Excerpts from Books and Wikipedia
"At the dawn of the Industrial Revolution 250 years ago, CO2 levels in the atmosphere were approximately 280 parts per million (ppm). Since then, humankind has been pouring billions of tons of extra greenhouse gases into the atmosphere, causing more and more heat to be trapped. The main human-caused greenhouse gas is CO2, and the rate of growth of human-caused CO2 emissions has been accelerating. Emissions today are six times higher than they were in 1950. Moreover, CO2 levels now exceed 400 parts per million. As a result, the Earth has warmed 1.5°F (0.85°C) since 1900. Most of this warming, approximately 1°F, has occurred only since 1970." [Romm, p. 2] World population was less than 1 billion at the beginning of the Industrial Revolution in the 1750s. It now approaches 8 billion. "In 1970, CO2 levels were around 325 ppm, which means that most of the rise in CO2 from preindustrial levels has occurred in the last five decades, matching a time of rapid growth in industrial energy use and CO2 emissions." [Romm, p. 9-10]