题目内容：

what is global warming?

优质解答

Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation.Global surface temperature increased 0.74 ± 0.18 °C between the start and the end of the 20th century.
全球变暖指的是在一段时间中,地球的大气和海洋温度上升的现象.在20世纪,全球平均接近地面的大气层温度上升了摄氏0.74度.
科学界发现过去50年可观察的气候改变的速度是过去100年的双倍,有理由认为该时期的气候改变是由人类活动所推动.