the death of many animals, plants, and possibly humans, especially as a result of climate change (= changes in the world's weather caused especially by increasing levels of carbon dioxide in the atmosphere)

He said Earth's atmosphere can only stay this loaded with man-made carbon dioxide for a couple more decades without changes such as mass extinction, ecosystem collapse and dramatic sea level rises. 他说，对目前这样的人为二氧化碳负荷，地球的大气层只能再承受几十年了，在这段时间内不会发生大规模灭绝、生态系统崩溃和海平面急剧上升等变化。

Biologists say five mass extinctions have occurred since life began on Earth. 生物学家说，自地球生命开始以来，已经发生过五次大规模灭绝。