氣象學家終於明確偵測到過去一個世紀中，人為造成全球降水模式改變的證據。這些科學家的研究成果將在7月26日出刊的《自然》（Nature）期刊中發表，顯示人類活動已經明顯造成過去一個世紀全球降雨模式的改變。
過去在國際性的研究中一直都沒有測得人類造成降水模式改變的證據，一部份的原因是，某些區域逐漸變乾的狀況，被其他區域逐漸變潮濕的狀態所抵銷，因而降低全球變遷的徵候。
在此研究中，科學家以不同緯度線的降水模式變化作觀察分區，取代過去以全球平均的計量方式。
研究成員之一的東安格里亞大學（University of East Anglia）表示：「這次研究開拓氣候變遷研究的新疆界」。這些科學家們研究大氣中溫室氣體與硫酸鹽氣濃度對於過去一個世紀全球陸地降水的複合效應。 研究顯示，過去一個世紀的氣候紀錄指出，因為溫室氣體與硫酸鹽氣排放，明確地造成全球降水模式的變動。
由全球各大區域的平均降水狀況，對照人類改變氣候引發的降水模式變化，科學家們已可確認人類引發的氣候變遷，的確造成北緯50°以北地區降水量的增加，這些地區包括加拿大、俄羅斯及歐洲，而在南半球也有類似的情形。
人類引發的氣候變遷，也是赤道以北廣大區域氣候逐漸變乾燥很重要的原因，這些區域包括墨西哥、中美洲、及非洲北部。
這些變動可能已經對生態系、農業、及人類健康，造成很明顯的影響，尤其是在一些對於降水變化敏感的地區，例如非洲北部薩赫勒地區（Sahel region，譯註：撒哈拉沙漠和非洲雨林之間的地區），影響更大。有些證據顯示，火山活動等自然因素也在過去一個世紀中對全球降水模式改變扮演重要角色，但其造成的影響遠低於人類活動造成的結果。
For the first time, climate scientists have clearly detected the human fingerprint on changing global precipitation patterns over the past century. Their study to be published in tomorrow's issue of the journal "Nature" demonstrates that "human activities have contributed significantly to shifts in global precipitation patterns over the past century."
Human-induced changes have not previously been detected in global studies of precipitation, partly because drying in some regions cancels moistening in others, reducing the global signal.
Here the scientists used the patterns of the changes in different latitude bands instead of the global average.
In the study, which the University of East Anglia says "breaks new ground in climate change research," the scientists studied the combined effect that changes in greenhouse gases and sulphate aerosol concentrations in the atmosphere have had on global precipitation over land during the past century.
According to the study, over the past century, climate records indicate there have been sizable shifts in precipitation patterns around the globe as a result of the emission of greenhouse gases and sulphate aerosols..
Looking at average conditions over broad regions of the globe, and comparing them to changes anticipated due to human influence on climate, scientists have determined that human-induced climate change has caused most of the observed increase in precipitation north of 50° latitude, a region that includes Canada, Russia and Europe, as well as in the southern hemisphere.
Human-induced climate change has also made important contributions to the drying observed in a broad region north of the equator that includes Mexico, Central America and northern Africa.
These shifts may have already had significant effects on ecosystems, agriculture and human health, especially in regions that are sensitive to changes in precipitation, such as the Sahel region in northern Africa.
The evidence suggests that natural factors, such as volcanic activity, have also contributed to the changes in global precipitation patterns over the past century, although to a much smaller extent than human activity.
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