Just because we have not discovered, or identified earlier civilisations, does not prove that earlier civilisations did not in fact exist. But historic records are rejected as myths.
Edgar Cayce mentioned the Essene several times in the Readings. And what he said was only proven later, after his death. When they discovered the Dead Sea Scrolls in 1948, and the scientists managed to piece together the texts.
My point here is that he also talked about lost civilisations, like Atlantis and Mu, and that the Cheops pyramid was built 10490-10390 BC. And he talked about the Hall of Records, under the Sphinx.
(See links provided)
The only danger concerning CO2 levels in the atmosphere would be if we really were able to remove and measurably lower it.
Life on earth is Carbon-based. Not silica-based like sci-fi speculates could be a reality.
Plants pull the Carbon from the CO2, and release Oxygen (O2) back into the atmosphere. In the photosynthesis process.
Different plants have different minimum levels they can endure. Endurance is also modified by temperature.
Plants most likely suffer CO2 deficiency at current levels. As shown in controlled environment like a Greenhouse.
This reduces the plants ability to grow abundantly, and we also find low temperature inhibits growth.
A side note: Oxygen levels are around 21% of the atmosphere, but there was a time when it was 30%.
Wish it would be that high today. People would have no problem breathing at high elevation.
People from near sea level, suffer when they reach high elevation like in Chile.
We now have instruments that measure it directly, and in real time. But when we use historical records, we use other methods. Like sampling ice cores, and trees. So the methods used is not equal. We could still use ice and tree samples to compare to historic records. To evaluate and monitor nature's response to modern levels.
As for higher temperatures. It is proven that measuring stations are misplaced, like on airports. Measuring temperatures in an environment with asphalt, concrete and heat exchangers nearby is not sound science.
And cities are warmer than other areas. Which should surprise nobody.
More stations in highly populated areas = higher average temperature.
I live in a region where the population has been reduced by over half the past 100 years. As people moved to towns and cities.
Hall of Records
Great Pyramid and Sphinx