What if there were 1 trillion more trees? - Jean-François Bastin

譯者: Lilian Chiu 審譯者: Zoe Walmsley

Standing at almost 84 meters tall,

直立高聳約八十四公尺高，

this is the largest known living tree on the planet.

這是地球上活著的最高大的一棵樹。

Nicknamed General Sherman,

這棵巨大的紅杉被暱稱為薛曼將軍，

this giant sequoia has sequestered roughly 1,400 tons of atmospheric carbon

封存了約 1400 公噸大氣中的二氧化碳，

over its estimated 2,500 years on earth.

約在它存活於地球的 2500 年期間裡。

Very few trees can compete with this carbon impact,

這成就沒有幾棵樹能比得過，

but today, humanity produces more than 1,400 tons of carbon every minute.

但如今人類平均每分鐘的碳排量 早已高過 1400 公噸。

To combat climate change,

要對抗氣候變遷，

we need to steeply reduce fossil fuel emissions,

我們必須銳減石化燃料排放量，

and draw down excess CO2 to restore our atmosphere’s balance

降低多餘的二氧化碳，

以恢復大氣中溫室氣體的平衡。

of greenhouse gases.

But what can trees do to help in this fight?

樹木是否能幫助我們打贏這場硬仗？

首先，它們如何做到碳封存呢？

And how do they sequester carbon in the first place?

Like all plants, trees consume atmospheric carbon

和所有植物一樣，

樹木透過光合作用的化學反應 來消耗大氣中的碳。

through a chemical reaction called photosynthesis.

This process uses energy from sunlight

這個過程利用太陽光的能量，

to convert water and carbon dioxide into oxygen

將水和二氧化碳轉換為氧氣

and energy-storing carbohydrates.

及含有能量的碳水化合物。

Plants then consume these carbohydrates in a reverse process

接著在呼吸作用的反向過程中，

called respiration, converting them to energy

將碳水化合物換成能料消耗掉，

and releasing carbon back into the atmosphere.

同時再將碳排放回大氣中。

In trees, however, a large portion of that carbon isn’t released,

然而，就樹木來說， 有很大一部分的碳不會被釋放，

and instead, is stored as newly formed wood tissue.

而是貯存在新形成的木質組織中。

During their lifetimes, trees act as carbon vaults,

樹木活著時，扮演碳的儲存庫的角色，

and they continue to draw down carbon for as long as they grow.

在生長過程中持續降低大氣中的碳。

However, when a tree dies and decays,

然而，當樹木死亡腐爛後，

some of its carbon will be released back into the air.

其中部分的碳又被釋回大氣中。

A significant amount of CO2 is stored in the soil,

土壤中也存有很大量的二氧化碳，

where it can remain for thousands of years.

且可長達數千年。

But eventually, that carbon also seeps back into the atmosphere.

但是最終那些碳也會重回大氣。

So if trees are going to help fight a long-term problem

所以，如果要以樹木對抗 氣候變遷這類長期的問題，

like climate change,

they need to survive to sequester their carbon

除了要能活得越久，以便封存越多碳，

for the longest period possible, while also reproducing quickly.

同時還必須能快速繁殖。

Is there one type of tree we could plant that meets these criteria?

有哪一種樹符合這些條件嗎？

Some fast growing, long-lived, super sequestering species

有沒有長得快、壽命長、 又有超強封存能力的樹

we could scatter worldwide?

能在世界各地種植？

Not that we know of.

就我們所知，沒有。

But even if such a tree existed,

但就算真的有，

it wouldn’t be a good long-term solution.

也不會是長期的解決方案。

Forests are complex networks of living organisms,

森林是複雜的生物網路，

and there’s no one species that can thrive in every ecosystem.

沒有一個物種能在 所有的生態系統中都茂盛生長。

The most sustainable trees to plant are always native ones;

最永續的樹種選擇向來都是原生種；

species that already play a role in their local environment.

