Carbon Dioxide In Earth's Atmosphere Hits Highest Levels In Human History


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Forest fire.

Current levels of atmospheric carbon dioxide are comparable to those seen 4.1 to 4.5 million years ago. Image credit: Vladimir Melnikov/

Despite the slight slump in emissions seen in the early days of the COVID-19 pandemic, carbon dioxide levels in the Earth’s atmosphere are the highest they’ve been throughout the whole of human history. In fact, the planet has not seen this level of carbon dioxide in its atmosphere for around 4 million years. 

Scientists from the National Oceanic and Atmospheric Administration (NOAA), and the Scripps Institution of Oceanography at the University of California San Diego have just announced the Mauna Loa Atmospheric Baseline Observatory saw a record concentration of atmospheric carbon dioxide, peaking in May 2021 with a monthly average of 419.13 parts per million.


Last year, there was some optimistic speculation that the COVID-19 pandemic and its many disruptions, from less air travel to reduced economic production due to global lockdowns, may help to combat the relentless release of greenhouse gases. While the world did see a very short-term reduction of greenhouse gas emissions, it quickly became apparent the effect was negligible in the grander scheme of things. 

"The ultimate control knob on atmospheric CO2 is fossil-fuel emissions,” Ralph Keeling, a geochemist who runs the Scripps program at Mauna Loa, said in a statement. “But we still have a long way to go to halt the rise, as each year more CO2 piles up in the atmosphere. We ultimately need cuts that are much larger and sustained longer than the COVID-related shutdowns of 2020."

The levels seen in May 2021 were the highest ever recorded since the NOAA began measurements at the weather station on Mauna Loa back in 1974. Measurements at the Hawaiian weather station are considered a global benchmark for atmospheric carbon dioxide measurements and holds the title for being the longest unbroken measurement of carbon dioxide in the atmosphere.

In May 2020, the Mauna Loa station saw the seasonal peak in atmospheric carbon dioxide break 417.1 parts per million for the first time in human history. The increase seen over the past 12 months has actually been slightly less than seen in the recent yearly increase, although it’s still close to the average annual increase from 2010 to 2019.


This year-on-year carbon dioxide rise is fuelling the mounting climate crisis facing our planet. Carbon dioxide released through human activities such as deforestation and burning fossil fuels builds in the atmosphere where it traps more of the Sun’s heat, warming the planet. 

Current levels of atmospheric carbon dioxide are comparable to those seen during the Pliocene Climatic Optimum, a period between 4.1 and 4.5 million years ago. The world was a very different place back then — and vastly less habitable for humans. Homo sapiens were still millions of years away from existence, forests covered the Arctic, sea levels were 23 meters (78 feet) higher than today, and summer temperatures were around 8°C (14.4°F) warmer.

The future vision of the planet is still uncertain, but it's clear we need to drastically cut our carbon emissions if we wish to avoid irreversible changes to the environment and crash headfirst towards a full-blown climate crisis. 

“We are adding roughly 40 billion metric tons of CO2 pollution to the atmosphere per year,” explained Pieter Tans, a senior scientist with NOAA’s Global Monitoring Laboratory. “That is a mountain of carbon that we dig up out of the Earth, burn, and release into the atmosphere as CO2 — year after year. If we want to avoid catastrophic climate change, the highest priority must be to reduce CO2 pollution to zero at the earliest possible date.”  

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