The Levels of Carbon Dioxide in the Atmosphere

Question 21
Multiple Choice

The levels of carbon dioxide in the atmosphere A) peaked around 1950 and have begun slowly decreasing since then. B) are high but not higher than the highest estimated levels in the last 420,000 years. C) are estimated to be higher than at any time in the past 420,000 years. D) began decreasing when the burning of fossil fuels increased.