????全球氣候變暖的烏云背后其實也透著一線光芒——地理學家們預測，到本世紀中葉，融化的海冰將在北極開辟新的商業航線。它將大大縮短船只在夏末的航行時間，還將削弱俄羅斯對橫跨北極航運的控制。破冰船將破天荒地徑直穿越北極，貫穿加拿大北極群島的那條危機四伏、但令人垂涎欲滴的西北航道（NWP）終于有望成為一條可行的商業航線。

????美國加州大學洛杉磯分校（UCLA）的勞倫斯?C?史密斯和斯科特?R?斯蒂芬森在《美國國家科學院院刊》（Proceedings of the National Academy of Sciences）上發布了這項研究成果。這兩位學者運用計算機模型，根據7項獨立的氣候模型，對本世紀中葉(2040-2059) 北大西洋和白令海峽之間的最優航運路線進行了預測。他們把研究限定在北極冰處于最低值的9月份。下面是他們的發現：

????? 北冰洋東部沿俄羅斯海岸的北海航線（NSR）——目前唯一可行的橫跨北極航線——將變得更加通暢。北海線路將向更多普通的、無加固船體的開放水域船只（目前使用的絕大多數運輸船都是這種）開放，起航自北大西洋的最佳航線將由俄羅斯海岸向北轉移，進而脫離它的領土管轄范圍。

????? 如今散落著約5萬座高達300英尺巨型冰山的西北航道（NWP）將就此打開。相比于北海航線，往返北美的航程將減少30%。對于極地6級船只（Polar Class 6，波羅的海國家現在使用的輕量級破冰船）來說，它將成為夏末全天候通暢的最優航線，普通的開放水域船只在相當長的時間內也可以在這條航線上通行。“這的確令人稱奇，因為西北航道的可航行度一直不如北海航線，冰封程度也遠大于后者，”史密斯說。“這是一個非常難以駕馭的地方。”西北航道的開放或將迫使加拿大、美國和歐洲著手解決這條貿易路線究竟是位于加拿大水域，還是位于國際水域這個爭執已久的問題。

????? 隨著冰層變薄，北極將成為往返歐洲的破冰船的最優航線，可能會吸引一些北海航線的船只。到本世紀中葉，極地6級船只“幾乎可以去任何一個它們想去的北極地區，”史密斯說。“屆時，如果打算在大西洋和太平洋之間航行，最短的路線就是直接穿越北極。”

????盡管目前還無法搞清楚所有這一切具有的經濟意義，但隨著冰層退去，北極地區的航運已經開始升溫。2010年夏，冰層變得足夠薄的時候，有幾艘運輸船只首次通過了北海航線。去年夏天，46艘運送石油、天然氣和硬礦石的船只曾經從俄羅斯、挪威和丹麥經由這條航線駛往中國，阿拉斯加費爾班克斯大學（University of Alaska Fairbanks）地理和北極政策教授勞森?布里格姆說。

????Call it a silver lining: Geographers are predicting that by mid-century, melting sea ice will open up new commercial shipping routes in the Arctic. That would shave off costly travel time in the late summer and reduce Russia's control over trans-Arctic shipping. For the first time, icebreakers will be able to make a straight shot over the North Pole, and the treacherous but coveted Northwest Passage through Canada's Arctic Archipelago will become a viable commercial route.

????UCLA's Laurence C. Smith and Scott R. Stephenson reported the findings on what they're calling "Supra-Polar" routes Monday in the journal Proceedings of the National Academy of Sciences. The pair used computer modeling to predict optimal navigation routes for mid-century (2040-2059) between the North Atlantic and the Bering Straight based on seven independent climate models. They restricted their study to September, when Arctic ice is at its minimum. What they found:

????? The Northern Sea Route (NSR) along Russia's coast in the eastern Arctic Ocean -- the only viable trans-Arctic shipping route today -- will continue to become more navigable. The NSR will open up to more ordinary open-water ships without reinforced hulls (the vast majority of shipping vessels in use today), and optimal routes from the North Atlantic will shift northward away from Russia's coast and out of its territorial jurisdiction.

????? The Northwest Passage (NWP), which today is littered with some 50,000 giant icebergs up to 300 feet tall, will open, reducing by 30% the distance for vessels traveling to and from North America compared with the NSR. It will be the optimal late-summer route for Polar Class 6 vessels (lightweight icebreakers used in the Baltic states today) 100% of the time and for ordinary open-water ships much of the time. "This is a surprise because the NWP has always been less navigable and more icy than the NSR," Smith says. "It's a very stubborn place." The opening up of the NWP may force Canada, the U.S. and Europe to settle a longstanding dispute over whether the trade route is in Canadian or international waters.

????? The North Pole will become the optimal route for ice-breaking ships traveling to and from Europe as the ice thins, which could pull traffic away from the NSR. Polar Class 6 vessels will "pretty much go wherever they please" in the Arctic by mid-century, Smith says. "At which point, if you're trying to get between the Atlantic and the Pacific, the shortest route is directly over the North Pole."

????Although it's too soon to know what all this means in economic terms, shipping is already ramping up in the Arctic as ice retreats. A handful of shipping vessels first navigated the NSR in 2010, when the summer ice thinned sufficiently there. Last summer, 46 ships carried oil, gas, and hard minerals from Russia, Norway, and Denmark to China, says Lawson Brigham, a professor of geography and Arctic policy at the University of Alaska Fairbanks.