Yes, that was hypothesized in the early days. But something to keep in mind is that even if the conclusion about the ultimate direction the temperature change would take was off (by some) all knowledgeable parties believed that human activities were plenty large enough to have an effect of catastrophic magnitude. As I'm sure you know, these phenomena are very non-linear with many known tipping points and doubtless many yet undiscovered. Also known then, and sometimes forgotten even now, is that the effects could be wildly different depending on where you live. E.g. the well known case of the AMOC system. Collapse or major change to the AMOC could give the British Isles a climate more like St. Petersburg, even as the rest of the world simmers.