02_2 Earth Systems Forcings

Unifying Theories

  • Definition of a theory:

    • A hypothesis that has survived repeated testing and has been modified as needed

    • Confirmed by extensive observations by numerous scientists

    • Still a “living” statement and can be slightly modified over time

  • Examples of unifying theories mentioned:

    • Evolution

    • Quantum Chemistry

    • Earth Systems

    • Plate Tectonics

The dynamic climate system

  • Climate is a complex, dynamic system with many interacting parts

  • Figure 1.1 (Mathez, 2009) emphasizes that Earth’s climate is complicated

  • Implication: understanding climate requires looking at how components interact, not just isolated parts

Systems science: foundational definitions

  • System: a group of components that interact with each other

  • Component: objects, groups of objects (a subsystem), or measurable quantities like temperature or pressure

  • Implication: studying subsystems helps understand the whole, and subsystems can be analyzed individually or in combination

Digestive System (example of a system in the body)

  • Questions to frame system study:

    • What are some of the components?

    • How would you diagnose a problem?

  • Example components listed:

    • Liver, Colon, Finger, Gallbladder, Tongue, Esophagus, Stomach, Pancreas, Small Intestine

  • Source link: http://www.strangebuttrewe.com/knitGl.htm

Subsystems of the human body

  • Each subsystem is a component of the body

  • Subsystems can be studied separately or together with other parts of the body

  • Other subsystems mentioned:

    • Nervous

    • Cardiovascular

    • Digestive

    • Muscular

    • Skeletal

    • Respiratory

    • Integumentary (Skin, hair, nails)

Earth Systems Theory (introductory framework)

  • The climate system can be split into subsystems: Gases, Water (includes Cryosphere), Solid Earth, All living things (biosphere: plants, animals, humans, microorganisms, etc.)

  • Cryosphere is a subsystem of the Hydrosphere and refers to ice

  • Subsystems interact with each other, leading to feedbacks and responses in the climate

  • Subsystems listed: Lithosphere, Biosphere, Hydrosphere, Cryosphere, Atmosphere

  • Source for Cryosphere: https://newsela.com/read/natgeo-lithosphere/id/44339/

Interactions among subsystems and expertise

  • Subsystems interact with each other, producing feedbacks and responses in climate

  • Different scientists specialize in different subsystems (analogous to medical specialists):

    • Geochemist (air chemistry changes like smog)

    • Glaciologist (ice thickness changes)

    • Paleontologist (fossil species through geologic time)

  • Analogy: like neurologist, cardiologist in medicine

Summary of Earth Systems Theory

  • The climate system can be split into subsystems

  • Each subsystem or component can be studied separately

  • Interactions between subsystems lead to past or future climate changes

  • Subsystems include Lithosphere, Biosphere, Hydrosphere, Cryosphere, Atmosphere

Forcings and Feedbacks in the climate system

  • How we frame climate interactions:

    • Forcing: Any process or disturbance that drives a change

    • Feedback: A process that alters changes underway in the climate

  • Positive feedback: amplifies or enhances change

  • Negative feedback: reduces or moderates change

Climate Forcing (examples)

  • Forcing is any process that drives change; examples across subsystems:

    • Lithosphere: changes in plate tectonic motion

    • Biosphere: changes in Earth’s orbit

    • Hydrosphere: changes in strength of the Sun

    • Cryosphere: changes in human behavior

    • Atmosphere: other forcings (e.g., emissions, aerosols)

  • Framing note: forcings initiate changes that propagate through interactions among subsystems

Feedback: how the climate responds

  • Forcing acts as the initial driver; feedbacks are the system’s responses

  • Positive feedback examples: amplification of the initial change

  • Negative feedback examples: moderation or dampening of the initial change

  • Visualization elements referenced as Fig A (positive) and Fig B (negative)

Feedback loops: examples

  • Grassland-forestry vegetation feedback (illustrative loop)

    • Grassland converts to forest, leading to changes in transpiration and precipitation

    • Forest increases transpiration and precipitation, reinforcing forest cover

    • Diagrammatic sequence (summary): Grassland → Forest replacement → Increased transpiration → Increased precipitation → More forest growth

  • Purpose: to illustrate how vegetation can create feedbacks with climate variables

Pancreas and blood sugar: a feedback loop example

  • Pancreas feedback loop (biological example):

    • Insulin released → Blood sugar lowered

    • Glucagon released → Blood sugar increased

    • Body detects blood sugar too low → triggers responses

  • Question raised: Is this loop best described as negative or positive feedback?

