Concluding remarks

Interaction between the natural environment and the human society

• Very complex
• In the 21st century, this cause-and-effect chain cannot be ignored:
  carbon dioxide emission from fossil fuel use" -> climate change (global warming)" -> impacts on human society

Stock-and-flow structure

Time lag, not simple delay, but time-integral, exists.

• Carbon cycle: stock and flow of (mass of) carbon atoms
  • Emission from fossil fuel is a flow component.
  • Other natural flow components exist, and their quantities may be modified.
  • (For policymaking) mass of carbon dioxide in the atmosphere is the stock to be mainly considered.
  • Other major stocks: mass of organic matter on land (plants, soil etc.), and mass of carbonates in the ocean, etc.
• Climate system: stock and flow of energy
  • Radiative forcing is the major flow term.
  • Changes in atmospheric CO₂ content modifies radiative forcing. There is no appreciable time lag here.
  • (For century time scale) heat content of the upper (wind-driven) ocean is the major stock.
• Human society: (probably many)

(Correlation between "cause" and "effect" time series is not usually very good.)