U. SHEFFIELD (UK)—The onset of summer-like temperatures in England has been advancing since the mid 1950s, a new study shows.
Researchers from the University of Sheffield examined records of the first blooming date of early summer flowering plants (phenology) and the timing of first occurrences of warm “summer” temperatures—events linked with the onset of summer.
Results revealed that the occurrence of “summer” temperatures had advanced by 11 days in the 1990s compared to the period 1954–1963, while early summer flowering had advanced by three days. If this analysis is extended to 2007, the advance reaches 18 days.
Globally, research has shown the climate has undergone increasingly significant warming in the last half century, with the second half of the 20th century likely to be the warmest period in at least the last 1,300 years.
Earlier research into seasonal change has focused on and demonstrated an early onset to spring and a delay in the onset of autumn, as opposed to any changes in the onset of summer and focused on phenological records only as an indicator for change, without considering temperature.
The research combined both phenology and a mean daily temperature series from the Hadley Centre’s Central England Temperature.
Mean temperature was chosen because it is less susceptible to local microclimate influences than maximum temperature. For the purpose of the study, the threshold temperature chosen to represent summer onset in the mean temperature series was 14oC.
For the phenology side of the research, the first flowering dates of 385 plant species that flower in early summer (May and June) were used as an indicator of the start of summer.
Grant Bigg, professor and head of the department of geography, now hopes to investigate whether or not this advancement of summer may have encouraged drought or heat wave conditions by prolonging the period of warm temperatures and lower rainfall in which these events occur.
“There has been a lot of attention paid to the shift to earlier springs but we’ve shown similar advancement in summer conditions,” Bigg says.
“This could have the same implications as the shift to earlier springs for increased ecological divergences, as well as extending the time for summer weather extremes.”
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