How are
people changing
the climate?

Basics

Unit 1:
Man-made climate change?

Past climate change

The Earth’s climate is always changing. Only 20,000 years ago, much of Northern Europe was covered in an enormous glacier that was up to three kilometers thick! The Alps and the Pyrenees mountains were covered with smaller ice caps. Sudden climate shifts happened quite frequently during the Ice Age, and made the ice expand or contract. In the cold climate south of the ice-covered areas, small groups of people hunted reindeer, wild horses, and bison.

People living in the Ice Age left behind stone tools and fantastic cave paintings but their way of life was about to disappear. Over thousands of years, the Earth’s orbit around the sun changed, summers became warmer and the ice began to melt. The Ice Age ended around 10,000 years ago. Since then, the climate in Northern Hemisphere has been warmer and far more stable. Over the last 10,000 years the climate has been milder and people have developed agriculture, cities, and civilization – which would have been far more difficult during the Ice Age.

We will always be at risk of unexpected and unpleasant climate changes resulting from natural causes. For example, around 400 years ago Europe experienced a relatively cold period called the Little Ice Age (but not as cold as a real ice age). What is different about the situation today is that we risk rapid changes in climate caused by people. Because of our increasing emissions of CO₂ and other greenhouse gases, we expect that over the next hundred years we will see the fastest warming of the Earth since the end of the Ice Age.

From local to global problems

As long as we humans have existed on Earth, we have affected the environment around us. In the past, the effects of our hunting or agricultural activities on the environment were local.  This changed with the Industrial Revolution which began round 1750 and accelerated in the 1800s and 1900s. A revolution is a dramatic social change.
 

The Industrial Revolution took place when people began to mass produce goods in large factories using machines that ran on energy from coal, and later using oil, natural gas, and electricity.  This made it much easier for people to produce goods and helped the development of modern technology.  In pre-industrial times – that is, the time before the Industrial Revolution – there were no trains, cars, planes, electric lights, factories, telephones, or televisions.

The more we produce and consume, the more we affect the environment around us. Over the last 50 years we have seen clear signs that humans affect the environment of the entire planet.  We are creating environmental problems that are not only local but also global. One of these global environmental problems is man-made climate change, also known as global warming.

Global climate change

Man-made climate change occurs because we emit greenhouse gases into the atmosphere. These emissions come from many sources, including factories and agriculture that supply us with food and other material goods, power plants which provide us with electricity and cars and planes that take us where we need to go.
 

Greenhouse gases affect the Earth’s climate by increasing the greenhouse effect.  This is a natural phenomenon where water vapor, carbon dioxide and other gases in the atmosphere allow sunlight to pass reach the Earth's surface, but then absorb much of the reflected heat from the Earth that otherwise would have escaped to outer space. Without the natural greenhouse effect, the average temperature would be about minus 18°C, and the Earth would be uninhabitable (choose the topic Lower atmosphere if you want to read more about the greenhouse effect).

Emitting greenhouse gases in large amounts increases the concentration of these gases in the atmosphere.  This increases the greenhouse effect so that more heat is trapped by the atmosphere. This increases the temperature of the atmosphere and changes the Earth's climate.

Next page

About this Page:

Author: Camilla Schreiner - CICERO (Centre for International Climate and Environmental Research - Oslo) - Norway.
Scientific reviewers: Andreas Tjernshaugen - CICERO, Norway - 2003-09-15 and Dr. Knut Alfsen - Statistics Norway, Norway - 2003-09-08.
Educational reviewer: Nina Arnesen - Marienlyst School, Oslo, Norway - 2004-03-10.
Last update: 2004-03-27.