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Earth's Changing Climate All over the Earth-from the Arctic to
Africa's highest peak, Mt. Kilimanjaroice is melting. Earth's surface temperature is about l.O°F (0.6°C) warmer today than it was 100 years ago. In fact, 2005 was the warmest year on record.
Scientists say that the world will continue to heat up in the coming century. Already Earth's climate is changing. Sea ice and glaciers are melting, and sea levels are rising. Patterns of rainfall are changing as well. Climate models predict that extreme weather may become more common. Hurricanes may become more intense, and drought and fires more frequent. Ultimately, the changing climate will impact where people live, where they get their water, and how they grow food.
Why is Earth's climate changing now? What factors affect climate? These are important questions-ones that many scientists are trying to answer.
Climate in the Past One key to understanding climate change is to look to the past. Earth's climate has changed many
The World
Environmental Case Study
times. Paleoclimatologists are scientists who study past climates. They drill into glaciers, slice through layers of sediment at the bottom of lakes, measure tree rings, and study ancient weather records to find clues about past climates. They hope to understand the factors that cause climate to change.
Sun and Earth The most important factor impacting climate is the sun, which provides nearly all of the energy for Earth's climate. Any change in the brightness of the sun can affect climate.
Some scientists believe sunspots may affect climate. Sunspots are giant magnetic storms on the surface of the sun. They appear as darker, or cooler, areas on the sun's surface. Changes in sunspots occurred during a cold snap known as the Little Ice Age (early 1500s to mid-1800s).
The wobble of Earth also impacts climate. As Earth orbits the sun, it wobbles a bit, like a top. Sometimes the wobble brings Earth closer to the sun, and sometimes it takes Earth farther away. Earth's
Global Temperature Change OF °C
33.4 0.8.-----------------------------.....,
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g 32.7 0.41------------------ -t--- -----.___.rIIl-- II&---d--''-I--A-f-----tf----l c ~ 32.4 0.2 1----,,.-----,.------II---::-- -----.r-----Ic-----...-- ----.--flk-ft-.....-____ Wl-#-----1...-.~ ______ ---''-----------I .. ~ ~ 32.0 0 .. [31.6 _0.2 1-V-- ---+-lIF----IIf----------"------tr--------------------I E ~ 31.3 -0.41----------------------------------1
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Source: NASA
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wobble helps explain changes in climate that occur over thousands of years or more, such as the beginning of ice ages.
Volcanoes can also influence climate. Throughout Earth's history, violent volcanic eruptions have spewed ash and gases into the air. These particles create a haze that blocks sunlight. Violent eruptions sometimes cause the weather to cool for months or years. When Mt. Pinatubo erupted in the Philippines in the early 1990s, the world's climate was cooler for two years after the massive blast.
Living in a Greenhouse Another factor affecting climate is the makeup of the atmosphere-the layer of air that blankets Earth. Every day, light rays from the sun pass through the atmosphere and warm Earth. Some of that heat is reflected back into space. Certain gases in the atmosphere, however, trap the heat from the sun. These heat-trapping gases are called greenhouse gases. They include carbon dioxide, methane, and water vapor.
The capacity of these gases to trap heat is called the greenhouse effect. To picture the greenhouse effect, think of a car parked in the sun on a hot day. Sunlight shines through the glass windows of the car and warms the air trapped inside.
The natural greenhouse effect has an important impact on climate. Without the greenhouse effect, Earth's average temperature would be a chilly O°F (-18°C).
Climate Ch~nge Today During Earth's history, the amount of greenhouse gases has varied. When greenhouse gas levels have been high, temperatures have been warmer.
Most scientists say the climate is changing today because greenhouse gases are trapping too much heat. The main culprit is carbon dioxide. When people drive cars or burn fossil fuels (like coal, natural gas, and oil), carbon dioxide is released into the air. For the past 140 years, the amount of carbon dioxide in the air has increased. Earth's temperature has crept up along with it. '
Nearly all scientists say the ,greenhouse effect is behind global warming. Some scientists believe other factors may be involved too, such as a change in the sun's heat output.
As vehicles and factories release more greenhouse gases into the air in the corning years, Earth will continue to get warmer. In the meantime, scientists continue to study the problem, trying to predict the future for Earth's climate.
1. Astrologers kept records of sunspots beginning around 467 or 466 B.C.
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In China, astrologers who failed to keep good records were sometimes put to death.
2. The greenhouse effect keeps the planet Venus a toasty 887°F (47S0C).
3. Trees remove carbon dioxide from the air. One way to reduce global warming is to plant more trees.
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Extreme weather, droughts, famine, a swiftly changing climatethis is what happened from the early 1500s to the rrtid-1800s during an era known as the Little Ice Age. During these years, temperatures dipped sharply in Europe and America. In Europe, winters were 1.8° to 2.7°F (1 ° to 1.5°C) colder than normal.
The icy temperatures caused widespread famine, because crops could not grow in the colder temperatures. At one point in Bohemia (where the Czech Republic is today), up to half the population starved.
As temperatures fell, northern glaciers moved southward. The Atlantic Ocean was so filled with ice that boats had great difficulty reaching Greenland. These glaciers drove Norse settlers from Greenland.
Some scientists believe low solar activity caused the cold snap. Over a 30-year period during the Little Ice Age, astronomers observed only 50 sunspots, compared with 40,000 to 50,000 that normally would occur.
Review the Facts Directions: Read the information about climate change and examine the graph. Then answer the following questions.
1. Specifying By about how much has Earth's temperature risen in the last 100 years?
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2. Identifying What do paleoclimatologists examine for clues about Earth's past climate?
3. Explaining How do volcanoes affect climate?
4. Explaining How do greenhouse gases keep Earth warm?
5. Determining Cause and Effect Why do scientists say humans are changing the climate?
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Create a Greenhouse in a Jar
'" For Investigation • two identical glass jars,
Simulate the greenhouse effect by creating a greenhouse using a glass jar. Rays of sunlight pass easily through the glass walls of the jar. Inside the jar, the light energy changes into heat. Heat rays have a different shape than light rays and cannot pass through the glass. The heat gets trapped inside the jar.
one with a lid • two small thermometers • sunshine or sunlamp • clock or watch • paper • pencil
What to Do
1. Lay two jars on their sides in a sunny spot or under a sunlamp. Place the jars so that the top of each jar faces away from the sun.
2. Place a thermometer in each jar. Be sure the bulbs of the thermometers are not resting in a shadow.
3. Put the lid on one jar. Leave the other jar open.
4. Record the starting temperature inside the jars. Without touching the jars, record the temperature inside each jar once every minute
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for 10 minutes. Describe your results. Explain what happened in your experiment.
Assessment Checklist Assess your experiment using the checklist below:
D Followed directions
D Recorded initial temperature
D Recorded subsequent temperatures
D Explained lab results in complete sentences
D Wrote a thoughtful explanation
D Cleaned up work area
