12.2 Climate sensitivity and uncertainty in projections

Climate sensitivity measures how Earth's temperature responds to doubling CO2. It's crucial for predicting future climate change impacts. Higher sensitivity means bigger temperature changes and more severe effects for the same greenhouse gas increase.

Climate models face uncertainties from emissions scenarios, feedback processes, and natural variability. These affect projections of future warming. The range of climate sensitivity estimates (1.5°C to 4.5°C per CO2 doubling) adds to the challenge of predicting long-term climate change.

Climate Sensitivity and Uncertainty in Climate Projections

Climate sensitivity definition and role

Top images from around the web for Climate sensitivity definition and role

• 

  Attribution of recent climate change - Wikipedia View original

  Is this image relevant?

• 

  PAGES - Past Global Changes - PAGES Magazine - Products - PAGES Magazine articles - Science ... View original

  Is this image relevant?

• 

  Attribution of recent climate change - Wikipedia View original

  Is this image relevant?

• 

  PAGES - Past Global Changes - PAGES Magazine - Products - PAGES Magazine articles - Science ... View original

  Is this image relevant?

1 of 2

Top images from around the web for Climate sensitivity definition and role

• 

  Attribution of recent climate change - Wikipedia View original

  Is this image relevant?

• 

  PAGES - Past Global Changes - PAGES Magazine - Products - PAGES Magazine articles - Science ... View original

  Is this image relevant?

• 

  Attribution of recent climate change - Wikipedia View original

  Is this image relevant?

• 

  PAGES - Past Global Changes - PAGES Magazine - Products - PAGES Magazine articles - Science ... View original

  Is this image relevant?

1 of 2

• Measures how much Earth's average surface temperature changes in response to doubling atmospheric CO2 concentration
  • Expressed in °C of warming per doubling of CO2
• Higher climate sensitivity means larger temperature changes for a given increase in greenhouse gas concentrations
  • Implies more significant future climate change impacts (sea level rise, more frequent heatwaves)
• Lower climate sensitivity suggests smaller temperature changes and less severe impacts for the same increase in greenhouse gases
• Key factor in determining magnitude and rate of future climate change in response to human-induced greenhouse gas emissions (fossil fuel combustion, deforestation)

Sources of climate model uncertainty

• Uncertainty in future greenhouse gas emissions scenarios
  • Depends on factors like population growth, economic development, climate policies
• Incomplete understanding of certain climate feedback processes
  • Cloud feedbacks, carbon cycle feedbacks (permafrost thaw), ice-albedo feedback
• Natural climate variability on various timescales
  • El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO)
• Limitations in climate model resolution and representation of physical processes
  • Models may not capture all relevant processes or may simplify complex interactions (atmosphere-ocean coupling)
• Uncertainty in the magnitude of climate sensitivity itself
  • Estimates range from about 1.5°C to 4.5°C per doubling of CO2

Equilibrium climate sensitivity estimates

• Long-term (multi-century) change in global average surface temperature after doubling atmospheric CO2 concentration
  • Assumes climate system reaches a new equilibrium state
• Estimated using various methods:
  1. Climate model simulations
  2. Analysis of historical temperature and forcing data
  3. Paleoclimate evidence from past climate changes (ice cores, tree rings)
• Intergovernmental Panel on Climate Change (IPCC) provides likely range for ECS of 1.5°C to 4.5°C
  • Represents 66% probability interval based on multiple lines of evidence
• Wide range of ECS estimates contributes to uncertainty in long-term climate change projections

Implications for policy and planning

• Higher climate sensitivity implies more severe impacts and greater need for ambitious mitigation efforts to limit warming
  • May require more stringent emissions reductions to meet temperature targets (Paris Agreement goals)
• Lower climate sensitivity suggests less severe impacts, but does not eliminate need for mitigation and adaptation
  • Even at lower end of sensitivity range, significant climate change impacts still expected (coastal flooding, crop yield reductions)
• Uncertainty in climate sensitivity and projections complicates decision-making and risk assessment
  • Policymakers must consider range of possible outcomes and plan for resilience across scenarios
• Adaptation planning should account for uncertainty by considering multiple climate change scenarios
  • Strategies should be flexible and robust to perform well under range of possible future conditions (drought-resistant crops, flood protection infrastructure)
• Iterative risk management approaches can help navigate uncertainty
  • Involves ongoing assessment, adjustment, integration of new information as it becomes available