Samenvatting
Summary Lectures System Earth (MAQ23306)
- Instelling
- Wageningen University (WUR)
Extensive overview of the contents of the lectures from System Earth (MAQ23306)
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Voorbeeld 4 van de 61 pagina's
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Voorbeeld van de inhoud
SummaryChapter 1: Global change
Climate and global change impacts:
- Netherlands: Potential flooding depth and economical damage
- Bangladesh: increased risk of flooding
Largest impacts of climate change might be seen in regions:
1. That contribute relatively little to the problem
2. Where society cannot easily adapt to climate change
Effects of climate/global change:
- Sea level rise
- Salt intrusion
- Drying
- Amazon die-back
- Permafrost melting
- Ocean acidification
- Changing ocean circulations
- Changing food distribution
- Declining biodiversity
- …
Natural drivers of climate system and of climate change/variability:
1. The sun
o Sun is becoming brighter
o In the past, solar radiation was very low
2. Earth’s orbit
o Earth rotates and wobbles like a top
▪ Moon reduced wobbling; how is this relevant for Earth’s climate?
3. Atmospheric composition
o Greenhouse effect
4. Continents and tectonics
o Position of continents
o Radiation balance
, o Volcanism and weathering
▪ Weathering takes CO2 out of the atmosphere
5. Ice dynamics
6. Life
o Already around 3.8 billion of years ago
o Enhances weathering
o Photosynthesis lowers CO2
▪ CO2 + H2O → CH2O + O2
o Methane production
enhances greenhouse
effect
▪ CO2 + 4H2 → CH4 +
2 H2O
o The Anthropocene
Geological clock
Rise of oxygen about 2 billion years ago:
- Ecosystem changed radically: ecological disaster
- Strong decrease in CH4 and CO2: ice ages
Very limited information through small number of observations.
To close the story we need:
1. To conduct system analysis
2. To understand the behaviour of system Earth
3. Combining the information based on limited observations with models & development of
hypotheses
To learn from understanding the past how the future might be
Chapter 2: Daisy World
What are systems?
- An entity composed of diverse but interrelated parts that function as a complex whole
- Examples:
o Human body; respiration system
o Biosphere; photosynthesis system
o Economy; capitalistic system
The state of a system is a set of attributes, state variables, that characterizes the system at a
particular time
- State variables:
o E.g. temperature, pressure, mass
, o State variable is a parameter, develops depending on where it comes from
System Earth
- Subsystem of the solar system
- Components:
o Atmosphere
o Biosphere
o Hydrosphere
o Lithosphere
o Cryosphere
o Anthroposphere
- State variables
o Energy balance
o Pressure
o Earth’s orbital rotation state
o Composition
- Component interactions
o Exchange of energy, H2O, matter, etc. ‘
Feedback is a self-perpetuating (enable or effect) mechanism of a change and a response to that
change
Jimmy Carter with electrical blanket example
Equilibrium state: the state in which the system will remain unless the system is disturbed
- How far do we have to push as system to reach an alternative stable state
- Are we currently pushing our system Earth so far away from a stable equilibrium that we
might soon reach this peak where the system will switch to another (unknown) stable
equilibrium?
- Reaching a tipping point
- Examples:
o Ecosystems
o Glaciation
Perturbations: temporary disturbance of the system
- E.g. Vulcanic eruption
- Fertilization of oceans from mineral dust of Sahara
Forcing: a more persistent disturbance of the system
- Milankovitch cycles
Daisy world:
- Self-regulating systems
- Natural systems can be self-regulating on a global scale without the need for intelligent
intervention
- Forcing, albedo and temperature
o High albedo, low T
o Low albedo, high T
- Daisy growth depends on temperature
o Minimum, optimum, maximum
- Daisy coverage leads to lower average surface temperature
- Daisy coverage is affected by temperature
- When both graphs are put into one, the points where lines connect (p1, p2) are the
equilibrium states
, - On any other point then p1 or p2 on the parabola, the effect of T on daisy cover is correct but
not the effect of daisy cover on T
- Assuming that daisy cover does not increase with solar luminosity but only depends on
temperature
o Temperature increases, T line moves up
o Parabola: smaller temperature change, than temperature change without the
feedback
o Delta Teq = Delta T0 + delta Tfeedback (<0)
o Feedback factor f = Delta Teq / Delta T0
▪ Value of feedback factor is between 1 and 0
- Positive feedback loop: no feedback factor (or >>1) for the system in the unstable state:
o Runaway effect
Gaia hypothesis:
- Living organisms interact with their inorganic surroundings on Earth to form a synergistic and
self-regulating, complex system that helps to maintain and perpetuate the conditions for life
of the planet
- Livelock suggested that global biological feedback mechanisms could evolve by natural
selection, stating that organisms that improve their environment for their survival do better
than those that damage their environment
- Doolittle argued that nothing in the genome of individual organisms could provide the
feedback mechanisms proposed by lovelock and therefore the Gaia hypothesis is not relying
on any specific mechanism
- Dawkins stated that organism to act in concert would required foresight and planning, which
is contrary to the current scientific understanding of evolution
- Evolutionary biologist Hamilton added that it would take another Newton to explain Gaian
self-regulation takes place through Darwinian natural selection
CLAW hypothesis:
- Proposes a negative feedback loop that operates between ocean ecosystems and the Earth’s
climate
- Phytoplankton produce DMS are responsive to variations in climate forcing, and that these
responses act to stabilise the temperature of the Earth’s atmosphere
Summary
- Introduction in the key parameters of Earth system studies: systems, components, state,
couplings and feedbacks
- Use of system diagrams and advantage of following a system approach
- Feedback is a self-perpetuating mechanisms of a change and a response to that change
- Combination of- and quantification of feedbacks
- Equilibrium, stability
- Perturbations and forcing
- Self-regulating systems; Daisy world
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