A few interesting points I uncovered when trying to track down the source.
It appears this graph has been altered quite a few times from what I presume is the original source.
The below graph is the most inaccurate alteration.
Note the Y axis says "Global Surface Temperatures", whereas yours says Global deep ocean temperatures. (Yours is correct by the way)
It looks as if some person has disingenuously altered the original graph to try an make it say something that it certainly doesn't say.
By the way, it looks like the original graph that yours is "adapted from" is this one below (
https://arxiv.org/abs/0804.1126) (Target atmospheric CO2: Where should humanity aim?) I think your graph has exaggerated the graph a little bit as it shows a 16C change in temp, where as both these graphs show just above a 12C change (Although I admit, I am not 100% sure this is where your graph has been adapted from).
Regardless, the authors of this paper state that;
"Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago,
the planet being nearly ice-free until CO2 fell to 450 ± 100 ppm; barring prompt policy changes, that critical level will be passed, in the opposite direction, within decades. If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is
adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects."
By the way, you can read the interpretation of your graph here in the link I provided above on page 7, and it is very difficult to understand with a lot of scientific jargon. It even took me a few reads to get it.
So, with regards to your quote
"This says it all. A trend is not always your friend. So the 1970s and 1980s fears of further ice age are more credible. Obviously, no connection to CO2 or humans."
This is just a very inaccurate statement.
Also, there were more scientific papers (off the top of my head, I think the number is 7:1) in that time period that predicted warming in the future, as opposed to cooling, So the whole "fears of further ice age" are certainly not more credible.
(20min delay)