An Unusual Summer in Hudson Bay – What Does It Mean for Polar Bears?

“Climate is what you expect, weather is what you get” goes a saying among climatologists. It reminds us that weather is chaotic and can yield surprising variations that are, however, consistent with our understanding of climate overall.

This year’s weather and sea ice behavior in Hudson Bay is such an example. Home to two important groups of polar bears, the Western and Southern Hudson Bay populations, it is a region in the Subarctic that scientists keep a close eye on. 

For most of May, a strong high pressure system parked itself over northern Canada just North of Hudson Bay (Figure 1, left panel). It’s not uncommon for high pressure systems to do that in spring and summer in this region, but usually they are located farther north and are not as persistent. High-pressure systems spin clockwise in the Northern Hemisphere, thus causing winds to blow from east to west on their southern flank. This is the opposite of hurricanes, for example, which are just very strong low pressure systems. 

This year’s weather configuration led to strong winds blowing from east to west right across Hudson Bay. At this time of year, the sea ice in Hudson Bay starts to thin as the melt season begins. The winds were strong enough to push the thinning ice towards the west, opening up Eastern and Southern Hudson Bay very early this year (top right panel in Figure 1). This caused ice to pile up in Western Hudson Bay, which remained completely full of ice through June (bottom right panel in Figure 1). The opposing behavior of sea ice in these two ecoregions is, in fact, the most lopsided ever recorded since reliable satellite measurements began in 1979. Never has Southern Hudson Bay been so low on sea ice this early in the year and never has Western Hudson Bay been so full of ice at the same time!

Naturally, such weird behavior prompts two questions: (1) “Is this related to climate change?” and (2) “What does this mean for polar bears?”

The answer to question (1) is “mostly no.” Weather variations have always been part of climate and will continue to be in the future. While some extreme events are expected to become more extreme with climate change, we don’t expect fundamental changes to the occurrence of high pressure systems over this region. They just end up in a slightly different place each year due to the chaotic nature of weather, sometimes affecting the movement of sea ice more than other times. However, there is a possibility that as sea ice thins earlier in spring due to global warming, it becomes more vulnerable to being pushed around by winds like this year. 

As with most questions in ecology, the answer to question (2), what does this mean for polar bears, is “it depends.” On the one hand, polar bears in Hudson Bay show a very strong fidelity to their onshore areas, often coming back to the same part of the coast every year when the ice melts. On the other hand, bears are adaptable and will go where the food is. 

For bears that typically summer in Western Hudson Bay, this pattern of sea ice could lead to a longer time on the ice foraging for seals and a shorter journey to their preferred summering area, which is good news for them. For bears that typically summer in Southern Hudson Bay, they will likely follow the ice to forage for seals as well, but that means they might end up far from where they typically spend the summer. Some bears may walk back to their typical summer locations, while others may decide to ride out the ice-free season in a different place.

Female bears that are in good enough condition to become pregnant may have the biggest choice to make. From what we know about polar bear denning, females tend to return to the same general area during subsequent years, though there is some flexibility. So, Southern Hudson Bay females that are looking to den must choose to leave the ice early near a preferred denning area or stay on the ice, potentially denning in a different location or make the long journey along the Hudson Bay coast back to their desired denning location. Each strategy involves energetic trade-offs that may impact the bears’ condition during their time on land when they must rely on stored fat reserves. 

These issues are heightened in James Bay, where polar bears live further south than any bears on earth and face increasingly challenging conditions. Although this year’s weather conditions may not have impacted the ice in James Bay as in the rest of Southern Hudson Bay, the ice broke up in James Bay near the beginning of June. This could put bears in James Bay on land for more than 6 months of the year. What this means for their condition, survival and whether they will abandon James Bay for more northern latitudes is not yet known. However, it will be very challenging for female bears to produce cubs under these conditions and pushes the known limits of polar bear abilities to fast on land.  

Dr. Flavio Lehner is Polar Bears International’s chief climate scientist and an assistant professor in Earth and Atmospheric Science at Cornell University. Dr. Joseph Northrup is a research scientist at the Ontario Ministry of Natural Resources.