在當地環境中早已佔據一角的物種。

Preliminary research shows that ecosystems

初步的研究顯示，

一個原就具有樹木多樣性的生態系統

with a naturally occurring diversity of trees have less competition

比較不需要去競爭環境資源， 也較能對抗氣候變遷。

for resources and better resist climate change.

This means we can’t just plant trees to draw down carbon;

這代表要降低碳量不是種樹就好；

we need to restore depleted ecosystems.

我們必須重建已耗竭的生態系統。

There are numerous regions that have been clear cut

有些區域樹木被砍伐殆盡、 土地被開發當作他用，

or developed that are ripe for restoring.

現在正可做生態復育。

In 2019, a study led by Zurich’s Crowtherlab

2019 年，位於蘇黎士的 柯勞瑟實驗室主導的一項研究

analyzed satellite imagery of the world’s existing tree cover.

利用衛星影像分析出 世界目前的樹木覆蓋率。

By combining it with climate and soil data

再與氣候及土壤資料整合，

and excluding areas necessary for human use,

扣掉人類所需的地區面積，

they determined Earth could support

他們研判除了現有森林外， 地球還能承載相當十億公頃的造林。

nearly one billion hectares of additional forest.

That’s roughly 1.2 trillion trees.

差不多等於一兆兩千億棵樹。

This staggering number surprised the scientific community,

這驚人的數字讓科學界十分訝異，

prompting additional research.

紛紛進行更多研究。

Scientists now cite a more conservative but still remarkable figure.

科學家之後提出的數字 比較保守但仍然很驚人。

By their revised estimates, these restored ecosystems

根據他們修正過的估計， 修復後的生態系統

could capture anywhere from 100 to 200 billion tons of carbon,

可以吸收一千至兩千億公噸的碳排量，

accounting for over one-sixth of humanity’s carbon emissions.

相當於人類碳排量的六分之一強。

More than half of the potential forest canopy

重新植木造林的潛在區域

for new restoration efforts can be found in just six countries.

有一半以上集中在六個國家。

And the study can also provide insight into existing restoration projects,

研究也針對現有的造林計畫提供洞見，

like The Bonn Challenge,

比方說「波昂挑戰」，

which aims to restore 350 million hectares of forest by 2030.

其目標是在 2030 年前 復育三億五千萬公頃的森林。

But this is where it gets complicated.

但這正是事態複雜之處。

Ecosystems are incredibly complex,

生態系統錯綜複雜，

and it’s unclear whether they’re best restored by human intervention.

由人類出手復育也難說是好是壞。

It’s possible the right thing to do for certain areas

在某些區域，袖手旁觀 或許才是正確的做法。

is to simply leave them alone.

Additionally, some researchers worry that restoring forests

此外，有些研究者擔心，

如此大規模的森林復育 可能會有意想不到的後果，

on this scale may have unintended consequences,

like producing natural bio-chemicals

比如環境中的生化物質產出速度加快，

at a pace that could actually accelerate climate change.

反而加速氣候變遷。

And even if we succeed in restoring these areas,

而且就算我們成功復育了這些區域，

future generations would need to protect them

未來的世代也需要保護它們，

from the natural and economic forces that previously depleted them.

免於再次因天然和經濟因素而耗竭。

Taken together, these challenges have damaged confidence

所有這些挑戰加起來，

已足夠摧毀世界各地復育計畫的信心。

in restoration projects worldwide.

And the complexity of rebuilding ecosystems

重建生態系統的複雜性

demonstrates how important it is to protect our existing forests.

顯示出保護現存的森林有多重要。

But hopefully, restoring some of these depleted regions

只能希望，藉由重建一些被耗竭的區域

will give us the data and conviction necessary to combat climate change

能夠給我們所需的資料和信念

大舉對抗氣候變遷。

on a larger scale.

If we get it right, maybe these modern trees will have time to grow

如果這次做對了，或許， 這些新生的樹木會有時間

into carbon carrying titans.

成長為身兼碳儲存庫的巨木。