In the United States, more than 90 people died across six midwestern and southern states
美国中西部及南部的六个州有90多人死亡。
when strong winds known as tornadoes destroyed homes, work buildings and religious centers on Friday night.
周五晚上，被称为龙卷风的强风摧毁了房屋、办公大楼和宗教中心。
Such weather events do happen in December, but they do not happen often this time of year
这类天气事件确实发生在12月份，但它们并不经常发生在一年中的这个时候，
because the temperature on the ground is not so different from air high in the sky.
因为这个时候地面温度与高空温度相差不大。
However, people in Kentucky said the air was warm and wet on Friday.
然而，肯塔基州的人们表示，周五那天的空气温暖且潮湿。
Weather scientists said the mixing of the warm and cold air can create "instability" which produces storms and the fast, spinning winds of tornadoes.
气候科学家说，暖空气和冷空气的混合会产生“不稳定性因素”，从而产生风暴和快速旋转的龙卷风。
The question is whether the deadly storm came because of climate change.
问题是这场致命的风暴是否是气候变化造成的。
The weather scientists, known as meteorologists, are not completely sure.
气候科学家，也被称为气象学家，并不完全确定。
Victor Gensini is a meteorologist at Northern Illinois University.
维克多·根西尼是北伊利诺伊大学的气象学家。
He said strong winds are common in the winter, but they do not create tornadoes because the air close to the Earth is also cold.
他说，强风在冬天很常见，但它们不会产生龙卷风，因为靠近地面的空气也很冷。
He called the tornado that traveled hundreds of miles on Friday "remarkable".
他称周五横扫数百英里的龙卷风“非同一般”。
The weather scientists say a warming planet has something to do with strong winter storms.
气候科学家说，全球变暖与强烈的冬季风暴有关。
The National Weather Service (NWS) noted
美国国家气象局（简称NWS）指出，
that since 1950 there had not been a November tornado recorded in the northeastern U.S. state of Connecticut.
自1950年以来，美国东北部的康涅狄格州就没有过11月份发生龙卷风的记录。
There was one last month, however.
然而，上个月就出现了一场龙卷风。
John Gordon of the NWS in Louisville, Kentucky called what happened on Friday "the worst-case scenario".
肯塔基州路易斯维尔的国家气象局气象学家约翰·戈登称，周五发生的事情是“最糟糕的情况”。
Gensini said the tornado traveled about 300 kilometers.
根西尼说这次的龙卷风约横扫300公里。
Normally, tornadoes die out in minutes, he said, but this one lasted for hours.
他说通常情况下，龙卷风在几分钟内就会消失，但这次的龙卷风却持续了几个小时。
He said the storm moved as fast as a car going down a large roadway.
他说，这次风暴的速度就像汽车在大马路上驶过一样快。
Harold Brooks studies tornadoes at the National Severe Storms Laboratory.
哈罗德·布鲁克斯在美国国家强风暴实验室研究龙卷风。
While the U.S. has more tornadoes than any other country, tornadoes only form once out of every 10 strong storms.
虽然美国的龙卷风比其他任何国家都多，但每10场强风暴中只有1场能形成龙卷风。
As a result, he said, it is hard to say if the winter tornadoes are closely related to climate change.
因此，他说很难确定冬季龙卷风是否与气候变化密切相关。
Gensini, however, said the conditions for strong storms are becoming more common in the winter as the planet warms up.
然而根西尼说，随着全球变暖，达到冬季发生强风暴的条件变得更普遍。
In the past, Brooks said, tornadoes happened more often during warm days in the summer.
布鲁克斯说在过去，龙卷风在夏季暖和的日子更频发。
However, as the winter becomes warmer, especially in the southern U.S., tornado season will shift.
然而，随着冬季变暖，尤其是在美国南部，龙卷风出现的季节将发生改变。
More will happen in the winter and fewer will happen in the summer.
龙卷风将更多出现在冬天，夏天出现得更少。
Jason Furtado is a meteorologist at the University of Oklahoma.
杰森·福塔多是俄克拉荷马大学的气象学家。
He said people who live in places like Kentucky,
他说，住在像肯塔基州这样的地方的人，
which suffered the most from Friday's storms, are now living in an area where tornadoes are common.
现在生活在龙卷风频发的地区。肯塔基州是周五那场风暴的重灾区。
That is a shift south and east from the past.
与过去相比，龙卷风在向南和向东转移。
He said the people in that area of the U.S. are "becoming increasingly vulnerable".
他说，美国该地区的人们将“越来越容易遭到龙卷风袭击”。
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