Alan Robock Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey USA Climate Models

Alan Robock Department of Environmental Sciences What is a model?

Alan Robock Department of Environmental Sciences What is a climate model?

Alan Robock Department of Environmental Sciences Why do climate modeling?

Alan Robock Department of Environmental Sciences Why do climate modeling? We can’t bring the entire atmosphere, ocean, land, and biosphere into the laboratory. We can’t do experiments in the real world.

Alan Robock Department of Environmental Sciences Types of experiments: simulations of current climate – first test of any model simulations of past ice ages last 165 years (historical runs) sensitivity to different forcings sensitivity to different feedbacks predictions test different scenarios of future

Alan Robock Department of Environmental Sciences Types of climate models: Determined by: spatial resolution and representation time step size, or steady-state portion of climate system that is included Classification: 0-dimensional  3-dimensional atmosphere only (with fixed sea surface temperatures), or mixed-layer ocean, or complete dynamic ocean inclusion of aerosols, chemistry, biosphere, detailed stratosphere...

Alan Robock Department of Environmental Sciences Types of climate models: Energy-balance models Zero-dimensional, steady-state: Zero-dimensional, time-dependent:

Alan Robock Department of Environmental Sciences Types of climate models: Energy-balance models Disadvantages of this model: no predictive value as sensitivity and C cannot be evaluated here describes only global average Advantages of this model: easily understood can be used to interpret more complex models

Alan Robock Department of Environmental Sciences Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC), an upwelling-diffusion energy-balance model

Alan Robock Department of Environmental Sciences What is an RCM?

Alan Robock Department of Environmental Sciences What is an RCM? 1. Radiative-Convective Model, also now called a Single Column Model (SCM) or fractional cloudiness Advantages: can look at radiation parameterizations cloud parameterizations and feedbacks water vapor feedbacks lapse rate feedbacks surface interactions and feedbacks effects of different atmospheric composition, including CO 2 O 3 at different levels aerosols at different levels Disadvantages: cannot look at horizontal distributions, albedo feedbacks, dynamics

Alan Robock Department of Environmental Sciences What is an RCM? 2. Regional Climate Model Advantages: can look in detail at specific locations takes less computer time than a global simulation Disadvantages: complicated to connect to boundaries (spectral nudging helps) reproduces in detail the climate determined by the boundary conditions, but cannot change the basic climate The Weather Research & Forecasting Model (WRF) There are other models and regional strategies, such as stretched grids.

Alan Robock Department of Environmental Sciences Example of WRF domains from: Sertel, Elif, Alan Robock, and Cankut Ormeci, 2010: Impacts of land cover data quality on regional climate simulations. Internat. J. Climatology, 30, , doi: /joc.2036.

Alan Robock Department of Environmental Sciences General Circulation Models (GCMs) Sometimes people now say GCM stands for global climate model, but that is not actually correct, as even a simple energy balance model is a global climate model and what makes a GCM distinctive is that it explicitly models the general circulation of the atmosphere (or ocean). All climate models are energy-balance models. All climate models are global climate models.

Alan Robock Department of Environmental Sciences Evolution of processes included in state-of- the-art climate models FAR: First IPCC Assessment Report SAR: Second Report TAR: Third Report AR4: Fourth Report IPCC AR4, Chapter 1

Alan Robock Department of Environmental Sciences AOGCM = Atmosphere-Ocean General Circulation Model. ESM = Earth System Model

Alan Robock Department of Environmental Sciences IPCC AR4, Chapter 1

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences General Circulation Models (GCMs) 1 Basic Physical Laws: Conservation of energy (First law of thermodynamics) Conservation of momentum (Newton’s second law of motion) Conservation of mass (Continuity equation) Conservation of moisture Hydrostatic equilibrium Gas law

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences General Circulation Models (GCMs) 2 Physical Processes That Must or Can Be Included: WindSea ice RadiationSnow PrecipitationGlaciers Soil moistureVegetation Ground waterOcean biota Aerosols Clouds, convective and large-scale Air-sea exchanges of moisture, energy, and momentum Air-land exchanges of moisture, energy, and momentum Chemistry, particularly O 3 and CO 2 Ocean temperature, salinity, and currents

Alan Robock Department of Environmental Sciences Real World vs. Model World

Alan Robock Department of Environmental Sciences Theory of Climate Model Development

Alan Robock Department of Environmental Sciences Typical grid spacing of a GCM is now 1°x1° latitude-longitude by 1 km in the vertical. Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8. When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.

Alan Robock Department of Environmental Sciences To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be “parameterized.” One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box. Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.

Alan Robock Department of Environmental Sciences Rows and flows of angel hair And ice cream castles in the air And feather canyons everywhere; I’ve looked at clouds that way. But now they only block the sun. They rain and they snow on everyone. So many things I would have done But clouds got in my way. I’ve looked at clouds from both sides now. From up and down, and still somehow It’s cloud illusions I recall. I really don't know clouds at all. — Joni Mitchell Both Sides Now, 1967

Alan Robock Department of Environmental Sciences Model Intercomparison Projects (MIPs) First was AMIP: Atmospheric Model Intercomparison Project, using specified sea surface temperatures, and running from 1979 through CMIP (Coupled Model Intercomparison Project) CMIP3 used for IPCC AR4 and CMIP5 used for AR5. CMIP6 is now being organized. There are also MIPs for just parts of the climate system, like the Program for Intercomparison of Land- surface Parameterization Schemes (PILPS) catalogue/modelling-wgcm-mips-2

Alan Robock Department of Environmental Sciences Taylor et al. (BAMS, 2012)

Alan Robock Department of Environmental Sciences Climate Model Intercomparison Project 6 (CMIP6) design proposal Meehl, G. A., R. Moss, K. E. Taylor, V. Eyring, R. J. Stouffer, S. Bony and B. Stevens, 2014: Climate model intercomparisons: Preparing for the next phase, Eos, 95, 77-78, doi: /2014EO

Alan Robock Department of Environmental Sciences Meehl, G. A., R. Moss, K. E. Taylor, V. Eyring, R. J. Stouffer, S. Bony and B. Stevens, 2014: Climate model intercomparisons: Preparing for the next phase, Eos, 95, 77-78, doi: /2014EO

Alan Robock Department of Environmental Sciences Meehl, G. A., R. Moss, K. E. Taylor, V. Eyring, R. J. Stouffer, S. Bony and B. Stevens, 2014: Climate model intercomparisons: Preparing for the next phase, Eos, 95, 77-78, doi: /2014EO

Alan Robock Department of Environmental Sciences Meehl, G. A., R. Moss, K. E. Taylor, V. Eyring, R. J. Stouffer, S. Bony and B. Stevens, 2014: Climate model intercomparisons: Preparing for the next phase, Eos, 95, 77-78, doi: /2014EO I’m involved in GeoMIP and VolMIP, which both were formally endorsed two weeks ago.

Alan Robock Department of Environmental Sciences Model Intercomparison Projects (MIPs) All find that models are different from each other and different from observations, so what is the point? -models are tested in a controlled regime, and modelers find errors in models when comparing to observations -estimation of range of confidence or uncertainty in models -identification of outliers -development and dissemination of data sets that can be useful to all

Alan Robock Department of Environmental Sciences Model Intercomparison Projects (MIPs) Most have found that: - no one model is best at everything - no one test evaluates all aspects of models - after excluding outliers with serious errors, the model consensus outperforms any individual model

Alan Robock Department of Environmental Sciences AOGCM is an Atmosphere-Ocean General Circulation Model. ESM means Earth System Model, and includes more components of the climate system.

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences Earth System Models of Intermediate Complexity (EMICs) Do not explicitly model atmospheric dynamics, so can run much faster and include more processes to study long-time period processes.

Alan Robock Department of Environmental Sciences

Alan Robock Department of Environmental Sciences Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC), an upwelling-diffusion energy-balance model

Alan Robock Department of Environmental Sciences Go to live.magicc.org, register, and then conduct the following experiments. For a description of the emission scenarios, see a. For emissions scenario RCP8.5 (representative concentrations pathway with +8.5 W/m 2 radiative forcing by 2100): i. Describe the fossil CO 2 time series for the 21st Century. ii. On the next page, choose Standard run mode, CMIP3: DEFAULT for the Climate Parameters and C4MIP: DEFAULT for the Carbon Cycle settings. Click Advance Settings and report the Climate Sensitivity. (This is one place where you can change parameters for your own experiment - see d-g and j below). iii. Click Next to run the model. What is the global average temperature in 2100? iv. Click on the file symbol to download the output files. Download the DAT_SURFACE_TEMP.OUT file and rename it for this experiment. b. Repeat the same experiment in a. for the RCP3-PD (which as well goes by the name RCP2.6) scenario. c. Using Excel, Matlab, or by hand, plot on the same graph the global- mean temperature for the two experiments above for How do they compare? Why are they different?

Alan Robock Department of Environmental Sciences Go to live.magicc.org, register, and then conduct the following experiments. For a description of the emission scenarios, see d. Repeat a. with a climate sensitivity of half of the standard one. e. Repeat a. with a climate sensitivity of twice the standard one. f. Repeat b. with a climate sensitivity of half of the standard one. g. Repeat b. with a climate sensitivity of twice the standard one. h. Add the results of experiments d-g to the graph you did in part c. This will result in a graph with 6 curves. Create another version of the graph with time only going from 2000 to 2100, so as to see the results more clearly. Include both graphs with your assignment. How do the results compare? Why are they different? Are the differences linear? (That is, is the climate response proportional to the forcing and to the sensitivity?) i. Repeat a. and b. with the Probabilistic, Multi-model ensemble option. Do a screen capture and present each of these results. Is the spread between models as large as the differences caused by the different scenarios? j. Design and carry out your own experiment to elucidate the climate response. Describe what you did, why you did it, and your results.