First, there's about a 30-year lag between emissions and their full heating effect, much like it takes time for water to boil after you turn on the stove. More

First, there's about a 30-year lag between emissions and their full heating effect, much like it takes time for water to boil after you turn on the stove. More importantly, if we go beyond about +2 degrees C, it's likely that positive feedbacks will take over and add several more degrees, with no more help from us. Feedbacks include ice cap melt (so less sunlight is reflected away), CO2 and methane emissions from melting permafrost, and forest fires brought on by drought. We know this is likely, because you're right about those cycles. In geological history, there have been times when orbital variations caused a small initial heating, and shortly after we see a big rise in greenhouse gases and temperature. That's why we're worried about fixing things really soon, before that kicks in. (We are not currently in one of those natural warming cycles, btw.)