This winter, massive cracks riddled the sea ice. Forming over an ice sheet nearly 80 percent thinner than in 1980, these cracks appeared suddenly and grew with astonishing speed. Covering hundreds of miles in minutes, they laid bare the ocean beneath, venting heat into an already quickening atmosphere (read more about the crack-up here).
2012 was the hottest La Nina year on record and the 9th hottest year on record globally. It was a year that saw a massive collapse in summer Arctic sea ice continue with a vengeance. Sea ice volume, as measured by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) fell to 3,264 cubic kilometers by September of 2012. This was 750 cubic kilometers below 2011’s record low and 3,200 cubic kilometers below 2007’s record low.
(Image credit: PIOMAS)
Even more disturbing is the fact that from the period of 2005 to 2012, two large, precipitous drops in sea ice volume occurred. In 2010, 2460 cubic kilometers of sea ice volume was lost. And in 2007, 3440 cubic kilometers of sea ice volume faded into the ocean.
With minimum sea ice volume for 2012 now sitting at 3264 cubic kilometers, a single melt year with weather conditions like 2007 would bring the total down to zero volume by end of summer 2013. This event may be unlikely to happen. But there is still a significant risk, a 10% potential, that something on this order may happen in 2013. Based on past sea ice losses and a current, ongoing melt trend, we can’t rule it out. So for the first time ever in the modern record, there is a chance that summer sea ice will completely disappear this year.
But even if we saw a repeat of 2010’s massive melt, volumes would be pushed very low — down to a paltry 800 cubic kilometers. And, in such a case, a complete melt by 2014 or 2015 becomes almost certain.
Taking into account the average rate of melt from 2005-2012, we see losses of 740 cubic kilometers per year. If these average losses continue through 2013-2017 total melt occurs sometime in the summer of 2017. But any catastrophic melt similar to 2007 results in a complete melt during any one of these five years.
Even if melt is ‘mild’ compared to averages over the past 8 years, it is almost certain that all summer sea ice will be gone by 2020. For these reasons, it is very important to sound the alarm for total summer sea ice collapse now. Given current trends, it appears less likely that summer sea ice will remain and more likely that the world will see an open Arctic Ocean sometime within the next five years and, almost certainly, by the end of this decade.
Looking at the risk trends, it appears 10% likely that zero summer sea ice volume will be reached by the end of 2013. That likelihood jumps to 25% by the end of summer 2014. By 2015, if current trends bear out, the chance is around 40%. Moving on to 2016, we get into the range of higher probabilities with a 50% likelihood of total summer melt. And without some kind of negative feedback or the intervention of weather less favorable for melt, there is more than a 60% likelihood that all sea ice will have disappeared by summer of 2017 (These probabilities are based on trends analysis and are not based on any official climate model).
Feedbacks To Play a Role?
There are a number of feedbacks taking place in the Arctic that may play a role in either preserving a small remnant of summer sea ice or in hastening the ice sheet’s eventual collapse. Some of these feedbacks are visible now. But there are, likely, others that have not yet been identified. Here are a few of the major players:
The first is sea ice melt itself. As sea ice melts more of the white, reflective ice is replaced by dark, heat absorbing, water. As less and less of the Arctic Ocean is covered by ice during the summer months, more and more dark ocean is available to absorb the near-constant summer sun’s rays. This feedback, called loss of albedo, would push for a faster melt and, if it comes to dominate, would result in a more rapid melt of far more fragile ice.
Fragile ice. As sea ice becomes thinner it is subject to an increasing array of mechanical forces that may hasten its break-up. Thin ice is less resilient to storms, for example. And as the ice breaks into smaller and smaller chunks a greater portion of its surface area is exposed to the sun’s rays and to the surrounding, warmer water. Again, this feedback would push for a more rapid melt.
Methane and CO2 release. Large portions of the frozen land-mass called permafrost are melting in the Arctic. When the organic matter in the permafrost breaks down either methane or CO2 is released. In addition, large volumes of methane are bubbling up from the sea-bed both from freed methane hydrates and from submerged and thawing permafrost. These releases produce local spikes of the greenhouse gasses methane and carbon dioxide while also amplifying global, human-caused climate change. Methane release local to the Arctic tends to increase Arctic heat trapping, resulting in more rapid ice melt.
Greenland melt. Over the past few years, an ever-increasing volume of cold, fresh water has been melting from the vast glaciers of Greenland. Ironically, this cold water melt may produce one of the the few negative feedbacks in the Arctic environment. Cold water flushing into the Arctic Ocean and North Atlantic may perturb heat transport to the Arctic via the Gulf Stream. Large volumes of fresh water also freeze at higher temperatures than the saltier ocean water, potentially restoring some albedo to the Arctic. So, in this case, large pulses of water from Greenland may result in a small volume of ice remaining to the north of Greenland during late summer. Even larger pulses may result in some recovery of the ice pack. But such an event would come at the cost of rapidly rising seas, powerful storms, and dangerous, large water pulses from Greenland. The question in such a case is if the positive human forcing on the climate system and the strength of other amplifying feedbacks in the Arctic is enough to overwhelm the negative feedback of water pulses from Greenland.
Because it appears less likely that water pulses from Greenland will grow large enough to produce a powerful enough negative feedback to overwhelm summer ice melt short-term, it appears that complete summer ice melt by 2013-2017 is a high risk and total ice melt by 2020 is almost certain.
After that time, all eyes turn to Greenland as the great ice sheets begin to play their role in re-establishing equilibrium to the Arctic environment. The surrounding heat of the oceans, air, and the amplifying feedbacks coming from the Arctic environment itself will almost certainly push Greenland into a very rapid melt phase by the late 2010s onward. And this next phase of Arctic melt will be far more dangerous and troublesome than the rapid sea ice melt period of 1979-2020.
Cracks of Doom
In parting, I will leave you with this graphic provided by the US Navy. It shows a broad but very thin ice sheet covering much of the Arctic. It shows the remaining, small portion of thick ice hovering just north of the Arctic Archipelago and the north shore of Greenland. It shows how much of the thick sea ice has already been flushed out through the Fram Straight.
What it does not show are the cracks that appear, periodically, like Arctic lighting over the now fragile ice sheet.
This is the state in which the Arctic enters its 2013 melt season. Thin. Depleted. Fragile. And with the cracks of its eminent demise now riddling its surface.
(Image credit: US Navy)