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