Nearly two-thirds of all bird species in North America will be at an increased risk of extinction if the world does not act to reign in climate change, a new report has found.
Among the most vulnerable species are those in Canada’s boreal forest and Arctic regions, where the rate of warming owing to greenhouse gas emissions is rapidly outpacing the global average.
The report, released on Thursday by the U.S.-based National Audubon Society, is among the most comprehensive attempts to date to discern the future impacts of a warming climate on avian life cycles and breeding ranges across the continent. The analysis looked at bird distribution in fine-grained detail, dividing up the continent into one-kilometre by one-kilometre squares and looking at probable changes to habitat that would play out under different climate scenarios. For the majority of species, the report found significant risks associated with greater warming.
“The pattern is pretty clear, and it’s been borne out in the last few decades by what we’ve already seen with a lot of these species,” said Jeff Wells, an ornithologist who leads the organization’s boreal conservation efforts.
The report follows on the heels of multiple assessments that have documented declines in many bird species over the past 50 years as a result of habitat loss, pesticides and other pressures related to human activity. One widely reported study published last week in the journal Science estimates that these pressures have led to a cumulative population loss among North American species that is now approaching three billion birds.
The Audubon report differs from those studies by projecting trends forward in time to examine the likely impact of climate change on 604 North American bird species under different emissions scenarios.
As the planet warms over the next century, birds will be hit by a range of effects including increased heat waves, heavy rains, drought, forest fires and “false springs” (when an early thaw followed by a sudden freeze reduces food availability). Many bird species are expected to shift in response to these and other climate-related factors, losing range in some areas while gaining range elsewhere. The Audubon analysis combined two measurements – how much total range a species occupied and the ratio of lost to gained territory under climate change – to arrive at a measure of its vulnerability under different warming scenarios.
In one scenario, where unconstrained emissions lead to a global warming of three degrees over the next century, the report found that 389 species, or 64 per cent, are moderately to highly vulnerable to shifting climate conditions, including 98 per cent of boreal species and 100 per cent of all bird species in the Arctic.
The net gain or loss in number of species during breeding season under a 3°C warming scenario is expected to cause reduced diversity across most of the continent and a shift toward the north and to higher altitudes for some species.
The increased vulnerability stems from a number of effects and is most pronounced during the breeding season when many species are critically dependent on seasonal food sources, including insects and plants.
Many Canadian species, including the iconic snowy owl, fared poorly in this scenario by essentially having nowhere to go as the North becomes increasingly warmer and the owl’s preferred habitat disappears. Not all species will be as adversely affected, the report suggests. For example, the common loon is expected to gain range, which makes it less susceptible to climate-related impacts. Over all, however, there are far more losers than winners in the high-emissions scenarios.
In contrast, the vulnerability score drops to 54 per cent if countries adhere to the 2 C limit imposed by the Paris climate agreement and 47 per cent under the more stringent 1.5 C target. (The global average temperature is currently estimated to be about 1 C above preindustrial levels, primarily because of increased atmospheric concentrations of carbon dioxide from fossil fuel emissions.)
Steven Price, president of Bird Studies Canada, said the report shows the looming impact of climate change on bird life through a complex and intertwined network of environmental effects.
“Climate change is both a direct threat to birds and other wildlife but also a driver of almost every other threat, which exacerbates their effects,” he said.
While Bird Studies Canada was not involved in the report, the organization provided about 60,000 individual records to the Audubon Society’s data analysis effort.
Dr. Wells said the results should serve as a wake-up call that illustrates the stark differences between taking timely policy action on climate change and delaying efforts to reduce emissions – and a harbinger of the broader potential effects that climate change could have on humans in the coming century.
“We really need to seriously look at which future we want to have,” Dr. Wells said, adding that the report demonstrates that “things can be vastly better if we choose the least increase in temperature and the maximum in lowering greenhouse gas emissions and protecting habitat.”
The Globe and Mail, October 10, 2019