利用電腦模型和20年來的衛星觀測資料，科學家已證實，氣候暖化和強烈暴風雨的發生之間，存在相關性。
在暖季時大雨發生的情形較為頻繁，而冷季則相反，美國佛羅里達和英格蘭的科學家7日表示他們提供了第一個觀測證據，連結暖化天氣和強雨的關係的研究。
「我們使用衛星觀測和模型模擬以測試熱帶的降雨對地表溫度和大氣濕度變化的反應。」他們解釋道。這個研究聚焦在和聖嬰現象有關的海面溫度變化，聖嬰現象來自中部熱帶太平洋的海水異常地持續變暖，導致全世界洪水、乾旱和其他的災害。
聖嬰現象發生的間隔並不規律，大約2到7年，通常持續1到2年。由衛星觀測和模型模擬，科學家發現熱帶的大量降雨和溫度有極明顯的連結。
該研究的作者索丹博士表示：「暖化的大氣層中含有大量的水氣，促進了豪大雨的發生。」索丹是邁阿密Rosenstiel海洋和大氣科學學院的氣象與物理海洋學的助理教授。
觀測結果和研究模型都指出暖化的天氣導致強烈的降雨量，但是索丹和他的團隊發現由衛星觀測到的異常降雨的情形比電腦模型預測的結果要「顯著性地嚴重」。
這個結果表示因為全球暖化造成的極端降雨情形其嚴重性可能被低估，而未來大量降雨的狀況可能會比之前想像的還要嚴重。
「比較觀測資料和電腦計算的結果可以增進對全球暖化帶來降雨情形的瞭解，」瑞丁大學（University of Reading）裡環境系統科學中心的艾倫博士（Richard Allan），同時也是該篇研究報告的共同作者這樣表示，「這個差距又可能是來自於測量法或是過去用來預測未來氣候變遷的缺陷」。
索丹表示地球氣候對溫室氣體增加的敏感度由雲量和水分的蒸發而定。
「透過衛星觀測和地球氣候的數學模型，我的研究希望可更瞭解大氣的水分對氣候和氣候變遷的影響。」索丹在他的網站表示，「這個研究源自於需要瞭解人類活動如何改變地球氣候。」
該份報告「大氣暖化和極端降雨的增加」(Atmospheric Warming and the Amplification of Precipitation Extremes)將於下一期的科學雜誌刊登。
The link between a warmer climate and more powerful rainstorms has been confirmed by scientists using both computer models and satellite observations gathered over a period of 20 years.
Heavy rain events increase during warm periods and decrease during cold periods, according to the scientists in Florida and England who said today that their research is the first to provide observational evidence linking higher temperatures with heavier rains.
"We use satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content," they explained.
The study focused on changes in sea surface temperatures associated with El Niño, a pattern of warming in the central tropical Pacific Ocean off the coast of South America that results in floods, droughts, and other disturbances around the world.
El Niño patterns occur at irregular intervals of two to seven years and usually last from one or two years.
Based on satellite observations combined with data from computer models the scientists found "a distinct link" between tropical rainfall extremes and temperature.
"A warmer atmosphere contains larger amounts of moisture which boosts the intensity of heavy downpours," said study author Dr. Brian Soden, an associate professor of meteorology and physical oceanography at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.
Both observations and models indicated an increase in heavy rainstorms in response to a warmer climate, but Soden and his team found the amplification of rainfall extremes observed by satellite was "substantially larger" than that predicted by the computer models.
This means that projections of future changes in rainfall extremes due to global warming caused by human activities may be underestimated, and future rains may be even heavier than previously thought.
"Comparing observations with results from computer models improves understanding of how rainfall responds to a warming world," said co-author Dr. Richard Allan of the University of Reading's Environmental Systems Science Centre. "Differences can relate to deficiencies in the measurements, or the models used to predict future climatic change," he said.
Soden says the sensitivity of the Earth's climate to an increase in the greenhouse gas carbon dioxide depends on the response of clouds and water vapor.
"My research strives to better understand the role of atmospheric hydrologic processes in governing climate and climate change through the use of satellite observations and mathematical models of Earth's climate," Soden says on his website. "This research is motivated by the need to better understand how human activities are altering Earth's climate."
The report, "Atmospheric Warming and the Amplification of Precipitation Extremes," is set for publication in an upcoming issue of the journal "Science."
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