Doesn't mean that CERN isn't interfering in that natural process. Truth is there is a lot we don't really know. So, you are right that the magnetic fields move on their own, but the only way to be sure that CERN has no effect would be to shut down CERN for at least a decade.. Probably if it has any affect, it's most minimal at best, I'll agree. But really we do not know that to be true or even false. It's more of an assumption.
More Info On Earth's Magnetic Fields