Wk9: Earth's Spheres

What are Earth’s major spheres? 

Atmosphere, hydrosphere, biosphere, lithosphere, anthroposphere — all interconnected.

Definition of the atmosphere 

Envelope of gases gravitationally bound to Earth; 78% N₂, 21% O₂, stratified by temperature.

Why the atmosphere is considered “thin” 

99% of atmospheric mass lies below ~30 km compared to Earth’s 6371 km radius.

What drives global atmospheric circulation? 

Uneven solar heating → Hadley cells, pressure belts, jet streams.

What is the greenhouse effect? 

Atmosphere traps outgoing infrared radiation, warming Earth’s surface.

Relationship between CO₂ emissions and temperature 

Global temperature increases linearly with cumulative CO₂ emissions (TCRE).

Definition of the hydrosphere 

All water on Earth: oceans, rivers, lakes, groundwater, soil moisture, ice.

Ocean properties that vary spatially 

Sea surface temperature, salinity, and density.

Definition of the biosphere 

All living and recently dead (not yet decomposed) carbon‑based life on Earth.

What causes seasonal CO₂ fluctuations in the Keeling Curve? 

Northern Hemisphere plant photosynthesis (summer drawdown, winter release).

Definition of the anthroposphere 

Total human presence and activity influencing the Earth system.

Definition of the Anthropocene 

Proposed epoch when humans became a dominant force shaping Earth systems.

Examples of early human Earth‑system impacts 

Megafauna hunting, early agriculture, tropical forest modification, fire use.

The Columbian Exchange Earth‑system impact 

Mass mortality → forest regrowth → CO₂ drop (~3.5 ppm) around 1610 CE.

The Great Acceleration 

Post‑1950 exponential rise in population, energy use, emissions, land conversion, and resource extraction.

Planetary boundaries concept 

Defines safe operating space for humanity; several boundaries now transgressed (e.g., climate, biosphere integrity).

Definition of a tipping point 

Threshold where a system shifts abruptly and irreversibly to a new state.

What is the AMOC? 

Atlantic Meridional Overturning Circulation — a major heat‑transport system driven by temperature and salinity.

How AMOC collapse affects climate 

North Atlantic cooling, Southern Hemisphere warming, shifting rain belts, sea‑level rise on US east coast.

Amazon rainforest tipping risk 

Deforestation + drought + fire reduce resilience → potential shift from rainforest to savannah, weakening global carbon sink.