“Another year, another record,” quipped Ralph Keeling, head of the Scripps CO2 Program, as atmospheric carbon dioxide hit 430 parts per million (ppm) for the first time in May 2025 a benchmark that a decade earlier would have been unthinkable. This measurement, taken at NOAA’s Mauna Loa Observatory and supported by Scripps Institution of Oceanography, is not only a record-breaking measurement; it is 3.5 ppm above last year’s measurement, a pace which has climate researchers buzzing all over the world.
Levels of CO2 are more than ever recorded in at least 30 million years when the Earth planet’s climate was in none of human world history. In the Eocene, for instance, the Arctic Circle hosted crocodiles and Antarctica was covered by temperate rainforests. The Earth was around 14°C warmer than it is today, and sea levels were tens of meters higher. Today’s acceleration, however, was unparalleled. As reported by the NOAA Global Monitoring Laboratory, CO2 growth rate during the past 60 years is 100–200 times quicker than natural build-up to the end of the previous ice age 100–200 times quicker than the rate of rise to the end of the previous ice age.
The Keeling Curve, once the noble graph soon to be named after Charles David Keeling, has been the world’s definitive record of atmospheric CO2 since 1958. Keeling’s exceedingly precise measurements, initially on Mauna Loa and later at a sequence of global stations, recorded not only the biosphere’s annual “breathing” CO2 building up in May and falling as vegetation takes it up during the growing season but also the inexorable annual rise tied to the combustion of fossil fuels. As Global Carbon Project chair Rob Jackson summed up, “These measurements have revolutionized our thinking about how the Earth functions” These measurements have revolutionized our thinking regarding how the Earth works.
CO2 concentrations are now more than 50% higher than they were before industrial times CO2 concentrations in the atmosphere are now more than 50% higher than they were before the industrial age started. This increase is mainly caused by the combustion of fossil fuels, which puts carbon that has been stored deep in the earth for millions of years into the atmosphere within a few hundred. Natural “sinks,” or plants and oceans, only absorb half of these emissions, leaving the other half to add to the greenhouse effect. Therefore, carbon dioxide is to blame for an incredible 80% of the total global warming impact of all of the greenhouse gases emitted by humans since 1990 carbon dioxide alone is to blame for approximately 80 percent of the total global warming impact. Its effects are already noticeable.
Increased CO2 is a global heat blanket that traps heat near and raises the temperatures globally. Its effects are more than to warm the air and thaw ice. Oceans, which have taken up about a third of all CO2 emitted by human activity, are themselves undergoing a once-in-a-lifetime chemical transformation. The process, ocean acidification, is lowering seawater pH at a pace about ten times quicker than throughout any interval within the last 55 million years a rate of change about 10 times quicker than throughout any interval within the last 55 million years. Surface water pH has already fallen from 8.21 to 8.10 since the Industrial Revolution, a 26% boost in acidity. Ocean acidification interfere with the process of sea creatures corals, shellfish, and certain plankton to form their calcium carbonate shells and skeletons.
As carbonate levels decline, these animals are fighting for survival, collapsing food webs and industries along with it. The United States shellfish industry alone stands to lose more than $400 million per year by 2100 if trends continue. The country’s shellfish industry will lose more than US $400 million a year by 2100 because of ocean acidification. Coral reefs, essential for protecting coasts and supporting tourism, will decline as acidification hinders their recovery from bleaching and storms. The accuracy and stability of the Keeling Curve have led it to become a foundation of climate science.
The 11,141-foot-high Mauna Loa Observatory was selected since it is remote from local vegetation and pollution and positioned to take a global sample of atmospheric conditions. Even natural disasters have not interrupted the record: following the 2022 Mauna Loa eruption filled roads to reach the observatory, scientists re-started measurements on nearby Maunakea promptly, proving resilience for the program Scripps and NOAA resumed measurements on nearby Maunakea. Paleoclimate science is in clear perspective.
The Eocene, when CO2 was this high before, had Earth’s climate not only warmer but different in character. The conversion of a “greenhouse” to an “icehouse” Earth by glaciation of Antarctica was achieved by a reduction of atmospheric CO2 only simulations assuming a reduction of atmospheric CO2 could reproduce a cooling consistent with the temperature record. Past research indicates that Earth’s climate is more sensitive to change in CO2 when the planet is already warm, and this increases the dangers of further emissions the climate is warmer when it is sensitive to change, as during the Eocene. The difference now is the rate of change.
While previous fluctuations in CO2 and temperature occurred over thousands or millions of years, this specific peak is occurring within the span of a single human lifetime. The Intergovernmental Panel on Climate Change has calculated that, without conditions, air-borne CO2 would rise to 500 ppm in 30 years a figure not achieved since the Oligocene, when ice shelves had blanketed Antarctica’s sea and forest and sea levels were radically higher CO2 levels in order to achieve 500 ppm in 30 years. As Ralph Keeling also pointed out, “They’re telling you about your whole system health with a single-point measurement. We’re getting a holistic measurement of the atmosphere from really a kind of simple set of measurements.” The Keeling Curve is also a smoldering reminder: the increasing CO2 of the atmosphere is a number but a sign of expansive and expanding global change.
