July 16, 2011 — andyextance

Climate change’s recent impact on Earth’s life has backed up previous assessments calling it “one of the major threats to global biodiversity”. Ilya Maclean and Robert Wilson at the University of Exeter, UK, compared predictions of warming’s effects on species since 2005 and actual measurements made in that time. Both predictions and observations gave an average extinction risk across all species by 2100 close to one in ten. “I was dismayed by the magnitude of potential extinctions that could occur, but was also relieved that we were able to show that scientific predictions were, on the whole, accurate,” Maclean told Simple Climate.

Individual studies on climate’s effects on species inevitably give a limited picture as they typically only focus on a few plants or animals at one time. Similarly, scientists’ predictions of the likely impacts of climate change are often met with scepticism. Maclean and Wilson therefore sought to bring prediction and measurements across different species together to address both issues. They gathered together data from 74 studies published since 2005, comparing their findings against well-established methods of judging extinction threats. 42 of these were predicting extinctions, movements of and changes in species’ populations, while 32 had recorded details of the actual responses to recent changes.

The differences between the various studies meant the scientists needed to find a way to judge them fairly against each other. “We wanted a single yardstick against which the accuracy of predictions could be measured, as lots of different yardsticks would confuse the issue,” Maclean said. Studying just one type of response, like change in how large, or how widely spread, a population is and ignoring the others could have delivered that simplification. However, it would also have limited how broadly representative the scientists’ results were.

Exchange rate

Consequently, the researchers converted all responses to extinction risk using the well-established International Union for Conservation of Nature (IUCN) Red List criteria. “The Red List has several categories for assessing the relative extinction risk to different species over a set time period,” Maclean said. “Crucially, a species can be assigned to a category using several different measures: change in population size or change in the area over which a species is distributed, for example. This provided us with an ‘exchange rate’ if you like, for converting different types of responses and predictions to extinction risk.”

While species reacted differently to climate change across the world, not all were in decline – although more were suffering than thriving. In their Proceedings of the National Academy of Sciences of the USA paper, published Monday, Maclean and Wilson found average observed extinction risk was actually marginally higher than average predicted risk. “One might expect the effects of climate change to get worse as the climate continues to warm, so probably, if anything, the predictions are a bit too cautious,” Maclean explained. “However, the two measures are well within the same order of magnitude, so between them are likely to give a realistic ballpark figure. The average size in the predicted responses, as measured by extinction risk, closely matched the size of responses that had already happened.”

Yet, though the Red List ‘exchange rate’ ensured the scientists could include as many studies as possible, there were still clumps of similar research types among them. For example, more studies reported threats from changes in temperature and rainfall, but the few studies on the effects of reductions in sea ice and changes in ocean circulation patterns showed higher predicted extinction risk. This, Maclean said, may reflect scientists’ interests. “I think it suggests that there is a bias towards work on some of the less threatening aspects of climate change and actually the impacts could be worse. However, because there are fewer studies of the effects in the marine environment, it’s hard to know whether the effects are really as bad as the few marine examples we found suggested.”

Disclaimer: I am close friends with a number of University of Exeter employees, although not Maclean and Wilson.