Greenhouse Gases and the Greenhouse Effect
The greenhouse effect happens when certain gases—known as greenhouse gases—collect in
Earth’s atmosphere. These gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), fluorinated
gases, and ozone.
Greenhouse gases let the sun’s light shine onto the Earth’s surface, but they trap the heat that reflects back up
into the atmosphere. In this way, they act like the glass walls of a greenhouse. This greenhouse effect keeps the
Earth warm enough to sustain life. Scientists say that without the greenhouse effect, the average temperature of
the Earth would drop from 14˚C (57˚F) to as low as –18˚C (–0.4˚F).
Some greenhouse gases come from natural sources. Evaporation adds water vapor to the atmosphere. Animals
and plants release carbon dioxide when they respire, or breathe. Methane is released naturally from some lowoxygen environments, such as swamps. Nitrous oxide is produced by certain processes in soil and
water. Volcanoes—both on land and under the ocean—release greenhouse gases, so periods of high volcanic
activity tend to be warmer.
Since the Industrial Revolution of the late 1700s and early 1800s, people have been releasing large quantities of
greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas
emissions increased 70 percent between 1970 and 2004. Emissions of CO2, the most important greenhouse gas,
rose by about 80 percent during that time. The amount of CO2 in the atmosphere today far exceeds the natural
range seen over the last 650,000 years.
Most of the CO2 that people put into the atmosphere comes from burning fossil fuels. Cars, trucks, trains, and
planes all burn fossil fuels. Many electric power plants do, as well. Another way humans release CO2 into the
atmosphere is by cutting down forests, because trees contain large amounts of carbon.
People add methane to the atmosphere through livestock farming, landfills, and fossil fuel production such
as coalmining and natural gas processing. Nitrous oxide comes from agriculture and fossil fuel burning.
Fluorinated gases include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs),
and hydrofluorocarbons (HFCs). These gases are used in aerosol cans and refrigeration.
All of these human activities add greenhouse gases to the atmosphere. As the level of these gases rises, so does
the temperature of the Earth. The rise in Earth’s average temperature contributed to by human activity is known
as global warming.
The Greenhouse Effect and Climate Change
Even slight increases in average global temperatures can have huge effects. Perhaps the biggest, most obvious
effect is that glaciers and ice caps melt faster than usual. The meltwater drains into the oceans, causing sea
levels to rise.
Glaciers and ice caps cover about 10 percent of the world’s landmasses. They hold about 75 percent of the
world’s freshwater. If all of this ice melted, sea levels would rise by about 70 meters (230 feet). The
Intergovernmental Panel on Climate Change states that the global sea level rose about 1.8 millimeters per year
from 1961 to 1993, and 3.1 millimeters per year since 1993.
Rising sea levels could flood coastal cities, displacing millions of people in low-lying areas such as Bangladesh,
the U.S. state of Florida, and the Netherlands. Millions more people in countries like Bolivia, Peru, and India
depend on glacial meltwater for drinking, irrigation, and hydroelectric power. Rapid loss of these glaciers would
devastate those countries.
Greenhouse gas emissions affect more than just temperature. Another effect involves changes in precipitation,
such as rain and snow. Over the course of the 20th century, precipitation increased in eastern parts of North and
South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa,
the Mediterranean, and southern Asia.
As climates change, so do the habitats for living things. Animals that are adapted to a certain climate may
become threatened. Many human societies depend on specific crops for food, clothing, and trade. If the climate
of an area changes, the people who live there may no longer be able to grow the crops they depend on for
survival. Some scientists also worry that tropical diseases will expand their ranges into more temperate regions
if the temperatures of those areas increase.
Most climate scientists agree that we must reduce the amount of greenhouse gases released into the atmosphere.
There are lots of ways to do this, including:
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Drive less. Use public transportation, carpool, walk, or ride a bike.
Fly less. Airplanes produce huge amounts of greenhouse gas emissions.
Reduce, reuse, and recycle.
Plant a tree. Trees absorb carbon dioxide, keeping it out of the atmosphere.
Use less electricity.
Eat less meat. Cows are one of the biggest methane producers.
Support alternative energy sources that don’t burn fossil fuels.
Greenhouse Gases and the Greenhouse Effect Questions
Directions: After reading the article, answer the following questions CSRQ.
1. What are the greenhouse gases? Circle the gases that are a part of the carbon cycle.
2. Describe 3 natural sources of greenhouse gases.
3. Describe 3 manmade sources of greenhouse gases.
4. How has the amount of greenhouse gases in the atmosphere changed in the past? In your answer, refer
to the statistics provided in the text.
5. The article mentions a type of chemical called chlorofluorocarbons (CFCs). Describe 2 negative
impacts that CFCs have on our environment.
6. Why do scientists think that greenhouse gases are connected to global warming? Be specific in your
explanation and refer back to the text for support.
7. When you think of global climate change, you probably think of ice melting and sea levels rising;
however, global climate change can have a much larger impact than you think. Choose one impact that
global climate change could have on Earth. In the space below, draw and color a picture showing this
impact. (NO polar bears floating on ice! Pick something else!)