有機食物對氣候傷害更大
包括瑞典查爾姆斯理工大學的國際研究團隊，在發表於期刊《自然》(Nature)的新研究中，發現有機耕作的食物對氣候的衝擊比慣行耕作的食物還大，原因為有機耕作需要更多的土地。
有機耕作每公頃產出的作物比較少，間接造成森林砍伐而釋放出更多二氧化碳。
研究人員發展出新方法來估計土地利用方式對氣候的衝擊，接著結合其他方法比較有機和慣行的食物生產過程。結果顯示有機食物會排放出更為大量的碳。
負責進行這項研究的科學家之一，查爾姆斯理工大學的助理教授Stefan Wirsenius表示：「我們的研究顯示在瑞典種植的有機豌豆對氣候的衝擊比慣行種植的豌豆高出約50%。某些食物兩個農法之間的差距甚至更加巨大，比方說瑞典的有機冬小麥相較而言就高出將近70%。」
有機食物對氣候如此不友善的原因是每公頃的產量低了許多，主要是不用肥料的緣故。因此，若要產生等量的有機食物，就需要更大的土地面積。
這項新發現的突破之處在於結論指出，土地利用方式的差異導致有機食物對氣候的衝擊更加重大。
「有機耕作所需的大量土地造成森林砍伐，間接排放出更多二氧化碳。」Stefan
Wirsenius解釋。「國際貿易主導了世界上的食物生產，因此我們在瑞典所用的耕作方式會影響到熱帶的森林砍伐。如果我們要用更多的土地才能生產相同數目的糧食，就會間接造成世上某個地方的森林砍伐得更加嚴重。」
Stefan Wirsenius聲稱從氣候的觀點來看，甚至連有機肉類和乳製品都比以慣行農法生產出來的更加不利。
「由於有機肉類和乳製品的生產過程是用有機飼料，所以它們比起慣行農法也需要更大的土地面積。意謂我們從有機小麥和豌豆上得到的發現，原則上也適用於肉類和乳製品。不過這篇論文中我們沒有針對肉類跟乳製品進行計算，也沒有呈現出實際案例。」
新的度量系統：碳機會成本(Carbon Opportunity Cost)
研究人員運用一種他們稱為「碳機會成本」的新度量系統，來計算使用更多土地如何影響森林砍伐，進而排放出更多的二氧化碳。此度量系統考量了有多少碳儲存在森林，以及砍伐森林使這些碳變成二氧化碳釋放出來的量。這是世上第一篇運用此度量系統做出的研究。
「過去比較有機和慣行食物時，通常沒有考慮到使用更多土地會對氣候造成更嚴重的影響。」Stefan
Wirsenius表示。「這是一個重大疏忽。就像我們研究顯示的，此效應可以比一般分析中納入的溫室氣體造成的影響多出好幾倍。而我們也需要嚴肅看待這項結果，因為今日瑞典有些政治人物的目標是提高有機食物的產量。如果真的實行，瑞典因為糧食生產而對氣候造成的影響可能會增加許多。
」
為什麼之前的研究沒有考慮到土地利用，以及它跟二氧化碳排放之間的關係？
「可以確定的是有很多因素。我認為其中一個重要的原因不過是先前缺乏易於運用的好方法來測量此效應。相對來說，我們新的測量方法可以讓我們輕易地在更多環境層面進行比較。」
研究結果發表期刊《自然》，論文標題為「Assessing the Efficiency of Land Use Changes for
Mitigating Climate Change」。作者為Timothy
Searchinger、Stefan
Wirsenius、Tim
Beringer和Patrice
Dumas。
深入探討：從消費者的角度
Stefan Wirsenius強調這項發現不代表有意識的消費者就應該完全轉而購買非有機食物。
「食物的種類通常更加重要。比方說，有機豆類或是有機雞肉相較於慣行方法養出來的牛肉，對氣候來說更加有益。」他說。「有機食物在某些方面確實比慣行農法產生的食物更加有益。」他接著說明。「舉例而言，這可以讓農場裡的動物獲得更好的福祉。但論及對氣候的衝擊，我們的研究顯示總體來看有機食物是相當差勁的糧食生產方案。」
對於想要投身有機食物生產方式的益處，卻又不想對氣候造成更多衝擊的消費者來說，一個有效的作法是改把重點放在飲食中不同蔬果和肉類對氣候的影響程度。把牛肉、羊肉和硬質乳酪替換成植物性蛋白質(如：豆類)具有最大的效益。除此之外，豬肉、雞肉、魚肉和雞蛋對氣候的影響也比牛肉和羊肉少了許多。
深入探討：不同環境目標之間的衝突
有機耕作杜絕肥料的使用，目的是要以更為長期而永續的方法來利用能源、土地和水等資源。作物的養分主要來自土壤本身，主要目標是要增加生物多樣性並在動植物的永續生存中取得平衡。次外，有機耕作也只使用取自天然成分的殺蟲劑。
提倡有機食物的論點主要放在消費者健康、動物福祉以及其他方面的環境政策。這些論點的立場確實是正當的；然而，根據瑞典國家食品管理局和其他機構，並沒有太多科學證據顯示有機食物整體來說比慣行農法的食物更加健康，或者對環境更加友善。而每個農場之間的差異也很大，根據它們注重的環境目標不同，對有機農法的解釋方法也有差別。這使得目前的分析方法無法涵蓋所有的面向。
研究作者宣稱有機耕作的食物因為用到更多土地，使它們對氣候的影響更加不利。他們得出此論點用的資料來自瑞典農業局統計2013至2015年，瑞典有機耕作和慣行耕作的總產量以及每公頃產量。
深入探討：生產更多生質燃料也會增加二氧化碳排放量
研究人員在同一篇論文中主張大量投資生質燃料也會危及氣候，因為種植生質燃料需要用到大面積可以栽種作物的土地。基於同樣的邏輯，這會讓全球更多森林遭到砍伐。
研究顯示所有常見的生質燃料(從小麥、甘蔗、玉米提煉的乙醇，以及從棕櫚油、油菜籽、大豆提煉出的生質柴油)的碳機會成本都比化石燃料和柴油排放出來的二氧化碳還多。研究人員表示從廢棄物或副產物提煉出的生質燃料雖然不會造成此效應，但它們的潛力還是不高。
研究人員在瑞典報紙《每日新聞》的社論對頁版中敘述他們對生質燃料的研究成果，他們指出所有從可耕作物提煉出的生質燃料都會排放十分大量的二氧化碳，使得種植生質燃料絕對無法稱為「氣候智慧型農業」。
Organic food worse for the climate
