Since the outset of the Industrial Revolution in the late 1700s, the portion of Earth’s atmosphere that is comprised of carbon dioxide has increased from 0.028% to 0.042%, or by about 51%. This is measurable before the era of modern science because perennial snow accumulations in permafrost regions trap air bubbles that leave records of past airborne CO2 concentrations, and these local records are globally representative because regional CO2 concentrations vary by less than 10 parts per million over the Earth.