CARBON THROUGH THE SEASONS 1 TIME:Introduction: 60–90 minutes LEARNING OBJECTIVES: Students will: Learn about the carbon cycle Understand how seasonal variations affect global atmospheric CO2 concentrations Understand how CO2concentrations in the atmosphere are changing overall in recent decades NATIONAL SCIENCE STANDARDS: Content Standard A: Science as inquiry Content Standard D: Earth and space science Content Standard E: Science and technology ADAPTED FROM:National Oceanic and Atmospheric Administration (NOAA): ducation/poet/CO2-Seasons.pdf. DESCRIPTION In this lesson plan, students learn about the carbon cycle and understand how concentrations of carbon dioxide (CO2) in the Earth’s atmosphere vary as the seasons change. Students also learn that even with these seasonal variations, the overall amount of CO2is increasing in the atmosphere as a result of people’s activities, which are changing the natural carbon cycle. BACKGROUND Carbon is a chemical element that is found all over the world and in every living thing. Oxygen is another element that’s found in the air we breathe. When carbon and oxygen bond together, they form a colorless, odorless gas called CO2. In the Earth’s atmosphere, CO2is a greenhouse gas, which means it traps heat. This “greenhouse effect” naturally helps to keep the Earth’s temperature at a level that can support life on the planet. The atmosphere isn't the only part of the Earth that has carbon. The oceans store large amounts of carbon, and so do plants, soil, and deposits of coal, oil, and natural gas deep underground. Carbon constantly moves from one part of the Earth to another through a natural repeating pattern called the carbon cycle. The carbon cycle helps to maintain a balanced level of CO2 in the Earth’s atmosphere. But right now, people are changing this natural balance by adding more CO2to the atmosphere whenever we burn fossil fuels (such as coal, oil, and natural gas)—whether it's to drive our cars, use electricity, or make products. This extra CO2is being added to the atmosphere faster than natural processes can remove it, causing the atmosphere to trap more heat and causing the Earth’s average temperature to rise. Scientists have found that the recent levels of CO2in the atmosphere are abnormally high compared with the long-term historical trend, and these levels are continuing to increase at an unprecedented rate. The amount of CO2 found in the atmosphere varies over the course of a year. Much of this variation happens because of the role of plants in the carbon cycle. Plants use CO2from the atmosphere, along with sunlight and water, to make food and other substances that they need to grow. They release oxygen into the air as a byproduct. This process is called photosynthesis. Another process that is part of the carbon cycle is respiration, by which plants and animals take up oxygen and release CO2back into the atmosphere.