Greenhouse Effect

In this lesson, students focus on greenhouse gasses in Earth’s atmosphere, which trap energy from the sun and keep the planet at a livable 14 degrees Celsius. But scientists believe a dramatic increase in the amount of greenhouse gasses in the atmosphere, mostly caused by human activity, is related to global warming and climate change.

• The trace gasses in Earth’s atmosphere have a major impact on warming Earth even though they make up such a small percentage of the atmosphere.
• Greenhouse gasses, including carbon dioxide, methane, and water vapor, trap thermal energy in a similar way to how the glass walls and ceilings of a greenhouse trap sunlight, keeping the heated air inside.
• The greenhouse gasses is what makes the Earth a livable 14 degrees Celsius (57 degrees Fahrenheit). Without greenhouse gasses, scientists estimate that Earth’s surface would be too cold for life at about -19 degrees Celsius (-2 degrees Fahrenheit).
• There are many factors that cause the amount of greenhouse gasses in the atmosphere to change.
• Scientists believe that human activities are causing Earth’s climate to change.
• Scientists don’t know exactly why Earth has experienced global warming in the last hundred years, with its temperature increasing by 0.6 degrees Celsius (1 degree Fahrenheit), but many believe that the increasing amounts of carbon dioxide and other greenhouse gasses in the atmosphere are responsible.

• Why are greenhouse gasses called that?
• Why aren’t oxygen and nitrogen aren’t greenhouse gasses, even though the atmosphere is made up mostly of those two gasses?
• What would happen to Earth’s climate if there were no greenhouse gasses?
• How can a volcanic eruption cause Earth’s climate to change?
• How are forest fires connected to the carbon cycle?
• Why do scientists think human activities are responsible for global warming?
• Why do many scientists consider carbon dioxide to be an urgent greenhouse gas to focus on, even though it is not the only one?
• What are some human activities that release carbon dioxide into the atmosphere?
• What factors can influence how much different regions/countries emit greenhouse gasses?
• Why, given that different countries emit different amounts of greenhouse gasses, is global warming considered a global problem?

Misconception: Global warming and the greenhouse effect are the same.

Fact: The greenhouse effect is essential for life on Earth because it keeps the planet at a habitable temperature. Most scientists believe that the current global warming is caused by a dramatic increase in the number of greenhouse gasses in the atmosphere, which upsets the natural balance of the carbon cycle.

Carbon cycle : the circulation and transformation of carbon back and forth between living things and the environment

Climate change : a significant change in the average weather in a location over 30 years or more, including changes in temperature, precipitation, or wind patterns

Greenhouse gas : molecules in the atmosphere that absorb thermal energy from the sun and warm Earth’s surface and atmosphere; include carbon dioxide, water vapor, and methane

Studying Earth’s Atmosphere

Scientists have turned an airplane into a moving laboratory. This plane has 20 scientific instruments, and it will spend the summer of 2016 flying around the world. Its mission is to take samples of Earth’s atmosphere. It will start in California and then fly to the equator and back.

After that, it will fly to the North Pole, then to the tropics, the Southern Ocean around Antarctica, and across to the southern tip of South America before flying north toward Greenland. After Greenland, it will cross North America on its way back to California.

The goal of this study is to learn more about Earth’s atmosphere. Most of Earth’s atmosphere is made up of just two gasses: nitrogen (78 percent) and oxygen (21 percent). A third gas, argon, makes up about 1 percent of the atmosphere. Carbon dioxide (CO2), water vapor (H2O), and methane (CH4) are also found in the atmosphere, but in such small quantities they are called trace gasses.

Scientists are interested in Earth’s atmosphere because it plays a major role in regulating Earth’s climate. This is because the trace gasses have a major impact on warming Earth even though they make up such a small percentage of the atmosphere. They act in a similar way to the glass walls of a greenhouse, trapping thermal energy from the sun. For this reason, carbon dioxide, water vapor, and methane are called greenhouse gasses.

Earth’s Atmosphere Traps Heat

The trapped energy from the greenhouse gasses is essential for life. Greenhouse gasses make Earth a livable 14 degrees Celsius (57 degrees Fahrenheit). Without greenhouse gasses, scientists estimate that Earth’s surface would be too cold for life at -19 degrees Celsius (-2 degrees Fahrenheit).

When the sun transfers energy to Earth, it is in a form called visible light. After Earth’s surface absorbs some of the sun’s energy, it re-emits that energy, but not as visible light because the Earth is much cooler than the sun.

Instead, the energy is released as a different form of light energy called infrared radiation. We can’t see it, but we feel it as heat. Greenhouse gasses in the atmosphere absorb this outgoing infrared radiation because they are bonded loosely together. This loose bonding causes them to vibrate when they absorb energy.

Greenhouses trap energy from the sun in the same way that greenhouse gasses in Earth’s atmosphere trap energy that warms the planet. In contrast, nitrogen and oxygen molecules are so tightly bonded together that they cannot vibrate, which is why they do not absorb energy or contribute to the greenhouse effect.

Scientists involved in the flying laboratory want to study Earth’s atmosphere to get a better understanding of how greenhouse gasses enter into the atmosphere, how they change the atmosphere, and in the end, how they are removed from the atmosphere. This is important for researchers who want to understand Earth’s climate today and in the future.

This is particularly important because scientists believe that human activities have caused Earth’s climate to change. Scientists know that Earth has experienced global warming in the last hundred years, with its temperature increasing by 0.6 degrees Celsius (1 degree Fahrenheit). They don’t know exactly why, but many believe that the increasing amounts of carbon dioxide and other greenhouse gasses in the atmosphere are responsible.

There are many factors that cause the amount of greenhouse gasses in the atmosphere to change. For example, water in clouds holds in some of the heat from Earth's surface because water vapor is the most common greenhouse gas, accounting for more than half of all greenhouse gasses. But the bright white tops of clouds also reflect some of the sunlight back to space, helping to cool Earth's surface. Scientists are still trying to figure out how much clouds affect the warming or cooling of Earth's clouds surface. Sudden events, such as a volcanic eruption or a forest fire, can also impact the climate. Volcanic eruptions send ash particles into the environment, blocking sunlight from reaching Earth’s surface. This contributes to Earth’s cooling. However, volcanoes also release carbon dioxide, which over millions of years causes warming.

Forest fires release carbon dioxide into the atmosphere. But if a forest re-grows after the fire, the trees and other plants will remove about the same amount of carbon dioxide that was released into the environment during the burning.

In this lesson students develop a model to investigate the phenomenon of the greenhouse effect and then analyze data to evaluate the claim that human activities are major factors in the current rise in Earth’s surface temperatures. In the first section, students compare an open system and a closed system to figure out the phenomenon of the effects of greenhouse gasses on Earth’s temperature. In the second section, students figure out the relationship between the concentration of greenhouse gasses in different locations in the atmosphere and human activities over the past century, along with global population increases.