Arctic melting: The science behind the ice

Blogpost by Sune Scheller

© Nick Cobbing / Greenpeace

Two of the scientists travelling with Greenpeace on the Arctic Sunrise are Dr Julienne Stroeve, a research scientist at the US National Snow and Ice Data Centre (NSIDC), and Nick Toberg, an ice scientist at Cambridge University. I asked them what research they would be able to do on the ice, and for some insight into why Arctic sea ice is so important, and what impact the melting would have on our climate.

What will you be doing on the ice?
Julienne: I’ll be measuring ice thickness – it’s a more important measure than ice extent as it tells you about volume (total) loss. I can measure thickness in different spots by drilling with a hand augur, which can go two metres deep. I also hope to look at snow thickness, whether there are melt pools on the ice and whether they are frozen. As the ship is travelling we will also measure the ocean temperatures.

Nick: We will test impact of ocean waves as they hit the ice edge, using buoys fitted with accelerometers. This will fill in the missing physics of how the strength of the waves adds to the ice breaking up and melting. Broken ice reflects sunlight less well as the sun’s rays are
absorbed into the ocean beneath. The lack of ice creates even stronger waves which break the ice up more the following year.

What is happening to the sea ice this year?
Julienne: This year the ice edge has pulled back significantly – in some places by hundreds of miles. By June, the ice edge had pulled back to where it would usually be at the end of September (just after the minimum) in some places. It reached its lowest point ever – 3.51 million sq. km and is still melting.

Why is this year so different, has it been particularly warm, like in 2007 (when the previous record was set)?
Julienne: I’m quite amazed by the level of melting this year, as we knew the ice was getting thinner but hadn’t realised by how much. This year the weather was not particularly warm or conducive to melting. So it must be because the ice is very thin. As more thick ice melts, it is being replaced with first year ice which is much thinner, so the fast melting will continue every year now. I really think, if this year we’d had the weather patterns of 2007, the sea ice extent would be below 3 million sq. km.

Nick: In 2007 the weather conditions were right for the ice to shrink. Last year [2011] there were no unusual weather conditions but the ice came close to beating the 2007 minimum. Due to previous melting, the sun’s rays which used to be reflected by the ice, have been absorbed into the oceans, heating up them up. So once this pre-conditioning is there, the long-term trend is towards increased melting. We’ll see ice free summers in all of our lifetimes.

What are the different functions of ice thickness (volume), and ice extent (surface area)?
Julienne: Well, ice extent is important for reflecting the sun’s rays and keeping the atmosphere cool. But if we lose ice volume, the ice becomes very thin and melts more easily. The decrease in thickness is why we are losing so much surface area of the ice. Thickness also affects polar bears as they cannot hunt on thin ice, they will just fall through.

As surface area continues to shrink how is melting affected?
Julienne: The heat which was previously reflected by the ice is now mostly absorbed by the ocean; but in autumn when the ice begins to refreeze the heat is absorbed by atmosphere, leading to more clouds and greater moisture in the atmosphere. More clouds in autumn and winter actually keep the atmosphere even warmer. This pushes heat back down to the ocean’s surface, accelerating the ice loss.

How do we know the melting is caused by human activities?
Julienne: We know the heating is caused by humans, by measuring the carbon in the atmosphere and tracing where the carbon is coming from; there is a difference between natural carbon in the atmosphere and carbon from burning fossil fuels. It is hard to differentiate between natural warming and that caused by human activity. But when you create models and leave out the human caused CO2 levels in the atmosphere, none
of the models show this level of warming. Based on new climate models, a paper I have just published in Geophysical Research Letters [August 2012] estimates that 60% of the rate of decline in summer sea ice extent is due to human activities.

Nick: Arctic sea ice extent has gone down 10% per decade since the 1970s. The Arctic has had very substantial ice cover for the last 13 million years (shown by recent research on sediments). When it has reduced as a result of natural cycles it has done so over tens of
thousands of years. What is significant now is the speed with which sea ice cover is reducing.

What is the long term picture?
Nick: If the remaining 4 million sq. km of sea ice disappear in summer, that would equal adding 20 years’ worth of CO2 to the atmosphere (at today’s levels of CO2 emissions). In the 1970s we had 8 million sq. km of summer sea ice, so it has halved in the last 30 years.

Julienne: If we keep warming the atmosphere, the Arctic could be ice free in the summer by 2030. While natural climate variability could increase ice levels for a few years, it is on a downward long term trend. We have entered a new climate state in the Arctic – a new year
round warmer era.

This year is significant – we’re on the extreme end of current climate models. Our observation is that sea ice decline is happening much faster than most of the new IPCC models.

What are the impacts on areas of the world beyond the Arctic?
Nick: The ice is a big cooling system and the earth’s weather patterns depend on it. There will not be the same dispersion of cold and heat – for example, warm water currents will not move past Britain any more – making it less temperate. Britain is actually at the same latitude as Siberia and is made warmer by the North Atlantic current.

