Explanation:

- Statement: The statement suggests that the super-hot summer should serve as a signal or indication, especially given past events.

- Option 1: Entertaining

- This option doesn't fit the context. Extreme weather isn't amusing.

- Option 2: Caning

- This implies punishment but doesn’t align with the context.

- Option 3: Warning

- This fits perfectly. Extreme weather should alert us to environmental issues and climate change.

- Option 4: Banning

- Unrelated to the context since banning usually refers to prohibiting actions or items.

- Option 5: Earning

- The context is about the environment, not financial gain.