EARTH'S CLIMATE SYSTEM - Chapter 2 Flashcards
Overview
Topic: Earth’s climate system and its components; aims include understanding heat movement from the Sun through the climate system back to space, the greenhouse effect, albedo, ocean heat transport and stability, thermohaline circulation, atmospheric circulation (Coriolis effect and Hadley Cells), monsoons, sea ice, glacial ice, continental ice, and biosphere interactions with climate.
The material ties energy input to planetary response and highlights key feedbacks between atmosphere, oceans, ice, and life.
Greenhouse Effect
The greenhouse effect traps longwave radiation emitted by the Earth’s surface, leading to a warmer surface climate.
It is stated to trap about
~95% of longwave radiation emitted from the Earth’s surface, keeping the surface warm.
Resulting surface temperature is about T_{ ext{surface}} \,\approx \,15\,^{\circ}\mathrm{C} rather than the ~-16\,^{\circ}\mathrm{C} that would occur without the effect.
Atmosphere composition (major constituents):
Nitrogen: N_2\approx 78\%
Oxygen: O_2\approx 21\%
Water vapor: less than 1\% of dry atmosphere
Carbon dioxide: \mathrm{CO_2} \approx 0.04\%
Methane: \mathrm{CH_4} \approx 0.00018\%
Implication: The greenhouse effect is a natural and essential process for maintaining habitable temperatures, but changes in greenhouse gas concentrations influence radiative balance and climate.
Energy Budget and Albedo (Shortwave vs Longwave; Latitudinal Effects)
Incoming solar radiation at the top of the atmosphere is about S\approx 342\ \text{W m}^{-2} (often denoted as solar constant times geometric factors).
At the top of the atmosphere: 100% of incoming shortwave energy is considered for the budget.
Distribution of shortwave radiation (as shown in the material):
Reflection/scattering by the atmosphere: 26\%
Absorption by the Earth's surface: 23\%
Absorption by the Earth system overall: 47\%
Longwave radiation and heat transfer (interaction with the atmosphere and surface):
Reflection/scattering of longwave radiation: 30\%
Radiated longwave energy toward space: 70\%
Back radiation and heat transfer details emphasize:
Back radiation to the surface constitutes a major component of the energy budget, helping to keep surface temperatures elevated relative to space.
A portion of energy is lost to space via latent and sensible heat fluxes: approximated as 29\% (latent+sensible heat losses).
Key takeaway: The balance between absorbed shortwave energy and emitted longwave energy, moderated by back radiation (greenhouse effect) determines the near-surface climate state.
Albedo, Latitude, and Absorption/Reflection
Albedo and geometry determine how much solar energy is absorbed vs reflected.
Conceptual point: "ANGLES + ALBEDO = DIFFERENT ABSORPTION AND REFLECTION".
Latitude effects:
At the poles (e.g., North/South Pole), radiation is spread over a large area but may arrive at shallow angles, affecting absorption and reflection.
At the equator, radiation is spread over a smaller area? (in practice, the equator receives more direct sunlight per unit area, leading to higher local heating but global energy balance depends on redistribution).
A schematic relationship (as described): Radiation arriving at different latitudes interacts with surface and cloud albedo differently, leading to latitudinal variations in absorbed energy and hence climate patterns.
Observed values (illustrative): The solar input at the top of the atmosphere is about 342\ \text{W m}^{-2}; portions are reflected by clouds and surface, and portions absorbed by oceans and land.
Seasons, Solstices, and Equinoxes
Equinoxes and solstices mark the tilt-driven seasonal cycle.
March 21–22 (March equinox): Sun vertical at the equator (0° latitude).
June 21–22 (summer solstice): Sun vertical at 23.5^{\circ}\mathrm{N} (Tropic of Cancer).
September 22–23 (autumn equinox): Sun vertical at the equator (0°).
December 21–22 (winter solstice): Sun vertical at 23.5^{\circ}\mathrm{S} (Tropic of Capricorn).
Implication: Seasonal distribution of solar radiation shifts with latitude, driving seasonal heating, ITCZ migration, and monsoon dynamics.
