KH

Exam 1 Review: Climate and Energy Balance

Weather vs. Climate

  • Weather: Actual state of the atmosphere at a particular time and place.

  • Climate: Statistical description of weather over a period, usually several decades.

  • Mark Twain: "Climate is what you expect; Weather is what you get."

What is Climate

  • Environment: Complex system of atmosphere, hydrosphere, cryosphere, lithosphere, biosphere, and their interactions.

  • Climate Change: Any systematic change in long-term statistics of climate elements (temperature, precipitation, winds) sustained over several decades.

  • Climate Normal: 30 years.

Open vs. Closed System

  • System: Arbitrary portion of the universe with boundaries, containing matter, energy, or both.

  • Open System: Exchanges both energy and mass with its environment.

  • Closed System: Exchanges energy but not mass with its environment.

Earth's Coordinate System

  • Equator.

  • Tropics: 1/2 of Earth's surface.

  • Mid-latitudes: 1/3 of surface.

  • Polar regions: 1/6 of surface.

How Science Works

  • Scientific Method: Systematic observation, measurement, experimentation; formation, testing, and modification of hypotheses; drawing conclusions and reporting.

  • Peer Review: Experts critically review work for errors or weaknesses; a highly effective filter.

Climate Change vs. Variability

  • Climate Variability: Deviations of climatic statistics over short periods (e.g., month, season, year) compared to long-term statistics.

  • Climate Change: Systematic change in long-term climate elements over several decades.

Temperature Record

  • Focus on Global Average Temperature; direct impact of increased GHGs.

  • Reliable in-situ data since mid-1800s; long-term records from ice and rock chemical analysis.

  • Temperature Anomaly: Difference between absolute temperature and a reference (typically a 30-year Climate Normal).

  • Earth has warmed by 1.29 ^{\circ}C ([2014-2023] - [1850-1900]); warming is not equally distributed, Northern Hemisphere warms faster (more land).

  • Satellite Measurement: Lowest 8 km atmosphere, trend: +1.3 ^{\circ}C/century, agrees with surface record.

  • Cherry Picking: Selecting short data segments to show results opposite to the full dataset.

Glacier/Ice Sheet Formation & Features

  • Glaciers form where snowfall exceeds snowmelt over many years.

  • Accumulating snow compacts into firn, then re-crystallizes into solid ice with air bubbles.

  • Loss of 1 tonne/m^2 ice = loss of 1.1m thickness.

  • Ice Sheets: Greenland and Antarctica; if melted, sea level would rise over 200 feet.

  • Arctic sea ice is melting faster than Antarctic.

Ocean Temperatures & Sea Level Rise

  • Majority (>90%) of excessive heat absorbed by oceans.

  • Sea Level Rise: Primarily due to land ice melting (glaciers and ice sheets) and water expanding as it warms (thermal expansion).

  • Melting sea ice has little impact on sea level rise.

Evidence Climate is Changing

  • Evidence is "unequivocal" that Earth is warming.

  • A single storm, hot/cold day, or single year are not signs of climate change.

Proxy Climate Records

  • Proxy Climate Records: Climate information prior to the instrument era, from sources like bedrock, sediments, ice cores, tree rings, fossils, etc.

  • Paleoclimatology: Reconstruction of past climates.

  • Tree Rings (Dendroclimatology): Wider rings = wet/warm years, dating back ~1000 years.

  • Glacial Erratic: Large rock or boulder transported and deposited by a glacier.

  • Ice Cores: Contain climate information (temperature from isotopes, CO_2 from air bubbles, dust from winds/volcanoes); dating back to ~2 million years.

  • Isotopes: Atoms with same protons but different neutrons (e.g., Oxygen--16, Oxygen--18).

    • Warmer Climates: More Oxygen--16 in oceans, more Oxygen--18 in ice cores.

    • Colder Climates: More Oxygen--18 in oceans, more Oxygen--16 in ice cores.

