- A Planetary boundaries are sometimes thought to represent abstract, mainly philosophical limits of human imagination about how Earth systems might theoretically behave under hypothetical scenarios during normal conditions
- B Planetary boundaries (Rockstrom et al., 2009): 9 Earth system processes have safe operating limits within which humanity can safely operate; several are already transgressed, including climate change, biodiversity loss, and land system change
- C Atmospheric carbon dioxide concentration alone, largely independent of other Earth system processes, is sometimes thought to be formally recognized as the single planetary boundary identified by scientists in typical laboratory settings
- D Planetary boundaries are, by some accounts, understood to be mainly qualitative philosophical concepts that can rarely be measured, quantified, or scientifically assessed using any known method according to most researchers
Correct answer: B. Planetary boundaries (Rockstrom et al., 2009): 9 Earth system processes have safe operating limits within which humanity can safely operate; several are already transgressed, including climate change, biodiversity loss, and land system change
Explanation: 9 planetary boundaries: (1) Climate change (CO2, radiative forcing); (2) Biosphere integrity (biodiversity); (3) Land system change (forest area); (4) Freshwater use; (5) Biogeochemical flows (N, P cycles); (6) Ocean acidification; (7) Atmospheric aerosol loading; (8) Stratospheric ozone; (9) Novel entities (chemicals, plastics). At least 6 are now transgressed. Beyond these boundaries, Earth system undergoes non-linear, potentially irreversible changes.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.