Clouds and Heat Capacity
Clouds introduce complexity into the climate system by affecting both the receipt (shortwave) and reflection (albedo) of solar radiation.
Key questions raised in the material:
How do clouds affect heat receipt in deserts vs. oceans?
How does heat capacity differ between low-latitude oceans and low-latitude landmasses?
What is the response time of cloud/ocean/land feedbacks to forcing?
These questions highlight major uncertainties and the role of feedbacks in the climate system.
Oceans and Heat Transport
Oceans contain a large reservoir of heat and therefore dominate much of the climate system’s energy storage and transport.
Specific heat of water is high, contributing to large thermal inertia; this leads to smaller diurnal and seasonal temperature swings on a global average, and strong coastal versus inland differences in temperature change.
The oceans act as a global heat engine, distributing energy via currents and mixing processes, which stabilizes or destabilizes regional climates.
Heat Transfer in the Oceans
Large-scale latitudinal variation in heat transfer within the oceans is shown (e.g., latitudinal bands such as 60^{\circ} and 30^{\circ} N/S).
Mechanisms include advection by currents, upwelling, and mixing which transport heat from equatorial regions to higher latitudes and influence regional climate stability.
Deep Ocean Circulation (Thermohaline Circulation)
Key concepts:
Thermocline: a layer in the ocean where temperature changes rapidly with depth, separating surface mixed layer from deep ocean.
Thermohaline circulation: driven by density differences caused by salinity and temperature changes; denser water sinks (deepwater formation) and returns via upwelling and slower deep currents.
Driving factors:
Salinity (salt content) and temperature differences influence water density and vertical movement.
Timescale:
Deep ocean circulation has a long response time, of the order of \tau\approx 10^3\ \text{years} for the full cycle from surface to deep and back.
How does it come back to the surface?
Upwelling and vertical mixing bring deep water back toward the surface in certain regions, enabling exchange between deep and surface layers and sustaining nutrient and heat transport.
Atmospheric Circulation: Hadley Cells and Coriolis Effect
Hadley cells:
Large-scale tropical circulation patterns with warm air rising near the equator (low pressure), moving poleward aloft, then sinking in subtropics (high pressure) and returning equatorward near the surface.
Coriolis effect:
Deflects moving air due to Earth’s rotation, contributing to the characteristic wind patterns and the offset of weather systems from the equator.
Fronts and ITCZ (Intertropical Convergence Zone):
The convergence of trade winds near the equator forms a band of rising air with fronts and heavy precipitation; ITCZ location migrates seasonally with the Sun.
Typical Hadley circulation indicators in the material indicate actions at around 30° latitude and ITCZ variability with seasons.
Monsoons and Orographic Precipitation
Monsoons arise from differential heating between land and sea, amplified by seasonal shifts in solar radiation.
A Summer Monsoon:
Strong solar radiation heats landmass, creating a low-pressure system.
Onshore moisture transport leads to heavy rainfall over the land.
A Winter Monsoon:
Weaker solar radiation cools the land, creating a relatively high-pressure system.
Cooler, drier air results in a different wind pattern and weaker rainfall.
Orographic precipitation:
Mountains force air to rise, cooling and condensing moisture, producing heavy precipitation on the windward slopes.
In the diagram, low pressure over warmer seas and high pressure over cooler land surfaces drive the seasonal monsoon dynamics.
Sea Ice
Sea ice acts as a barrier to heat exchange by insulating the ocean from the atmosphere and by altering albedo.
Albedo effect:
Sea ice reflects more solar radiation than open water, increasing reflectivity and reducing heat absorption.
Seasonal dynamics:
Antarctic sea ice forms and melts annually; Arctic sea ice can persist for several years in some regions.
Sea ice maximum extent occurs in spring; minimum extent occurs in autumn (seasonal cycle opposed to the maximum/minimum phrasing common in other contexts).
Implications for sea level:
Sea ice melt does not by itself raise sea levels (ice already floating); melting of land-based ice (glaciers, ice sheets) does contribute to sea level rise.
Glacial Ice
Mountain glaciers:
Can reach sea level in the coldest places; typically several kilometers long and hundreds of meters wide/thick.
They respond to climate by advancing/retreating based on balance between accumulation and ablation.
