Hello,
A yearly allocation for the LCRC cluster has been requested with the
following updated information:
Submitter/PI: Robert Jacob
Project Name: Climate_Emulator
Division: MCS
Project title: Building a climate emulator for use in energy policy analysis
Associated funding: NSF, UC-Argonne Seed Grant.
Other Systems:
Science: State-of-the-art general circulation models (GCMs) provide the best estimates of future climate change. While they are valuable tools for assessing impacts of climate change for a given scenario of future greenhouse gas emissions, they cannot be used in iterative economic models since a single multi-century simulation can take weeks to months to run and the iterative models require hundreds of thousands of iterations. For this reason, we aim to develop a statistical emulator that will accurately and efficiently reproduce GCM forecasts of regional climate change for an arbitrary trajectory of CO2 concentrations by using a library of pre-computed GCM output. Library based statistical emulation has not been possible to this date because there is no consistent and comprehensive library of climate model runs corresponding to a range of scenarios of future CO2 concentrations. Computing time on Fusion will enable us to build this unique resource by performing a series of s
imulations using the Community Climate System Model (CCSM3).
Since library-based statistical emulation is currently not possible, the most common approach to emulating regional climate uses linear pattern scaling, in which changes in regional temperature and precipitation are assumed to be linearly proportional to the change in global mean temperature (GMT). That is, regional climate is effectively assumed to depend solely on GMT, and not on the rate or duration of warming. Our preliminary analysis of CCSM3 output from the Climate Model Intercomparison Project (CMIP3) archive shows that this assumption is not valid for temperature projections over time scales of multiple centuries and breaks down for projections of precipitation even over decadal time scales. The CMIP3 archive, however, is not sufficient for full statistical emulation, since it is both restricted in number of runs and inconsistent in its treatment of regional climate forcing. The carefully designed library we propose here will be used to develop and test a number of
alternative approaches for emulating climate model responses, including (i) nearest neighbor interpolation, (ii) a variant of pattern scaling that accounts for the rate of warming, and (iii) principal component analysis (PCA).
The intended outcome of this research is a new climate emulator that will aid in the evaluation of energy policies for greenhouse gas mitigation. We anticipate that there will be a wide interest in a user-friendly, computationally tractable emulation tool from the policy, economics, and climate communities. The library itself will also be made public for further use by the community
Project description: To assist in analysis of climate-related policies, we have pioneered the technique of library-based climate model emulation, in which a library of pre-computed model runs is used to generate a statistical tool that reproduces the output of complex models in a fraction of the time it takes to run the full model. Because no existing archive of climate model runs is appropriate for this purpose, building a new climate library is a prerequisite for developing and testing a climate model emulator. We used Fusion computing time in FY2011 to develop a prototype climate library from runs of CCSM3 (the open-source Community Climate System Model 3 built by the National Center for Atmospheric Research), and are applying here for computing time to continue that library development.
This library represents a substantial advance over the largest extant archive of climate model runs, the CMIP3 archive that holds the runs incorporated in the periodic reports of the Intergovernmental Panel on Climate Change. The CMIP3 archive contains only three scenarios for future CO2 concentration growth, does not study CO2 growth beyond 2100, and considers different regional sulphate aerosol emissions for each scenario, complicating any understanding of regional climate patterns expected in a warming world. The library we are developing is consistent and comprehensive, with a large number of scenarios, multiple realizations of each scenario, and multi-century simulations. It will serve as tool both for basic science and to make possible new emulation methods.
The dominant computational requirements in CCSM3 are its atmosphere and ocean components. The atmosphere component is the Community Atmosphere Model, which currently supports three different numerical cores for solving the basic equations: a spectral transform method, a Semi-Lagrangian scheme, and a finite-volume scheme. The ocean component is a finite-difference model called the Parallel Ocean Program and was developed at Los Alamos. CCSM3 requires Fortran90 and C compilers and the MPI and NetCDF libraries to run.
In FY2011, computing time on Fusion was used to build a library of CCSM3 runs with T31 (3.5ox3.5o) resolution. These runs have been used to develop and test a climate model emulator that accurately replicates future temperate and precipitation projections within the intrinsic uncertainty of the model. In FY2012 we will expand our climate library to explore the importance of parametric uncertainty on climate model projections (especially in parameters relating to cloud coverage and water content, which have been shown to be key drivers of uncertainty in climate projections). The work bears some similarities to the well-known “climateprediction.net” project which used community-donated computing time over many years to do a similar experiment on a higher-resolution version of a British climate model. We have found however that similar physical insights can be recovered at more modest computing requirements by lowering the resolution to T31.
We will perform T31 CCSM3 simulations with three values for each of three cloud parameters (nine combinations). For each combination we will spin-up the climate using a 500 year control run and a 140 historical forcing run (1870-2010). Based on results from our FY2011 simulations, we will require three scenarios of future CO2 concentrations from 2010-2160, with three realizations of each scenario, in order to “train” our statistical model. To test the emulator we will require another two scenarios, but will consider only one realization of each. The total requirements for this experiment are
9 * (500 + 140 + 3*150*3 + 2*150) = 21,000 model years. The T31 resolution version of CCSM3 requires 38 core hours per model year, which gives a total of 21,000*38 or approximately 800,000 core hours.
In FY2011 we used approximately 550K core hours from an allocation of 900K. Our ability to use our entire allocation was limited by long queue times on Fusion, and having to run a large number of simulations sequentially. In the FY2012 experiments we will be running more simulations in parallel, as simulations for different parameter combination will be run at the same time, allowing for higher usage rates. We are storing data on the Argonne/UChicago PADS system and so have sufficient disk space to store the output offsite.
Project URL:
Current FY Hours Used: undetermined amount
New FY Requested allocation: 800000
Q1: 200000
Q2: 200000
Q3: 200000
Q4: 200000
Justification: Our allocations so far have allowed us to perform thousands of years of simulations using CCSM3 at T31. This provides us with detailed statistics on the time required to run this model configuration on Fusion. Using 8 nodes (64 processors) takes an average of 38 core-hours for a simulation of one model year. Several simulations can be run at the same time to scale the project out to the full machine if available. CCSM3 was the recipient of a great deal of tuning and evaluation by combined DOE and NCAR computational scientists so we do not expect further improvements in the per node performance.
Thank You,
The LCRC Accounts System