Atmospheric CO₂ passes 425 ppm

Carbon dioxide is the single most important driver of human-caused climate change, and its atmospheric concentration is the most closely watched number in earth science. In 2024 the global annual mean reached a record 422.8 ppm (NOAA), while the benchmark Mauna Loa record recorded an annual mean of 424.6 ppm.

A record that keeps accelerating

The level is now roughly 52% higher than the pre-industrial baseline of about 280 ppm. The rate of increase is itself climbing: 2024 saw a one-year jump of about 3.75 ppm at Mauna Loa, the largest annual rise in the record, lifted by a strong El Nino and extensive wildfire emissions.

In May 2025 the monthly mean at Mauna Loa peaked above 430 ppm for the first time in human history, a level the planet has not experienced in several million years.

Why the number matters

CO₂ is long-lived, so concentrations reflect the cumulative total of past emissions, not just the current year. Fossil-fuel CO₂ emissions hit a record 38.1 billion tonnes in 2025, which is why the atmospheric burden continues to grow even as clean energy expands.

• Pre-industrial: ~280 ppm
• 2024 global mean: 422.8 ppm
• First monthly reading above 430 ppm: May 2025

Stabilising the concentration — and eventually the climate — requires global emissions to fall to net zero. Until then, each year adds another few parts per million to the total.