Climate News Network

Polar bears feel the heat as frozen habitat shrinks

December 19, 2014, by Alex Kirby

Loss of sea ice is affecting some polar bear populations as they depend on it for hunting and mating.
Image: Kathy Crane/NOAA

As climate change increasingly affects the Arctic, some polar bear populations are suffering because rising temperatures are reducing the sea ice vital for their survival. LONDON, 19 December, 2014 − The Arctic is changing faster under the influence of the warming climate than anywhere else on Earth, scientists have confirmed. The US National Oceanic and Atmospheric Administration (NOAA) says Arctic air temperatures continue to rise more than twice as fast as they do globally − a phenomenon known as Arctic amplification. The extent of snow cover in April 2014 in Eurasia was the lowest since 1967, and sea ice extent in September was the sixth lowest since 1979.

Badly affected

Some Arctic polar bear populations have been badly affected by the progressive shrinking of Arctic sea ice. But NOAA says: “Natural variation remains, such as the slight increase in March 2014 sea ice thickness and only a slight decrease in total mass of the Greenland ice sheet in summer 2014.” Increasing air and sea surface temperatures, a decline in the reflectivity of the ice at the surface of the Greenland ice sheet, shrinking spring snow cover on land and summer ice on the ocean, and the declining populations and worsening health of some bear populations are among the findings described in NOAA’s Arctic Report Card 2014. “Arctic warming is setting off changes that affect people and the environment in this fragile region, and has broader effects beyond the Arctic on global security, trade and climate,” Craig McLean, of NOAA, told the annual American Geophysical Union Fall meeting in San Francisco. “This year’s Arctic Report Card shows the importance of international collaboration on long-term observing programmes that can provide vital information to citizens, policymakers and industry.”

“Arctic warming has broader effects beyond the Arctic on global security, trade and climate”

The Report Card, published annually since 2006, updates changes affecting the Arctic. This year’s report − written by 63 US and other authors − covers key indicators, and also includes a new report on the status of the bears. This section, written by the Norwegian Polar Institute and Polar Bears International, assesses the animals’ populations in some areas where there is good long-term data available. There are clear variations between areas.

Ice break-up

The most recent data shows that a population decline in western Hudson Bay, Canada, was caused by earlier sea ice break-up and later freeze-up. The bears depend on sea ice to travel, hunt, mate and, in some areas, to den. But in the southern Beaufort Sea, north of Alaska, their numbers have now stabilised after a decline of about 40% since 2001. In the Chukchi Sea, between Alaska and Russia and immediately to the west of the Beaufort, the condition of the bears and their reproductive rates have been stable for 20 years. The Report Card says there are now twice as many ice-free days in the southern Beaufort as there are in the Chukchi Sea. It notes that polar bears have been through “long and dramatic periods of population decline” during the last million years, and that during periods with little sea ice, polar bears and brown bears have often interbred. The report says Alaska recorded temperature anomalies more than 10°C higher than the January average during 2014. Snow cover across the Arctic during the spring was below the long-term average for 1981-2010, with a new record low set in April for Eurasia. North America’s June snow extent was the third lowest on record. Snow disappeared three to four weeks earlier than normal in western Russia, Scandinavia, the Canadian sub-Arctic and western Alaska because of below-average accumulation and above-normal spring temperatures. The eight lowest sea ice extents since 1979 have occurred in the last eight years (2007-2014). There is still much less of the oldest, thickest (greater than 13 feet, or four metres) and most resilient ice than in 1988, when it made up 26% of the ice pack. This year’s figure is 10%.

Extent of melting

As sea ice retreats in summer, sea surface temperature across the Arctic Ocean is increasing. In the Chukchi Sea, it is increasing at 0.5°C per decade. Melting occurred across almost 40% of the surface of the Greenland ice sheet in summer 2014. For 90% of the summer, the extent of melting was above the long-term average for 1981-2010. In August 2014, the reflectivity (albedo) of the ice sheet was the lowest recorded since satellite observations began in 2000. When less of the sun’s energy is reflected by ice, melting increases. The total mass of the ice sheet remained essentially unchanged between 2013 and 2014. Declining sea ice allows more sunlight to reach the upper layers of the ocean, triggering increased photosynthesis and greater production of phytoplankton − the tiny marine plants that form the base of the food chain for fish and marine mammals. − Climate News Network

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