。
