每日英語跟讀 Ep.K414: How climate change drives heatwaves and wildfires in Europe
Europe is in the grip of a record-breaking heatwave and wildfires are raging across the Mediterranean. Here’s how climate change drives these events.
HOTTER, MORE FREQUENT HEATWAVES
Climate change makes heatwaves hotter and more frequent. This is the case for most land regions, and has been confirmed by the UN’s global panel of climate scientists (IPCC).
Greenhouse gas emissions from human activities have heated the planet by about 1.2°C since pre-industrial times. That warmer baseline means higher temperatures can be reached during extreme heat events.
But other conditions affect heatwaves too. In Europe, atmospheric circulation is an important factor.
FINGERPRINTS OF CLIMATE CHANGE
To find out exactly how much climate change affected a specific heatwave, scientists conduct “attribution studies”. Since 2004, more than 400 such studies have been done for extreme weather events, including heat, floods and drought — calculating how much of a role climate change played in each.
This involves simulating the modern climate hundreds of times and comparing it to simulations of a climate without human-caused greenhouse gas emissions.
For example, scientists with World Weather Attribution determined that a record-breaking heatwave in western Europe in June 2019 was 100 times more likely to occur now in France and the Netherlands than if humans had not changed the climate.
HEATWAVES WILL STILL GET WORSE
The global average temperature is around 1.2°C warmer than in pre-industrial times. That is already driving extreme heat events.
Temperatures will only cease rising if humans stop adding greenhouse gases to the atmosphere. Until then, heatwaves are set to worsen. A failure to tackle climate change would see heat extremes escalate even more dangerously.
Countries agreed under the global 2015 Paris Agreement to cut emissions fast enough to limit global warming to 2°C and aim for 1.5°C, to avoid its most dangerous impacts. Current policies would not cut emissions fast enough to meet either goal.
CLIMATE CHANGE DRIVES WILDFIRES
Climate change increases hot and dry conditions that help fires spread faster, burn longer and rage more intensely.
Hotter weather also saps moisture from vegetation, turning it into dry fuel that helps fires to spread.
CLIMATE CHANGE ISN’T THE ONLY FACTOR IN FIRES
Forest management and ignition sources are also important factors. In Europe, more than nine out of 10 fires are ignited by human activities, like arson, disposable barbeques, electricity lines, or littered glass, according to EU data.
Countries, including Spain, face the challenge of shrinking populations in rural areas, as people move to cities, leaving smaller workforces to clear vegetation and avoid “fuel” for forest fires building up.
Some actions can help to limit severe blazes, such as setting controlled fires that mimic the low-intensity fires in natural ecosystem cycles, or introducing gaps within forests to stop blazes rapidly spreading over large areas.
But scientists concur that without steep cuts to the greenhouse gases causing climate change, heatwaves, wildfires, flooding and drought will significantly worsen.
歐洲正受破紀錄熱浪的侵襲，地中海地區野火肆虐。氣候變化如何造成這些事件，說明如下。
更熱、更頻繁的熱浪
氣候變化使熱浪變得更熱、更頻繁。大部分陸地區皆然，此業經聯合國政府間氣候變化專門委員會（IPCC）證實。
人類活動所排放的溫室氣體，使地球溫度較前工業時期升高了約攝氏一點二度。較暖的基線表示極端高溫事件所達到的溫度可以更高。
但其他條件也會影響熱浪。在歐洲，大氣環流是個重要因素。
氣候變化的指紋
為準確了解氣候變化對一個熱浪的影響程度，科學家進行了「歸因研究」。自二○○四年以來，已有逾四百項針對高溫、洪水及乾旱等極端天氣事件的此類研究──計算氣候變化在各事件中之作用。
其研究方式為模擬現代氣候數百次，並將之與無人為溫室氣體排放的模擬氣候進行比較。
例如，科學家及世界氣候歸因組織確定，二○一九年六月西歐破紀錄的熱浪，現今在法國及荷蘭發生的可能性較人類未改變氣候時高一百倍。
熱浪仍將加劇
全球平均氣溫比前工業化時期高攝氏一點二度左右。這已在造成極端高溫事件。
只有人類停止在大氣中增加溫室氣體，溫度才會停止上升，否則熱浪勢必將惡化。若無法抑止氣候變化，極端高溫將會升高到更危險的地步。
根據二○一五年全球《巴黎協定》，各國同意以足夠快的速度減少排放，以將全球暖化限制在 2°C，並以 1.5°C 為目標，以避免其衝擊達到最危險的地步。目前的政策減少排放的速度不夠快，這兩個目標都無法達到。
氣候變化造成野火
氣候變化讓炎熱及乾燥加劇，這樣的條件助長了火勢，讓其蔓延速度更快、燃燒時間更長、肆虐得更猛烈。
更熱的天氣也會吸乾植被中的水分，把它變成助長火勢蔓延的乾燥燃料。
氣候變化並非火災之唯一因素
森林管理和火源也是重要因素。根據歐盟資料，在歐洲，十分之九的火災是人類活動所引發，例如縱火、拋棄式烤肉架、電線或亂丟的玻璃。
包括西班牙在內的國家面臨農村人口減少的挑戰，因為住民移居城市，讓勞動力變少，不足以清理植被，避免其成為森林大火的「燃料」。
一些行動對抑制嚴重的火災有所幫助，例如進行計畫火災，模仿自然生態系統循環中的低強度火災，或是在森林中導入空隙，以防止火災迅速蔓延至大區域。
但科學家一致認為，若不大幅減少導致氣候變化的溫室氣體，熱浪、野火、洪水及乾旱將會大幅惡化。