Climate context of the cold summer of 2014 in Toronto, ON, Canada

Abstract

Toronto, Ontario, Canada, experienced a cooler summer in 2014, in spite of worldwide record temperatures. In this work, we assess the relative coldness of summer 2014 from a climatological perspective. Using historical temperature data and several thermal metrics, summer 2014 was ranked using three time periods, 1840–2014 (175 years), the full extent of the local instrumental data; 1965–2014, the most recent 50 years; and 1985–2014, the most recent 30 years. For each of the periods, rank within the time period, recurrence interval and average temperature were calculated. Summer of 2014 in Toronto was ranked 118th since 1840 (175 years of data) using the mean daily temperature. The summer of 2014 with an average mean temperature of 20.8 °C was not extreme in nature and is in fact warmer than the average temperature of the time period (19.9 °C). For the more recent time periods, however, the summer was cooler than average but not an extremely cold summer. A monthly analysis showed in particular a cooler July compared to June and August, ranking July 2014 as the 4th coldest July since 1985 whereas June and August were 21st and 10th coldest during the 30-year period, respectively. Recurrence rates did not exceeded 5 years for the seasonal data and 8.3 years for the monthly data. Although the summer of 2014 was cooler than some recent summers, it was not an extreme event such as the Mount Pinatubo-induced cool summer of 1992 which it was explicitly compared to. Finally, an air mass analysis showed that the cooler July of 2014 was the result of a reduced frequency of warm air masses compared to 1992 when there was both a reduction of warm air masses and an increase in colder ones.