But it really used to be this.

但它其實曾經是這樣的。

And it could again.

而且可以重拾舊貌。

The Great Green Wall is an epic project that aims to grow an 8,000-kilometer belt of vegetation across the entire width of the African continent. 

綠色長城是一個工程浩大的計畫，目標是種植長 8 千公里的植被帶，橫跨整個非洲大陸。

If completed, it would be three times larger than the Great Barrier Reef, and be the largest living structure on the planet.

如果完工，它將比大堡礁大三倍，並且將是全球最大的活建築。

But can this massive geo-engineering project transform the landscape into the fertile, tropical place it once was? 

但是這個浩大的地球工程計畫能將景緻轉變回曾經豐饒、熱帶的樣貌嗎？

So, here’s the thing: This part of Africa is heating up.

事情是這樣的：非洲這個區域正在升溫。

Particularly in the Sahel, which sits between the southern edge of the world’s largest hot desert, the Sahara, and humid savannahs to the south.

尤其是座落在世界最大、炎熱的撒哈拉沙漠南端以及南邊潮濕草原之間的撒赫爾地區。

Vegetation is scarce in this semi-arid belt of land, and the UN has identified it as a hotspot for climate change.

在這個半乾旱土地上，植被很稀少，而聯合國也已經將其判定為氣候變遷熱點。

Temperatures in the Sahel region are increasing 1.5 times faster than the rest of the world, and the Sahara Desert is now 10% larger than it was in 1920.

撒赫爾地區的溫度較全球提升速度要快 1.5 倍，而撒哈拉沙漠現在比 1920 年時大了 10%。

Periodic drought, deforestation, and unsustainable agricultural practices have reduced the productivity of the Sahel, causing desertification.

週期性乾旱、砍伐森林和不永續的農業活動降低了撒赫爾地區的生產力，導致沙漠化現象。

This has led to massive food insecurity and displacement of people in the region.

這引起了該區大規模糧食不足和人民流離失所。

And with temperatures expected to be 3 to 5 degrees Celsius warmer by 2050, these problems are expected to get worse.

而隨著氣溫預期在 2050 年前提升攝氏 3 至 5 度，這些問題會惡化。

But not all is lost.

但並非完全絕望。

Remember when we said the Sahara used to be green?

記得我們說過撒哈拉曾經是綠地嗎？

Well, that was about 11,500 years ago; back then, there was grass, lakes, and animals like hippos and antelopes.

嗯，那大約是 1 萬 1 千 5 百年前，當時有草地、湖泊，還有河馬和羚羊等動物。

Dubbed the African humid period, also known as the "Green Sahara", this era was the result of intense West African monsoons, which were stronger and brought more summer rainfall than today.

被稱為非洲潮濕期或是「綠色撒哈拉」的這個時期，是強烈西非季風的產物，而這些季風更強帶來了比今天更強、更多的夏季降雨。

Over thousands of years, the intensity of the monsoon is affected by a slow wobble in the Earth’s orbit known as precession, which strengthens solar radiation in the summer, driving moist air inland. 

在接下來的數千年間，季風的強度受到地球軌道緩慢擺動（亦即前移）的影響，進而加強了夏季太陽輻射，促使溼潤空氣進入內陸。

The African humid period ended some 5,000 years ago, though traces of the period still remain.

非洲潮濕期在大約 5 千年前結束，不過該時期的痕跡仍然存在。

In the 1930s, explorer László Almásy found Neolithic cave paintings in Egypt of people swimming.

1930 年代時，探險家拉茲洛·阿馬希在埃及發現刻畫人類游泳的新石器時代的洞穴壁畫。

But an orbital shimmy-shake doesn't tell the whole story; changes to the land can have a big impact on monsoonal rains, too.

但是，軌道的晃動並不能說明全貌，土地的變化對於季風降雨也可能有很大影響。

When the Sahara was greener, its vegetation allowed more water to circulate from the soil into the atmosphere, increasing humidity and rainfall.

當撒哈拉沙漠較綠時，其植被允許更多水分從土壤循環到大氣中，增加溼度和降雨。

The greenery also reduced the amount of dust in the atmosphere, allowing more sunlight to reach the ground.

綠色植物也減少了大氣中的灰塵量，促使更多陽光照射到地面。

Being darker than the light-desert sands, the plants absorbed more solar radiation, which caused more precipitation.

