We're projected to reach temperatures not seen in more than an estimated 20 million years due to our actions within a couple centuries. Harder may end up being a massive understatement.
You may be right that I overstated that. In 2013 there was a study finding it had not changed this rapidly in 65 million years, though since then there have been studies suggesting there may have been incidents of very rapid change in the distant past. Here are some relevant links I found: