Global Climate Projections

• Coupled Model Intercomparison Project
• Use specified emissions scenario to drive coupled climate models
• Comprehensive model runs for various scenarios through 2100
• Projected changes in climate
• Temperatures
• Considerable spread between models, but trends are clear
• About half of projected 2011-30 change already committed
• Projected changes differ in magnitude but show similar spatial patterns
• Warming greatest in tropical upper troposphere and near surface in north polar regions
• Warming greatest on continents
• Clouds and precipitation
• Precipitation and pressure changes indicate expanded Hadley Cells
• Cloud cover decreases in midlatitude regions
• Soil moisture and runoff decrease in most subtropical and midlatitude regions
• Sea ice
• Substantial declines in both hemispheres, particularly in summer
• Arctic sea ice nearly disappears in summer
• Variability and extremes
• Mean becomes more El Nino-like, but not clear if El Nino cycle strengthens or weakens
• Increase in both precipitation intensity and dry days
• Large decrease in frost days, increase in heat waves, longer growing season
• Biogeochemical changes
• Carbon/climate feedbacks
• Increasing temperature leads to decreased carbon uptake
• Requires reduced emissions for stabilization, but uncertainty is large
• Ocean chemistry
• Acidification leads to possible undersaturation and dissolution of calcium carbonate
• Estimates of uncertainty
• Model agreement good for temperature and large scale precipitation
• Internal variability substantial at small scales, but not at large scales
• Uncertainty increases substantially with time - differences between models and scenarios
• Sea level change
• Thermal expansion of around 0.2m - 0.3m by 2100
• Overall change of 0.3m - 0.4m by 2100, but with large uncertainty