CO2 now comparable to levels seen 4 million years ago: NOAA

Climate Milestone: Earth's CO2 Level Passes 400 ppm

environment - Are we in a low CO2 period, compared to the last 590 million years? - Skeptics Stack Exchange

3 million years ago, the CO2 levels were the same or higher than now, and we had global warming without any industrial intervention. Today, is it a coincidence that we are contributing

Increase in atmospheric methane set another record during 2021

CO2 Science

Earth's CO2 Level Highest In 4 Million Years At 419 PPM In May 2021

Carbon Dioxide Through Time EARTH 103: Earth in the Future

Greenhouse gas now at highest level in over 4 million years

Carbon Dioxide Passes 400 PPM Milestone, NOAA Finds

CO2: Past, Present, & Future - Time Scavengers

NOAA reports carbon dioxide reaches levels not seen in millions of years

CO2 now comparable to levels seen 4 million years ago: NOAA

CO2: Past, Present, & Future - Time Scavengers