Scientists have established the first casual link between climate change and the timing of a natural event, which is namely the emergence of the common brown butterfly.
Although there have been strong correlations between global warming and changes in the timing of events such as animal migration and flowering, it has been hard to show a cause-and-effect link.
According to a report in New Scientist, this is what Michael Kearney and Natalie Briscoe of the University of Melbourne, Australia, have now done.
The researchers compared temperature changes in Melbourne - where the butterfly is common - with recorded observations of the first brown butterfly to be seen in the spring since the 1940s.
With each decade, the butterflies emerged 1.6 days earlier and Melbourne heated by 0.14 degree Celsius.
"Overall, the butterfly now emerges on average 10.4 days before it did in the 1940s," said Kearney.
"And we know the rise in air temperature links to butterfly emergence in a cause-and-effect pattern," he added.
The pair are confident in the cause-and-effect relationship for two reasons.
First, they placed eggs of the butterfly, Heteronympha merope, in chambers where temperature could be controlled and found that each larval stage has a different response to warmer-than-normal conditions.
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