Many of the threats we know are related to climate change are moving slowly. Gradually rising seas, a steady increase in extreme weather events, and more, all mean gradual change is coming across much of the world. But we also recognize that there could be tipping points, where certain aspects of our climate system suddenly shift toward new behaviors.
The challenge with tipping points is that they are often the easiest to identify in retrospect. We have some evidence that our climate has experienced them in the past, but it can be difficult to reconstruct how quickly a system topples or the forces that caused the change. Now a team of Norwegian scientists suggests it has seen the climate reach a tipping point: The loss of Arctic sea ice has turned the Barents Sea from a buffer between the Atlantic and Arctic oceans to something closer to an arm of the Atlantic. ocean .
Decades of data
The Norwegian work is not based on another breakthrough in technology. Instead, it is based on long-term data collection. The Barents Sea has been monitored for things like temperature, ice cover and salinity, in some cases going back more than 50 years. This provides a good basis to pick up on long-term changes. And in the case of the Barents Sea in particular, it means we happened to be watching a great change take place.
The Barents Sea is located north of Norway and Russia and is bordered by Arctic islands such as Svalbard and Franz Josef Land. To the west lies the North Atlantic Ocean and the Arctic Ocean to the north. And data from before the year 2000 indicates that the Barentsz acted as a buffer between the two oceans.
In the north, the Arctic Ocean is dominated by sea ice, which extends into the Barents in winter. The ice acts as a barrier to heat exchange with the atmosphere and blocks sunlight from reaching ocean waters, keeping the Arctic colder in summer. As it melts, the Barentsz also creates a layer of fresh water that doesn’t mix well with the salt water below, and it’s light enough to stay on the surface. The waters of the Atlantic Ocean are warmer but saltier and better mixed at the depths.
In between, in the Barentsz, the two influences create a layer of intermediate water. Arctic surface water and sea ice keep the Barents Islands fresher and cool. And while the Barentsz is warmed up from below by the dense, salty Atlantic water, it’s not enough to get the two layers mixed well. This helps to keep the surface water of the Barents Sea cold and fresh, which can cause it to freeze in winter.
The researchers behind the new work say this layered structure was “remarkably stable” from 1970 through 2011. But change began to take place in the area, even as the layers persisted. The atmosphere over the Arctic has warmed faster than any other area on Earth. Partly because of this, the amount of ice covering the Arctic Ocean began to decline dramatically. In 2007 and 2008, it reached what were then record lows. As a result, the Barents Sea was relatively ice-free in the Arctic summer, reducing the freshwater present in the surface layer.
Sea ice drift in the Barents Sea decreased enough that the 2010-2015 average was 40 percent lower than the 1979-2009 average. The researchers checked precipitation on some islands bordering the Barents Sea, and they confirmed that the loss of freshwater at the surface was due to the loss of ice, not a change in weather patterns.
(For context, the Barents Sea is essentially ice-free at this point, even though the melt season typically lasts until September.)
Triple Threat
The loss of ice also means that the surface water in this area exchanges heat with the atmosphere and absorbs more sunlight during the long Arctic summer days. These two have combined to dramatically heat the top 100 meters of water. Taking the average of the temperature from 1970-1999 as a baseline, the temperatures from 2010-2016 are almost four standard deviations higher. 2016 – the most recent year for which we validated data – was 6.3 standard deviations higher.
As a result, the intermediate water is heated from above. Meanwhile, the warm Atlantic water will warm it from below. As a result, the cold intervening water has essentially disappeared from the Barents Sea, turning the area into a basin dominated by Atlantic water. The entire water column, from the surface to the seafloor, has both warmed and become saltier, all from the late 2000s.
Although dramatic, that in itself does not constitute a tipping point. But the authors state that current conditions make it extremely difficult for sea ice to regenerate itself during the winter: “Increased influx of Atlantic water has recently increased the area where sea ice cannot form, increasing the size of the sea ice.” sea ice has decreased.” The water starts out warmer and has increased salinity, making freezing more difficult.
Essentially, the authors state that the entire Barents Sea is beginning to behave like an arm of the Atlantic Ocean. Unless an external factor restores the freshwater layer at the surface, “the entire region may soon have a warm and well-mixed water column structure and be part of the Atlantic domain.”
Tip of the ice cream
From a strictly people-oriented position, the changes are not necessarily something terrible. In terms of ecosystems, the authors describe the Barents as “divided into two regions with different climatic regimes – the north has a cold and harsh Arctic climate and an ice-associated ecosystem, while the south has a favorable Atlantic climate with a rich ecosystem and lucrative fishing.” .” The expansion of this fishery, at the expense of the native ecosystem, could be a boon for the countries bordering the region.
But the general thrust of the research is considerably more ominous: Not only have we discovered a climate tipping point, but we’ve noticed it after the system has likely already changed to a new regime. It also gives an idea of what to expect from the future. Instead of seeing the entire planet undergo some dramatic changes, we will probably see many regional tipping points that have more of a local effect. The future will be the sum of these events and their interactionsmaking it a bit more difficult to predict what changes to plan.
Nature Climate Change2018. DOI: 10.1038/s41558-018-0205-y (About DOIs).