The earlier emergence of brown butterflies in Australia over the last six decades has coincided with warming temperatures, a finding that researchers say is evidence of the causal link between climate change and the timing of natural events. Researchers at the University of Melbourne say the butterfly, which is common to the region, has emerged 1.6 days earlier each decade since the 1940s — or about 10.4 days earlier than it did 65 years ago. During that period, temperatures in Melbourne have increased 0.25 degrees F per decade, or roughly 1.5 degrees F overall since the 1940s. In addition, butterfly eggs placed in a controlled laboratory setting also responded to warming conditions, with each larval stage responding in different ways to increased temperatures, said Michael Kearney, lead author of the study and professor at the university’s Department of Zoology. “Shifts in these seasonal life cycle events represent a challenge to species, altering the food and competition present at the time of hatching,” Kearney said. “Studies such as ours will allow better forecasting of these shifts and help us understand more about their consequences.” The study will be published in the journal Biology Letters.