A second famine caused Isaac and Rebekah to go Gerar. This is another example, similar to Abraham and Sarah going to Egypt, of making a bad decision rather than trusting the Lord.
Abraham experienced the first of 3 generational famines. It caused he and Sarah to go to Egypt. This is very symbolic and it's usually used to picture the bad decisions that we make when we are walking by sight, not by faith.
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.
If you don't understand mainstream science (SciPop) well enough to know that it's not a threat to the Bible, and try to live a Christian life without the truth of the Bible, then you have no armor of light.