It was necessary for the children of Israel to sojourn in Egypt for over 400 years, during which time they became a great nation. God got Jacob and his family to Egypt by causing a famine throughout the land of Canaan.
God used famines in the lives of Abraham, Isaac and Jacob to test their faith. It indicates that the climate was unstable, or cyclical, with periods of warming and cooling. There has been a net loss of global ice ever since.