Finding CO2 levels that are 2,500 times higher in 5,000-year-old fulgurites than in modern samples, scientists have speculated that the extra CO2 resulted from vaporization of organic material by lightning. Could some of this gas reflect elevated atmospheric CO2? And if so, could current laments regarding “unprecedented levels” of CO2 be insupportable?

John M. Corboy
Mililani, Hawaii

Other archives of preindustrial carbon dioxide, such as ice cores and corals, don’t indicate that concentrations of the greenhouse gas were abnormally high 5,000 years ago .—S. Perkins