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PCIC Research on Hot Summers Featured in the Media

Recent research on extremely warm summers, led by PCIC research associate Chao Li and co-authored by PCIC Director Francis Zwiers, has been published in Earth’s Future and featured on both CBC News and UVic News, as well as local Victoria media. Their research examines historical and projected changes to summer mean wet bulb globe temperatures (WBGT), an indicator that takes into account both air temperature and humidity, and is often used as a measure of potential heat stress on people. The authors’ results suggest that, by the middle of the century, summers may get so hot that the historical record warm summer, as measured but summer mean WBGT, may be the norm over most of the land areas in the Northern Hemisphere. Specifically, in the projections that they use, which assume a business-as-usual emissions scenario, at least half of all summers exceed the current maximum summer average WBGT on record by the 2030s and by mid-century 95% of all summers surpass it.

Examining the period of 1973-2012 in a number of regions comprising most of the Northern Hemisphere, the authors compare climate model simulations and observations using a rigorous statistical “fingerprint” method to tease out the effect that humans have had on record-high summer average WBGT. They find that the changes in summer mean WBGT cannot be explained by natural influences alone and that anthropogenic influences have made it at least 70 times more likely that summer mean WBGT would exceed the historic record at the end of the 40 year period than at the beginning of the period. In most regions, the human influence in the likelihood of extreme summer mean WBGT is about ten times larger than the human influence in the likelihood of extreme summer high temperatures alone.

Read the CBC story.
Read the UVic News story.
Read the original paper.

Li, C., X. Zhang, F. Zwiers, Y. Fang and A. Micha, 2017: Recent very hot summers in northern hemispheric land areas measured by wet bulb globe temperature will be the norm within 20 years. Earth's Future, accepted, doi:10.1002/2017EF000639.