Safe Upper Atmospheric CO2 Concentration for Human Health

Establish upper limits for atmospheric carbon dioxide concentrations that can be considered safe for human health.

Background

Beyond radiative forcing, the article emphasizes CO2’s biochemical activity, including effects on ocean acidity and aerobic respiration, and surveys emerging evidence of adverse human health and cognitive outcomes at modestly elevated concentrations. Despite these concerns, the authors state that current knowledge does not allow reliable specification of a health-protective upper bound for atmospheric CO2.

The conclusion suggests such a limit, if it exists, may be near pre-industrial concentrations given human evolutionary history, while noting that present levels exceed 420 ppm—higher than any previously experienced by humans—underscoring the urgency of defining health-based thresholds.