The Arctic has been warming at the fastest rate of any place on Earth. There have long been observations of amplification of Arctic warming, meaning that its temperature increases have been well above what would be expected from the global temperature rise.
Many climate models have attributed this warming to the melting of sea ice. As the bright white ice disappears for longer periods of the year, the dark surface waters that are exposed absorb sunlight rather than reflecting it back into space the way the ice does. This is known as the ice-albedo feedback. But it does not entirely explain the amount of warming in the Arctic.
Researchers at the Scripps Institution of Oceanography have developed a new theory that helps to explain what is going on.
In the areas of the Arctic Ocean where there is sea ice, the water is actually warmer at depth and colder near the surface. The deeper waters are fed by the relatively warm Pacific and Atlantic Oceans while the surface water is cooled by the ice. The increasing temperature difference between surface and deeper water causes a greater upward flow of heat. This was first observed in research cruises that revealed evidence that the Arctic Ocean water was becoming more turbulent over time.
According to computer modeling, this phenomenon is responsible for about 20% of the amplification of global warming that occurs in the Arctic.
There are multiple ongoing studies looking at the Arctic warming trend. Other factors that have contributed over time are the presence of chlorfluorocarbons in the atmosphere. That contribution is waning since the use of CFCs has been phasing out over time.
Photo, posted April 19, 2017, courtesy of Markus Trienke via Flickr.