Pennsylvania State University offers some online course work that is very informative (and for me, strangely reassuring) on the subject of global warming in the past, present and future.
They begin:
"Our planet is warming. Data shows that the average temperature of Earth has increased by 0.6 degrees C since 1950. The Northern Hemisphere just recorded its 333rd month with temperatures above the 20th century average. In fact, Earth is warming at a rate not experienced for many millions of years, if ever before. This warming and a myriad of associated environmental changes will challenge modern society throughout the 21st century. Scientists are striving to improve predictions of how the environment will change as well as understand the impacts on humans. This course, Earth in the Future: Predicting Climate Change and Its Impacts Over the Next Century is designed to provide the state of the art of climate science, the impacts on humans and natural ecosystems, as well as ways humans can mitigate and adapt to climate change."
https://www.e-education.psu.edu/earth103/
Be sure to scroll to the bottom of the above link to the section entitled MODULES. One example of what you'll find is:
Module 1: Past Episodes of Climate Change
This gives you a selection of more detailed titles that leads you onward.
For example:
"The PETM was associated with the largest deep-sea mass extinction event in the last 93 million years and remarkable diversification of life in the surface ocean and on land."
Ancient Climate Events: Paleocene Eocene Thermal Maximum
https://www.e-education.psu.edu/earth103/node/639
An interesting excerpt from the above:
"... as warmer waters hold less oxygen than cold waters, PETM deep waters in many locations likely were possibly close to a condition that is known as hypoxia. Finally, the input of so much CO2 into the ocean caused ocean waters to become more acidic and led to a condition known as ocean acidification. Acidification of the deep ocean during the PETM is well accepted and is observed by complete dissolution of all CaCO3 shells that rained down on the sea floor...."
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