This means 4 harsh months
Hades said that he had felling for her.
After a long time and a lot of searching Demeter Pessephone's mom went to Zeus and begged her to be free of the underworld but Zeus said no so she was mad and made the world turned cold.
Then Zeus sent a messenger to the underworld but Persephone ate 4 pomegranate seeds so she had to spend 4 months a year in the underworld. Demeter was happy for 8 months that is why there is 8 warm months and the months that the months that Persephone spent in underworld will be cold because she is sad.