A recent study shows that wild bumblebee populations are declining in both North America and Europe due to global warming, rather than pesticide overuse or habitat loss.

Researchers made over 420,000 observations and sifted through data on nearly 70 bumblebee species that lived on both continents over the course of more than 100 years. The team also assessed how much temperatures changed in the meantime, especially from 1974 through 2010 when rising temperatures became a worldwide problem.

The data helped scientists find a link between shrinking ranges of bumblebees and global warming. The team argue that extreme heat waves made the southernmost edges of the animals’ ranges less of a welcoming home. They also learned that those ranges shrank by 3 miles per year since 1974.

Paul Galpern, co-author of the study and researcher at the University of Calgary, Canada, said that he and his colleagues were intrigued to learn that the trend was the same on two separate continents.

“Bumblebee species are responding quite similarly across continents since climate change began to really accelerate from 1975,”

Mr. Galpern added.

Dave Goulson, a bee expert from the University of Sussex in Britain who was not involved in the study, argues that the finding is not that spectacular because bees usually like cooler environments. So, it is no surprise that they abandoned the southern edges of their ranges when things got too hot for their taste.

Yet, Mr. Goulson noted that the bumblebees are not trying to colonize the north, maybe because those regions are not suitable for them.

Sydney Cameron of the University of Illinois and wild bumblebee specialist challenged the findings although she had deemed the study “noteworthy.” She argues that the conclusion that bumblebees would eventually fail to move north and die off depicts a “dire future.”

She also said that the role of global warming is rather “correlative, not causal.” Dr. Cameron also said that a two-degree change in global average temperatures cannot be held accountable for the shifting patterns in bumblebee ranges.

The University of Illinois also said that study authors are wrong when they propose “assisted migration,” or physically relocating the species to the north, as a solution. She believes that the method is “impractical,” and can lead to ecosystem disruptions as bumblebees can spread pathogens.

However, Dr. Alana Pindar from the University of Guelph who was involved in the study argues that the shrinking ranges are the result of global warming. Dr. Pindar explained that her team adjusted the results for other risk factors such as pesticide overuse and habitat loss, but the results remained consistent.

Image Source: Cirrus Image