  • Source: https://commons.wikimedia.org/wiki/File:Negative%20Feedback%20Gif.gif

  • Note: The slide prompts debate on loop interpretation and whether this is the only way to draw the loop

Climate feedbacks in more detail

  • Forcings lead to feedbacks in the climate system across all subsystems: Lithosphere, Biosphere, Hydrosphere, Cryosphere, Atmosphere

  • Changes can occur in:

    • Human behavior

    • Plate tectonic motion

    • Strength of the Sun

    • Earth’s orbit

    • Other factors

  • Feedbacks result in changes to:

    • Chemistry of the atmosphere or oceans

    • Ice cover

    • Temperature

    • Precipitation

    • Species and ecosystems

    • Other factors

Timescales of climate changes (examples of slow vs fast changes)

  • Plate tectonics: slow changes, typically in the millions to tens of millions of years

    • Expressed as: extPlatetectonics:exttimescale<br>ightarrow106extto107extyearsext{Plate tectonics: } ext{time scale} <br>ightarrow 10^6 ext{ to } 10^7 ext{ years}

  • Atmospheric chemistry: fast changes, year-to-year timescales

    • Expressed as: extAtmosphericchemistry:exttimescale<br>ightarrow1extyeartoafewyearsext{Atmospheric chemistry: } ext{time scale} <br>ightarrow 1 ext{ year to a few years}

  • Emphasizes that different subsystems operate on very different timescales

Activity prompt example (for students)

  • Task: Write down an example of a positive or negative feedback (using scientific definitions, not social definitions) from your own life

  • Steps:

    • Choose one example from your group

    • Try drawing a feedback loop diagram for this example

  • Educational purpose: practice identifying forcing and feedback structures in real-world contexts

Cause and Effect: building hypotheses

  • To create a hypothesis, explain how two observations are related

  • Definitions:

    • Cause: the producer of a result or consequence

    • Effect: the result or consequence

Cause and Effect in practice

  • Bacteria / Cadaveric matter as cause; Sepsis / Childbed fever as effect

  • Counterpoint: in climate science, relationships are rarely this straightforward

  • Example: insomnia with multiple potential causes

    • Anxiety for tests

    • Staying up later

    • Drinking tea with caffeine at night

    • Could be all, none, or some of these

  • Diagrams:

    • Several pages present different orderings of these factors to illustrate how cause and effect can be ambiguous

Cause or Effect? graphic differentiation

  • Example orders shown to illustrate that cause/effect can be arranged differently in a diagram:

    • Staying up late, caffeine, anxiety, insomnia

    • Anxiety, caffeine, staying up late, insomnia

    • Anxiety, staying up late, insomnia, caffeine

  • Concept: Causality is not always obvious from a single diagram; the forcing may precede the effect, but feedbacks can complicate the sequence

  • On page 27: The idea that the “Forcing” is what happens first and the “Feedback” is the loop that results in the ongoing change

Causation vs Correlation

  • Correlation: two things may be related but one does not necessarily cause the other

  • Important caution: correlation does not imply causation

  • Observed correlation examples:

    • Positive correlation: both variables increase or decrease together

    • Negative correlation: one variable increases while the other decreases

  • Example link for spurious correlations: https://www.tylervigen.com/spurious-correlations

Global temperature vs pirates (illustrative plot)

  • A humorous example demonstrating correlation does not imply causation

  • Cartoon data shows a correlation between global average temperature and number of pirates, highlighting spurious relationships

  • Source: joke figure (reference to Flying Spaghetti Monster Wikipedia)

Causation or Correlation in climate science: methodological approach

  • How to determine relationships between many variables:

    • Look at data and observed trends

    • Build models (hypotheses) based on current scientific understanding

    • Use models to make predictions and test them against new data

  • Example focus: predicted changes in global temperature for the year 2100

Climate Models: applying Earth Systems Theory

  • Approach: models incorporate forcings to create changes; outputs include feedbacks

  • Subsystems are modeled and linked to form complex models

  • Subsystems included: Lithosphere, Biosphere, Hydrosphere, Cryosphere, Atmosphere

  • Forcings and feedbacks operate within and across these subsystems

  • Examples of forcing-driven changes:

    • Human behavior

    • Plate tectonic motion

    • Strength of the Sun

    • Earth’s orbit

    • Other factors

Climate model architecture (examples)

  • Models simulate interactions among atmosphere and ocean subsystems using grids:

    • Horizontal grid (spatial resolution)

    • Vertical grid (height or pressure)

  • Physical processes represented include:

    • Atmosphere dynamics

    • Ocean currents and heat transport

    • Sea ice and open ocean interactions

    • Land surface and hydrology

  • Example models and tools mentioned: -GENIE (Grid Enabled Integrated Earth system model) –

    • Hydrosphere, biosphere, atmosphere, lithosphere coupling

    • Website: www.genie.ac.uk

Core takeaways and implications

  • The climate system is a network of interacting subsystems; understanding requires looking at both individual components and their couplings

  • Forcings initiate changes; feedbacks determine the magnitude and direction of the response

  • Positive feedbacks can amplify changes, potentially leading to tipping points, while negative feedbacks can stabilize the system

  • Timescales vary widely across subsystems, from fast atmospheric chemistry to slow tectonic processes

  • Distinguishing causation from correlation is crucial in climate science; models and data are used to test hypotheses

  • Climate models integrate multiple subsystems and processes to simulate past, present, and future climate states; they rely on forcings, feedbacks, and observed data to validate predictions

Key references and links mentioned

  • Digestive system component image: http://www.strangebuttrewe.com/knitGl.htm

  • Negative/positive feedback GIF: https://commons.wikimedia.org/wiki/File:NegativeFeedbackGif.gif

  • Lithosphere/NatGeo lithosphere article: https://newsela.com/read/natgeo-lithosphere/id/44339/

  • Spurious correlations: https://www.tylervigen.com/spurious-correlations

  • GENIE model: www.genie.ac.uk