People didn't cause the climate change that occurred thousands or millions of years ago, so it must have happened for other natural reasons.Įxplore the list below to learn about some natural factors that have changed the Earth's climate in the past. Our species (Homo sapiens) is the only one that is present on all continents. Source: EPA's Climate Change Indicators (2016) and Petit et al. Notice the strong connection between carbon dioxide and temperature. They do not include the most recent increases in carbon dioxide and temperature caused by humans. These graphs are based on the Vostok ice core from Antarctica. Can you see this pattern in the graph below? Over at least the last 650,000 years, temperatures and carbon dioxide levels in the atmosphere have increased and decreased in a cyclical pattern. There have been times when most of the planet was covered in ice, and there have also been much warmer periods. Geologists have calculated that it takes on the average several thousand years to erode one foot. These clues tell us that the Earth's climate has changed many times before. Glaciers will break away rocks and carry them along.

But we know a lot about what the Earth's climate was like way back then because of clues that remain in rocks, ice, trees, corals, and fossils. The Earth was formed about 4.5 billion years ago-that's a very long time ago! It's hard to say exactly what the Earth's daily weather was like in any particular place on any particular day thousands or millions of years ago. Source: EPA's Climate Change Indicators (2016). Along with other greenhouse gases, this extra carbon dioxide is trapping heat and causing the climate to change. Today, it's up to nearly 400 parts per million, and the amount is still rising. For hundreds of thousands of years, the concentration of carbon dioxide in the atmosphere stayed between 200 and 300 parts per million.

Greenhouse gases are at record levels in the atmosphere.

People are also adding other heat–trapping greenhouse gases, such as methane and nitrous oxide, to the atmosphere. By burning lots of fossil fuels like coal, oil, and natural gas, people are overloading the atmosphere with carbon dioxide and adding to the greenhouse effect.

People's activities are the main cause.

None of the natural causes of climate change, including variations in the sun's energy and the Earth's orbit, can fully explain the climate changes we are seeing today.

Today's climate change is different from past climate change in several important ways:

Earth thousands of years later