You sent questions to our environment correspondent David Shukman as he travelled through the Northwest Passage on the Canadian Coast Guard vessel, the Amundsen.
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Here, he answers those questions, with the help of Professor Jean-Eric Tremblay, the chief scientist of the expedition; and Professor Simon Belt from the University of Plymouth, the senior British scientist on board.
Professor Tremblay is an expert in Arctic ecosystems. Professor Belt is a specialist in sea ice.
From Mark Kidger, Madrid, Spain: The obvious question is whether or not today's retreat of the ice cap has been a freak event, or are we at a "tipping point" as portrayed to the public in The Day After Tomorrow in which slow change becomes catastrophic change. We know that in the past there have been moments when the poles have been virtually or completely ice free, yet life continued and thrived; should we fear the retreat of polar ice so much, or even applaud the opportunity to cultivate previously barren lands?
Professor Jean-Eric Tremblay: The Arctic is characterised by a high inter-annual variability and a particularly low-ice year may partly reflect this natural phenomenon. As for the tipping point, the key element here is the complete loss of some multi-year ice and the thinning of that which remains.
It takes years to build this type of ice and once lost it would take many particularly cold winters to rebuild, which is unlikely given the current trend. We suspect that the rate of decline is accelerating but catastrophic changes like those portrayed in The Day After Tomorrow are unrealistic (see www.realclimate.org for a list of reasons).
Past changes in climate occurred over long geological timescales, giving the ecosystems ample time to reach new equilibria. The present rate of change is astronomical in comparison and, this time, Inuit are part of the equation.
Whether we should applaud or not is a matter of perspective. There will be new opportunities for industry, but as a society we should ask ourselves if the ecological and human price of our actions is not too high.
From Eucliffe Loague, Kingston, Jamaica: Do you think that the melting could be caused by cosmic cyclical factors rather than global warming and ozone layer damage - just a thought based on the historical perception that the Norsemen apparently in times past found a way using less sturdy vessels, and also the realities of the Ice Ages in time past?
Professor Simon Belt: It is almost certain that the factors that you refer to will have played a contribution to climate change in the past. However, we are currently experiencing a more diverse range of contributions to climate change and the key scientific endeavour is to establish the relative contributions of these and, in turn, determine whether we are in a position to control them.
From Andrew, NJ, USA: How are the native peoples of the north there taking this ice melting? How are their food supplies of polar bear and seal being affected by this? Do they blame the rest of the world for the progressive speed up of the melting ice by global warming?
J-ET: The Inuit I have met hold no personal grudge against us, but are rightfully worried about the future. They expect western science to provide some answers, while building their own capacity for research. The food supply issue has three dimensions: social structure, safety and resource availability.
The passage of information from the elders to the younger generations is a cornerstone of Inuit social structure. Since the ice became unpredictable in several regions, the environmental lore of the elders is not entirely reliable and accidents happen.
The polar bears and seals are still widely available in most regions but getting to them is not always safe. There are reports of a decline in the physical condition of polar bears, but the evidence regarding the overall size of bear and seal populations remains inconclusive.
From Brian Rheinberger, Sydney, Australia: Would you please explain why the sea level has not changed although three million sq km of ice has melted?
David Shukman: It's because all that ice, though vast in extent, was floating and therefore won't affect sea level. When the ice cubes in a drink melt, the level of liquid doesn't change if the volume of water used to make the ice is taken from the glass in the first place. By contrast, the melting of the ice sheet covering the landmass of Greenland would make a difference.
From Deborah A. Hutter, Fort Lee, New Jersey, USA: Why are so many efforts being made to exploit this passage for commercial use when we should be working to preserve and restore this ecosystem? What do we have to lose (in the global and environmental sense) if this route becomes heavily commercialised?
J-ET: I agree that no efforts should be spared to preserve this ecosystem. Increased navigation and commercial use pose two kinds of risks. The Arctic ecosystem is very fragile and the fauna strongly depends on the ice for its survival. The seasonal fast ice that serves as a hunting platform for coastal communities is very sensitive to heavy traffic. Even the Amundsen is a source of concern, and we take great care to consult with the Inuit and steer clear of sensitive ice.
The second risk concerns eventual accidents, such as oil spills and groundings in the narrow and treacherous channels of the passage. We hear a lot of talk about "right of passage", but distressingly little about duties and responsibilities to the ecosystem and the Inuit. I can only hope this will be at the forefront of negotiations to come.
From Johnny Phillips, Bristol, UK: With the melting, is there an expectation of more fascinating archaeological finds from the Franklin and Pre-Franklin expeditions?
SB: I particularly like this question as our route through the Northwest Passage has just taken us past the western shores of King William Island which represents the end-point of Franklin's expedition. Whether it is due to ice melting or simply more extended access to such sites due to longer warm summer periods, there is still much that we should be able to learn from this historic location, not least, a more detailed account of Franklin's movements during his last days.
