Australian scientists say they have uncovered a "causal link" between the early emergence of a common butterfly and human-induced global warming.

Dr Michael Kearney of the University of Melbourne and colleagues report their study on the butterfly Heteronympha merope in this week's issue of Royal Society journal Biology Letters.

"It's now coming out about 10 days earlier than it was 60 years ago," says Kearney.

"When you look at the air temperatures over that time, it's getting warmer."

Kearney says the local Wurundjeri Aboriginal people have traditionally defined one of their seasons as beginning when they see the male of the common brown butterfly on the wing.

"That part of their calendar would be shifted 10 days earlier," he says.

Kearney says that while previous studies have found a correlation between global warming and animals coming out earlier in spring, this study is the first to provide evidence of a causal link between this phenomenon and human-induced global warming.

He says, his team has carried out laboratory experiments to quantify the physiological effect of rising temperatures on butterflies and has also shown the measured temperature increases are not due to natural climatic variation.

"It's causal all the way through," says Kearney.


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