(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Climate Models Primary Source: IPCC WG-I Chapter 8 - Climate Models and Their Evaluation

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Part 1: Model Structure

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) The Climate System How do we simulate this?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Starting Point: Fundamental Laws of Physics 1. Conservation of Mass 2. First Law of Thermodynamics 3. Newton’s Second Law Plus conservation of water vapor, chemical species, … But - these are complex differential equations! How can we use them? By solving them on a grid.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Global Climate Models: Structure (Bradley, 1999)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Resolution Increases over Time Increased computing power has allowed increased resolution Computing demand increases inversely with cube of horizontal resolution.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Development of Global Climate Models (GCMs) … and increasing complexity. Which should be favored?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Differing scales: distributed surface properties Global Climate Models: Land-Atmosphere Link

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Global Climate Models: Development of Ocean Models (Bradley, 1999)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Global Climate Models: Parameterization What’s a model to do? Important processes smaller than a grid box: e.g., thunderstorms (atmospheric convection) few km ( Parameterization: Represent the effects of the unresolved processes on the grid. Assume that unresolved processes are at least partly driven by the resolved climate.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Higher Resolution Can Help Regional (limited-area) Climate Model ~ 0.5˚ (lat) x ~ 0.5˚ (lon) Part of a Global Climate Model 2.5˚ (lat) x 3.75˚ (lon) 2.5˚ (lat) x 3.75˚ (lon)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Higher Resolution Can Help Regional (limited-area) Climate Model ~ 0.5˚ (lat) x ~ 0.5˚ (lon) Part of a Global Climate Model 2.5˚ (lat) x 3.75˚ (lon) 2.5˚ (lat) x 3.75˚ (lon)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) End Part 1: Model Structure

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Part 2: Model Evaluation

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) How Are Models Evaluated? Testing against observations (present and past) Testing against observations (present and past) Comparison with other models Comparison with other models Metrics of reliability Metrics of reliability Comparison with numerical weather prediction Comparison with numerical weather prediction

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) What Limits Evaluation? Unforced (internal) variability Unforced (internal) variability Availability of Observations Availability of Observations Accuracy of Observations Accuracy of Observations Accuracy of Boundary Conditions (Forcing) Accuracy of Boundary Conditions (Forcing) These help determine what is “good simulation”.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) GCM Simulations of Global T ~ 5-95% confidence limits (obs) 58 simulations, 14 GCMs Ensemble Average

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Time Average Surface Temperature ( ) Mean Model: Average of 23 GCMs ˚C

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Errors in Simulated Surface Temperature ( ) Lines: Observed mean Colors (top): Ensemble mean - obs. Colors (bottom):RMS differences in simulated- observed time series (i.e., typical error) Spatial pattern correlation: ~ 98% (individual models)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Annual Variability (Seasons) Lines: Observed Standard Deviation (of monthly means) Colors: Ensemble mean - observations

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Diurnal Temperature Range ( ) Mean Model: Average of 23 GCMs ˚C Tendency to be smaller than observed Problems with clouds? Boundary layer?

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Atmospheric Zonal Average ( ) Mean Model: Average of 20 GCMs Vertical Axes: Left - Pressure (millibars) Right - Elevation (kilometers) Tendency for cool polar tropopause. Persistent feature of GCMs, though now smaller K

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Mean Reflected Solar Radiation Satellite Observations (solid) Average of 23 GCMs (dashed) Colors: Individual Models ( )

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Mean Emitted Infrared Radiation Satellite Observations (solid) ( ) Average of 23 GCMs (dashed) Colors: Individual Models

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Zonal Average Precipitation Observations (solid) ( ) Average of 23 GCMs (dashed) Colors: Individual Models

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Annual Mean Precipitation ( ) Observations Average of 23 GCMs

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Atmospheric Specific Humidity ( ) Mean Model: Average of 20 GCMs Moist bias in tropical troposphere g/kg Vertical Axes: Left - Pressure (millibars) Right - Elevation (km) (bias) - 40% + 40%

