美國氣候學家於26日出刊的《國家科學院學報》中發表，全球氣溫上升的情況至少是1萬2千年來所未見的。研究人員表示，暖化的腳步在過去30年間變得更快，而人類活動無疑為其主因。
研究推斷，現在地球是在兩個冰河期之間的最高溫標準，甚至是超過了已維持將近1萬2千年的溫度標準。研究人員亦指出。高溫正迫使動物植物向兩極位置遷移。
全世界測量溫度的儀器在過去一世紀中均顯示出：地球在過去30年內，每10年均提高華式0.36 度（攝氏0.2度）。這種暖化速度與1980年代所預測的暖化速率結果相似，當時為偵測溫室氣體的變動標準而發展出模擬全球氣候的模組。
而且，在最近數十年，暖化已經使得在過去百萬年來的全球最高溫度又調高了約華式1.8度（攝氏1度）。此研究共同作者美國太空總署的韓森表示，「這意味著之後全球溫度每升高攝氏1度就是一個臨界點。如果暖化是一直持續低於這個溫度，那麼全球暖化效應也許可以處理。」
韓森說：「但如果地球暖化達到攝氏2或3度，我們很可能將會看到地球變成另一個我們不認識的星球。最後就是回到像當初300萬年前上新世（Pliocene）中期的時候，海平面會比現在高出將近80呎。」
一份2003年《自然》期刊的研究指出：在20世紀的後50年，有1700種動植物以每10年平均4哩的距離，向兩極地帶遷移。韓森又提到，此種遷移速率跟不上在1975至2005年間，以每10年25哩速度前進的一個已知溫度帶狀區域的運動現行速率。
另外關鍵性的發現，就是在「聖嬰現象」（El Niño）發生的太平洋地區溫度的變化。「聖嬰」在每2至7年發生一回，當溫暖的海水從西太平洋向西流向南美洲時，其中發生的氣候結構轉變進而影響世界氣候。韓森及他的工作團隊提到：在東西太平洋區日增的氣溫變化，可能催化另一波強大的聖嬰效應，就像在1983年和1988年發生的一樣。
The world's temperature has increased to levels not seen in at least 12,000 years, U.S. climate scientists reported in today's issue of "Proceedings of the National Academy of Sciences." Rapid warming has occurred in the past 30 years, the researchers said, and there is little doubt that human activities are the primary factor.
The study concludes the Earth is now reaching and passing through the warmest levels in the current interglacial period, which has lasted nearly 12,000 years. This warming is also forcing a migration of plant and animal species toward the poles, the researchers said.
Worldwide instrumental temperature measurements during the past century show the planet warmed at a rate of 0.36 degree Fahrenheit (0.2 degree Celsius) per decade for the past 30 years. This observed warming is similar to the warming rate predicted in the 1980s in initial global climate model simulations with changing levels of greenhouse gases, the researchers said.
Furthermore, the warming in recent decades has brought global temperature to a level within about 1.8 degree Fahrenheit (one degree Celsius) of the maximum temperature of the past million years. "That means that further global warming of 1 degree Celsius defines a critical level," Study coauthor James Hansen of NASA's Goddard Institute for Space Studies said. "If warming is kept less than that, effects of global warming may be relatively manageable."
"But if further global warming reaches 2 or 3 degrees Celsius, we will likely see changes that make Earth a different planet than the one we know," he said. "The last time it was that warm was in the middle Pliocene, about three million years ago, when sea level was estimated to have been about 80 feet higher than today."
A 2003 study that appeared in the journal "Nature" found that 1,700 plant, animal and insect species moved poleward at an average rate of about 4 miles per decade in the last half of the 20th century. Hansen said that migration rate is not fast enough to keep up with the current rate of movement of a given temperature zone, which has reached about 25 miles per decade in the period 1975 to 2005.
Another key finding is the temperature change in the area of the Pacific Ocean where the sometimes dramatic weather pattern known as El Niño develops. An El Niño is an that typically happens every two to seven years when the warm surface waters in the West Pacific push eastward toward South America, in the process altering weather patterns around the world. Hansen and his colleagues suggest that increased temperature difference between the Western and Eastern Pacific may boost the likelihood of strong El Niños, such as those of 1983 and 1998.
