These students in Shishmaref, Alaska live on frozen ground. But frozen ground matters to people all over the world, even if the ground is not frozen where they live. —Credit: Angela Alston

Introduction

People may not think much about frozen ground, but they notice what can happen when the ground freezes. The frozen ground may spit out fence posts, or make roads very bumpy. In some places, entire towns are built on ground that stays frozen all year around. People there count on the ground under their houses to stay frozen hard. Animals and plants, too, have figured out how to take advantage of frozen ground.

We can't always see the ways that frozen ground matters. Even people who live where the ground never freezes depend on frozen ground. Frozen ground around the world is connected to Earth's climate. If all, or even just a lot of the frozen ground around the world thawed out, everyone would notice. In the Arctic, some ground that used to be called permanently frozen ground, or permafrost, has already thawed out. It is changing the way people in those areas live.

What is frozen ground?

Frozen ground occurs when the ground contains water, and the temperature of the ground goes down below 0° Celsius (32° Fahrenheit). It can make a big difference if the ground stays frozen all year, or if the ground freezes and thaws. More than half of all the land in the Northern Hemisphere freezes and thaws every year, and is called seasonally frozen ground. One-fourth of the land in the Northern Hemisphere has an underground layer that stays frozen all year long. Ground that stays frozen for at least two years in a row is called permafrost.

What is there to know about frozen ground?

All About Frozen Ground explores what is going on in and under the ground when it freezes and thaws. Find out how frozen ground works, and how it makes a difference all over the world:

• How will climate change affect frozen ground?
• Can plants and animals find water when the ground is frozen?
• Does frozen ground damage buildings?
• How do scientists study permafrost from space?

Tingjun Zhang, a permafrost scientist at the National Snow and Ice Data Center, studies frozen ground. He said, "The more we learn, the more we realize that frozen ground isn't just important when we build roads or houses. Frozen ground is important to people, wildlife, and climate all over the world."