科普：全球升温1.5度和2度區別到底有多大？

　　聯合國氣候報告反覆強調，要把全球升温幅度控制在1.5攝氏度以內。此前《巴黎協定》提出的目標是，要把升幅控制在2攝氏度以內，同時盡力不超過1.5攝氏度。全球升温1.5度和2度的區別到底有多大？

　　在格拉斯哥舉行的聯合國氣候變化大會上，世界各國領導人反覆強調，必須把全球變暖幅度控制在1.5攝氏度以內。

　　Over and over at the UN climate summit in Glasgow, world leaders have stressed the need to limit global warming to 1.5 degrees Celsius.

　　2015年達成的《巴黎協定》中，各國政府承諾將全球平均温度控制在比前工業化水平升温2攝氏度以內，並努力達到升温1.5攝氏度以內的目標。

　　The 2015 Paris Agreement commits countries to limit the global average temperature rise to well below 2°C above pre-industrial levels, and to aim for 1.5°C.

　　科學家指出，升温幅度超過1.5攝氏度意味着人類、野生動植物和生態系統都可能遭受氣候變化帶來的更嚴重後果。

　　Scientists have said crossing the 1.5°C threshold risks unleashing far more severe climate change effects on people, wildlife and ecosystems.

　　防止全球升温超過1.5攝氏度要求我們在2030年前將全球碳排放量減少為2010年的一半，並在2050年前實現淨零排放。

　　Preventing it requires almost halving global CO2 emissions by 2030 from 2010 levels and cutting them to net-zero by 2050.

　　但是全球升温1.5攝氏度和升温2攝氏度有什麼不同呢？

　　But what is the difference between 1.5°C and 2°C of warming?

　　當前，全球温度已經比前工業化水平高出約1.1攝氏度。過去四個十年的氣温比1850年以來的任何一個十年都更高。

　　Already, the world has heated to around 1.1°C above pre-industrial levels. Each of the last four decades was hotter than any decade since 1850.

　　德國氣候服務中心的氣候科學家丹妮拉·雅各布説：“僅僅數十年就升温這麼多，這樣的全球變暖是從未發生過的。升温0.5度意味着更極端的天氣會更頻繁地出現，極端天氣會更惡劣或持續更長時間。”

　　"We never had such a global warming in only a few decades", said climate scientist Daniela Jacob at the Climate Service Center Germany. "Half a degree means much more extreme weather, and it can be more often, more intense, or extended in duration."

　　就在今年，歐洲西部暴雨引發的洪水令數百人喪生。太平洋西北地區的破紀錄高温天氣也導致數百人死亡。格陵蘭島冰川大規模融化。地中海地區和西伯利亞野火肆虐。巴西部分地區遭遇了史上罕見的旱災。

　　Just this year, torrential rains flooded Western Europe, killing hundreds of people. Hundreds more died when temperatures in the Pacific Northwest hit record highs. Greenland saw massive melting events, wildfires ravaged the Mediterranean and Siberia, and record drought hit parts of Brazil.

　　東英吉利亞大學的氣候科學家瑞秋·沃倫説：“氣候變化已經影響到了人類居住的每個角落。”

　　"Climate change is already affecting every inhabited region across the globe," said climate scientist Rachel Warren at the University of East Anglia.

　　全球升温超過1.5攝氏度將會加劇氣候變化的影響。比如，高温將會更頻繁地來襲，程度也會更嚴重。

　　More warming to 1.5°C and beyond will worsen such impacts. For example, heatwaves would become both more frequent and more severe.

　　氣温升高還會讓大氣變得更濕潤，引發更多強降雨，從而增加洪水風險。蒸發量增加還會導致更嚴重的乾旱。

　　A warmer atmosphere can also hold more moisture, resulting in more extreme rainfall that raises flood risks. It also increases evaporation, leading to more intense droughts.

　　賓夕法尼亞州立大學的氣候科學家邁克爾·曼恩説：“如果升温幅度在1.5攝氏度以內，我們還有可能防止格陵蘭島和南極西部的大部分冰蓋融化崩塌。”

　　"At 1.5°C, there’s a good chance we can prevent most of the Greenland and west Antarctic ice sheet from collapsing," said climate scientist Michael Mann at Pennsylvania State University.