因為植物顏色比淺色沙漠上的沙子更深，所以吸收了較多的太陽輻射，引起更多的降水。

And when it rained, it poured!

而一雨則傾盆！

The combined effects intensified monsoonal winds, bringing about 10 times the rainfall than the desert gets today.

這些綜合影響都強化了季風，帶來了大約比今日高出 10 倍的降雨。

Like the African humid period, the Great Green Wall could re-green the Sahel.

如同非洲潮濕期，綠色長城可能再度綠化撒赫爾。

The ambitious multi-national initiative launched in 2007, with the idea of building a tree line on the edge of the desert.

這項野心勃勃的跨國計畫在 2007 年啟動，想法是在沙漠邊緣種植林木線。

But like with most ambitious projects, it’s having a rough time.

但就像其它具野心的計畫一樣，它進行不易。

80 percent or more of the planted trees have died.

超過 80% 以上種植的樹木已經死亡。

Reasons include a lack of proper irrigation and not having management systems in place. 

原因包括缺乏適當的灌溉以及缺乏管理制度。

There were also other issues: Non-native species didn’t adapt, grazing animals ate the seeds, and a lack of support from local stakeholders.

還有其它問題：非本土物種無法適應、放牧動物會食用種子、缺乏當地利害關係人的支持。

The wall has since evolved into a patchwork of sustainable land-use practices, like the circular drought resistant gardens known as "tolou keur".

長城在此後演變成了一個拼湊起來的可永續土地應用，像是被稱為 tolou keur 的圓形抗旱花園。

And for a while now, scientists have been looking at whether this project could actually work.

而一段時間以來，科學家們一直在研究這個計畫是否能夠真正奏效。

In 2021, preliminary research was presented on how the wall could have a profound effect on climate. 

2021 年提出該長城如何能夠對氣候產生深遠影響的初步研究。

They created hi-res computer simulations, both with and without a green wall.

他們創建了有綠色長城和沒有綠色長城的高解析電腦模擬圖。

They found that if the wall is completed, it could as much as double rainfall in some parts of the Sahel and decrease average summer temperatures around the Great Green Wall.

他們發現，如果長城建成，撒赫爾某些地區的降雨量可能會增加一倍，並降低綠色長城周圍的夏季平均氣溫。

But on the downside, the hottest parts of the desert would get even hotter.

但缺點是，沙漠最炎熱的地區會變得更熱。

The wall may also have unintended consequences that extend far beyond the region.

長城可能也會有預期之外的後果，影響遠超出該區域。

For one, it could reduce the amount of dust that travels across the Atlantic, impacting the fertility of the Amazon.

第一，它可能減少傳播跨越大西洋的灰塵量，影響到亞馬遜地區的肥沃度。

It might even be capable of increasing the intensity of tropical cyclones.

它甚至可能增加熱帶氣旋的強度。

But in spite of this, the project is still moving forward, aiming to plant 100 million hectares of trees, shrubs, and grasses by 2030.

但儘管如此，計畫仍然進行中，目標在 2030 年種植 1 億公頃的樹木、灌木以及草地。

The project got a boost in January of 2021, receiving more than 14 billion dollars from donors like the World Bank to fast-track the effort.

計畫在 2021 年 1 月時獲得了一大助力，收到來自世界銀行等捐贈者超過 140 億美元的捐款，目的在加快速度。

But having community support is really key to making the effort work.

但擁有社區的支持是讓努力有結果的真實關鍵。

If successful, the program could be a game-changer for the continent by restoring degraded landscapes and potentially transforming millions of lives.

如果成功的話，該計劃可能透過恢復退化地貌並可能改善數百萬人生活的方式，大大改變該洲現況。

And who knows? Maybe one day, we’ll see hippos in the Sahara again. 

而且誰知道呢？也許我們有一天會在撒哈拉沙漠再次看到河馬。

If you love hearing about big ideas to combat climate change, the next one is large, shaggy, and has a trunk.

如果你喜歡聆聽對抗氣候變遷的大想法，接下來的故事巨大、蓬亂且有著長鼻子。

Check out this video on how scientists are trying to bring back the woolly mammoth to help with global warming.

看看這部影片，了解科學家正如何嘗試透過讓真猛獁象復活來減緩全球暖化。

Know of any other cool geo-engineering projects? Let us know in the comments below.

知道其它很酷的地球工程計畫嗎？請在留言區讓我們知道。

Make sure to subscribe, and thanks for watching.

請務必訂閱，並感謝各位觀看。