气候变化是当今世界面临的最大环境挑战。

___Climate ___change is the greatest environmental challenge facing the world today.

许多科学家对气候变化的影响深感担忧。

Many scientists are deeply concerned about the effects of ___climate ___change.

极端天气事件日益频繁是气候变化的明显迹象。

The increasing frequency of extreme weather events is a clear sign of ___climate ___change.