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.

科学家们正在研究气候变化以理解其影响。

Scientists are studying ___climate ___change to understand its effects.

政府需要采取行动缓解气候变化。

Governments need to take action to mitigate ___climate ___change.