Long Term Changes in Climate

Chapter 14 Section 3

Essential Questions Ch14 S3

1. What principle do scientists follow in studying ancient climates?

2. What changes occur on Earth’s surface during an ice age?

3. What factors can cause climate change?

Studying Climate Change

In studying ancient climates, scientists follow an important principle: If plants or animals today need certain conditions to live, then similar plants and animals in the past also required those conditions.

Scientists study ancient climates to find out how climates have changed during the history of Earth. Changes in climate may have affected many regions around the world.

When scientists study ancient climates, they assume that the ancestors of today’s plants needed the same conditions to live. For example, if a palm tree needs a hot and rainy climate to live today, scientists assume that palm trees long ago also needed hot and rainy climates.

One source of information about ancient climates is pollen. Pollen is made by plants. Scientists find pollen in plant material at the bottoms of some lakes.

Another source of information about ancient climates is tree rings. A tree ring forms every year a tree grows. The size of the ring depends on how much the tree grows.

Ice Age

During each ice age, huge sheets of ice called glaciers covered large parts of Earth’s surface.

Ice Age

An ice age is a period in Earth’s history when glaciers covered large parts of Earth. Over millions of years, warm periods have alternated with ice ages.

Scientists think we are now in a warm period between ice ages.

Ice ages can last 100,000 years or more. The last ice age ended about 10,500 years ago. When that ice age ended, the ice melted and the Great Lakes formed

Causes of Climate Change

Possible explanations for major climate changes include variations in the position of Earth relative to the sun, changes in the sun’s energy output, major volcanic eruptions, and the movement of continents.

Over thousands of years, Earth’s orbit around the sun shifts a little. The tilt of Earth’s axis also changes slightly. The combined effects of these changes may be the main cause of ice ages.

Sunspots are dark, cooler regions on the surface of the sun. When there are many sunspots, Earth’s temperature may increase.

When volcanoes erupt, they release gases and ashes into the atmosphere. These materials can block sunlight. As a result, huge volcanic eruptions may lower Earth’s temperatures.

About 225 million years ago, there was a single continent on Earth called Pangaea (pan JEE uh). Pangaea broke apart, and the continents have been moving ever since. As the continents have moved, climates have changed

Essential Questions Ch14 S31. What principle do scientists follow in

studying ancient climates?It a condition is needed to survive now

similar conditions were needed long ago.

2. What changes occur on Earth’s surface during an ice age?

The surface is covered in ice.3. What factors can cause climate

change?Variation in the Earth’s position,

change in the sun’s energy output, major volcanic eruptions, & movement of the continents