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.

  • 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.

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 . 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 to around 405 ppm. Three 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 an 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.

Future Climates—The Great Uncertainty

How much will climate change in the future because of our actions? Atmospheric scientists know that climate is warming because of a build-up of from fossil fuel use, but how much climate will warm in the future depends on the decisions people make about the amount of fossil fuels we use. And we don't know when people will stop using fossil fuels. Scientists are still studying how climate change now and in the future will affect humans and natural ecosystems. Because the Earth is complex and it's systems are interconnected, a change to one aspect of the planet - like greenhouse gas concentrations - can have impacts on many other aspects of the planet like global temperature, drought and floods, and even the temperature and acidity of the ocean. Because the impacts of climate change are far reaching and can appear to be indirect, people debate about the level of danger.

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.