Arctic sea ice attacked by warmth from above and below
Arctic sea ice is melting rapidly. There are many ways to quantify this. A look at the ice chart from 2000 to 2015 reveals that thick old ice is becoming smaller and smaller. The earth is warming as a whole, and as it warms, the ice melts.
People use computer model predictions to guess how quickly the average area of Arctic sea ice is declining.
There are uncertainties in climate models. People run different models and make different assumptions, based on different models they think are better.
“That gets you a big spread which is the difference among different computer models. But the whole range is going down. There is no confusion about the earth getting warmer and the ice melting,” Jennifer MacKinnon said. MacKinnon is with the Scripps Institute.
Computer models show the ice going down at a certain rate, but the reality is that the ice has been receding faster and faster. “So the models must be missing something. The hypothesis that has motivated our team is that there is possibly extra heat coming up from the ocean below that could be accelerating the rate of sea ice melt,” MacKinnon said.
“We don’t understand how that works, so it is not included on the models. So we went out there on the Sikuliaq for a month to see if we could see hints of that process and how it works so we could improve the ice melt forecast models,” MacKinnon said.
“To understand how that might work, the heat getting trapped in the ocean and possibly melting the ice from below, we need to know a little bit about how the Arctic works.”
Most of the oceans in the world are warm on the top and cold on the bottom, because warm water is light and cold water is dense. “So the worm water floats on the top; the cold water sinks to the bottom and some of it stays there for quite a long time. The Arctic is somewhat of a funny one. It has a different structure. What controls how dense the water is is not so much temperature, but the salinity—how salty it is. There’s a cool but fresh layer of water right on top, that comes from melting ice, comes from rivers, comes from rain. So this water that floats on top is cold because it is very fresh, because it does not have a whole lot of salt in it. Below that you can potentially have water below that which is floating in the middle because it is medium. It is warmer because it is saltier. At the bottom, you have cold and salty water that is very dense.
“The question is, how do you get pockets of warm water that are beneath the surface? How do they come into the Arctic, how do they swirl around and how might their heat be mixing upward to accelerate the sea ice melt rates?
“There’s warm, comparatively warm, from the perspective of sea ice water that comes through the Bering Strait and up through the Chukchi and then enters where we were working over here so we know that water that is fairly warm is coming in this direction. Up here in the central Beaufort is where you have all the cool fresh surface water, a layer that is floating on top.
“The question is, what is happening to all this warm water that is coming in? Some of it hangs a right and goes along the coast, goes along the North Slope. Some of it hangs a left and goes this way. What we observed on our trip last month is that some of it actually dives underneath this cool, fresh water and when that water dives beneath, it can swirl around potentially for a long time and potentially go quite a distance taking that heat with it, kind of lurking below the sea ice, potentially releasing that heat in autumn and delay the autum freezeup or release it in spring and make the spring melt come much earlier. We’re interested in pockets of heat just below the ice because it can melt the ice. Thousands of feet down is not our focus right now,” MacKinnon said.
“This is a multi-year project funded by the Office of Naval Research and they are very interested in predicting how the Arctic is changing. The project comprises the trip we just completed on the Sikuliaq and a bunch of our colleagues out there on the USCG icebreaker Healy putting instruments in the ocean for a whole year to monitor other processes. So they are putting in mooring with a floaty ball on top with instruments. They are putting in autonomous sort of robots that are sort of gliding around. They are putting things in the ice. All those instruments are going to measure different facets of the project,” MacKinnon said.
The group of scientists sat by a shelf break near the Arctic Slope watching the warm salty water dive below the cooler surface water in several places in areas that had not yet receive that type of in low.
“The crew uses a sort of fast fishing reel that zooms down and measures the temperature on the way up. So you reel it out, reel it in, reel it out, going up and down and up and down so it measures the distribution of the temperature.
So the heat comes in here, dives in under and goes along the slope in this current,” according to Mackinnon.
Dramatic, rapid warming in the Arctic is putting a message on what is happening on the globe elsewhere in bold type. While scientists, politicians, marine safety experts, commercial interests and the folks around the morning coffee gatherings debate the causes and duration, most will agree: Climate change is happening.
“I think something’s happening. Something’s changing and it’ll change back again,” U.S. Pres. Donald Trump said last week. “I don’t think it’s a hoax. I think there’s probably a difference. But I don’t know that it’s manmade. I will say this: I don’t want to give trillions and trillions of dollars. I don’t want to lose millions and millions of jobs.”
A policy report released Oct. 8 by a United Nations international consortium of scientists warns that world response to global warming must be pulled back from a target reduction from two degrees Centigrade to 1.5°C, as soon as possible.
The report finds that the consequences of global warming will be upon us sooner and more serious than scientists thought. The Paris climate agreement, from which the United States has withdrawn, set a goal of no more that 2°C above pre-industrial temperature levels, asking that nations try for 1.5°C.
Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.2°C.
If warming continues at the current rate, global warming is likely to reach 1.5°C between 2030 and 2052.
“Climate-related risks to health, livelihoods, food security, water supply, human security, and economic growth are projected to increase with global warming of 1.5°C and increase further with 2°C,” according to the report.
One of the biggest differences between 1.5°C and 2°C is the impact on coral reefs, which support about 25 percent of all known marine species. Coral reefs are very vulnerable to the combination of hotter and more acidic ocean waters resulting from carbon pollution. At 1.5°C, the Intergovernmental Panel on Climate Change, IPCC for short, estimates that we’ll lose about 80 percent of coral reefs. At 2°C, virtually all coral reefs will be gone. Summers with no remaining Arctic sea ice are also ten times more likely at 2°C than 1.5°C (at least once per decade vs. once per century according to the IPCC report), which in turn causes weather systems to hover in place for extended periods of time. This can lead to particularly intense heat waves, floods, droughts and other extreme weather events.
The volume of sea ice in the Arctic has already declined by about 70 percent over the past 40 years. The ICPP is the United Nations body assessing the science of climate change, its risks, its potential future impacts and possible response options.
A big message from the 91 authors and review editors from 40 countries who produced the report is that we have 30 years to avert the worse changes. The authors and editors prepared the report in response to an invitation from the U.N. Framework Convention on Climate Change (UNFCCC) when it adopted the Paris Agreement in 2015, a mission to fight climate change. The group produced the report to guide global leaders in making policy.
“One of the key messages that comes out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes,” said Panmao Zhai, Co-Chair of Intergovernmental Panel on Climate Change Working Group I.
The Sikuliaq is operated by University of Alaska Fairbanks. It is owned by the National Science Foundation. The Sikuliaq joined the Arctic Research Icebreaker Consortium in February, a group formed to coordinate access to ice breakers to facilitate Arctic research. The effort involves 14 partners from 13 countries, coordinate by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research. The European Union funded the project with six million Euros (about $7 million).