Overview

• The Mauna Loa Observatory logged a May 2025 monthly average of 430.2 ppm, up 3.5 ppm from May 2024’s reading of 426.7 ppm.
• NOAA’s Global Monitoring Laboratory reported a parallel May average of 430.5 ppm, marking the highest seasonal peak in its data series.
• Today’s CO₂ concentrations stand more than 50% above preindustrial levels, reflecting continued growth driven by fossil fuel combustion.
• Scientists warn that current atmospheric CO₂ is at a level not seen in tens of millions of years, far outside Earth’s recent climate history.
• Long‐running measurements by Scripps and NOAA at Mauna Loa, supported by a worldwide monitoring network, remain the benchmark for tracking global greenhouse gas trends.