Hainan is not cold in winter.

海南冬天不冷。

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If the winter is not very cold, their leaves may stay green.

如果冬天不是很冷，它们的叶子可能会保持绿色。

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I am not afraid of cold winter.

我不怕寒冷的冬天。

youdao

If the winter is not cold enough to freeze the ground, you can grow and harvest carrots the same way as during the summer months.

VOA: special.2009.02.24

"They were believed to be spreading because the winter was not cold enough to kill them, and that's destroying forests, " he said.

CNN: Ice melting across globe at accelerating rate, NASA says

Not every spring day is going to be warm, and not every winter's day cold.

NPR: Not All Seasons Are Created Equal

You should also be aware that almost none of us have air conditioning: our peak energy demand is very definitely in these cold winter snaps, not in summer for cooling.

FORBES: Why Wind Power Doesn't Work