Yes. In IB ESS Subtopic 6.2: Climate change: causes and impacts (SL and HL), the syllabus states that evidence suggests Earth has already crossed the planetary boundary for climate change.
The planetary boundaries model identifies limits to human disturbance of major Earth systems. Remaining within these limits defines a safe operating space for humanity; crossing a boundary increases the risk of abrupt, large-scale, and potentially irreversible environmental change.
Anthropogenic emissions from fossil-fuel combustion, deforestation, agriculture, and industry have increased atmospheric concentrations of greenhouse gases. These gases absorb and re-emit infrared radiation, strengthening the enhanced greenhouse effect and causing global warming. This disrupts the global energy balance and affects connected systems such as oceans, ice, ecosystems, and human societies.
| Evidence or process | Significance |
|---|---|
| Rising atmospheric carbon dioxide | Strengthens the enhanced greenhouse effect |
| Increasing global mean temperature | Indicates sustained warming rather than short-term weather variation |
| Melting glaciers and declining Arctic sea ice | Reduces surface albedo, creating an amplifying positive feedback loop |
| Sea-level rise and biome shifts | Demonstrate impacts across ecological and societal systems |
A named example is the Arctic, where declining sea ice exposes darker ocean water. More solar radiation is absorbed, causing further warming and melting. This positive feedback may move the climate system closer to tipping points.
A common misconception is that crossing the boundary means immediate, unavoidable global collapse. It does not. A planetary boundary is a risk threshold, not necessarily a tipping point; crossing it means the probability of severe and irreversible change has increased. Mitigation can still reduce further disturbance, while adaptation can reduce societal impacts.
For HL, connect this to environmental justice: countries least responsible for greenhouse-gas emissions are often among the most vulnerable to climate impacts.
Exam technique: For an “explain” question, link emissions to the enhanced greenhouse effect and system impacts. For “evaluate” or “to what extent,” consider evidence, uncertainty, mitigation, contrasting perspectives, and finish with a supported judgement.