Organically
farmed food has a bigger climate impact than conventionally farmed food, due to
the greater areas of land required. This is the finding of a new international
study involving Chalmers University of Technology, Sweden, published in the
journal Nature.
The researchers developed a
new method for assessing the climate impact from land-use, and used this, along
with other methods, to compare organic and conventional food production. The
results show that organic food can result in much greater emissions.
“Our study shows that organic peas, farmed in
Sweden, have around a 50 percent bigger climate impact than conventionally
farmed peas. For some foodstuffs, there is an even bigger difference – for
example, with organic Swedish winter wheat the difference is closer to 70
percent,” says Stefan Wirsenius, an associate professor from Chalmers, and one
of those responsible for the study.
The
reason why organic food is so much worse for the climate is that the yields per
hectare are much lower, primarily because fertilisers are not used. To produce
the same amount of organic food, you therefore need a much bigger area of
land.
The ground-breaking aspect of the
new study is the conclusion that this difference in land usage results in
organic food causing a much larger climate impact.
“The greater land-use in organic
farming leads indirectly to higher carbon dioxide emissions, thanks to
deforestation,” explains Stefan Wirsenius. “The world’s food production is
governed by international trade, so how we farm in Sweden influences
deforestation in the tropics. If we use more land for the same amount of food,
we contribute indirectly to bigger deforestation elsewhere in the world.”
Even organic meat and dairy products
are – from a climate point of view – worse than their conventionally produced
equivalents, claims Stefan Wirsenius.
“Because organic meat and milk
production uses organic feed-stocks, it also requires more land than
conventional production. This means that the findings on organic wheat and peas
in principle also apply to meat and milk products. We have not done any
specific calculations on meat and milk, however, and have no concrete examples
of this in the article,” he explains.
A
new metric: Carbon Opportunity Cost
The researchers used a new metric,
which they call “Carbon Opportunity Cost”, to evaluate the effect of greater
land-use contributing to higher carbon dioxide emissions from deforestation.
