1. Key Points

♦

According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (AR5–IPCC), the main factor contributing to uncertainty in the rise of global temperatures caused by increased greenhouse gas concentrations is the uncertainty of predictions of clouds.

♦

We analyzed high-resolution climate simulation data derived from global nonhydrostatic icosahedral atmospheric model (NICAM) predictions for approximately 100 years in the future. We found that under an atmosphere with advanced global warming, cloud organization in the tropics became impaired, making the development of large cumulonimbus cloud ensembles less likely.

♦

It has been suggested that increases in the number of small cumulonimbus cloud ensembles could cover the upper atmosphere, which may exacerbate the greenhouse effect of infrared radiation and thereby accelerate climatic warming.

2. Overview

A collaborative study was conducted by groups at the Research Center for Environmental Modeling and Application (CEMA) of the Research Institute for Global Change at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the Atmosphere and Ocean Research Institute at the University of Tokyo, and the National Institute for Environmental Studies. Data were obtained from simulated predictions of the Earth approximately 100 years in the future using a global nonhydrostatic icosahedral atmospheric model (NICAM*1). Analysis of this data indicated the possibility that populations of cumulonimbus clouds in the tropics may become smaller (i.e., cloud disorganization) (Figure 1).

The tropics are the primary determinant of Earth’s thermal balance, and clouds in the tropics are a driving energy source for atmospheric flow on a global scale. In the study reported here, detailed predictions of future cloud formation and elimination suggested that clouds in the tropics would become disorganized, and that the weakening of global atmospheric flow in the tropics (hereafter “general atmospheric circulation”) was a contributing factor (Figure 2). Additionally, the size distribution of cold pools of air created by clouds was also consistent with cloud disorganization (Figure 3). This suggests that tropical clouds enhance warming in an atmosphere with advanced warming due to the increased emissions of anthropogenic greenhouse gases (Figure 4). The results also show that there may be an effect on the frequency of mild winters in Japan and the number of typhoons generated each year. We hope that this research will contribute to future reports, such as the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC).

This study was implemented with support from the Integrated Research Program for Advancing Climate Models of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Priority Issue 4, “Advancement of Meteorological and Global Environmental Predictions Utilizing Observational ‘Big Data,’” of the application development and research into high-priority social and scientific issues to be tackled using the “Post-K” supercomputer (“Fugaku”) (Project Nos.: hp160230, hp170234, hp180182, and hp190152). The results of this study was published in the online edition of the Journal of Advances in Modeling Earth Systems on September 13, 2019 (JST).

Title: Responses of clouds and large-scale circulation to global warming evaluated from multi-decadal simulations using a global nonhydrostatic model
Authors: Akira T. Noda¹, Chihiro Kodama¹, Yohei Yamada¹, Masaki Satoh^2,1, Tomoo Ogura³ and Tomoki Ohno¹
1. Research Institute for Global Change, JAMSTEC
2. Atmosphere and Ocean Research Institute, The University of Tokyo
3. National Center for Environmental Studies