It's technically correct (the worst kind of correct): as I understand it, the global climate has been warmer than it is now. But there weren't any humans, and it didn't warm up nearly as fast.

It is true though. The climate has been both warmer and colder than it is now just several centuries ago (little ice age, medieval warm period). This is well documented and accepted by scientists even though reasons are not clear (definitely not human activity at that time obviously).

In our current era humans are contributing to the changing climate in a very big way given our industrialization, the extreme levels of population and economy dependent on extracting oil and coal from the ground and burning it. That does not change the fact that climate has been changing even before humans could have any noticeable impact on it, and those changes were often very fast and sometimes cyclical.

You seem more knowledgeable on this than I am. Is it cyclical, but the change has been heavily increased by human activity?

If it's just cyclical, then why are we blaming our activity?

Just show them this XKCD graph https://xkcd.com/1732/