　　這有助於在本世紀末將海平面上升水平控制在幾英尺以內，儘管海平面上升幾英尺仍然會造成鉅變，包括侵蝕海岸線、淹沒一些小島國和沿海城市。

　　That would help limit sea level rise to a few feet by the end of the century - still a big change that would erode coastlines and inundate some small island states and coastal cities.

　　曼恩説，但是如果升温幅度超過2攝氏度，冰蓋就會瓦解，海平面會上升10米之多。不過，不確定這一天來得會有多快。

　　But blow past 2°C and the ice sheets could collapse, Mann said, with sea levels rising up to 10 metres - though how quickly that could happen is uncertain.

　　全球升温1.5攝氏度會摧毀至少70%的珊瑚礁，但是如果升温2攝氏度，超過99%的珊瑚礁都會死亡。這對於依賴珊瑚覓食和棲息的魚羣是一個毀滅性打擊。

　　Warming of 1.5°C would destroy at least 70% of coral reefs, but at 2°C more than 99% would be lost. That would destroy fish habitats and communities that rely on reefs for their food and livelihoods.

　　全球升温由1.5攝氏度到2攝氏度還會加大對糧食生產的影響。

　　Warming of 2°C, versus 1.5°C, would also increase the impact on food production.

　　倫敦大學學院的氣候科學家西蒙·路易斯説：“如果世界上的幾個糧食主產地同時發生農作物歉收，大範圍的食品價格飛漲和饑荒將會席捲全球。”

　　"If you have crop failures in a couple of the breadbaskets of the world at the same time, then you could see extreme food price spikes and hunger and famine across wide swathes of the world," said climate scientist Simon Lewis at University College London.

　　全球變暖會導致攜帶瘧疾和登革熱病毒的蚊蟲大範圍滋生。相比升温1.5攝氏度，升温2攝氏度會讓更多昆蟲和動物失去大部分棲息地，還會增加森林火災風險，進而危及野生動植物的生存。

　　A warmer world could see the mosquitoes that carry diseases such as malaria and dengue fever expand across a wider range. But 2°C would also see a bigger share of insects and animals lose most of their habitat range, compared with 1.5°C, and increase the risk of forest fires - another risk to wildlife.

　　隨着全球變暖，地球達到“臨界點”的風險也會增加。一旦到達這個臨界點，就會觸發地球系統不可逆轉的連鎖效應。但是具體何時到達臨界點還不確定。

　　As the world heats up, the risk increases that the planet will reach "tipping points", where Earth’s systems cross a threshold that triggers irreversible or cascading impacts. Exactly when those points would be reached is uncertain.

　　舉例來説，乾旱、降雨減少以及對亞馬遜雨林持續性的砍伐，將會導致雨林系統崩潰，結果就是將二氧化碳釋放到空氣中而不是將二氧化碳儲存起來。北極永久凍土的融化會導致冰封多年的生物遺骸腐爛，從而產生大量的二氧化碳。

　　Droughts, reduced rainfall, and continued destruction of the Amazon through deforestation, for example, could see the rainforest system collapse, releasing CO2 into the atmosphere rather than storing it. Or warming Arctic permafrost could cause long-frozen biomass to decompose, releasing vast amount of carbon emissions.

　　科學家指出，全球升温2.7攝氏度會導致熱帶和亞熱帶地區在一年中的部分季節“因為炎熱而無法居住”。生物多樣性會遭到極大破壞，糧食安全將受到衝擊，極端天氣將會超出多數城市基建的應對能力。

　　Warming of 2.7°C would deliver "unliveable heat" for parts of the year across areas of the tropics and subtropics. Biodiversity would be enormously depleted, food security would drop, and extreme weather would exceed most urban infrastructure's capacity to cope, scientists said.

　　曼恩説：“如果我們能把全球升温控制在3攝氏度以內，人類文明可能還能夠適應氣候變化的影響，但是升温幅度達到2.7攝氏度後，我們的日子就會很難過。”

　　"If we can keep warming below 3°C we likely remain within our adaptive capacity as a civilization, but at 2.7°C warming we would experience great hardship," said Mann.

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