  • CO2 and temperature are correlated; current CO2 concentrations: 425 ppm.

  • Ocean Sediments: Continuous record from sedimentation; identification of organisms and isotope analysis distinguish past climatic episodes; dust indicates weather patterns.

Past Climate Fluctuations

  • Paleocene-Eocene Thermal Maximum (PETM) (55 MYA): Abrupt warming (5-9 ^{\circ}C) over a few thousand years, driven by massive GHG release.

Temperature

  • Measure of internal energy.

  • Scales: Fahrenheit (32^{\circ} freeze, 212^{\circ} boil), Celsius (0^{\circ} freeze, 100^{\circ} boil), Kelvin (SI unit, absolute; 0K = -273^{\circ}C).

Energy Transfer

  • Photon: Discrete energy packet with characteristic wavelength.

  • Conduction: Transfer of kinetic energy via collisions (contact).

  • Convection: Transfer of heat by mass movement of a fluid.

  • Electromagnetic Radiation: Transfers energy at speed of light through vacuum.

Radiation Characterization

  • Wavelength (\lambda): Distance between successive wave ridges/troughs; shorter wavelength means higher energy.

  • Frequency (f): Number of wavelengths passing a point per unit time.

  • c = f \lambda (inversely related, c = speed of light).

  • Electromagnetic Spectrum: Differentiates waves by wavelength.

    • Visible radiation: Perceptible to human eye.

    • Infrared (IR) radiation: Longer wavelengths, connected to atmospheric heating.

Blackbody

  • Idealized object absorbing all incoming radiation and emitting radiation across a range of wavelengths based on its temperature.

  • Examples: Sun, Earth (models how Earth absorbs and emits radiation).

  • Wein's Displacement Law: Wavelength of most intense radiation (\lambda_{max}) emitted by a blackbody is inversely proportional to its absolute temperature (T).

    • \lambda{max} = \frac{2897}{T} (\lambda{max} in \mu m, T in K).

    • Hot objects (Sun) emit peak at short (visible) wavelengths; cold objects (Earth) emit peak at longer (infrared) wavelengths.

  • Stefan-Boltzmann Law: Energy emitted per square meter (E) by a blackbody is proportional to the fourth power of its absolute temperature (T).

    • E = \sigma T^4 (\sigma is Stefan-Boltzmann constant).

    • If temperature doubles, emitted energy increases by 16 times.

Energy Balance

  • Radiative equilibrium: Incoming absorption (E{in}) equals outgoing emission (E{out}), leading to stable temperature.

    • E{in} > E{out} \Rightarrow warm; E{out} > E{in} \Rightarrow cool; E{in} = E{out} \Rightarrow stable temperature.

  • Solar Constant: Average solar radiation received per unit area at top of Earth's atmosphere when Sun is directly overhead; Earth's solar constant = 1360 W/m^2.

  • Albedo (\alpha): Fraction of incident photons reflected to space.

    • Earth's Albedo (\alpha) = 0.3 (i.e., \sim 30\% of solar energy is reflected).

  • Expected Earth Temperature without Greenhouse Effect: Setting E{in} = E{out} leads to T = 255K (-18^{\circ}C), lower than actual 288K (15^{\circ}C).

  • Greenhouse Effect: Atmosphere selectively absorbs infrared radiation from Earth's surface but transmits shortwave radiation.

    • N2 and O2 are not good absorbers of visible or infrared radiation.

    • Essential for life; without GHGs, Earth's equilibrium temperature would be below freezing.

  • N-Layer Model: Surface temperature depends on number of atmospheric layers (n), solar constant (S), and albedo (\alpha).

  • Takeaway: Earth's surface temperature is set by the requirement of energy-in = energy-out equilibrium; changes in n, S, or \alpha adjust temperature.

  • Planetary Examples: Venus has much higher temperature than Earth due to massive greenhouse effect, despite less E_{in} than Mercury, which has almost no atmosphere.