Jul 25, 2014

Attributing the increase in Northern Hemisphere hot summers since the late 20th  century

Kamae, Youichi, Shiogama, Hideo, Watanabe, Masahiro, Kimoto, Masahide
Geophysical Research Letters
  • States that anomalously high summertime temperatures have occurred with increasing frequency since the late 20th century
  • States it is not clear why hot summers are becoming more frequent despite the recent slowdown in the rise in global surface air temperature
  • Examines factors affecting the historical variation in the frequency of hot summers over the Northern Hemisphere (NH)
  • Conducts three sets of ensemble simulations with an atmospheric general circulation model
  • Finds that decadal variabilities in the Pacific and Atlantic Oceans accounted for 43 ± 27% of the recent increase over the NH middle latitudes
  • Finds that the direct influence of anthropogenic forcing also contributes to increasing the frequency of hot summers since the late 20th century
  • Results suggest that the heat extremes can become more frequent in the coming decade even with the persistent slowdown in the global-mean surface warming