NORMAN, Okla. — Some people might recall dodging flying bumblebees as kids, or finding the bees flitting around flowers in their front yard.
If those moments seem few and far between these days, it's because in North America and Europe the effects of climate change have reduced the odds of seeing a bumblebee by more than 30% on average since the 20th century, according to a new study published Thursday in the journal Science.
Researchers from the University of Ottawa in Canada examined changes in the populations of 66 bumblebee species across the two continents, and compared that with climate changes in those locations.
Their findings highlighted that as climate change causes temperatures and precipitation to increase beyond what bumblebees can tolerate, so does their risk for extinction.
"The things [we] grew up with as kids are fading away very fast," said Dr. Jeremy Kerr, senior author of the study and a biology professor at the University of Ottawa.
"It's not just that we're looking at what our kids will experience; it's that we are looking back not even a full generation, just to when we were kids, and saying, 'Could we take our children to places we loved and find what we found?' What our study says is that that answer is no across entire continents."
Populations are declining by the decade
The researchers evaluated changes in the presence and diversity of bumblebee species across North America and Europe using a database of around 550,000 records.
They estimated the distribution of the species across the two continents during two time periods: the first from 1901 to 1974, and the second from 2000 to 2015. They then examined whether the average monthly temperatures and total precipitation in the locations exceeded the bees' tolerance level.
Bumblebees tend to prefer cooler, slightly wet climates in which there's a variation in seasons. Declines in their populations are associated with increasing frequency of hotter temperatures and drying out of habitats, which raises bumblebees' risk for extinction and diminishes their chances of colonizing a new area and creating more species.
The researchers found rapid and widespread declines in bumblebee populations across both continents. The likelihood that a bumblebee species would be present between 2000 and 2015 in the areas studied dropped by 46% in North America and 17% in Europe compared to the older period.
"Colonization is when an animal goes to a new place and there was no population of that animal there before, and it establishes a new population," Kerr said. "If that's happening a lot, then the species might be doing okay."
"The amount of local extinctions we saw were eight times more common than these colonization events. Climate change is making these species disappear at a rate they couldn't keep up with at all to replace themselves."
Climate across the US and Europe has changed drastically due to human activity during the time periods the authors analyzed. In the past few hundred years, we have warmed the planet to 1.3 degrees Celsius -- close to the 1.5 degrees that's considered a critical warming threshold.
This has driven stronger and more widespread bumblebee declines than previously reported, the authors said.
The loss of bumblebees can contribute to decreasing biodiversity and impairment of ecosystem services, which impact food and water supply; the control of climate and disease; and supporting nutrient cycles and oxygen production.
Bumblebees pollinate plants such as cucumbers, tomatoes, squash, blueberries and melon.
"Bumblebees are among the best pollinators we have in the wildlife system," said Peter Soroye, co-author and PhD candidate at the University of Ottawa. "[They're] out for really long periods of the year in a lot of different weather conditions and they visit a really broad range of flowers. They're really a critical piece of these natural landscapes that we like to enjoy."
"Plants and crops that rely on pollination from bumblebees are likely to suffer if bumblebee populations continue to decline or vanish altogether, which could result in incredible consequences for the ecosystem," said Haley Todd, director of programs and education at Planet Bee, a San Francisco non-profit focused on bee conservation. Todd was not involved in the study.
Helping bees survive climate change
Other factors that affect bumblebee populations are the widespread use of pesticides and changing land use that reduces flora available to them.
In the study, the effects of climate change on bumblebees were observed independent of these human practices, meaning if those are accounted for, too, the risk of extinction would be even greater.
"Interactions between these factors are expected to accelerate biodiversity loss for bumblebees and other [species] over broad areas," the study said.
However, there are still "different and distinct conservation actions that can help combat these drivers of extinction," Soroye said.
Those include reducing the use of pesticides, planting a diverse array of flowers and shrubs to prevent habitat loss and providing bumblebees with occasional shelter from the sun "during extreme weather events that they're being subjected to more frequently because of climate change," Soroye said.
Beekeepers can protect bumblebees from excessive sun and rain exposure by planting shrubs in addition to flowers, and by building hive shelters with roofs and surrounding protective materials such as wood.
The authors suspect that their findings can also be applied to other species facing extinction, such as butterflies and birds.
"There are things we can do and recovery is a feasible thing," Kerr said. "We're not saying that what we all need to do is immediately start living in a hut in the woods to recover the situation. It points to a hopeful direction if we choose to intervene."