Julienne: The Arctic drives Northern Hemisphere weather patterns. Open water absorbs heat, which is transferred into the atmosphere, making the atmosphere warmer. This alters the movement of air, which changes the jet stream. The wind speed becomes slower, extreme weather conditions stay longer, producing drought conditions in the US for example. It is very early to be sure of this, but it does make physical sense.

How do you think the world will respond?
Nick: It’s disturbing that we have changed the face of the planet in a way we can visually see. But people won’t really change until it affects them on a day to day level.

Julienne: I hope that this year’s sea ice loss will have an impact on the US government and change thinking.

  • Steve

    Hi Sune,

    Julienne says:

    “Based on new climate models, a paper I have just published in Geophysical Research Letters [August 2012] estimates that 60% of the rate of decline in summer sea ice extent is due to human activities.”

    And then adds:

    “If we keep warming the atmosphere, the Arctic could be ice free in the summer by 2030.”

    Let me follow the logic here. Jullienne is afraid that we will have no summer ice in 2030, a mere 18 years away. She has also discovered that the declining trend in sea ice is 40% natural (that is, not caused by human emissions of CO2). That suggest to me that (using the back of a handy envelope) if we stopped all human emissions of CO2 tomorrow, natural forcing would still give us an ice free arctic in the summer of 2057!

    Note, this is a tongue in cheek back of the envelope calculation intended for entertainment purposes only … … though the point remains … Julienne’s study shows that we would have eventually lost the summer ice regardless of human emissions of CO2 due to that natural warming she agrees is occurring … (To lose 100% of summer sea ice by 2030, using Julienne’s figures, means that natural causes are responsible for 2.2% ice loss per year … meaning it will take 45 years for natural causes to remove the summer ice).

  • Steve

    Hi Sune

    Summer Arctic sea ice extent is undoubtedly declining and I would suggest it has been declining naturally since the end of the Little Ice Age when the globe began to warm in the early to mid 1800s (Akasofu 2010).

    This natural warming occurs in fits and starts. NASA shows that the Arctic warmed 1.6C over the 19 year period from 1918-1937 at a rate of 0.84C/decade, almost twice as fast as the 0.48C/decade from 1980-2000.

    Consequently, as Professor Ole Humlum shows, there was a dramatic decline in summer sea ice during the 1930s as revealed by Polyakov et al 2003.

    In fact, Polyakov et al concluded:

    “…examination of records of fast ice thickness and ice extent from four Arctic marginal seas (Kara, Laptev, East Siberian, and Chukchi) indicates that long-term trends are small and generally statistically insignificant, while trends for shorter records are not indicative of the long-term tendencies due to strong low-frequency variability in these time series, which places a strong limitation on our ability to resolve long-term trends”. “Correlation analysis shows that dynamical forcing (wind or surface currents) is at least of the same order of importance as thermodynamical forcing for the ice extent variability in the Laptev, East Siberian, and Chukchi Seas ”

    I draw your attention to the conclusion that:

    “… dynamical forcing (wind or surface currents) is at least of the same order of importance as thermodynamical forcing for the ice extent variability…”

    I notice your article does not mention the impact of wind on the recent record lows, which I find surprising since you wanted to talk about the science.

    Regarding the previous record low sea ice extent in 2007, Osagi and Wallace (2012) in a peer reviewed paper concluded:

    “Strong summertime anticyclonic wind anomalies over the Arctic Ocean, with anomalous flow toward the Fram Strait, during summer months of 2007 contributed to the record-low the Arctic sea-ice extent observed in September of that year.”

    Regarding this year I refer you to another NASA article on August 9 which talks about a massive storm over the arctic:

    “ Arctic storms such as this one can have a large impact on the sea ice, causing it to melt rapidly through many mechanisms, such as tearing off large swaths of ice and pushing them to warmer sites, churning the ice and making it slushier, or lifting warmer waters from the depths of the Arctic Ocean.

    “It seems that this storm has detached a large chunk of ice from the main sea ice pack. This could lead to a more serious decay of the summertime ice cover than would have been the case otherwise, even perhaps leading to a new Arctic sea ice minimum,” said Claire Parkinson, a climate scientist with NASA Goddard. “Decades ago, a storm of the same magnitude would have been less likely to have as large an impact on the sea ice, because at that time the ice cover was thicker and more expansive.”

    So, NASA says the recent record low is the result of a storm. Granted the sea ice may be thinner, but that is not unexpected since the arctic is, after all, recovering from the Little Ice Age.
    Sune, I find it curious that you, Dr Julienne Stroeve or Nick Toberg failed to mention this dramatic weather event which even NASA expected to cause a record low way back in August.

    Sure, Nick states:

    “In 2007 the weather conditions were right for the ice to shrink.”
    Which I take to mean, the big winds that Osagi and Wallace found … but there is no reference to this year’s big storm.

    And Julienne says:
    “I really think, if this year we’d had the weather patterns of 2007, the sea ice extent would be below 3 million sq. km.”

    But that’s just the point, Julienne, we did have weather patterns conducive to sea ice decline!

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