Over recent decades, the timing of many spring events has occurred progressively earlier year on year. Though these seasonal shifts are linked to rising temperatures, attributing them to climate change has proven difficult. Now scientists have shown that the common brown butterfly has begun to emerge from its chrysalis 1.6 days earlier per decade over a 65-year period. The shift tallies with a rise in air temperatures of 0.14 °C per decade over the same era.
A team led by Michael Kearney of the University of Melbourne, Australia, compiled information on the emergence date of Heteronympha merope in Melbourne over the period 1941 to 2005. In the laboratory, they raised eggs, larvae and pupae from ten field-collected females and calculated the rate of development at various temperatures. Combining the data on sensitivity to temperature with historical monthly climate data, they used a microclimate model to predict that the emergence date would shift 1.3 days earlier per decade over the same period, close to the observed rate.
Results from four global climate models show that the temperature trend over the 65-year period is very unlikely to result from natural climate variability alone. The authors deduce that the seasonal shift is directly linked to human-induced warming.
Rights and permissions
About this article
Cite this article
Heffernan, O. Early emergence. Nature Clim Change 1, 35 (2010). https://doi.org/10.1038/climate.2010.25
Published:
Issue Date:
DOI: https://doi.org/10.1038/climate.2010.25
