Seriously!! ;) The systematic monitoring of carbon dioxide levels in the Earth's atmosphere began in the 1950s. The Mauna Loa Observatory in Hawaii, established

Seriously!! ;) The systematic monitoring of carbon dioxide levels in the Earth's atmosphere began in the 1950s. The Mauna Loa Observatory in Hawaii, established in 1958, has been continuously monitoring atmospheric carbon dioxide levels. So anything before that, I'd take with a grain of salt and maybe extra some cayenne pepper.