That is exactly what happens. In fact, it happens in cycles. There is the sunspot activity cycle which is like every 12 years. Then there is a cycle at around 100 years that has been identified. But then ere are also cycles at even larger time scales around 1500, 6000, and 12000 years. With the 12000 year cycles being the most intense. And we know this because the polar direction and intensity of the magnetic field are recorded at the time a lava deposit solidifies. Which as we know is an ongoing never ending process; there is ALWAYS lava flowing somewhere on earth.