The polar bear, with the scientific name Ursus maritimus (it means sea bear), is the biggest bear in the world. Males can weigh from 300 to 800 kg. Polar bear fur seems white or yellowish, but it is actually transparent. They have a black nose and also have black skin. Polar bears are closely related to brown bears, but they are slenderer, their skull is narrower, and their neck is longer. Polar bear teeth are really sharp, so they are perfect for cutting meat. Their paws are really big (30 cm wide), which makes it easier to walk on ice,and they are also really good swimmers. Polar bear habitat is in the Arctic and areas around it. Polar bears are considered marine animals because they depend on marine ecosystems. They prefer to live on sea ice, but when the ice melts during the summer, they go on land but still stay in coastal areas. Polar bears are carnivores, and they are specialized in hunting ringed seals. This prey is typically taken by ambush. Polar bears usually stalk their prey in the sea or on ice. They can also wait for the prey in its breathing hole. They also eat walruses, beluga whales, and some land animals.
Like already said, polar bears depend on sea ice. They use it for travelling, hunting, resting, mating, and sometimes also for maternal duties. Their sea ice habitat has been and may be disparaging due to climate change. This is the main threat to polar bears across the Arctic, and therefore they were added to the US Endangered Species Act in May 2008. Because of global warming, sea ice melts earlier in the spring and also forms later in the fall, so polar bears are spending more time on the land. Polar bears spend more than 96% of their time on sea ice. Do find food, they are often attracted to the areas where people live.

The Arctic has been so far the most affected by global warming, and this trend is expected to continue. Some scientists say that before mid-century, we might see a nearly ice-free Arctic in the summer. Right now, polar bears have quite a good gene pool, which means that they have some hope of adapting to changing environments. However, their dependence on sea ice makes them extremely vulnerable to a changing climate.

Because of global warming, polar bears are forced to change their behaviour. They have to make changes to their biological events, for example, in breeding and denning.
Polar bears also have to make changes to their diet. Their main diet used to be seals. Now they also have to eat whale carcasses, sea duck eggs, and reindeer. For food, polar bears have to travel longer distances, and they also have to swim more, which means that they are also using more energy to do it. To get enough food, polar bears have also been noticed in human rubbish dumps, and this leads to conflicts between humans and polar bears.
European Arctic polar bear females have only one-third of a denning habitat left of what they used to have back in the 1980s. Scientists have found with their research that in the 1980s, polar bears spent only a few weeks on land during the summer. Now this time is almost two months. They also noticed that only 5% of bears went to the shore during the summer. Now the percentage is 50 or even higher. Warmer weather during the winter causes the collapse of dens. Female bears build them to protect their cubs. There is a study where scientists found that females give birth to a smaller litter of cubs if the summer is longer than usual. Since it is not that easy to find food, the females have to travel more, and that puts their cubs in danger.
Less ice makes it harder for polar bears to travel. That means that different populations become more isolated. Warming has also been associated with increased exposure to diseases.

Less sea ice means that polar bears and humans will have more conflicts in the future. A large portion of polar bear habitat is overlapping with oil and gas industry facilities. One project that makes scientists concerned is “The Willow Project.” With this project, the developers have planned around 250 oil wells and hundreds of miles of pipelines, and this all needs a road system for transportation. This project covers the areas that polar bears are using for denning. And to add to that, it is estimated that this project will add more than 250 million metric tons of carbon to the atmosphere in the next 30 years.

To determine species vulnerability, scientists have come up with a study that helps identify biological traits and other factors that make species vulnerable or resilient to changes. As already mentioned, polar bears are vulnerable to climate change. In different studies, scientists have noticed that polar bears rely on environmental cues for reproduction. That means that their breeding season is from March to May. The development of fertilized eggs starts between September and October. Females give birth to their cubs at the end of November and until early January. Since the ice formation and deformation times have changed, polar bears have had to travel longer distances to find denning spots. Due to this, the females are expending more energy. If females drop their body mass below 189 kg, then they become unable to reproduce successfully.

Sources:
https://www.worldwildlife.org/species/polar-bear
https://en.wikipedia.org/wiki/Polar_bear
https://interactive.carbonbrief.org/polar-bears-climate-change-what-does-science-say/
https://www.worldwildlife.org/pages/polar-bears-and-climate-change
https://defenders.org/blog/2022/11/polar-bears-affected-climate-change
http://assets.worldwildlife.org/publications/835/files/original/WWF_Polar_Bear_climate_assessment_web.pdf?1479741876&_ga=2.255871884.604088049.1708959841-424117094.1708959839