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Untitled Flashcard Set

Electromagnetic Radiation & Temperature

  • Photons

    • These are elementary particles of light, carrying energy proportional to their frequency. They are the packets of energy that make up electromagnetic radiation.

    • Energy of a photon is given by E = h
      u, where h is Planck's constant and \nu is the frequency.

  • Interaction with Different Matters

    • All matter with a temperature above absolute zero (0K) emits electromagnetic radiation.

    • The amount and type of radiation emitted depend on the object's temperature and surface properties.

    • Matter can absorb, reflect, scatter, or transmit radiation.

  • Wavelengths

    • Electromagnetic radiation exists across a spectrum of wavelengths, from short gamma rays to long radio waves.

    • The peak wavelength of emitted radiation is inversely proportional to temperature (Wien's Displacement Law: \lambda_{max} = b/T, where b is Wien's displacement constant and T is temperature in Kelvin).

    • Hotter objects emit more energy at shorter wavelengths (e.g., the sun emits visible light), while cooler objects emit more energy at longer wavelengths (e.g., Earth emits infrared radiation).

A Simple Climate Model

  • What does it consist of?

    • A basic climate model considers the balance between incoming solar radiation, the Earth's reflectivity (albedo), and the outgoing infrared radiation trapped by greenhouse gases in the atmosphere.

    • The Earth's average surface temperature is determined by this energy balance.

  • What will determine the temperature or atmosphere for the Earth?

    • The Earth's temperature is primarily determined by the amount of solar radiation absorbed, how much of that energy is radiated back to space, and the insulating effect of the atmosphere (greenhouse effect).

  • Pattern that’s not constant throughout time

    • Earth's climate has naturally varied over geological timescales due to various factors including orbital changes, volcanic activity, and continental drift.

  • Milankovitch Cycles

    • These are long-term cyclical variations in Earth's orbit around the sun that influence the amount of solar radiation received at different latitudes and seasons.

    • They include:

      • Eccentricity: Changes in the shape of Earth's orbit (from nearly circular to elliptical) over cycles of approximately 100,000 years.

      • Obliquity (Axial Tilt): Changes in the tilt of Earth's axis relative to its orbit, ranging from 22.1^\circ to 24.5^]circ over cycles of approximately 41,000 years. This affects the intensity of seasons.

      • Precession: The wobble of Earth's axis, which changes the timing of the seasons relative to Earth's position in its orbit, occurring over cycles of approximately 26,000 years.

  • Sun = Solar Constant

    • The solar constant (S_0) is the average amount of solar radiation received per unit area at the top of Earth's atmosphere, perpendicular to the incoming rays.

    • Its approximate value is 1361 W/m^2. While called a "constant," it experiences minor fluctuations (e.g., related to sunspot cycles).

  • 2nd component: Albedo

    • Albedo is the measure of the reflectivity of a surface, expressed as a fraction or percentage.

    • It represents the proportion of incident solar radiation that is reflected by a surface, ranging from 0 (no reflection, perfect absorption) to 1 (perfect reflection).

    • Surfaces can reflect all the energy

      • Highly reflective surfaces (like fresh snow) have high albedo, reflecting most incoming radiation.

      • Dark surfaces (like oceans or forests) have low albedo, absorbing most incoming radiation.

    • Different types of surfaces

      • Fresh snow: 0.8 - 0.9

      • Clouds: 0.3 - 0.8

      • Ice: 0.5 - 0.7

      • Deserts/sand: 0.3 - 0.4

      • Forests: 0.05 - 0.15

      • Ocean: 0.03 - 0.1

    • Important for feedback loops

      • Ice-albedo feedback: A critical positive feedback loop where increased temperatures lead to melting ice. Less ice means a lower albedo, which in turn leads to more solar radiation absorption, further warming, and more ice melt, creating a cycle: more cold = more ice, less ice = more warming.

    • Atmosphere/layers

      • The atmosphere plays a crucial role in regulating Earth's temperature through the greenhouse effect.

      • Many of the most abundant gases are transparent

        • Major atmospheric gases like nitrogen (N2) and oxygen (O2) are largely transparent to both incoming solar radiation and outgoing infrared radiation, and therefore do not contribute significantly to the greenhouse effect.

      • Greenhouse gases

        • These are gases that absorb and re-emit infrared radiation, thereby trapping heat within the Earth's atmosphere and warming the planet.

        • Examples include: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and water vapor (H_2O).

