Download Grade 10 Academic Science – Climate Change

Grade 10 Academic Science – Climate Change
Feedback Loops
Section 8.10 Pages 355-357
In climate change, a feedback loop is the equivalent of a vicious (...or possibly virtuous...) circle. A
feedback loop is something that accelerates or decelerates a warming trend. A positive feedback
accelerates a temperature rise; whereas, a negative feedback decelerates it.
An example of a positive feedback loop is
melting ice. Ice is light-coloured and
reflective. Thus, a large proportion of the
sunlight that hits ice is reflected back into
space. This feature limits the amount of
warming caused by ice. However as the
world gets hotter, ice melts and darkercoloured land or water beneath the ice is
exposed. As a result, more of the sun's
energy is absorbed, leading to more
warming, which in turn, leads to more ice
melting. The additional melting uncovers
more heat absorbing, dark-coloured
materials which, in turn, increases the
heating and melting...and so on. Another
example between temperature, permafrost
thaw and increased CO2 and CH4 loadings
to the atmosphere is illustrated
Albedo is a measure of how much of the sun’s
radiation is reflected by a surface. Ice, snow,
and other light-coloured materials typically have
HIGH albedos. Thus, light-coloured materials
reflect a lot of radiation (e.g., snow reflected
85% of incoming radiation). Dark-coloured
materials such as forests and water have a
LOW albedo (e.g., water only reflects 8% of
incoming radiation). On average, the Earth’s
surfaces reflect between 30-40% of incoming
radiation. Thus, Earth’s average albedo is
between 0.3 and 0.4. The feedback loop
described above illustrates the ALBEDO
EFFECT.
By altering the Earth’s climate with increased
temperatures, the Albedo Effect is also
impacted and a positive feedback loop is
created (see the illustration opposite).
Summary
 In a positive feedback loop, the effect increases the original cause
 In a negative feedback loop, the effect decreases the original cause
 Albedo Effect is a positive feedback loop
HOMEWORK / PRACTICE
 Page 357, Questions 1-3, 5, 6
Clues to Climate Change
Section 8.11 Pages 358-361
Written climate records have been kept for at least the last 200 years. Thus, you and I have a very
detailed understanding of climate changes in that recent period of Earth’s history. For a short period
before that, humans noted changes in paintings, farming records and stories (i.e., oral or verbal history).
What about Earth’s climate and any changes prior to records? What was Earth’s climate like? What
were the major climatic events?
Paleoclimatologists use PROXY RECORDS (i.e., climate information stored in chemical and physical
structures of natural materials such as fossils, ice cores and tree rings. This information can be
measured and compared with other time periods to give clues to the climatic conditions of that time
period). NOTE: proxy records are indirect measurements. They indicate the possible conditions, but
they are not collected during the actual time period.
ICE CORES
 Ice contains air bubbles that have
been trapped in the ice for long time
periods. An ice core is collected
vertically. The most recent time is
at the “top” of the core. As you go
“down” the core vertically, you are
looking at conditions further back in
time. The air from years ago offers
information about air quality (e.g.,
types and quantities of different
gases) in that period. Ice cores
have revealed that atmospheric CO2
levels have increased and
decreased many times in Earth’s
history (see illustration)
 Ice cores are also tested for oxygen.
By measuring the ratio of light to the
heavier isotopes of oxygen, air
temperatures can be determined. If the air is cold, the colder air bubble with hold more light.
 Ice cores also contain dust from volcanic eruptions and precipitation. Major volcanic eruptions
spew significant amounts of dust into the atmosphere. The dust prevents thermal radiation from
the sun from reaching the Earth’s surface. As a result, it can be colder.
TREE RINGS
 Trees grow one ring each year. When
growing conditions are favourable (e.g.,
adequate rainfall, good temperatures), large or
thick tree rings form.
 Tree rings can provide estimates of climatic
conditions from about 10,000 years ago
 The picture shows different size tree rings.
Good growing conditions are characterized by
thick rings, while poor or harsh growing
conditions are shown by thinner rings.
HOMEWORK / PRACTICE
 Page 361, Questions 1, 2, 5, 7