The Ice Man

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In this interview, Nick Hughes explains his role as ice consultant for the Northern Passage 2010 Expedition. Nick is Head of the Norwegian Ice Service, leading a staff that prepares ice charts of the Arctic and Antarctic and provides in-depth ice information for clients. Let’s hear what he has to say…

by Olav Grinde

“For the Northern Passage 2010 Expedition, I have been interpreting ice conditions based on satellite images. This involves converting available raw satellite data into maps that can be understood by the crew of the “Northern Passage”. In places where the ice was challenging, I have suggested navigational waypoints for the crew to follow through the ice, avoiding its greatest concentration,” says Nick Hughes.

The craft of forecasting
“To forecast ice conditions, you need information on where the ice is now, a good weather forecast including the expected wind conditions, as well as knowledge of factors such as ocean and tidal currents, and sea-water temperatures, that may affect the ice in a particular area.

“Børge was fortunate to obtain sponsorship from the Canadian Space Agency, which provided the expedition with a large number of images from “Radarsat-2”, a satellite that observes the Earth’s surface. This was vital both for planning the initial route and for following ice conditions near the “Northern Passage” during the two most critical months of the expedition. We are able to see the ice through clouds and at night,” explains the ice expert.

“Most of the time we used images with a medium resolution of 50–100 metres, which is ideal for seeing where there is ice over a wide area. When we wanted to follow the ice in more detail over a smaller area, for example the narrow Bellot Strait in the Northwest Passage, we could increase the resolution to up to 4 metres. In addition the Ice Service was able to provide coverage from the European Space Agency’s Envisat satellite, through our involvement in the MyOcean project, as well as publicly available images from NASA satellites.”

Concentrating on the route
“On most days we were able to obtain images for the relevant area. Fortunately we did not need to draw full ice charts, but could limit ourselves to where we knew the “Northern Passage” would be sailing.”

The standard charts released by the Norwegian Ice Service cover the area between Greenland and the Kara Sea, and from the Baltic Sea and up to the North Pole. These are issued on weeikdays, except on Norwegian public holidays. Recently the team has started production of weekly ice charts for the Antarctic, covering the area of the Antarctic Peninsula and the Weddell Sea. It must also be mentioned that the Norwegian Ice Service participates in international research projects.

The challenge of stealth ice
“One issue the radar satellites have with summer sea ice conditions is that melt water may form on the ice surface and make the ice almost invisible! I am considering suggesting a new official term for this: stealth ice. Sometimes I had to use visual images, between the cloud cover, from NASA satellites to check the status and position of ice that I knew to be in the area based on earlier images,” explains Nick.

Teamwork
It can be very difficult to predict the interplay between ice, wind and ocean currents. That is why ice expert Nick Hughes has worked closely with expedition meteorologist Marc De Keyser.

“Most times, sea ice will behave as expected, which is that unless there is a particular ocean or tidal current present it will be blown about by the winds. What can happen is that a large area of concentrated ice can require prolonged winds in a particular direction to overcome its initial inertia and get it moving. On the other hand, once the ice is moving, it can continue in that direction for some time even if the winds should die down or change direction.”

Any surprises?
He explains that ice conditions this year have been very favourable for navigation of the Northern Sea Route (Northeast Passage) and the Northwest Passage. “In view of summer conditions in the Arctic over the past decade, I have not been surprised. Where the expedition did encounter ice, it was in the areas where we expected it,” says Nick.

“The crew of the “Northern Passage” reported that they saw surprisingly little birdlife or animal life in much of the waters north of Russia. But in my experience the wildlife tends to very closely follow the ice edge and the algal bloom. Because the main ice edge was usually much further north than where “Northern Passage” was sailing, it came as no surprise that they saw so little wildlife.”

Man-made climate change
Many people insist that man-made climate change is a proven fact. Others dismiss the idea. We ask Nick Hughes for his opinion:

“My opinion and that of the Ice Service, whenever we are asked whether or not we are seeing man-made climate change, is that we are dealing with the ice here-and-now. Our role is to provide information that can aid navigation – not to speculate on the causes of climate change,” says the ice expert. “The processes that lead to climate change are highly complex, and the science and collection of observations that enable us to understand what is going on, is still being developed.”

“The historical records for ice charts in the Svalbard region go back to the beginning of the 1900s. However, only since 1978 have these been based on reliable continuous satellite observations. This record is too short to give an accurate indication of long-term climate change. The ice record does show a decline in the sea ice coverage in the Svalbard area, but mainly because of the very large ice extents recorded in the 1970s when there was less observation data available to the analysts.

“If you extend the observational record back further, as was done by the ACSYS project, you unveil evidence of earlier periods of low sea ice coverage, particularly in the 1920s and 1930s. Climate scientists are still accumulating evidence on what was going on at that time, and are trying to replicate historical and current conditions in their numerical models,” he explains.

Drastic reduction of sea ice
We ask whether it is true that the volume of Arctic sea ice has been reduced by about 70 percent in recent decades? Some people focus on area, others on volume. What is the significance of each type of reduction?

