Introduction

        Human-caused climate change is causing an upward shift in the entire temperature distribution, leading to an increase in extreme maximum daily temperatures and heatwaves. This shift amplifies the frequency, duration, and intensity of hot temperature extremes. The scientific evidence is overwhelmingly strong, indicating that many of the hottest temperature events in teh last decade would have been virtually impossible without anthropogenic greenhouse gas emissions. We are transitioning from a climate where extreme heat was an unusual occurrence to one where it has become a defining feature of the summer season.

        Even small increments of global warming cause statistically significant increases in hot extremes across our planet. Table 1 describes how the level global warming, relative to pre-industrial times, influences the frequency and intensity of extreme heat events.

Table 1 Global climate models used to forecast future near surface air temperatures and precipitation for Kelowna.

        Currently, the annual mean global surface temperature is about 1.5°C warmer than it was in pre-industrial times (before 1700).  

The June 2021 Western North America Heatwave

        At the end of June 2021 an intense heatwave developed over British Columbia, Washington State, and Oregon. This heatwave would have been virtually impossible without human-induced climate change. Statistical analysis of extreme daytime temperatures recorded indicated it was among the most extreme climate events ever seeen globally (Thompson et al., 2022 and White et al., 2023)

        The June 2021 heatwave resulted in Kelowna experiencing record-breaking daily maximum temperatures for several consecutive days. Notably, the highest temperature reached 45.7°C on June 29, 2021. Several of Kelowna’s daily highs during the period from June 26 to 30 were exceptionally rare, occurring with a probability of at least 1 in 1,000 compared to the historical record from 1951 to 2022. 

        Vernon also experienced a multi-day stretch of record-setting daily maximum temperatures during June 25–July 1, 2021, peaking at 44.2°C on June 29.

Human Response to Heat Stress

Danger of Heatwaves

References 

Thompson, V., Kennedy-Asser, A.T., Vosper, E.,  Lo, Y.T.E., Huntingford, C., Andrews, O., Collins, M., Gabrielle C. Hegerl, G.C,. & Mitchell, D. 2022. The 2021 western North America heat wave among the most extreme events ever recorded globally. Science Advances, 8 (18), eabm6860. https://doi.org/10.1126/sciadv.abm6860

White, R.H., Anderson, S., Booth, J.F., Braich, G., Draeger, G., Fei, C., Harley, C.D.G., Henderson, S.B. , Jakob, M., Lau, C.-A., Admasu, L.M., Narinesing, V., Rodell, C., Roocroft, E., Weinberger, K.R., & West, G. 2023. The unprecedented Pacific Northwest heatwave of June 2021. Nature Communications, 14, 727. https://doi.org/10.1038/s41467-023-36289-3