Modeling the Atmos.-Ocean System Objectives: Climate Models The strengths and weaknesses of GCMs The application of GCMs 12/3/2018 1:43:43 AM UNBC
Climate models Use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. Climate models are mainly used for predictions and simulations. 12/3/2018 1:43:43 AM UNBC
Dynamical/physical models Using physical principles to describe the 12/3/2018 Dynamical/physical models Using physical principles to describe the relationship among different components of climate system in the form of mathematical equations. These mathematical equations are called dynamical models. By solving the equations, we can simulate and predict the components of the earth climate system. 12/3/2018 1:43:43 AM UNBC
Climate Model – what does it do? Starts with known physical laws – conservation of momentum, energy, & mass. Views atmosphere, ocean, land as a continuum (i.e. all spatial scales present satisfying same laws). Find and use numerical approximations to the continuum physical laws. Integrate in time to develop climate statistics same as observed-evaluate success by extent of agreement. On global scale, this agenda is very successful. 12/3/2018 1:43:43 AM UNBC
Climate Model Scaling/parameterization Need to describe details within the grid boxes 12/3/2018 1:43:43 AM UNBC
Global climate model These models are the most complex. The models divide atmosphere or ocean into a horizontal grid with a typical resolution of 2-4 degree latitude by 2-4 degree longitude and 10-20 layers in the vertical. They directly simulate winds, ocean currents and many other processes. Feedback processes are simulated in the coupled atmosphere and ocean GCMs - water vapor, clouds, seasonal snow and ice. 12/3/2018 1:43:43 AM UNBC
Scheme of a coupled atmosphere ocean model and supplementary models. 12/3/2018 1:43:43 AM UNBC
Ideal gas 12/3/2018 1:43:43 AM UNBC
Newton's law 12/3/2018 1:43:43 AM UNBC
Navier Stokes Equations 12/3/2018 1:43:43 AM UNBC
Coriolis force 12/3/2018 1:43:43 AM UNBC
First law of thermodynamics UNBC
Prognostic & diagnostic Eq. u, v, T, S w, p, 12/3/2018 1:43:43 AM UNBC
The derivative of a function f at a point x is defined by the limit: Thus, we can use finite differences to approximate derivatives. 12/3/2018 1:43:43 AM UNBC
For example, consider the ordinary differential equation The Euler method for solving this equation uses the finite difference to approximate the differential equation by 12/3/2018 1:43:43 AM UNBC
Model Grid: 12/3/2018 1:43:43 AM UNBC
Climate Model Scaling/parameterization Need to describe details within the grid boxes 12/3/2018 1:43:44 AM UNBC
Weather forecast --------- initial value problem Seasonal climate forecast ------ boundary forcing (surface condition) Projection of the climate change ------- Many… data assimilation + ensemble 12/3/2018 1:43:44 AM UNBC
Types of GCM AGCM (Atmospheric) Atmospheric GCM model the atmosphere and impose sea surface temperatures. OGCM (Ocean ) This model simulated the global sea patterns. AOGCM (Atmospheric and Ocean) Coupled atmosphere-ocean GCM is a combine models e.g. CCSM4, HadCM3, GFDL Hardware Behind the Climate Model
Development of Climate Models Taken from IPCC (modified)
Numerical weather forecast is one of the most significant achievements of sciences and technologies in the 20th century. 12/3/2018
Projections of future climate change GCMs use a transient climate simulation to project/predict future temperature changes under various scenarios. These can be idealized scenarios (most commonly, CO2 increasing at 1%/y). 12/3/2018 1:43:44 AM UNBC
Confidence of climate projection Confidences come from (1) the foundation of the models; (2) ability to reproduce observed features of current and past climate change 12/3/2018 1:43:44 AM UNBC
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Global mean near-surface temperatures from observations (black) and as obtained from 58 simulations produced by 14 different climate models driven by both natural and human-caused factors that influence climate. The mean of all these runs is also shown (thick red line). Temperature anomalies are shown relative to the 1901 to 1950 mean. Vertical grey lines indicate the timing of major volcanic eruptions. 12/3/2018 1:43:44 AM UNBC
equilibrium climate simulation greenhouse gas concentrations are suddenly changed (typically from pre-industrial values to twice pre-industrial values) and the model allowed to come into equilibrium with the new forcing. transient climate simulation a mode of running a global climate model in which a period of time (typically 1850-2100) is simulated with continuously-varying concentrations of greenhouse gases so that the climate of the model represents a realistic mode of possible change in the real world. 12/3/2018 1:43:44 AM UNBC
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Accuracy of models that predict global warming: (1) albedo errors (2) external factors not taken into consideration (3) model resolution (4) initial conditions (5) the role of clouds on climate changes 12/3/2018 1:43:44 AM UNBC
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Evidence of some uncertainties: (1) The individual models often exhibit worse agreement with observations. (2) All models have shortcomings in their simulations of the present day climate of the stratosphere, which might limit the accuracy of predictions of future climate change. (3) There are problems in simulating natural seasonal variability. (4) Coupled climate models do not simulate with reasonable accuracy clouds and some related hydrological processes. 12/3/2018 1:43:44 AM UNBC
Evidence of model reliability: (1) The model mean exhibits good agreement with observations. (2) Surface air temperature is particularly well simulated. (3) For nearly all models the r.m.s. error in zonal- and annual-mean surface air temperature is small compared with its natural variability. 12/3/2018 1:43:44 AM UNBC
Conclusion ============= The majority of climatologists agree that important climate processes are imperfectly accounted for by the climate models but don't think that better models would change the conclusion. 12/3/2018 1:43:44 AM UNBC