Abstract
Since the late 1990s, land surface temperatures over Japan have increased during the summer and autumn, while global mean temperatures have not risen in this duration (i.e., the global warming hiatus). In contrast, winter and spring temperatures in Japan have decreased. To assess the impact of both global warming and global-scale decadal variability on this enhanced seasonal temperature contrast, we analyzed the outputs of 100 ensemble simulations of historical and counterfactual non-warming climate simulations conducted using a high-resolution atmospheric general circulation model (AGCM). Our simulations showed that atmospheric fields impacted by the La Nina-like conditions associated with Interdecadal Pacific Oscillation (IPO) have predominantly contributed to the seasonal temperature contrast over Japan. Compared with the impact of negative IPO, the influence of global warming on seasonal temperature contrasts in Japan was small. In addition, atmospheric variability has also had a large impact on temperatures in Japan over a decadal timescale. The results of this study suggest a future increase in heatwave risk during the summer and autumn when La Nina-like decadal phenomena and atmospheric perturbations coincide over a background of global warming.
Highlights
In the first decade of the 21st century, surface temperatures in Japan have increased during summer and autumn (June–November, hereafter JJASON), and decreased during winter and spring (December–May, hereafter DJFMAM) [1]
This suggests that warming events during the summer and autumn may increase under negative Interdecadal Pacific Oscillation (IPO) conditions, which goes against the global warming hiatus associated with negative IPO [4,5,6,7]
Time series of surface air temperature anomalies in Japan smoothed by five-year running means were compared with the Japan Meteorological Agency (JMA) in-situ observations and the ALL run (Figure 1)
Summary
In the first decade of the 21st century, surface temperatures in Japan have increased during summer and autumn (June–November, hereafter JJASON), and decreased during winter and spring (December–May, hereafter DJFMAM) [1]. Oscillation (IPO) [2,3] has been observed and is associated with conditions analogous to the La Nina phenomenon in the tropical Pacific Ocean. Atmospheric re-analysis, and ocean assimilation datasets, Urabe and Maeda [1] showed that the enhanced seasonal temperature contrast in. Japan is associated with La Nina-like conditions and large-scale teleconnection patterns. This suggests that warming events during the summer and autumn may increase under negative IPO conditions, which goes against the global warming hiatus (i.e., a slowdown in the global surface temperature rise since the late 1990s) associated with negative IPO [4,5,6,7]. It is well established that El Nino (La Nina)
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