Earth Systems and Interactions
This section covers Earth systems and interactions. The exam tests whether you can treat Earth as coupled reservoirs of matter and energy, trace fluxes between geosphere, atmosphere, hydrosphere and biosphere, and reason about feedbacks and timescales rather than naming parts in isolation.
Reservoirs, fluxes and feedbacks
- A reservoir stores matter or energy; a flux is the transfer per unit time; residence time is reservoir divided by flux.
- Positive feedback amplifies a perturbation; negative feedback damps it. Always state the mechanism and the timescale.
- Carbon couplings include photosynthesis and respiration, ocean solubility and biological pumps, carbonate compensation, and silicate weathering, the long-term CO2 sink.
- Water and energy couplings include evaporation, latent heat, snow and ice albedo, and cloud radiative effects.
Worked example
An explosive volcano injects sulfur dioxide into the stratosphere. Sulfate aerosols reflect sunlight, producing surface cooling for one to three years. This is a negative radiative forcing, but it is short-lived because aerosols are removed by sedimentation and washout. The same eruption's CO2 has a much smaller immediate radiative effect but accumulates over centuries and warms. Reasoning: identify the reservoir, the flux, the residence time and the sign of the forcing before predicting climate response.
Traps
- Confusing a large reservoir with a fast flux: the ocean holds much carbon but exchange with the atmosphere is not instantaneous.
- Assigning a feedback sign without a mechanism.
- Mixing short-lived aerosol cooling with long-lived CO2 warming.
- Ignoring timescale: tectonic and biological feedbacks operate over very different periods.