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Ocean (Potential) Temperature ( ) Mean Model: Average of 18 GCMs

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Ocean Salinity ( ) Mean Model: Average of 18 GCMs PSU Vertical Axes: Depth (m) PSU = “practical salinity units” based on conductivity of electricity in water based on conductivity of electricity in water PSU = 35  water is 3.5% salt PSU = 35  water is 3.5% salt

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Ocean Heat Transport (Feb 85 - Apr 89) Models:

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Sea Ice Simulation March September 14 GCMs ( ) “Number of Models” = models with ice cover > 15% in the 2.5˚ x 2.5˚ region. Red lines: Observed 15% concentration boundaries

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) El Niño - Southern Oscillation (ENSO) “Power” = amount of variability occurring for a cycle length (period) Recent GCMs (~ ) Previous generation GCMs (~ )

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Are Models Improving? - 1 “Normalized” = RMS error / observed space-time variability

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Are Models Improving? - 2 “Performance Index” combines error estimates of Sea level pressureTemperatureWinds HumidityPrecipitationSnow/Ice Ocean salinityHeat flux (Reichler and Kim, 2007)

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) End Part 2: Model Evaluation

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Part 3: Model Feedbacks

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) How does Earth’s temperature get established and maintained? Positive Feedback: Example

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) IR radiation absorbed & re-emitted, partially toward surface Solar radiation penetrates Greenhouse Effect - 1

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Greenhouse Effect - 2 IR radiation absorbed & re-emitted, partially toward surface Emitted IR: ~ W-m Net IR: ~ W-m

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Cooler atmosphere: - Less water vapor - Less IR radiation absorbed & re-emitted Solar radiation penetrates Greenhouse Effect - 3

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Cooler atmosphere: - thus less surface warming - cooler surface temperature Solar radiation penetrates Greenhouse Effect - 4

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) 1.Perturb climate system 2.Positive feedback moves climate away from starting point 3.A destabilizing factor Other examples: - ice-albedo feedback - ice-albedo feedback - CO 2 -ocean temperature feedback - CO 2 -ocean temperature feedback Positive Feedback

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) 1.Perturb climate system 2.Negative feedback moves climate back toward starting point 3.A stabilizing factor Example: 1.Decrease Earth’s temperature 2.Cooler Earth emits less radiation (energy) 3.Outgoing radiation < solar input 4.Net positive energy input 5.Earth warms up from net energy input Negative Feedback

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Key Feedbacks Water Vapor: Warmer atmosphere can contain more water vaporWarmer atmosphere can contain more water vapor Increased water vapor increases greenhouse effectIncreased water vapor increases greenhouse effect Atmosphere warms furtherAtmosphere warms further 2. Clouds: Clouds cool the climate (reflect sunlight) and warm the climate (block outgoing infrared radiation)Clouds cool the climate (reflect sunlight) and warm the climate (block outgoing infrared radiation) Changes in cloud distribution can thus amplify or reduce the warmingChanges in cloud distribution can thus amplify or reduce the warming

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Key Feedbacks Snow-ice albedo: Warmer climate has reduced snow and iceWarmer climate has reduced snow and ice Surface reflects less and absorbs more solar radiationSurface reflects less and absorbs more solar radiation Climate warms furtherClimate warms further 2. Lapse rate (decrease of T with height): In warmer climate, especially tropics, temperature decreases less with heightIn warmer climate, especially tropics, temperature decreases less with height Upper troposphere warms more than surfaceUpper troposphere warms more than surface Upper troposphere emits energy to space (infrared radiation) more effectively than surface, countering the greenhouse effect.Upper troposphere emits energy to space (infrared radiation) more effectively than surface, countering the greenhouse effect.

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) Feedback Strengths

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) End Part 3: Model Feedbacks

(Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 8) END Climate Models