41 readings September 10, 2023, 11:20 p.m
The polar bear (Ursus maritimus) has become a symbol of the consequences of global warming: its hunting territory (the ice floe) is shrinking and no longer offers enough food for population growth. . A new analysis claims to have quantified the connection between greenhouse gas emissions and the polar bear’s chances of survival.
The polar bear (Ursus maritimus) has become a symbol of the consequences of global warming: its hunting territory (the ice floe) is shrinking and it can no longer find enough food to increase its population.
In fact, Arctic sea ice has lost almost 45% of its surface area and 80% of its volume since 1979 due to global warming and is expected to almost completely disappear by 2050. However, sea ice is a vital hunting and habitat for polar bears.
According to the Red List of Threatened Species The polar bear is an endangered species whose population is expected to decline by 30% in the coming decades, particularly due to the decline of sea ice. “We have known for decades that continued warming and sea ice loss can ultimately only lead to a reduction in the distribution and abundance of polar bears,” said Steven Amstrup, chief scientist emeritus of Polar Bears. International and Associate Professor at the University of Wyoming.
A new study from the University of Washington and Polar Bears International claims to have quantified the connection between greenhouse gas emissions and the survival rate of polar bear populations.
This new article was published on the 50th anniversary of the Endangered Species Act and the 15th anniversary of the registration of polar bears with ESA in the United States in 2008.
The Arctic is probably the fastest warming region on earth and the sea ice is the hunting ground for polar bears. During the ice-free summer months, bears must fast or eat seals as well as other foods such as birds, eggs, small land mammals and even stranded whale carcasses. In the worst case, adult bears die but lose the ability to successfully raise young.
Polar bear expert Steven Amstrup and climate modeler Cecilia Bitz, a professor of atmospheric sciences at the University of Washington, have conducted analyzes that suggest a direct link between cumulative greenhouse gas emissions and polar bear demographic changes. This connection largely explains recent declining trends in some subpopulations of polar bears, such as those in western Hudson Bay, researchers say.
This study considers not only the survival of adult polar bears, but also their ability to have cubs and raise them to the age of independence.
In the Hudson Bay regions, which had ice-free months before 1979, there have been slightly longer fasting periods since 1979 (from an average of 110 days to 130 days). In the more closed waters of the Beaufort Sea and Chukchi Sea, the number of days polar bears are required to fast has increased dramatically (50 to 125 days and 10 to 140 days, respectively), and their inability to raise their offspring has also increased significantly, to about 20 % in the four regions examined.
According to the scientists’ observations, the three populations studied are therefore declining due to greenhouse gas emissions.
This alleged mathematical connection between cumulative greenhouse gas emissions and the decline of certain polar bear populations is a blessing because “so far, scientists have not provided any quantitative evidence of the connection between greenhouse gas emissions and population declines,” said second author Bitz, for exampleAn additional day of starvation for bears is caused by the emission of 14 gigatons of carbon dioxide equivalent (GtCO2e) more in the atmosphere.
Such numbers make communication much easier and also promote the reduction of greenhouse gas emissions. For example, the hundreds of power plants in the United States will emit more than 60 gigatons of greenhouse gases over their 30-year lifespan, reducing the survival of polar bear cubs in the southern Beaufort Sea population by about 4%.
However, the connection between global warming and declining polar bear populations is far from proven, even though polar bear populations have been doing better in recent decades.
Can we really make a connection between global warming and the disappearance of polar bears?
Such a link could be a “strange” abbreviation According to Susan Crockford, a Canadian zoologist who specializes in the study of polar bears and their Arctic habitat and runs a scientific blog, that contradicts the alarmist tone used when discussing polar bears.
Susan Crockford denounces an incomplete, non-peer-reviewed study with truncated data: “The claim that greenhouse gas emissions can be directly linked to polar bear cub survival (i.e. (i.e. more emissions, more polar bear deaths)) completely collapses when we do that “We know that the documented incidents of poor juvenile survival rates in western Hudson Bay in the 1980s (…) were not included in the 2020 base model used to model the results in this new paper,” denounces the zoologist , who recalls that in the 1980s the chances of survival of the young were so poor that several females lost their entire litters, especially in 1983, when melting Arctic sea ice was not yet a problem.
In 2022, Canadian government scientists announced a 27% decline in the number of polar bears in western Hudson Bay between 2017 and 2021. Media reports have largely linked this alleged decline to sea ice loss due to climate change, but sea ice conditions in this region have been quite favorable over the past five years. In addition, the state of the ringed seal population, the polar bears’ main prey, should also be taken into account.
After all, sightings of polar bears, a symbolic and majestic animal, are now commonplace, and it seems reasonable to question the lack of ample photographic evidence of their poor condition.
This supposed connection also deserves to be put into perspective with regard to research into past climate zones. In fact, between 11,300 and 9,700 years B.C., the Arctic experienced BC, at the beginning of the Holocene, a warming period known as the Holocene Climatic Optimum (HCO, in English Holocene Climatic Optimum). During the HCO, summer temperatures in the Arctic were 2-3°C warmer than current temperatures.
This increase in temperature led to the melting of large areas of sea ice in the summer, so that the Arctic was almost ice-free in the summer. On land that was once covered in ice, vegetation has taken hold, creating favorable habitats for wildlife. This warmer climate has influenced life in the Arctic. Animal and plant species have adapted to these conditions, and some species now typical of the Arctic, such as polar bears, have evolved to survive in an environment with ice-free periods in summer.
A powerful tool for communication and pressure on politicians
In any case, Steven C. Amstrup and Cecilia M. Bitz believe their study has implications that go beyond polar bears and sea ice. In fact, the same analysis method can be applied to other species and habitats that are directly related to global warming, such as coral reefs and many species whose habitat is shrinking due to global warming and rising temperatures.
This research also has strong and expected policy implications because it enables a formally assess the impact of our activities on polar bears. In the United States, polar bears became the first species to be listed under the Endangered Species Act in 2008 due to climate change. However, the Endangered Species Act requires that all federally approved projects, including oil and gas leases, not further endanger listed species. However, a document issued by the U.S. Department of the Interior in 2008 called the “Bernhardt Notice” required concrete evidence of how a proposed project’s greenhouse gas emissions would affect the survival of a species threatened by climate change before the Endangered Species Act was fully implemented.
“I hope that the U.S. government fulfills its legal obligation to protect polar bears by limiting greenhouse gas emissions from human activities,” Bitz said. “I hope that investments will be made in the alternatives to fossil fuels that exist today and in the discovery of new technologies that avoid greenhouse gas emissions.”
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