      • Atmospheric composition

        • The concentration of greenhouse gases in the atmosphere has varied naturally over Earth's history, but current levels, particularly of CO2 and CH4, are unprecedented in at least the last 800,000 years due to human activities.

      • Methane is more potent than CO2

        • While CO2 is more abundant, methane (CH4) is a more potent greenhouse gas on a per-molecule basis. Its Global Warming Potential (GWP) over a 100-year period is approximately 28 to 34 times that of CO2. This means one molecule of methane traps as much heat as 28-34 molecules of CO2 over 100 years.

      • Which are potent and which are less potent?

        • Highly potent: Methane (CH4), Nitrous Oxide (N2O), Chlorofluorocarbons (CFCs), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), Sulfur Hexafluoride (SF_6).

        • These gases often have very high GWPs and long atmospheric lifetimes.

        • Less potent (on a per-molecule basis, but very influential due to high concentration): Carbon Dioxide (CO_2).

        • Water vapor (H_2O) is also a strong greenhouse gas, but its concentration is largely controlled by temperature through evaporation and condensation, acting as a feedback rather than a primary forcing.

The Carbon Cycle

  • The carbon cycle describes the movement of carbon among four major reservoirs: the atmosphere, oceans, land (biosphere and soils), and sediments (including fossil fuels).

  • Carbon flows between these reservoirs through various physical, chemical, geological, and biological processes.

  • Carbon in the biosphere

    • Plants absorb CO_2 from the atmosphere through photosynthesis to build organic matter.

    • Animals and decomposers release CO_2 back into the atmosphere through respiration.

    • Carbon is stored in living biomass, dead organic matter, and soils.

  • Diagram of The Carbon Cycle

    • Illustrates the major reservoirs and fluxes:

      • Atmosphere: Carbon exists primarily as CO_2.

      • Oceans: Carbon dissolves into seawater, forms carbonic acid, and is taken up by marine life. It cycles between the surface and deep ocean.

      • Land (Terrestrial Biosphere): Carbon in plants, animals, and soil organic matter.

      • Sediments and Rocks: Long-term storage of carbon, including fossil fuels (coal, oil, natural gas) formed over millions of years from buried organic matter.

    • Fluxes (movement):

      • Photosynthesis: Atmosphere to Land/Ocean.

      • Respiration/Decomposition: Land/Ocean to Atmosphere.

      • Ocean-Atmosphere Exchange: CO_2 dissolves into and out of the ocean.

      • Combustion (natural and anthropogenic): Fossil fuels/biomass to Atmosphere.

      • Volcanic Activity: Earth's interior to Atmosphere.

Forcing, Feedbacks, and Climate Sensitivity

  • Forcing

    • A radiative forcing is any factor that alters the balance of incoming and outgoing energy in the Earth's climate system.

    • It is measured in watts per square meter (W/m^2).

    • Examples of forcings:

      • Changes in greenhouse gas concentrations (positive forcing).

      • Changes in solar irradiance.

      • Volcanic eruptions (can lead to negative forcing due to aerosols).

      • Changes in land cover (affecting albedo).

      • Aerosols (tiny particles in the atmosphere that can reflect sunlight or absorb heat, depending on their type).

  • Feedbacks

    • A climate feedback is a process that can either amplify (positive feedback) or diminish (negative feedback) the original forcing.

    • Positive feedback loops enhance the initial warming or cooling:

      • Ice-albedo feedback: Warming leads to ice melt, reducing albedo, leading to more absorption of solar radiation and further warming.

      • Water vapor feedback: Warming leads to more evaporation, increasing atmospheric water vapor (a greenhouse gas), which traps more heat and causes further warming.

    • Negative feedback loops counteract the initial warming or cooling, stabilizing the climate:

      • Cloud feedback (complex): Low clouds generally reflect sunlight (cooling effect), while high clouds can trap heat (warming effect). The net effect is uncertain.

      • Black body radiation: As Earth warms, it radiates more heat back into space, providing a fundamental negative feedback that prevents runaway warming.

  • Climate Sensitivity

    • Climate sensitivity is a measure of how much the Earth's global average surface temperature will change in response to a doubling of atmospheric carbon dioxide (CO_2) concentration.

    • It is a crucial metric for predicting future climate change and is typically expressed in degrees Celsius per doubling of CO_2.

    • The Intergovernmental Panel on Climate Change (IPCC) estimates the Earth's equilibrium climate sensitivity to be likely in the range of 2.5^]circ C to 4^]circ C.