This metric takes into account the amount of carbon that is stored in forests,
and thus released as carbon dioxide as an effect of deforestation. The study is
among the first in the world to make use of this metric.
“The fact that more land use leads
to greater climate impact has not often been taken into account in earlier
comparisons between organic and conventional food,” says Stefan Wirsenius.
“This is a big oversight, because, as our study shows, this effect can be many
times bigger than the greenhouse gas effects, which are normally included. It
is also serious because today in Sweden, we have politicians whoseal goals is
to increase production of organic food. If thoseat goals isare implemented, the
climate influence from Swedish food production will probably increase a
lot.”
So why have earlier
studies not taken into account land-use and its relationship to carbon dioxide
emissions?
“There are surely many reasons. An
important explanation, I think, is simply an earlier lack of good, easily
applicable methods for measuring the effect. Our new method of measurement
allows us to make broad environmental comparisons, with relative ease,” says
Stefan Wirsenius.
The results
of the study are published in the article “Assessing the Efficiency of Land Use
Changes for Mitigating Climate Change” in the journal Nature. The article is written
by Timothy Searchinger, Stefan Wirsenius, Tim Beringer och Patrice Dumas.
More
on: The consumer perspective
Stefan Wirsenius notes that the
findings do not mean that conscientious consumers should simply switch to
buying non-organic food.
“The type of food is often much more
important. For example, eating organic beans or organic chicken is much better
for the climate than to eat conventionally produced beef,” he says. “Organic
food does have several advantages compared with food produced by conventional
methods,” he continues. “For example, it is better for farm animal welfare. But
when it comes to the climate impact, our study shows that organic food is a
much worse alternative, in general.”
For consumers who want to contribute
to the positive aspects of organic food production, without increasing their
climate impact, an effective way is to focus instead on the different impacts
of different types of meat and vegetables in our diet. Replacing beef and lamb,
as well as hard cheeses, with vegetable proteins such as beans, has the biggest
effect. Pork, chicken, fish and eggs also have a substantially lower climate
impact than beef and lamb.
More
on: The conflict between different environmental goals
In organic farming, no fertilisers
are used. The goal is to use resources like energy, land and water in a
long-term, sustainable way. Crops are primarily nurtured through nutrients
present in the soil. The main aims are greater biological diversity and a
balance between animal and plant sustainability. Only naturally derived
pesticides are used.
The arguments for organic food focus
on consumers’ health, animal welfare, and different aspects of environmental
policy. There is good justification for these arguments, but at the same time,
there is a lack of scientific evidence to show that organic food is in general
healthier and more environmentally friendly than conventionally farmed food,
according to the National Food Administration of Sweden and others. The
variation between farms is big, with the interpretation differing depending on
what environmental goals one prioritises. At the same time, current analysis
methods are unable to fully capture all aspects.
The authors of the
study now claim that organically farmed food is worse for the climate, due to
bigger land use. For this argument they use statistics from the Swedish Board
of Agriculture on the total production in Sweden, and the yields per hectare
for organic versus conventional farming for the years 2013-2015.
More
on biofuels: “More biofuels will also increase carbon dioxide emissions”
Today's major investments in
biofuels are also harmful to the climate because they require large areas of
land suitable for crop cultivation, and thus – according to the same logic
– increase deforestation globally, the researchers in the same study
argue.
For all common biofuels (ethanol
from wheat, sugar cane and corn, as well as biodiesel from palm oil, rapeseed
and soya), the carbon opportunity cost is greater than the emissions from
fossil fuel and diesel, the study shows. Biofuels from waste and by-products do
not have this effect, but their potential is small, the researchers say.
All biofuels made from arable crops
have such high emissions that they cannot be called climate-smart, according to
the researchers, who present the results on biofuels in a op-ed article in the
Swedish Newspaper Dagens Nyheter.
1. 原始論文：Timothy D. Searchinger, Stefan Wirsenius, Tim Beringer, Patrice
Dumas. Assessing the efficiency of changes in land use for mitigating
climate change. Nature, 2018; 564 (7735): 249 DOI: 10.1038/s41586-018-0757-z
引用自：Chalmers University of Technology. "Organic food worse
for the climate?."
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