Continental Ice
Continental ice sheets exist in Greenland and Antarctica.
Spatial scale:
Hundreds to thousands of kilometers in horizontal extent; thickness ranges roughly from about 1 to 4 kilometers.
Sea-level impact:
They have the potential to contribute about \Delta SL \approx 70\ \text{m} of sea level change if fully melted (as per the slide’s estimate).
Dynamics:
They are dynamic systems with ablation and accumulation continually occurring, and they also serve as climate archives (ice cores).
Biosphere and the Carbon Cycle
Major carbon reservoirs (pre-industrial, gigatons):
Vegetation: 610\ \mathrm{Gt}\,\mathrm{C}
Atmosphere: 600\ \mathrm{Gt}\,\mathrm{C}
Soils: 1560\ \mathrm{Gt}\,\mathrm{C}
Ocean mixed layer: 1000\ \mathrm{Gt}\,\mathrm{C}
Deep ocean: 38{,}000\ \mathrm{Gt}\,\mathrm{C}
Sediments and rocks: 66{,}000{,}000\ \mathrm{Gt}\,\mathrm{C}
Carbon exchange rates (gigatons/year) – biosphere–atmosphere–ocean fluxes:
The diagram indicates a network of exchanges among vegetation, atmosphere, soils, and oceans with values in the tens to hundreds of gigatons per year, illustrating that the biosphere, soils, and oceans continually exchange carbon with the atmosphere.
Specific labeled values in the slide’s diagram include numbers such as 100, 50, 74.6, 0.6, 0.8, 37, 0.2, etc., but exact pairings between reservoirs are not clearly labeled in the provided text.
Biosphere impacts on climate:
When plants grow, they remove CO2 from the atmosphere; when they die, they add CO2 back.
Transpiration adds water vapor to the atmosphere, contributing to greenhouse effects and humidity patterns.
Climate influences biosphere productivity: more rainfall and optimal temperature promote growth; nutrient availability (notably nitrogen and phosphorus) controls growth and can be enhanced by upwelling.
Nutrient limitation and upwelling:
Upwelling delivers nutrients (N and P) to coastal regions, supporting biological productivity and carbon uptake.
Connections, Implications, and Practical Roles
The climate system is a coupled web:
Energy input from the Sun drives atmospheric circulation, ocean currents, ice formation/melt, and biospheric processes.
The atmosphere and oceans exchange heat, moisture, and gases, creating feedback loops (e.g., cloud feedbacks, ice-albedo feedback, biosphere carbon exchange).
Small changes in greenhouse gas concentrations can shift radiative balance and climate states due to system feedbacks.
The major reservoirs indicate that most carbon is stored in sediments/rocks and deep oceans, with humans currently perturbing the surface reservoirs (vegetation, soils, atmosphere, and shallow oceans).
Practical implications include understanding how regional climates respond to ocean heat uptake, how sea ice loss affects albedo and heat absorption, and how biosphere management could influence carbon uptake and climate feedbacks.
Summary of Key Quantities (for quick revision)
Shortwave input at top of atmosphere: S\approx 342\ \text{W m}^{-2}
Greenhouse effect outcome: surface temperature ~15^{\circ}\mathrm{C} vs ~-16^{\circ}\mathrm{C} without it
Atmospheric composition (dry): N2\approx 78\%, O2\approx 21\%, \mathrm{H2O}\lesssim 1\%, \mathrm{CO2}\approx 0.04\%, \mathrm{CH_4}\approx 0.00018\%
Latitudinal solar geometry concepts: Equator vs Poles in terms of energy absorption/reflection (ANGLES + ALBEDO)
Deep ocean circulation timescale: \tau\approx 10^3\ \text{yr}
Latitudinal bands important for heat transfer: around 60^{\circ}\, and 30^{\circ}\, N/S
Major carbon reservoirs (Gt C): Vegetation 610\,;\;\text{Atmosphere } 600\;\text{Soils } 1560\;\text{Ocean mixed layer } 1000\;\text{Deep ocean } 38000\;\text{Sediments/rocks } 66000000
Maximum/minimum sea ice extents and seasonal timing (Antarctic vs Arctic patterns).
// End of notes