What will aid these studies further are the recent advances in chemical and instrumental techniques that underpin such forensic investigations.
From Craig Smith, Wokingham, UK: I would like to know what you think about the rate arctic ice is retreating in comparison to the rate at which we are becoming greener. Excuse the clumsiness of the question, but I am of the opinion that use of green technology, recycling, renewable energy, etc is not moving anything like fast enough to keep up with the hugely increased rates at which the ice is melting.
SB: There is nothing clumsy about your question, but currently, we are not really in a position to provide a firm answer. What drives the "green" themes that you have mentioned is the recognition of a need to reduce our CO2 emissions and its greenhouse gas properties. Since we know that ice cover has changed in the past before any effects of man could be considered significant, a key and immediate scientific objective is to establish the relative contributions that natural processes and so-called anthropogenic effects have on the rates of change of polar ice cover.
From J. Peron, Ramsgate, UK: Isn't it true that numerous ships have made the journey through the Northwest Passage already, the first being over 100 years ago? If this is global-warming-related, why is the Antarctic ice pack at its largest size since the satellite observations began in 1978?
DS: You're right about previous crossings. Roald Amundsen was the first a century ago and between his journey and 1990 there was a total of 50. Since then there have been roughly the same number again. In the past couple of years, there have been 7-8 crossings a year. But almost all of these have involved ships specially reinforced (like the oil tanker the Manhattan in 1969) or icebreakers (like the Amundsen). The significance of the news last month was that the entire passage was seen in satellite pictures to be clear of ice, making it possible for normal vessels to make it through.
If the Arctic warming trend continues at its current rate, the passage is expected to become more navigable, not overnight, but over the coming years. As to the Antarctic, no one is claiming that climate change is happening at an even rate everywhere; and Antarctica, as a vast, cold continent, might be expected to be the last to warm.
From David Pickler, Edinburgh, UK: I spent two years as an officer on a Canadian Registered Antarctic Research ship and one thing we found different from the Arctic was the density of the "growlers", the mostly submerged ice chunks. Our ship had to be dry-docked every year to get the dents out of the hull. Did your vessel encounter harder ice than normal with the break-up of the older Arctic ice packs?
J-ET: We have not encountered growlers so far, but several floes of hard old ice descending from the Arctic. We do our best to go around those and usually avoid hitting them headlong. Paradoxically, a low-ice year in the central Arctic has a tendency to generate a lot of fragments that then descend into the Canadian Archipelago and obstruct navigation.
The record low in this year's ice extent is no exception. These observations show that even if the ice continues to decline, it will probably be a long time before the Northwest Passage is safe for commercial navigation.
From J. Protsyk, Flensburg, Germany: Why was the decision made to start this trip in October, as winter is starting, rather than earlier?
It will be quite a while before the passage becomes safely navigable
J-ET: The decision was a combination of science rationale and logistic constraints. The demand on the Amundsen for the International Polar Year is very high. The ship is based in Quebec City and it always accesses the Canadian Arctic from the eastern side. Projects that take place in this region were carried out first, including oceanographic surveys of Labrador Fjords and Hudson Bay. Then the ship was turned over to a medical team for a survey of Inuit health in the Canadian High Arctic.
Our segment of the expedition is based on an east-west comparison of conditions across the Northwest Passage, which is now taking us to our over-wintering site in the southeast Beaufort Sea. From a scientific perspective, sampling this late allows us to survey the ecosystem during its rapid transition toward winter, which we have not been able to do before in the passage.
From Jesse Vincent, Montreal, QC: There is a slight disagreement in the office concerning the sudden interest in the north due to global warming. Maybe you can help clear this up. In your opinion, is this newfound international interest in the ownership of the north due to the eventual use of a passage for trade purposes (as was its original intent), or is it because of possible oil in the area?
J-ET: Everyone in your office is right to a certain extent. The main interest in the eastern portion of the Northwest Passage is for navigation, both from a commercial and a strategic standpoint. The passage represents a tremendous economy of time and fuel. A lot of exploration remains to be done for natural resources, but at this time the large confirmed deposits are in the Beaufort Sea, which is already accessible from the Pacific Ocean via the Bering Strait. Of course, the sovereignty of the southeast Beaufort Sea is also a matter of contention, but this is not entirely related to the navigability of the Canadian Archipelago.
From Andrew Michaelides, Sevenoaks, UK: What do the locals make of the opening up of the Northwest Passage? Are they expecting that this will transform the economic fortunes of their communities or are they worried about the effects of increased traffic?
