Global Climate Change

This section provides a brief overview of processes and properties associated with global climate change. The general concepts found in this section are:

  • Earth's climate has always changed; it is the rate of change that is of current concern to scientists.

  • Carbon is critical to the biosphere and must continue cycling to support life on Earth.

  • The carbon cycle includes sources, sinks, and release agents.

  • Carbon dioxide is an important greenhouse gas.

  • Living organisms in an ecosystem can have profound effects upon the local atmosphere.

  • Changes in vegetation can have profound effects upon wind speed.

  • Understanding the major greenhouse gases is necessary to identify the current trends in atmospheric concentrations and climate change.

  • Human activity has been linked with increased greenhouse gases in the atmosphere.

This section includes seven classroom activities.

Climates Past

The climate of planet Earth is unstable. Our evolutionary origins lie in the warm, relatively benign climate of equatorial Africa, but our ancestors battled the cold, harsh, and unforgiving climate of the last ice age in order to spread across the planet.

Some 10,000 years ago, however, the ice age ended. We developed agriculture, civilization, industry, and technology generally in a global climate that was warm, pleasant, and mostly predictable. Regional climates have changed, sometimes drastically and disastrously for local human populations, but by and large the global climate has not dealt any significant long-term blows to the spread and development of human civilization.

One of the most significant accomplishments of our species is the discovery of fossil fuels and the means of turning the energy trapped within them into heat, transportation, and the basis for manufacturing and construction.

Present Climates and Human Activity

This discovery and the global industrial revolution that followed changed the world forever for our species. In general, fossil fuels are a legacy bequeathed to us by the biosphere of the distant past. On an ancient warmer Earth with a high concentration of carbon dioxide () in the atmosphere, photosynthetic organisms (algae and higher plants) absorbed the , and used it to produce abundant organic material. When these organisms died, they were buried deep within the earth and slowly turned into coal and oil.

Since the 1800s, we've been burning vast quantities of these fossil fuels to power our developing technological and global civilization. As a result, we've been releasing the trapped in the fuels in the form of energy-rich organic molecules back into the atmosphere, increasing the atmospheric concentration of . By itself, this is not a concern. Carbon dioxide comprises a very small proportion of the atmosphere, and no projected increase would affect our breathing. But has another significant property. As we explored in the Greenhouse Effect section, carbon dioxide absorbs heat. The other major component gases of Earth's atmosphere, oxygen () and nitrogen (), do not.

Since the 1800s, concentrations worldwide have increased from approximately 280 ppm (or 0.028%) to around 365 ppm (0.0365%). The increase seems trivial, but it also means that some 3 gigatons (3 billion metric tons) of are being added to the atmosphere every year. Because is a powerful greenhouse gas, we can reasonably conclude that the earth's temperature should go up as concentrations increase. In fact, climatologists have detected a steady but small increase in global average temperatures over the last few decades, based on weather data collected all around the world. Six of the last ten were the hottest years on record.

Regardless of the cause of the warming, we understand enough about global climate to predict that as the temperature goes up, the entire global climate system powered by heat energy should also change, although the magnitude and direction of the changes are uncertain.

Future Climates—The Great Uncertainty

Are we seeing the end of the long period of benign climate since the last ice age? Will the climate change for the worse because of our actions? In fact, no one knows for sure. Most atmospheric scientists believe that the global climate is warming at least partially because of a build-up of from fossil fuel use, but what that means to humans and natural ecosystems is largely unknown. The climate is vastly complex and strongly influenced by many factors other than greenhouse gas concentrations. (Some of these factors are explored in the Introduction to Climate Section.) This makes it extremely difficult to link any climatic events or characteristics to a single cause. As a result, controversy exists as to the magnitude and danger of global warming induced by greenhouse gases. Many scientists take the issue very seriously and support efforts to slow or reverse the build-up of atmospheric with the expectation that global warming will slow as a result. Others, however, contend that may not be affecting the climate and that the changes are part of natural, long-term climatic cycles. They suggest that efforts to reduce emissions are unnecessary and dangerous to economic growth and development. While the controversy rages, researchers around the world continue to gather atmospheric data, develop and refine predictive computer models, and try to reduce the uncertainty in our understanding of the earth's climate.

In this unit, you will explore the critical issues in climate change, exploring sources and sinks (or reservoirs) of , the nature of climate change and predictions of future changes, and the elements of the scientific and political debates that will ultimately determine how we respond to climate change.

Concluding Thoughts

We know that the earth's climate has changed over time. Throughout the earth's history, there have been periods of glaciation followed by warming trends in which the glaciers retreated toward higher altitudes and latitudes. Today's concerns focus on the current and projected rate of climate change based, in large part, on human activities. By going through this section, students should be able to answer the following questions:

  1. What has the earth's climate been over time?

  2. Why is the carbon cycle so important when looking at climate change issues?

  3. What major events in human history are thought to be factors in changing the earth's atmosphere?

  4. How do scientists measure gas concentrations in the atmosphere?

  5. Why are climate change and global warming considered to be controversial topics by some groups and individuals?


The following activities will help your students better understand the concepts covered in this section.

To proceed, either click on Activities in the menu at the top or click on another unit to switch units.