Could climate catastrophe be due to a rounding error?
Monthly Weather Review 2013 ; e-View
Song-You Hong,1 Myung-Seo Koo,1 Jihyeon Jang,1 Jung-Eun Esther Kim,2 Hoon Park,1,3 Min-Su Joh,4 Ji-Hoon Kang,4 and Tae-Jin Oh5
2 National Oceanic and Atmospheric Administration (NOAA)/Earth System Research Laboratory (ESRL), Boulder, Colorado, USA
This study presents the dependency of the simulation results from a global atmospheric numerical model on machines with different hardware and software systems. The global model program (GMP) of the Global/Regional Integrated Model system (GRIMs) is tested on 10 different computer systems having different central processing unit (CPU) architectures or compilers. There exist differences in the results for different compilers, parallel libraries, and optimization levels, primarily due to the treatment of rounding errors by the different software systems. The system dependency, which is the standard deviation of the 500-hPa geopotential height averaged over the globe, increases with time. However, its fractional tendency, which is the change of the standard deviation relative to the value itself, remains nearly zero with time. In a seasonal prediction framework, the ensemble spread due to the differences in software system is comparable to the ensemble spread due to the differences in initial conditions that is used for the traditional ensemble forecasting.