J-ET: Inuit are concerned by the disruption of the coastal fast ice (their hunting platform) by heavy traffic and by the possibility of environmental catastrophes such as oil or chemical spills. At the same time, they are aware of the economic opportunities related to tourism, population growth and natural resources. The issue is one of rate of change and adaptability. The Inuit have been catching up with the modern world at a tremendous speed and this is putting a lot of strain on their society.
A key mandate of ArcticNet is to integrate the environmental, economical and social dimensions of climate change and to inform stakeholders on the possible consequences of different courses of action.
From James, Auckland: Even though the summer ice melt may be huge, and greater than ever before, is it expected that the winter freeze will be the same as last year's freeze, and therefore no different; or will the freeze be smaller with less ice on the sea?
SB: This is an important but quite tough question to answer. There is often significant inter-annual variation in the ice cover so it is difficult to say for sure what the coming winter will bring. What is clear is that the reduction in the multi-year ice and the thinning of ice in general will require a series of very cold winters to reverse the situation. What is of note is that while we have seen an overall decrease in ice cover in recent years, this averaged data hides the fact that while many areas are seeing reduced ice cover, there are others, closer to your own home in fact, that are showing regions of enhanced ice cover.
From George Cook, Southampton, UK: Given the drastic reduction in ice and hence the opening of the Northwest Passage, are you concerned that all these countries vying for shipping rights will further disrupt the ecosystem in the area? Would frequent shipping mean further reductions of ice in the future, and should it therefore be stopped before it starts?
DS: It is a real risk but the governments in the region will want to balance the dangers of environmental damage with the economic benefits of opening up the Arctic to shipping and mineral exploitation. My impression is that the prevailing pressure for the latter is stronger. But one thing I learned on the voyage is that the Northwest Passage won't suddenly be declared fully open next year. The warming that melted the ice this summer also dislodged much older, heavy blocks of ice from further north and these have drifted into the passage. So for a while yet, any normal vessel would need to take care.
From Paul Bovingdon, Woking, Surrey: What is the night-time sky like; I imagine it must be stunning with clear visibility? Have you seen any occurrences of Northern Lights yet?
DS: I kept checking but never had clear skies at night. There were some mesmerising sights like the floodlights lighting up the ice at night and the drama of cracking through the ice. But despite being privileged to have reported from the Arctic nine times now, I've never seen the Northern Lights! I'm either here at the wrong time or it's cloudy.
From Mike Bush, Toronto, Canada: Everybody keeps talking about how surprising it is that the ice has retreated and the NW passage is now clear. But the passage must have been clear for Amundsen to get through 100 years ago (in a wooden boat, I've heard!), so clearly this kind of thing has happened before. Does the ship ever use guns and bombs to break the ice?
J-ET: Canadian icebreakers such as the Amundsen are not military ships and therefore are not outfitted with naval weaponry. We rely entirely on the strength of our hull and engines to plough through the ice. The passage was not clear for Amundsen and other explorers. These men and their crew were cunning and hardened, but most of all they had a lot of time on their hands and made very slow progress through hazardous waters. Many died and ships disappeared.
The safety requirements of modern navigation and the perpetual race against time that we are engaged in is a completely different story. For the NW passage to be commercial viable, ships need to pass through rapidly and safely, which requires open conditions and few stray floes of old ice.
From Nichola Marshall, London, UK: As well as polar bears, what other wildlife did you encounter? Did you see any species that wouldn't have been seen, but for the passage becoming accessible?
SB: We have been lucky enough to see a range of wildlife during our travels either "naturally" or through our scientific sampling programme. This vast array has included the usual species expected for the Arctic such as Arctic foxes, seals, beluga whales, northern fulmars, and those organisms that inhabit the sea floor like brittle stars, worms, bivalves and some of the lesser known sea spiders; one of which has a leg-span of larger than 10 inches! We have also collected various zooplankton and microalgae, but these await further inspection back in the laboratory before we are able to confirm whether we have discovered any new species.
The Amundsen is protected against hard ice
From T Shores, Tokyo, Japan: Although it's icy outside (and probably inside as well), does the crew (or you alone) indulge in a cold beer at the end of a tough day?
DS: I thought about a cold beer a lot! Sadly, or maybe wisely, it's a pretty dry ship. There is a bar open three nights a week with a limit of five drinks per person. But with some very steep stairs, icy decks and strong winds, it's probably safer that way.
From Paul Booth, Skipton, UK: You started your journalism career on a Coventry evening newspaper. Did you ever imagine you would progress to covering the Northwest Passage story?
DS: I do remember sitting in the courts or being sent out to road accidents or enduring council debates and wondering what one had to do to cover events on a more global scale. Questions like this remind me how lucky I've been. The Northwest Passage is destined to become more frequently visited and it's certainly top of my list of great journeys of the world.
The journey taken by the Amundsen