Future climate: projections, impacts on environments, tipping points

Climate Change: Future Projections, Impacts, Tipping Points & Governance

Learning Objective (AO1‑AO3)

Students will be able to:

• AO1 – Knowledge: describe future climate pathways, physical and human impacts, mitigation and adaptation measures, and the concept of climate‑tipping points.
• AO2 – Application & Analysis: interpret data (graphs, tables, maps) and analyse cause‑and‑effect relationships across scales.
• AO3 – Evaluation: assess the effectiveness of mitigation, adaptation and governance strategies, considering equity, legitimacy and flexibility.

Key‑Concept Reminders

Scale – from global emission pathways to local community actions.
Change over time – how projected temperature, sea‑level and extreme events evolve to 2100.
Cause‑and‑effect – links between greenhouse‑gas emissions, radiative forcing, feedbacks and impacts.
Systems & interactions – Earth‑system components (atmosphere, ocean, cryosphere, biosphere) and human systems (economy, health, agriculture).
Diversity, equality & inclusion – differing vulnerabilities of peoples, genders, ages and indigenous groups.

1. Future Climate Projections

1.1 Emissions Pathways & Global Carbon Budgets (AO1)

The IPCC uses Representative Concentration Pathways (RCPs) to describe possible trajectories of greenhouse‑gas concentrations and the associated radiative forcing by 2100. Each RCP can be translated into a global carbon budget – the total CO₂ that may be emitted while staying below a given temperature limit.

^†Median of CMIP5 model ensembles; ranges show model spread.

1.2 Climate Sensitivity & Radiative Forcing (AO1)

• Equilibrium Climate Sensitivity (ECS): temperature rise for a sustained doubling of CO₂, ≈ 3 °C (range 1.5–4.5 °C).
• Effective Climate Sensitivity (λ): relates total radiative forcing (F) to temperature change (ΔT):
  ΔT = λ · F where λ ≈ 0.8 °C (W m⁻²)⁻¹ for the present climate.
• Radiative Forcing (F): net change in Earth’s energy balance, measured in watts per square metre. CO₂ doubling ≈ 3.7 W m⁻².

1.3 Uncertainty & Model Spread (AO2)

Key sources of uncertainty:

• Cloud feedbacks and aerosol interactions.
• Earth‑system feedbacks (e.g., permafrost carbon release).
• Socio‑economic assumptions embedded in each RCP.

2. Physical Impacts of Climate Change (AO1‑AO2)

1. Temperature Extremes
   • More frequent/intense heatwaves → higher mortality (elderly, outdoor workers).
   • Poleward and upward shift of bioclimatic zones; species migrate to higher latitudes/elevations.
2. Hydrological Cycle
   • Intensified precipitation in mid‑latitudes → increased flood risk.
   • Higher evapotranspiration in arid zones → desert expansion, reduced groundwater recharge.
3. Sea‑Level Rise (SLR)
   • Thermal expansion + melting of glaciers/ice sheets.
   • Coastal erosion, salt‑water intrusion, loss of mangroves and low‑lying wetlands.
   • Estimated displacement: up to 280 million people by 2100 under RCP8.5.
4. Ocean Acidification
   • CO₂ absorption lowers pH, reducing carbonate ions.
   • Negative impacts on coral reefs, shell‑forming plankton and commercial fisheries.

3. Human‑System Impacts (AO1‑AO2)

• Agriculture
  • Shift in growing seasons; tropical rain‑fed crops may lose yield, while higher latitudes could gain.
  • Increased pest pressure and water stress.
• Health
  • Heat‑related illness and mortality.
  • Expansion of vector‑borne diseases (malaria, dengue, Lyme) into previously unsuitable regions.
• Infrastructure
  • Higher costs for flood defences, drainage upgrades, and building cooling.
  • Coastal roads, ports and airports threatened by SLR and storm surge.
• Migration & Displacement
  • “Climate refugees” from low‑lying islands (e.g., Kiribati) and drought‑prone inland areas.
  • Potential for conflict over water and food resources.

Social‑Justice Dimension (Diversity, Equality & Inclusion)

Vulnerability is uneven. Women often bear a disproportionate burden in agriculture and water collection; children and the elderly are more susceptible to heat stress; indigenous peoples may lose cultural sites and traditional livelihoods when ecosystems shift. Low‑income countries typically have less capacity to adapt, making equity a central theme in the syllabus.

4. Mitigation vs. Adaptation (AO1‑AO3)

5. Climate Tipping Points (AO1‑AO2)

A tipping point is a threshold beyond which a system rapidly shifts to a new, often irreversible, state.

Case‑Study Box – Permafrost Thaw in Siberia (High‑Income, Low‑Population)

Cause: Rising Arctic temperatures > 2 °C.
Impact: Release of up to 1,500 Gt C, increasing atmospheric CH₄ concentrations.
Management: Monitoring networks, research into geo‑engineering of permafrost (still experimental).
Evaluation (AO3): High scientific uncertainty limits policy action; however, early monitoring improves adaptive capacity.

6. Governance Responses (AO1‑AO3)

6.1 International Regimes

• UNFCCC – framework for global cooperation.
• Paris Agreement (2015) – nationally determined contributions (NDCs) to keep warming < 2 °C, pursue 1.5 °C.
• IPCC Assessment Reports – provide the scientific basis for policy.
• Global Carbon Budget initiatives – track emissions against pathways.

6.2 National Policies (Examples)

• Germany (High‑income): Renewable Energy Act (EEG) → > 40 % electricity from renewables by 2030; carbon‑pricing via EU ETS.
• Bangladesh (Low‑income): National Adaptation Programme of Action (NAPA) – flood‑plain zoning, cyclone shelters, climate‑resilient rice varieties.

6.3 Local & Community Action

• Urban heat‑island mitigation – green roofs, street trees, reflective paving.
• Community‑based disaster risk reduction – early‑warning networks, evacuation drills.
• Participatory coastal‑defence planning – managed retreat, mangrove restoration.
• Local renewable projects – solar PV schemes, micro‑hydro installations.

Evaluating Governance Effectiveness (AO3)

7. Suggested Diagram (for exam revision)

8. Summary Points (Quick Revision)

1. Future pathways are expressed as RCPs; each has a corresponding global carbon budget and temperature range (ECS ≈ 3 °C per CO₂ doubling).
2. Physical impacts include hotter extremes, altered hydrology, sea‑level rise and ocean acidification; uncertainties stem from feedbacks and socio‑economic scenarios.
3. Human systems face challenges in agriculture, health, infrastructure and migration, with clear equity dimensions.
4. Mitigation tackles the cause of climate change; adaptation reduces vulnerability. Both require evaluation against AO3 criteria.
5. Tipping points (e.g., Arctic sea‑ice loss, Greenland melt) could trigger rapid, irreversible change.
6. Effective governance operates at three scales, integrates mitigation and adaptation, and must be judged on legitimacy, effectiveness, equity and flexibility.