Overview

• Mauna Loa Observatory measured an average of 430.2 ppm in May 2025, marking a year-over-year rise of 3.5 ppm.
• NOAA’s Global Monitoring Laboratory reported a parallel surge to 430.5 ppm in its independent readings.
• Scientists attribute the continued increase to fossil fuel combustion trapping heat in the atmosphere.
• Current CO2 concentrations now exceed any in human history and likely mirror levels from millions of years ago.
• Elevated greenhouse gas levels are linked to more intense extreme weather events and ongoing ocean acidification.