And the volcanos errupt (read: it's what they do), spew dust and such into the atmosphere, and that cools things down. Mother Nature is smart.

That aside, the planet's behavior has ebbs and flows. This eco-chaos spans hundreds of thousands to millions of years. There are few if any patterns. To that point, historically the climate has always been changing; and temperature: it's either trending up or down (but it is not static).