Page 40 - Earth's Climate Past and Future

16 PART I • Framework of Climate Science

BOX 1-2 CLIMATE INTERACTIONS AND FEEDBACKS
Positive and Negative Feedbacks

he strength of a feedback on temperature, called the If f has a value of 1, no feedback exists. If the value of f
Tfeedback factor, or f, is defined as is greater than 1, the net temperature change is larger than
it would be without any feedback, and the climate system
temperature change with feedback
f = is characterized as having a positive feedback. If the value
temperature change without feedback
of f is less than 1, the temperature change is smaller than it
where “temperature change” refers to the full equilibrium would be in the absence of any feedback, and the climate
response. system is characterized as having a negative feedback.

components of the climate system. The changes in greenhouse gases (p. 10) positive feedbacks (p. 15)
some of these components will then further perturb cli- response time (p. 10) negative feedbacks
mate through the action of feedbacks. equilibrium (p. 11) (p. 15)
Positive feedbacks produce additional climate
change beyond that triggered by the factor that initiates feedbacks (p. 15) feedback factor (p. 16)
the change (Box 1-2). For example, a decrease in the
amount of heat energy sent to Earth by the Sun would
allow snow and ice to spread across high-latitude Review Questions
regions that had not previously been covered. Because 1. How does climate differ from weather?
snow and ice reflect far more sunlight (heat energy)
than do bare ground or open ocean water, an increase in 2. In what ways does climate science differ from
their extent should decrease the amount of heat taken traditional sciences such as chemistry and
up by Earth’s surface and further cool the climate in biology?
those regions. 3. How does climate forcing differ from climate
The positive feedback process also works in the response?
opposite direction. If more energy from the Sun arrives
and causes climate to warm, high-latitude snow and ice 4. In the example in which the Bunsen burner is lit
will retreat and allow more sunlight to be absorbed. and the beaker of water at first warms quickly and
The result will be further climatic warming. Positive then more slowly, how does the response time of
feedback acts as an amplifier, regardless of the direction the water change through time?
of change. 5. The climate system consists of many components
Negative feedbacks work in the opposite sense, by with different response times. What is the total
muting climate changes (see Figure 1-11). When an ini- range of time scales over which these responses
tial climate change is triggered, some components of vary?
Earth’s climate system respond in such a way as to
reduce the initial change. 6. Do positive feedbacks always make the climate
warmer?
Key Terms
Additional Resources
climate (p. 4) theory (p. 8)
weather (p. 4) evolution (p. 8) Basic Reading
Fahrenheit (p. 5) plate tectonics (p. 8) Climate Change: State of Knowledge. 1997. Washington,
Celsius (p. 5) climate system (p. 8) DC: Office of Science and Technology Policy.
Understanding Climate Change. 1975. Washington, DC:
Kelvin (p. 5) forcing (p. 8)
U.S. National Academy of Science.
resolution (p. 6) response (p. 8)
Earth system (p. 7) radiation (p. 10) Advanced Reading
climate science (p. 8) anthropogenic forcing Imbrie, J. 1985. “A Theoretical Framework for the Ice
hypothesis (p. 8) (p. 10) Ages.” Journal of the Geological Society 142: 417–32.