No one denies that the climate changed before and that it's a natural thing. The problem is that in 100 years we went from slow changes to 10 times the amplitudes ever recorded. The questions isn't "Do these cycles exist ?" it's "Are we sure we want to trigger one early ?"

Greenhouse effect is a very well studied effect. CO2 / other gases level are a very well studied field. CO2/other gases dramatically increased since the industrial revolution. Are you also denying that ?

When you study something you have to look at the settings in which it happens and look at the time frame. Sure changes happened 10k+ years ago, that's not invalidating anything related to our role in the current change.

> Thinking humans are responsible for global warming is like thinking humans are responsible for the rise and decline of tides because we drink water.

You won't win anyone over with such nonsensical arguments.

https://www.climatecentral.org/news/the-last-time-co2-was-th...

https://theconversation.com/the-three-minute-story-of-800-00...

https://www.ncdc.noaa.gov/global-warming/last-2000-years

https://xkcd.com/1732/