Someone I know posted a question about climate change that I do not know how to answer. While I do believe (for lack of better word) in climate change, I do not know how to answer this persons question. The tl;dr of the question is:
If climate change is not a natural phenomenon, then how did the last ice age end?
The person is implying that warming/cooling reoccurs periodically on the Earth, and that the current climate change threat is overblown.
I have searched online for answers, but cannot find anything concise on this specific subject. According to this wikipedia article,
There is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets, but it is difficult to establish cause and effect (see the notes above on the role of weathering). Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages, such as the movement of continents and volcanism.
In short, how and why did the last ice ages end? I am assuming that the carbon dioxide concentration during these ice ages is much lower than the current estimate of ~410 ppm. Aside from the difference in carbon dioxide levels, what evidence suggests that the climate change of today is different than the climate change that ended the ice age(s)?