These clues tell us that the Earth’s climate has changed many times before. There have been times when most of the planet was covered in ice, and there have also been much warmer periods. Over at least the last 650,000 years, temperatures and carbon dioxide levels in the atmosphere have increased and decreased in a cyclical pattern. Can you see this pattern in the graph below?
These two graphs show how the amount of carbon dioxide and the Earth’s temperature have changed over the last 650,000 years. Both graphs show a similar up-and-down pattern.
These graphs are based on the Vostok ice core from Antarctica. They do not include the most recent increases in carbon dioxide and temperature caused by humans. Notice the strong connection between carbon dioxide and temperature. Source: EPA’s Climate Change Indicators (2016) and Petit et al. (2001).
People didn’t cause the climate change that occurred thousands or millions of years ago, so it must have happened for other natural reasons.
https://www3.epa.gov/climatechange/kids/basics/past.html
BTTT!