Changing environment sounded alarm for old Chinese rulers (12)

I believe the answer is:

terraforming

I'm a little stuck... Click here to teach me more about this clue!

'changing' is the definition.
Both the definition and answer are present participle verbs.
Perhaps you can see an association between them that I can't see?

'environment sounded alarm for old chinese rulers' is the wordplay.
I cannot quite understand how this works, but
'old' could be 'o' (abbreviation as in OT - Old Testament) and 'o' is found in the answer.
'chinese' could be 'min' (Min is an example) and 'min' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.

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