By Doyle Rice, USA TODAY
Increasing amounts of carbon dioxide and other gases caused by the burning of the oil, gas and coal that power our world are enhancing the natural "greenhouse effect," causing the planet to warm to levels that climate scientists say can't be linked to natural forces.
Carbon dioxide levels were around 280 ppm prior to the Industrial Revolution, when we first began releasing large amounts into the atmosphere by the burning of fossil fuels.
For the past 800,000 years, CO2 levels never exceeded 300 parts per million, according to Scripps, which measures CO2 levels along with several other agencies, including NOAA. Records of past levels of CO2 are found in samples of old air preserved as bubbles in the Antarctic ice sheet, Scripps reports.
"The 400-ppm threshold is a sobering milestone, and should serve as a wake up call for all of us to support clean energy technology and reduce emissions of greenhouse gases, before it's too late for our children and grandchildren," said Tim Lueker, a Scripps oceanographer.