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

Global CO2 levels reach highest levels in human history

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

Atmospheric CO2 Just Hit a Peak Not Seen on Earth in 4 Million Years : ScienceAlert

USA

Greenhouse gas now at highest level in over 4 million years

Carbon dioxide reaches another milestone, continues to impact climate

Graphic: The relentless rise of carbon dioxide

Atmospheric carbon dioxide levels at 4-million-year high; El Nino could boost numbers in 2023, WMO says

New CO2 Record Prompts a Scientist to Ask, 'What's It Going to Take for Us to Wake Up?

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