專家：寒潮和全球變暖不矛盾
Beijing had its coldest morning in almost 40 years and its biggest snowfall since 1951. Britain is suffering through its longest cold snap since 1981. And freezing weather is gripping the Deep South, including Florida's orange groves and beaches.
Whatever happened to global warming?
Such weather doesn't seem to fit with warnings from scientists that the Earth is warming because of greenhouse gases. But experts say the cold snap doesn't disprove global warming at all - it's just a blip in the long-term heating trend.
"It's part of natural variability," said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo. With global warming, he said, "we'll still have record cold temperatures. We'll just have fewer of them."
Deke Arndt of the National Climatic Data Center in Asheville, N.C., noted that 2009 will rank among the 10 warmest years for Earth since 1880.
Scientists say man-made climate change does have the potential to cause more frequent and more severe weather extremes, such as heat waves, storms, floods, droughts and even cold spells. But experts did not connect the current frigid blast to climate change.
So what is going on?
"We basically have seen just a big outbreak of Arctic air" over populated areas of the Northern Hemisphere, Arndt said. "The Arctic air has really turned itself loose on us."
In the atmosphere, large rivers of air travel roughly west to east around the globe between the Arctic and the tropics. This air flow acts like a fence to keep Arctic air confined.
But recently, this air flow has become bent into a pronounced zigzag pattern, meandering north and south. If you live in a place where it brings air up from the south, you get warm weather. In fact, record highs were reported this week in Washington state and Alaska.
But in the eastern United States, like some other unlucky parts of the globe, Arctic air is swooping down from the north. And that's how you get a temperature of 3 degrees in Beijing, a reading of minus-42 in mainland Norway, and 18 inches of snow in parts of Britain, where a member of Parliament who said the snow "clearly indicates a cooling trend" was jeered by colleagues.
The zigzag pattern arises naturally from time to time, but it is not clear why it's so strong right now, said Michelle L'Heureux, a meteorologist at the Climate Prediction Center of the National Oceanic and Atmospheric Administration. The center says the pattern should begin to weaken in a week or two.
北京遭遇了近40年來最寒冷的清晨和1951年以來最大的降雪；英國正遭遇自1981年來持續時間最長的寒潮；美國包括佛羅里達的橘園和海灘在內的南部地區也未逃過嚴寒襲擊。
那麼全球變暖又是怎麼一回事？
科學家一直警告說溫室氣體排放正導致全球變暖，但這樣的天氣與這種說法似乎並不相符。但專家們稱，寒潮和全球變暖並不矛盾——這只是變暖過程中的一個暫時現象而已。
位於美國科羅拉多州博爾德的國家大氣研究中心的資深科學家傑拉爾德•彌爾說：“這是大自然易變性的一個表現。”他說，在全球變暖的同時，“我們仍然會遭遇創紀錄的低溫天氣，只是這樣的天氣會減少。”
位於北卡羅來納州艾西維爾市的國家氣象數據中心的德科•阿恩特指出，2009年將是自1880年以來氣溫最高的十年之一。
科學家說，人爲的氣候變化的確會帶來更爲頻繁和更嚴重的極端天氣，如熱浪、暴風雨、洪水、乾旱甚至持續的寒冷天氣。但科學家沒有把目前的嚴寒天氣和氣候變化聯繫在一起。
那麼這究竟是什麼原因呢？
阿恩特說：“我們看到的只是北極空氣在北半球人口密集地區的一次大爆發，北極空氣真的向我們發威了。”
在大氣中，大股大氣環流由西向東在北極和熱帶地區之間移動。這股氣流就像一個屏障，把北極空氣給禁錮了起來。
不過，最近這股氣流明顯呈“Z”形走勢，向南北方向蔓延。如果你居住的地區有南上氣流經過，那麼天氣將會變暖。事實上，華盛頓州和阿拉斯加州上週的溫度都創下歷史新高。
然而，和其他不太幸運的地區一樣，美國東部正遭遇一股從北方呼嘯而下的冷空氣。這就是爲什麼北京的氣溫會低至3度，挪威大陸的氣溫降到零下42度，英國部分地區會有厚達18英寸的積雪。英國某議員說大雪“表明氣候有變冷的趨勢”，結果遭到同事的譏笑。
國家海洋和大氣管理局氣候預測中心的氣象學家米歇爾•拉赫茹克斯說，這種“Z”形走勢不時出現，這很自然，但不清楚爲什麼現在會這麼強勁。該中心說這一走勢應該會在一兩週後開始減弱。
Vocabulary:
cold snap: 寒潮
disprove: to prove to be false, invalid, or in error 證明……是虛假的；反駁（Evidence has now disproved that theory. 事實現已證明那種理論是不正確的。）
blip:a temporary or insignificant phenomenon, especially a brief departure from the normal 偏離正常軌道的一個短暫現象
variability: the quality, state, or degree of being variable or changeable 變化性；變化的傾向
blast:a powerful hit, blow, or shot 衝擊波，氣浪
turn sb./sth. lose: to give up control of someone or something, so they can do what they want 放開，釋放；聽憑，放縱
pronounced: strongly marked; distinct 明顯的，顯著的
swoop down: to dive or plunge downward 俯衝
