Atmospheric Carbon Dioxide
From ice cores to real-time monitoring: tracking the relentless rise of atmospheric CO₂ from 280 ppm in 1750 to over 420 ppm today.
420 ppm
Atmospheric CO₂ concentration at Mauna Loa, December 2024. Pre-industrial level: 280 ppm.
+2.4 ppm/yr
Average annual increase over the last decade. Rate is accelerating: it was ~0.9 ppm/yr in the 1960s.
+50%
Human activities have increased atmospheric CO₂ by 50% since the Industrial Revolution began.
800,000+ Years
Current CO₂ levels exceed anything in the ice core record. Last time CO₂ was this high: the Pliocene, ~3 million years ago.
Atmospheric CO₂ at Mauna Loa: 1958–2024
The Keeling Curve is the longest continuous record of atmospheric CO₂. Started by Charles David Keeling in 1958, it shows both the seasonal "breathing" of the biosphere and the relentless upward trend driven by fossil fuel combustion. The sawtooth pattern reflects Northern Hemisphere vegetation: CO₂ falls during spring/summer growing season and rises during fall/winter decay.
Where Does the CO₂ Come From?
Fossil Fuels & Industry — 89%
Coal (39%), oil (33%), and natural gas (22%) combustion for electricity, transportation, and industrial processes. Cement production adds ~4%. Total: 36.8 billion tonnes CO₂ in 2023.
Land-Use Change — 11%
Deforestation (primarily tropical), agricultural expansion, and peatland drainage. Tropical forests alone account for ~8% of global emissions when cleared or burned.
About 45% of emitted CO₂ remains in the atmosphere. The rest is absorbed by carbon sinks: oceans (~25%) and land biosphere (~30%). However, sink efficiency may be declining as temperatures rise.
800,000 Years of CO₂ History
For 800,000 years, CO₂ oscillated between 180 ppm (glacial periods) and 280 ppm (interglacials) in a natural rhythm driven by Earth's orbital cycles. Never in this record did CO₂ exceed 300 ppm — until the 20th century.
In just 275 years (1750–2025), CO₂ has risen from 280 to 420 ppm — a 50% increase. The rate of increase is unprecedented: the current rise is ~100× faster than the natural increases that ended the last ice age.
Under current policies, CO₂ is projected to reach 500–550 ppm by 2100. Under a business-as-usual scenario, it could exceed 900 ppm — levels not seen since the Eocene, 50 million years ago, when the planet was ice-free.