過去氣候變遷時人類社會如何反應？
過去作物歉收的時候，生活在東亞的人投資心力種植更多樣的作物、加強貿易並發起大型公共建設計畫，這些改變或許幫助他們適應了氣候變遷。
Inga Kiderra
又一次，人類或許能從歷史中獲益良多。當氣候變遷，造成作物歉收、面臨飢荒的威脅時，古代的東亞人適時做出了應對：他們搬遷至別處、開始種植不同的作物，並且拓展新的貿易網路，同時在其他方面想出新的解決之道。
在西藏高海拔地區河谷中的農田。氣候變遷的影響在高海拔和高緯度地區中最為明顯。圖片來源：Jade
d’Alpoim Guedes
提出此說法的新研究作者為加州大學聖地牙哥分校的Jade
d’Alpoim Guedes，以及在Crow
Canyon考古中心、華盛頓州立大學與蒙大拿大學任職的Kyle
Bocinsky。
在發表於期刊《科學進展》(Science
Advances)的論文中，他們運用他們開發的電腦模型首度展示出5000到1000年前的亞洲，大宗作物在不同地區的不同時間點是茁壯成長還是收穫不佳。
當氣候變冷，人們會遷移或是投入畜牧業，因為牲畜可以在穀物無法生長的草原成長。此外，他們也開始加強貿易活動。D’Alpoim
Guedes和Bocinsky主張這些策略集合起來最終促成了絲路形成。而在某些地區的人們也轉而種植更為多樣的作物。
運用他們新開發的電腦模型，研究人員可以仔細探討變遷的氣候如何改變特定地區人們產生食物的方式，並瞭解文化轉型的原因。
「考古學中有大量文獻在探討過去的氣候，但是之前的研究大都只能把氣候和文明的變遷畫上關聯而已。」主要作者，加州大學聖地牙哥分校考古學系暨斯克里普斯海洋研究所的Jade
d’Alpoim Guedes表示。「我們在這項成果中具體呈現出溫度和雨量的時空變化如何實際衝擊到人類――透過影響他們能種植的作物種類。」
考古學家D’Alpoim
Guedes的專長為經由植物考古學，也就是分析古代植物的遺骸，來瞭解人類的生存策略隨時間的變化。而Bocinsky則是計算考古學家。這兩位學者結合了現今亞洲各處的氣象站資料，以及涵蓋北半球的古氣候重建結果，開發出電腦模型來模擬亞洲的氣溫跨越不同時空的變化。此外，他們也納入了考古遺址的資料以及在其中找到的種子紀錄。
大約在3700至3000年前發生了一次氣候劇變――全球氣候變得越來越冷。當時的情況就和現在一樣：氣溫變化在全球各地的影響並不一致，高緯度和高海拔地區受到的影響特別明顯。D’Alpoim
Guedes和Bocinsky顯示出這類地區變化的劇烈程度。舉例而言，3500年前左右蒙古和西藏高原的高粱和小米約有一半的時間無法收成。人們必須放棄這些作物轉而種植更耐冷的，像是小麥和大麥。
他們也主張氣溫降低使中國北方各地在西元291至360年越來越難種出主要的穀物。它造成的後果或許成為了關鍵因素之一，使得中國首都從西安搬遷至現在的南京(位在中國南方)。
遷都並非沒有付出代價――這可不像搬到鎮上另一頭較好的公寓那麼簡單。歷史文獻指出當時的收成狀況十分慘烈(也就是飢荒)。此外，研究作者表示大量人民舉家搬遷的同時也伴隨無數這類遷移經常引發的小型衝突，甚至爆發流血鬥爭。
作者表示氣候變遷也刺激亞洲各地發展交通建設，像是之後的隋朝決定投入大型公共計畫而建造出中國的「大運河」。大運河現為聯合國教科文組織認可的世界遺產，是世上最長也最古老的運河。它連結了黃河與長江，使得各地的人民往來更加便利，也助長了貨物流通。
D’Alpoim
Guedes和Bocinsky為他們發表在《科學前緣》的論文下了正面的標題――「氣候變遷刺激亞州各地的農業革新與交流」(Climate
change stimulated agricultural innovation and exchange across Asia)――但作者也警告不能完全保持著「波麗安娜」式的態度。(Pollyanna
principle意指人類的潛意識傾向關注正面訊息而非負面訊息。)
「雖然危機可以成為文化改變與創新的契機，」Bocinsky表示。「但我們現在所處的氣候變遷速度和規模都跟過往不同。」
D’Alpoim
Guedes表示過往的人類有4000年的時間去適應逐漸變冷的世界，但未來暖化造成的衝擊是更加迅速且劇烈的。「在全球暖化的影響之下，這種長久以來我們所適應的模式將會開始出現前所未見的變化。」她說。「而從當下全世界的政治情勢來看，人類的行為大概沒有足夠的彈性來適應。」
D’Alpoim
Guedes也表示農業的機械化與工業化，加上全球農業政策正促使我們栽培的作物單一化。她認為我們需要反其道而行。「像我們這類的研究顯示在適應氣候變遷時，人類最好的下注方式就是分散風險並多方投資。」她說。「這種方式讓我們成功適應了過去的氣候變遷，在面對未來時我們需要謹記在心。」
給想要重現此論文結果的人：研究用的程式碼為開放來源，任何使用免費統計軟體R的人都可以下載作者製作的套件來自己進行分析。其他研究人員也可以分析世上不同區域其他作物和地點的變化，進一步延伸d’Alpoim
Guedes和Bocinsky的發現。作者表示使用者甚至能修改他們的程式碼，說不定可以進而預測未來的作物歉收情形。
What happened in the past when the climate
changed?
