https://www.history.com/topics/natur...climate-change
A real simple timeline on the history of climate change. In a nutshell, we should have known we'd be altering the climate as far back as 1895. However, it wasn't until 1930 one scientist suggested we were doing just that. It took until 2006, when IPCC finally suggested it was "very likely" humans were causing climate change.
Lots of reading on their website:
IPCC
The discussion around "are humans causing climate change?" should be long over. Reducing carbon emissions is essential and will be ongoing, but humans should also start focusing on CO2 conversion at this point. And some are doing that. We simply reacted too slow and now it's a matter of dealing with climate change and slowing it down as opposed to stopping it.