If mankind is the cause of global warming, then how did the ice age end?
Variations in Earth's orbital cycles push the planet into and out of glacial periods, but the release of CO2 from the oceans at the end of a glaciation helps warming along.
Cold glacial periods and warm interglacial periods have happened on Earth for the past 2 million years or so. The primary reason is something called Milankovitch cycles, named after their discoverer. See pic 1. These variations in the Earth's orbit, wobble, and the tilt of its axis is enough to change the amount of incoming solar energy that heats the planet.
For example, when the planet tilts a bit further away from the sun, things get cold on Earth and when the planet tilts towards the sun a bit more, it warms up. These cycles operate on tens of thousands to 100s of thousands of years.
As the oceans start to warm, they release CO2 they absorbed during the cold glacial period. This is called a positive feedback loop and it accelerates warming.
The current anthropogenic warming is almost entirely due to human burning of fossil fuels ( and burning forests). About 97% of climate scientists are convinced that human activities are to blame. The confidence climate scientists have in the conclusion that humans are responsible for the current global warming is at the same level of confidence that health scientists have in linking smoking and lung cancer.