"Sometimes. Spirits do exist, although we don't know as much about them as we might like. Under most circumstances, it's hard to tell they're there because they just go around doing the same things their natural phenomena were going to do anyway - the tide comes in and goes out, fires burn, winds blow, rain falls. The earth stays still, except when it doesn't. But sometimes a spirit gets attached to or tangled up with a person somehow, and then you get a person who makes natural phenomena behave strangely around them, and that can look similar to ambient magic, especially uncontrolled ambient magic. Fortunately, possession is even rarer, and these days we understand ambient magic well enough to realize that it's not the same thing at all."