“This is a very topical question, as I am answering your questions while sitting in the offices of Professor Peter Wadhams at the Department of Applied Mathematics and Theoretical Physics (DAMTP) in the University of Cambridge. He is one of the world’s foremost experts in this field,” says Nick Hughes.

“Observations of sea ice thickness in the Arctic Ocean by U.S. and U.K. Royal Navy submarines go back to the 1950s, well before the satellite era. I myself took part in two expeditions by the Royal Navy submarine Tireless in 2004 and 2007 that investigated this. Looking at the measurements of sea ice draft, i.e. the portion of ice below water level that the submarine can measure using sonar, the data shows a decrease in thickness of around 40 percent. If you combine that with the decrease in area extent seen by satellites, then this does indeed work out to be a reduction in volume of around 70 percent,” confirms Nick.

“Scientists studying data on sea ice thickness are able to determine volume. Those working with satellite data tend to focus on area, as this is easily observable. There are techniques to measure sea ice freeboard, the portion of the ice above sea level, using satellite such as radar and laser altimeters, which have been available only since the early 1990s. However, as only about one-eighth of the ice is above sea level, and this is normally a few centimetres, satellites are not yet accurate enough to provide consistently reliable measurements.

Submarines and satellites
“While you may see reports of people saying they can measure sea ice thickness from satellite, this tends to be a yearly average based on autumn-to-spring data. This is because the satellites tend to be unreliable during summer, due to the melt of the ice surface. Also, an averaging of a large amount of data is required to extract the small ice freeboard signal from what we call the measurement noise. When you then try to convert the freeboard measurement to overall ice thickness, you also have to take into account factors including the snow cover and ice density, which are normally only known from localised field measurements. This introduces a further potential for large errors in the results.”

“If I go back to the submarine measurements that have been used to estimate the volume reduction, the submarines use an upward-looking sonar to measure their range from the ice or water above them. The sonar is echoed back from the underside of the ice, and since 7/8ths of the ice is below water level and there is no snow to affect the measurement, there is far less potential error,” explains the ice experts and adds:

“While there is a lot of attention paid to ice area every summer, because it is easy to observe by satellite, it is not a good indicator of the overall state of the ice. For example, you could have a record ice area, but the ice might only be a few centimetres thick, giving no warning that the ice will soon disappear. Volume is a much better indicator, as we take into account both area and thickness.”

Dramatic decline in the 1990s
“The most dramatic decline in sea ice thickness took place in the 1990s. However it has only been in the later part of the past decade, particularly with the record low of 2007, that this has manifested itself in a strong decline in ice area. It is dramatic. However, bear in mind that scientists are still trying to understand observations from the historical record. We are still developing methods for palaeo-measurements from proxy indicators of sea ice conditions, and interesting variations in sea ice are shown in those as well.

“Due to the decline in sea ice volume, the ice becomes easier to break up by wind stresses, and it is therefore more mobile. This makes it possible for prolonged winds to open up large expanses of open water along coastlines. This in turn has at different times led to record-low ice extents in all the shallow seas surrounding the Arctic Ocean,” he says.

Advantage over Nansen and Amundsen
“One of the key advantages this expedition has had over its predecessors is continuous, all-weather satellite reconnaissance. An interesting “what if” question is how well Nansen and Amundsen would have fared on their voyages, if they had had access to the ice information we have today?” Nick smiles and lets the question hang in the air.

“While there is less ice around today than a decade or two ago, the ice that remains is far more mobile, and this causes highly variable conditions. Although the Northern Sea Route and the Northwest Passage have been observed to open up for brief periods, it is still difficult to predict when this will occur and for how long,” he says, and adds:

“Use of these routes for commercial traffic requires significant advance planning, and because the ice conditions are still unpredictable it is necessary to either have an ice-class vessel or icebreaker escort. As these, and the planning and bureaucracy, add to the cost it still more cost effective to route a vessel by way of a guaranteed ice-free route. I would estimate it will be at least another 10 to 20 years, with the trend of ice retreat continuing, before these routes are open long enough to allow passage without these added costs.”

Sea temperatures
The crew members have numerous time remarked on the high sea temperatures they’ve measured. Objectively, have the temperatures been noteworthy, and if so, what does this signify?

“The “Northern Passage” has been transiting across the shallow seas surrounding the Arctic Ocean, and the crew has also commented about how shallow these are, around 10 to 20 metres in places. In such shallow waters there is little stratification of the water column; there is less of it to absorb heating, allowing it to heat up quite quickly. Conversely, this also means that this autumn it will lose heat rapidly and refreeze just as quickly.”

Nick explains that the lack of ice cover leads to a positive feedback loop whereby the water, being dark, will take up solar radiation rather than reflecting it. “One of my colleagues in Oslo has been investigating how a cloud-free patch of sky can allow heating of a localised area to a much higher temperature than the surrounding area. It seems that even small variations in cloudiness can play an important role in determining how warm the sea surface becomes.”

Anything you would like to add?
“I will only add that as well as supporting the Northern Passage 2010 Expedition, our regular ice charting can be found at http://polarview.met.no/. Our ice analysts can be consulted on current ice conditions by sending an e-mail to istjenesten@met.no. This address can also be used if you want to send us feedback on ice conditions and the quality of our ice charts,” concludes ice expert Nick Hughes.