CGER Reports

CGER’S SUPERCOMPUTER MONOGRAPH REPORT Vol.12

Climate Change Simulations with a Coupled Ocean-Atmosphere GCM
Called the Model for Interdisciplinary Research on Climate: MIROC

NOZAWA T., NAGASHIMA T., OGURA T., YOKOHATA T., OKADA N., SHIOGAMA H.

Summary - 79p -

This monograph summarizes the results of various climate change simulations carried out utilizing a climate model, with the goals of projecting future climate change resulting from human activities such as the release of greenhouse gases, and elucidating mechanisms of the observed historical long-term climate change. The model used in the simulations is the atmosphere-ocean coupled model called MIROC (Model for Interdisciplinary Research on Climate); this model was developed collaboratively by the National Institute for Environmental Studies, the Center for Climate System Research at the University of Tokyo, and the Frontier Research Center for Global Change at the Japan Agency for Marine-Earth Science and Technology. The model has a horizontal resolution of about 300 km in the atmosphere and 150 km in the ocean.

This monograph introduces primarily the below findings. The model reproduces very well observed temperature changes in the 20th century in a number of experiments taking into account all factors (both anthropogenic and natural causes) (Figure 1). Consideration of the results of simulations that take anthropogenic causes and natural causes into account separately indicate that recent trends toward global warming are attributable to anthropogenic factors, while increasing temperatures in the first half of the 20th century are mainly attributable to natural factors (Figure 1). Furthermore, we discovered that we must include the effects of carbonaceous aerosols (such as soot, etc.) in the model in order to reproduce climate change at the regional level (Figure 2). Results from simulations predicting future climate change based on the IPCC (Intergovernmental Panel on Climate Change) emissions scenarios made it clear that though the amplitude of change may differ based on the scenario, the spatial distribution of events such as rising temperatures and change in amounts of precipitation are quite similar.

Part of the results from the simulations in this monograph is distributed to researchers around the world, and is quoted in the IPCC 4th Assessment Report.

Figure 1: Temporal variations of global annual mean surface air temperature. The black line indicates observed values, while the red line represents the results of climate model simulations (average of the four-member initial-value ensemble experiments). Results from both observations and simulations indicate temperature variations from the 1881-1910 average. The light red area indicates the data spread of results from ensemble experiments. From the top of the figure, “FULL” refers to results factoring in all (both anthropogenic and natural) causes of climate variability; “NTRL” refers to results factoring in only natural causes; “ANTH” refers to results factoring in only anthropogenic causes; and “GHGS” refers to results factoring in only increasing concentrations of greenhouse gases.
Figure 2: Geographical distributions of the linear trend of surface air temperatures in the mid-20th century (1942-1979). The unit of measurement is the rate of increase in temperature (in °C / 10 years). From the top, (a) observation (Obs.); (b) results when anthropogenic emissions of sulfate and carbonaceous aerosols are fixed at pre-industrial era levels (AEFX); (c) results when increasing only sulfate aerosol emissions (CEFX); (d) results when increasing anthropogenic emissions (both sulfate and carbonaceous aerosols) (FULL)

Contents:

  • Foreword
  • Preface
  • Contents
  • List of Figures
  • List of Tables
  • Abstract
  • Chapter 1 General Introduction
  • Chapter 2 Model Description and Experimental Design
  • Chapter 3 Simulated Climate States in the Control Experiment
  • Chapter 4 Transient Climate Responses to Increasing CO2
  • Chapter 5 20th Century Simulations
  • Chapter 6 Projections of Climate Change under IPCC SRES Scenarios
  • Chapter 7 Summary and Conclusions