August 16, 2015, by Tim Radford
A speckled wood at rest: Carbon emissions could cause lethal droughts for British butterflies
Image: Didier Descouens via Wikimedia Commons
By mid-century carbon dioxide emissions in the United Kingdom could be causing recurrent droughts severe enough to force several butterfly species into extinction. LONDON, 16 August, 2015 – If 25 years from now you can’t see a speckled wood near the English woodland, it won’t be because of natural camouflage. And if you suddenly miss the large skipper, it won’t be because it has led the team off the field. Both species of British butterfly could be extinct because of global warming. And other flying insects, and even birds, may face similar jeopardy. Under a range of climate change scenarios, extreme droughts are expected to become more frequent. Tom Oliver of the UK Centre for Ecology and Hydrology and colleagues report in the journal Nature Climate Change that they looked at long-term butterfly population records from 129 sites monitored under the UK Butterfly Monitoring Scheme to work out how 28 species had fared during an extreme drought event in Britain in 1995, and identified six species more than usually sensitive to brilliant sunshine and extended dry seasons. Besides large skipper and speckled wood, these include the ringlet, large white, small white and green-veined white. The authors warn that by 2050 the recurring droughts forecast by climate scientists under a “business as usual” scenario, in which humans go on expanding the use of fossil fuels, thus putting more and more of the greenhouse gas carbon dioxide into the atmosphere to raise global average temperatures, could cause population collapses.
“Should this occur repeatedly, populations may be unable to recover, resulting in local extinctions,” they warn. The research was backed by the charity Butterfly Conservation, by the agency Natural England and by the University of Exeter. Butterflies, transient and brightly coloured, make good tests of local ecological health, and so are well studied. So has been their response to climate change. Some species have responded by extending their range uphill or northwards in response to the overall shift in average temperatures, while other populations have dwindled. A shift in climate is naturally expected to help some species flourish, others fade, But butterflies, like birds, are popular symbols of the natural world and there is pressure to conserve. The study is designed to examine the big challenges that will face conservation agencies by 2050. “We consider the average response across Great Britain. Losses are likely to be more severe in drier areas with more intensive land use, whilst wetter areas with less fragmented habitat will provide refugia.
“The study looked at butterflies but the conclusions are potentially valid for other species”
“We assume that butterflies won’t have time to evolve to become more drought-tolerant, because their populations are already small, and evolution would need to be very rapid. The study looked at butterflies but the conclusions are potentially valid for other species such as birds, beetles, moths and dragonflies,” said Dr Oliver. Worryingly, the researchers found that simply devoting more space and habitat to conservation – and in a world in which rising population means greater pressure on farmland, this would not be easy – and especially by creating corridors along which species could migrate, would not be enough. Even more worryingly, the scientists found that some species would be at risk of widespread extinction even under relatively favourable greenhouse emissions scenarios. “The results are worrying. Until I started this research, I hadn’t quite realised the magnitude and potential impacts from climate change,” said Dr Oliver. “For drought-sensitive butterflies, and potentially other taxa, widespread population extinctions are expected by 2050. “To limit these losses, both habitat restoration and reducing CO2 emissions have a role. In fact, a combination of both is necessary.” – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.