2. Climate as a SYSTEM
• System: A set of things-people, cells,
molecules, interconnected in such a way
that they produce their own pattern of
behavior over time, serving a particular
function or goal.
3. Systems Thinking
• Systems behavior comes out of the
system, not the individual elements,
people or actors in it.
• Feedback loops exist because
everything is inter-connected, and
systems are nested within systems.
5. Reinforcing Loops (Positive Loops)
• Reinforcing Loops (+) enhance or amplify
changes; this tends to move a system away
from its equilibrium state and make it more
unstable. Reinforcing loops produce growth
and decay.
• Example: POPULATION GROWTH: As
population grows, more workers produce
resources, life expectancy increases and birth
rate increases = more population growth.
6. Balancing Loops (Negative Loops)
• Balancing Loops (-) tend to dampen or buffer
changes; this tends to hold a system to an
equilibrium state making it more stable.
Example: Body Temperature:
• When the internal temperature of your body
increases, you sweat, and as that sweat
evaporates from the warm surface of your
body, you cool down: balancing the initial
increase.
8. • Reinforcing: (+) loops. Healthy populations
will continue to grow leading to a decrease in
resource availability, making the population
more unstable-- unless other factors keep it in
check.
• Balancing (-) loops. Predators or fisherman
keep populations in check, leading to a stable
fish population.
9. How do Feedback Loops relate to
Climate Change?
Net radiative forcing The
difference in the solar
energy absorbed by the
earth and the energy
radiated back into space
10. Questions:
• What would happen if we made a one time
change to the net radiative balance?
• Why does the balancing loop have a delay—
once a change happens it may take many
decades for the “balancing” to kick in.
• What is “net radiative forcing”?
11. Answers
• The equilibrium loop, on its own, cannot produce a runaway
global warming (or cooling) – the earth will eventually find a
new equilibrium in response to a change in net radiative
forcing.
• The balancing loop has a delay, because it takes a lot of
energy to warm the oceans. Once a change starts in this loop,
it takes many decades for the balancing effect to kick in.
• If we make a one-time change to the radiative balance, the
earth will slowly change its temperature until it reaches a new
balance point, and then will stay there, because the balancing
loop keeps it there. However, if there is some other force
that keeps changing the radiative balance, despite this loop’s
attempts to adjust, then the temperature will keep on
changing.
12. Climate Class Notes
• Net radiative forcing The difference in the solar energy
absorbed by the earth and the energy radiated back
into space.
• Be able to define BALANCING AND REINFORCING
LOOPS (from the reading)
• If we make a one-time change to the radiative balance,
the earth will slowly change its temperature until it
reaches a new balance point, and then will stay there,
because the balancing loop keeps it there. However, if
there is some other force that keeps changing the
radiative balance, despite this loop’s attempts to
adjust, then the temperature will keep on changing.
15. Aerosols
• Aerosols are tiny particles (smoke, dust)
produced when dirtier fossil fuels are burnt.
Coal is the worst but oil produces them as
well. Aerosols block visible light, and hence
reduce the incoming sunlight (like adding a
sunshade).
16. Greenhouse Gases (GHG’s)
• Greenhouse gases include carbon dioxide,
methane, water vapour, and a number of
other gases. By volume, CO2 is by far the most
common byproduct from fossil fuels, although
some of the rarer gases actually have a larger
“greenhouse effect”. Greenhouse gases
block infrared radiation, and hence reduce
the outgoing radiation from the planet (like
adding an extra blanket):
17. Discuss:
• Do aerosols reduce or increase net radiative
forcing?
• Do GHG’s reduce or increase net radiative
forcing?
• Which one is having the greatest effect on the
climate?
18. • However we look at it, the greenhouse gases
are having the biggest effect, by a large
margin. That should mean the planet is
warming. And it is:
19. Class Notes: Aerosols and GHG
• As we increase economic development we have
more demand for energy and burn more fossil fuels
(Reinforcing Loop +)
• As we burn more fossil fuels, the reserves decrease,
prices go up, as prices rise, rate of consumption
decreases. (Balancing Loop (-)
• Aerosols block visible light, causing cooling.
• Greenhouse gases block outgoing radiation causing
warming.
• Currently GHG’s are having the biggest effect on
climate, and the planet is warming.
Editor's Notes
Give one example of a simple system including the stock, inflow and outflow from the reading.
In this feedback example, a positive loop (Reinforcing Loop) of fish reproducing increases the overall size of a school of fish. At the same time, pressure from predators and fishermen form negative loops (Balancing Loops) that decrease the size of the school. If these loops are in balance, the fish population will remain stable.
Balancing Feedback: Tends to hold a system at equilibrium or make it more stable (also called Negative Loop)-predators and fishing pressures.
Reinforcing Feedback: Tends to move a system away from equilibrium making it less stable (also called Positive Loop)-population
Central Equilibrium Loop: What global climate patterns look like in equilibrium state-when the climate is not changing: The temperature of the planet is determined primarily by the balance between the incoming energy from the sun and the outgoing energy lost back into space. The incoming energy is in the form of shortwave radiation from the sun
Net radiative forcing The difference in the solar energy absorbed by the earth and the energy radiated back into space
If the incoming energy from the sun is greater than the outgoing energy, the imbalance causes the earth to retain more energy, and so the temperature rises. As a warmer planet loses energy faster, this increases the outgoing radiation, which in turn reduces the imbalance again (i.e. this is a balancing loop).
The structure of this loop always pushes the planet to find a (roughly) stable equilibrium: essentially, if the incoming and outgoing energy ever get out of balance, the temperature of the planet rises or falls until they are balanced again.
There is one more complication for this loop. The net radiative forcing determines the rate at which energy is retained, rather than the total amount. If the net forcing is positive, the earth keeps on retaining energy. So although this leads to an increase in temperature, and, if you follow the loop around, a decrease in the net radiative forcing, it will reduce the rate at which energy is retained (and hence the rate of warming), it won’t actually stop the warming until the net radiative balance falls to zero. And then, when the warming stops, it doesn’t cool off again – the loop ensures the planet stays at this new temperature.
Burning fossil fuels creates 2 reinforcing loops based on the byproducts of aerosols and GHG’s.
Aerosols reduce the net radiative forcing (causing cooling), and greenhouse gases increase it (causing warming).