When crops failed, investing in crop diversity, trade
and a large public project may have helped the people of Ancient Asia adapt.
Once again, humanity
might be well served to take heed from a history lesson. When the climate
changed, when crops failed and famine threatened, the peoples of ancient Asia
responded. They moved. They started growing different crops. They created new
trade networks and innovated their way to solutions in other ways too.
So
suggests new research by Jade d’Alpoim Guedes of the University of California
San Diego and Kyle Bocinsky of the Crow Canyon Archaeological Center in
Colorado, Washington State University and the University of Montana.
Their
paper, published in the journal Science Advances, describes a
computer model they developed that shows for the first time when and where in
Asia staple crops would have thrived or fared poorly between 5,000 and 1,000
years ago.
When
the climate cooled, people moved away or turned to pastoralism – herds can
thrive in grassland where food grains can’t. And they turned to trade. These
strategies eventually coalesced into the development of the Silk Road, d’Alpoim
Guedes and Bocinsky argue. In some areas they also diversified the types of
crops they planted.
With
their new computer model, the researchers were able to examine in detail how
changing climate transformed people’s ability to produce food in particular
places, and that enabled them to get at the causes of cultural shift.
“There’s
been a large body of literature in archaeology on past climates, but earlier
studies were mostly only able to draw correlations between changes in climate
and civilization,” said lead author d’Alpoim Guedes, an assistant professor in
the Department of Anthropology and Scripps Institution of Oceanography at UC
San Diego. “What we’re showing in this work is exactly how changes in
temperature and precipitation, over space and time, would have actually
impacted people – by affecting what they could and couldn’t grow.”
D’Alpoim
Guedes is an archaeologist who specializes in paleoethnobotany – analyzing
ancient plant remains – to understand how human subsistence strategies changed
over time. Bocinsky is a computational archaeologist. The duo developed their
model by combining contemporary weather station data from across Asia with a
hemisphere-wide paleoclimate reconstruction to create a simulation across space
and time of how temperature in Asia changed. They also added data on
archaeological sites and the record of seeds found there.
One
major transition in climate – global cooling at the time – happened around
3,700 to 3,000 years ago. And what is true now was true then: changing
temperatures don’t affect all regions of the globe equally. The effects are most
pronounced in high latitude and high-altitude areas, and d’Alpoim Guedes and
Bocinsky show how dramatic the changes were, for example, in Mongolia and the
Tibetan Plateau. There, around 3,500 years before the present, broomcorn and
foxtail millet would have failed to come to harvest about half of the time.
People had to abandon the crop in favor of more cold-tolerant ones like wheat
and barley.
They
also argue that cooling temperatures made it increasingly difficult to grow key
grain crops across Northern China between AD 291 and 360, something that may
have ended up playing a key role in the relocation of the Chinese capital to
from Xi’an to what is now Nanjing, in the south of the country.
This
was not a painless move – not like finding a better apartment across town.
Historical records report on catastrophic harvests (read: famines). And there
were major migrations of people, accompanied, the researchers say, by the
myriad little conflicts these migrations often bring, as well as bloody
struggles.
Climate
change also stimulated the development of transportation infrastructure across
Asia, the co-authors say, including the later Sui Dynasty’s decision to invest
in a major capital public project and create China’s Grand Canal. The Grand
Canal, now a UNESCO World Heritage Site, is the world’s longest and oldest
canal, linking the Yellow and Yangtze rivers. It was a major facilitator for
the movement of people and their trade goods.
D’Alpoim
Guedes and Bocinsky’s paper in Science Advances carries a
positive title – “Climate change stimulated agricultural innovation and
exchange across Asia” – but the co-authors also warn against a completely
Pollyanna view.
“Crises
are opportunities for culture change and innovation,” Bocinsky said. “But the
speed and scale of our current climate change predicament are different.”
The
impacts of warming going forward are going to be quicker and greater, and
humanity has had 4000 years to adjust to a cooler world, d’Alpoim Guedes said.
“With global warming these long-lasting patterns of adaptation will begin to
change in ways that are unpredictable,” she said. “And there might not be the
behavioral flexibility for this, given current politics around the world.”
Also
mechanized, industrialized agriculture and global agricultural policy are
pushing us toward mono-culture of crops, said d’Alpoim Guedes. We need to move
in the opposite direction instead. “Studies like ours show that bet-hedging and
investing in diversity have been our best bets for adapting to climate change,”
she said. “That is what allowed us to adapt in past, and we need to be mindful
of that for our future, too.”
For
those wishing to reproduce the paper’s findings: The code is open source and
any user of the free statistical software R can download the package the
authors are making available and run the analysis themselves. Researchers can
also extend d’Alpoim Guedes and Bocinsky’s findings by running analysis on
other crops and other locations in different parts of the world. It is even
possible, the co-authors say, to modify their code and then, potentially, to
project for future crop failures.
原始論文：Jade d’Alpoim Guedes, R. Kyle Bocinsky. Climate
change stimulated agricultural innovation and exchange across Asia. Science
Advances, 2018; 4 (10): eaar4491 DOI: 10.1126/sciadv.aar4491
引用自：University of California - San Diego. "What happened in
the past when the climate changed?”
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