Polar bears are one of the most iconic animals of the Arctic, but they are also one of the most vulnerable to the effects of climate change.
A new study published in Science1 has quantified the relationship between greenhouse gas emissions and the survival of polar bear populations, showing that the more emissions, the less likely the bears are to survive and reproduce.
How emissions affect polar bear hunting and fasting
OLIVIER MORIN/AFP via Getty Images
The study, led by researchers from the University of Washington and Polar Bears International, used a combination of past research and new analysis to provide a quantitative link between cumulative greenhouse gas emissions and polar bear survival rates.
The study used data from 13 polar bear subpopulations across the Arctic, covering about 80% of the global population.
The study found that the survival rates of polar bears depend on two factors: the availability of sea ice, which they use as a platform to hunt seals, their main prey; and the length of the ice-free season, which forces them to fast on land or swim long distances.
Both factors are influenced by greenhouse gas emissions, which cause global warming and sea ice loss.
The study showed that as emissions increase, sea ice declines, and the ice-free season lengthens, polar bears have less time and opportunity to hunt seals, and more time to spend fasting.
This reduces their body condition, reproductive success, and survival.
The study projected that under a high-emission scenario, most polar bear subpopulations would collapse by 2100, while under a low-emission scenario, some subpopulations could persist.
How the study can inform legal and political action
The study has important implications for the conservation and management of polar bears, as well as for the implementation of the Endangered Species Act (ESA), which protects threatened and endangered species in the United States.
Polar bears were listed as threatened under the ESA in 2008, because of the threat of climate change.
However, a legal opinion issued by the U.S. Department of the Interior in 2008, known as the Bernhardt Opinion, required specific proof of how a proposed project's greenhouse gas emissions would affect a species' survival before the ESA could be fully applied for species threatened by climate change.
The new study provides such proof, by linking emissions to survival rates. This means that any government-authorized projects that emit greenhouse gases, such as oil and gas leases, could be challenged under the ESA if they further endanger polar bears.
The study also provides a framework for assessing how different emission scenarios would affect polar bears in the future, and how mitigation measures could help them adapt.
The researches hoped that their findings will motivate governments and individuals to take action to reduce greenhouse gas emissions and limit global warming.
They also stressed that while climate change is the main threat to polar bears, other factors such as pollution, hunting, and human disturbance also need to be addressed, and called for a holistic approach to conserve polar bears and their Arctic habitat.
