Clue: Man's environment is as part of Earth; is running out of time (5,3)
Answer: IRISH SEA
Explanation: Definition: Man's environment
An envelope ('as part of'?) of 'is' in IRHSEA, an anagram ('running') of 'Ear[t]h is', minus the T ('out of time'). In the definition, Man, as often, is the Isle; the parsing is the best I can do, but is, to put it mildly, tortuous (or should that be torturous?).