Andrew Derocher is a professor and polar bear expert at the University of Alberta.
Polar bear waiting for sea ice to form. Churchill, Manitoba, Canada, November 2016. Photo: Sybille Klenzendorf / WWF To understand the threat to polar bears from climate change, one only has to examine the trends in sea ice across the Arctic. With 19 different polar bear populations, we’re seeing 19 different scenarios play out over time: none of them bode well for the long term. Polar bears were almost preordained to be the Arctic icon for climate change. It’s not because scientists and managers could see the future but rather because the 1973 International Agreement on the Conservation of Polar Bears required the five Arctic nations with polar bears to conduct national research programs.
In the earlier years, research focused on estimating population size, understanding their ecology, and calculating sustainable harvest levels. The baseline of information allowed scientists to examine the relationships between polar bears and sea ice. The absolute dependence of polar bears on sea ice for all aspects of their life history became increasingly clear. From this background, it has also become increasingly clear that loss of sea ice associated with climate change is a rapidly growing risk to the long-term conservation of polar bears. Without enough sea ice, there are no polar bears. The challenge is defining “enough”.
Polar bears use up about 1 kg of body mass per day that they’re not feeding on seals.
Consider that polar bears use up about 1 kg of body mass per day that they’re not feeding on seals. Changing ice formation or melt by a few days is well within the fasting capacity of most bears but the ice-free period across the Arctic is changing by at least 5 days/decade and some areas up to 75 days/decade depending on the population. As the ice-free period increases, it’s clear that more bears will run out of stored fat and succumb to starvation.
Once we cross about 180 days of ice-free time in an area, there’s little hope that a population will produce enough cubs to persist. Polar bear populations will blink out one-by-one. There’s little or no hope of adaptation – polar bears evolved as an obligate marine predator on seals. They won’t become more terrestrial as some wishfully hope: the terrestrial Arctic bear niche is already filled by the barren-ground grizzly bear. On the positive side, we should have polar bears to the end of the century in the Last Ice Area in the high Arctic.
The sea ice conditions in 2016 were challenging for some polar bear populations with an early melt. Of particular concern was that the September minimum sea ice cover was the second lowest on record. The situation, however, has gotten worse in some areas as the sea ice is at record lows for many areas through much of November. What will 2016 mean for polar bears across the Arctic? It’s always hard to know but some populations are already 25-50% lower in abundance than only a decade ago.
It’s a given that 2016 will present new challenges for polar bears and the communities across the Arctic. Hungry bears seek out food and northern communities are often right in path of hungry bears. More hungry bears in communities usually means more dead bears but it’s also a major safety concern for people as we move into the months long Arctic night.
Is 2016 the year that some populations crash? It’s possible but we won’t know until monitoring programs are in the field in 2017. Nonetheless, we won’t really have solid insights because the monitoring of polar bears is so episodic. Some populations have no monitoring and others are only followed every decade or two. The core monitoring populations in Western Hudson Bay, Southern Beaufort Sea, and Barents Sea near Svalbard are all showing similar concerns: loss of sea ice leads to lower body condition and then declines in reproduction and survival that lead to population declines.
It’s not complicated. Polar bears need sea ice and their habitat is disappearing at an alarming rate.
It’s not complicated. Polar bears need sea ice and their habitat is disappearing at an alarming rate. People understand that destroying the Amazon rainforest endangers species but sea ice is such a mysterious habitat for many people and polar bears are such amazing animals that they expect they’ll somehow manage. Wishful thinking is a poor means of conserving any wildlife species – it will have tragic consequences for polar bears.