一份關於全球暖化對動植物影響的研究顯示，暖化蔓延的速率每年約1/4哩(約400公尺)。一些無法忍受較大溫差的物種必須儘速進行遷移，才得以存活。研究也指出，熱帶低地、紅樹林與沙漠地區的物種受到的威脅較山區物種來的更大。
該研究結合了現今與預測的未來氣候資訊，以計算出世界不同地區的「溫度速率」，也就是溫度變化的速度。
研究人員發現，高山地區溫度變化的速率最慢，意即山區動物不需遷徙太遠以適應氣溫變化。然而，居住在濕草原、紅樹林及沙漠等平地物種，則需更大範圍的地理遷徙，才能保持在原本的氣候範圍內。研究人員也發現，目前大多數的保護區面積都不能讓物種有足夠遷徙的範圍。
加州科學院的應用生物資訊中心主任--哈密頓表示，「這項數據最有力的功能在於，可幫助我們評估，在全球氣候變遷下，現有的保護區網絡如何能保護生物多樣性。」
他進一步說明，「我們將某一個保護區現在的氣候條件，從區內一端移到另一端的整段所需時間，定義為【留存時間】 (residence time)。只有8%現有保留區的留存時間超過100年。如果我們想延長這個時間，我們不僅要減少碳排放，也要儘速擴張並連結全球的保護區網絡。」
此研究發現，熱帶與亞熱帶針葉林帶的暖化速率最低，每年移動約80公尺。高山草原及高山灌木區的暖化速率每年約為110公尺。
紅樹林沼澤地、濕草原及荒原等平地是全球暖化速度擴散最快的地區，每年移動速率可高於1公里。
然而，科學家指出，生存在暖化速率較慢地區的物種，並不代表受到較好的保護。闊葉林帶等棲地往往較小且較為破碎，使得物種較難遷徙。
科學家也強調，該研究檢視的是氣候區、而非物種的移動。這意味著，該研究很難預測單一物種受到的衝擊。相同地區的不同物種對氣溫變化的容忍程度可能不同；物種的遷徙也很難追蹤。
科學家表示，某些物種可能需要人為搬遷以協助它們適應氣候變化；此外保護區也必須加以擴張且相互連結。
Lowland tropics, mangroves and deserts at greater risk than mountainous areas as global warming spreads, study finds
guardian.co.uk, Wednesday 23 December 2009 18.20 GMT
Global warming creeps across the world at a speed of a quarter of a mile each year, according to a new study that highlights the problems that rising temperatures pose to plants and animals. Species that can tolerate only a narrow range of temperatures will need to move as quickly if they are to survive. Wildlife in lowland tropics, mangroves and desert areas are at greater risk than species in mountainous areas, the study suggests.
"These are the conditions that will set the stage, whether species move or cope in place," said Chris Field, director of the department of global ecology at the Carnegie Institution in the US, who worked on the project. "Expressed as velocities, climate change projections connect directly to survival prospects for plants and animals."
The study, by scientists at the Carnegie Institution, Stanford University, the California Academy of Sciences, and the University of California, Berkeley, combined information on current and projected future climate to calculate a "temperature velocity" for different parts of the world.
They found that mountainous areas will have the lowest velocity of temperature change, meaning that animals will not need to move very far to stay in the temperature range of their natural habitat. However, much larger geographic displacements are required in flatter areas such as flooded grasslands, mangroves and deserts, in order for animals to keep pace with their climate zone. The researchers also found that most currently protected areas are not big enough to accommodate the displacements required.
Healy Hamilton, director of the centre for applied biodiversity informatics at the California Academy of Sciences, said: "One of the most powerful aspects of this data is that it allows us to evaluate how our current protected area network will perform as we attempt to conserve biodiversity in the face of global climate change."
He added: "When we look at residence times for protected areas, which we define as the amount of time it will take current climate conditions to move across and out of a given protected area, only 8% of our current protected areas have residence times of more than 100 years. If we want to improve these numbers, we need to both reduce our carbon emissions and work quickly towards expanding and connecting our global network of protected areas."
The study found that global warming would have the lowest velocities in tropical and subtropical coniferous forests, where it would move at about 80 metres a year, and montane grasslands and shrublands - a biome with grass and shrubs at high elevations - with a projected velocity of about 110 metres each year.
Global warming is expected to sweep more quickly across flatter areas, such as mangrove swamps and flooded grasslands and savannas, where it could have velocities above 1km a year. Across the world, the average velocity is 420 metres each year. The results are published in the journal Nature.
Wildlife in areas with low projected climate change velocities are not necessarily better protected, the scientists point out. Habitats such as broadleaf forests are often small and fragmented, which makes it harder for species to move.
The study examines the movement of climate zones, not species, the scientists stress, which means it is difficult to predict what the impacts may be on individual trees, insects and animals. Some are more tolerant to changing temperature than others, and the movement of species can be difficult to track. While trees are estimated to have spread northwards through a warming Europe after the end of the last ice age at a speed of about 1km per year, this could be down to dormant seeds reseeding the landscape, which would not be possible if species are forced to shift to new territories.
The scientists say that global warming will cause temperatures to change so rapidly that almost a third of the globe could see climate velocities higher than even the most optimistic estimates of plant migration speeds.
Some plants and animals may have to be physically moved by humans to help them cope, the scientists say, while protected areas must also be enlarged and joined together.
全文及圖片詳見：guardian.co.uk
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