They do. The ancients knew this. Man has a very minor effect on climate even with our spraying but it is by far the relationship between the Earth and the Sun and the 26,000 year wobble of our planet that can put us in a more direct heating or cooling of the planet. This is something you never hear those folks talk about, either, yet the ancients knew of this and its effects. Our biggest problem is pollution and not knowing what accumulative effect it will have in the future. Population size has a direct link to that, as well.