Arctic Warming due to Snow and Ice Demise

Sea Ice

Loss of Arctic sea ice means that a lot more heat will be absorbed by the Arctic Ocean.

Sea ice reflects 50% to 70% of the incoming energy, while thick sea ice covered with snow reflects as much as 90% of the incoming solar radiation.

After the snow begins to melt, and because shallow melt ponds have an albedo of approximately 0.2 to 0.4, the surface albedo drops to about 0.75. As melt ponds grow and deepen, the surface albedo can drop to 0.15. The ocean reflects only 6% of the incoming solar radiation and absorbs the rest.

Sea ice typically reaches its lowest volume halfway in September. Given the shape the ice is in, 2014 will likely be one of the lowest minima on record. In fact, there is a chance that sea ice will disappear altogether in September 2014. As illustrated by above image, by Wipneus, an exponential curve based on annual minima from 1979 points at zero ice volume end 2016, with the lower limit of the 95% confidence interval pointing at zero ice end of 2014.


Latent Heat

Sea ice melting occurs due to heat from above, i.e. absorbed sunlight. Once the sea ice is gone, this heat will no longer go into melting and transforming ice into water. Instead, all absorbed sunlight will go into warming up the Arctic Ocean and the sediments under the seafloor.

In addition, sea ice is also melting due to heat from below, absorbed ocean heat. Much of this heat is carried by the Gulf Stream into the Arctic Ocean. Once the sea ice is gone, all this heat will go into warming up the Arctic Ocean and the sediments under the seafloor.

Loss of sea ice will allow more ocean heat to radiate out into the atmosphere, but at the same time more clouds will also deflect more heat back to the Arctic Ocean. In addition, more clouds will also trap more of the heat that was previously radiated out into space, i.e. while the sea ice was still there. More clouds will also form over land, with similar effects there.

In short, the sea ice acts as a buffer that absorbs heat. As long as there is sea ice, it will absorb heat and make sure there is no temperature rise in the Arctic. Once the sea ice is gone, this latent heat must go elsewhere.

As the sea ice heats up, 2.06 J/g of heat goes into every degree Celsius that the temperature of the ice rises. While the ice is melting, all energy (at 334J/g) goes into changing ice into water and the temperature remains at 0°C (273.15K, 32°F).

Once all ice has turned into water, all subsequent heat goes into heating up the water, at 4.18 J/g for every degree Celsius that the temperature of water rises.

The amount of energy absorbed by melting ice is as much as it takes to heat an equivalent mass of water from zero to 80°C. The energy required to melt a volume of ice can raise the temperature of the same volume of rock by 150º C.


Snow and Ice Cover on Land

Snow and ice cover on land takes up an even larger area than sea ice. The chart below with data up to 2012 shows how dramatic the decline of snow cover on land in the Northern Hemisphere was (until 2012 and without Greenland) for the month June.

The size of the June snow and ice cover is vitally important, as insolation in the Arctic is at its highest at the June Solstice. During the months June and July, insolation in the Arctic is higher than anywhere else on Earth, as shown on the image below, by Pidwirny (2006).

While Greenland remains extensively covered with snow and ice, the reflectivity of its cover can decline rapidly, as illustrated by an earlier post from the meltfactor blog. This rapid decline occurs not only due to exposure of darker soil, but also due to formation of melt ponds and because melting snow reflects less light. Furthermore, huge amounts of dust, soot and organic compounds originating from human activities get deposited on Greenland, reducing its reflectivity. Organic compounds in meltwater pools can furthermore lead to rapid growth of algae at times of high insolation.

Total Warming

The Arctic Ocean covers 2.8% of Earth's surface. Earth has a total surface area of 510,072,000 square km (196,888,000 square miles), as the table below shows, by Michael Pidwirny, or about 510 million square km.

Surface	Percent of Earth’s Total Surface Area	Area Square Kilometers	Area Square Miles
Earth’s Surface Area Covered by Land	29.2%	148,940,000	57,491,000
Earth’s Surface Area Covered by Water	70.8%	361,132,000	139,397,000
Pacific Ocean	30.5%	155,557,000	60,045,000
Atlantic Ocean	20.8%	76,762,000	29,630,000
Indian Ocean	14.4%	68,556,000	26,463,000
Southern Ocean	4.0%	20,327,000	7,846,000
Arctic Ocean	2.8%	14,056,000	5,426,000

Sea ice extent was below 4 million square km throughout September 2012, as the image below shows. This year, sea ice may well decrease to as little as 4 million square km, or collapse altogether, as discussed above. 

As said, sea ice extent was well under 4 million square km throughout September 2012, and this compares with an extent of under 8 million square km in 1980. In other words, the difference in sea ice extent between those two years is some 4 million square km. The albedo change associated with this difference will be even more dramatic, given the (slushy and this lower albedo) state of the ice in 2012.

How much radiative forcing would this represent, i.e. a retreat from an extent of 8 million square km to 4 million square km, and than another such change, i.e. a collapse from 4 million square km to zero?

Professor Peter Wadhams, University of Cambridge, once calculated that if a sea ice area of 4 million square km, with a summer albedo of about 0.60 (surface covered with melt pools) collapses and disappears altogether, the entire area is replaced by open water which has an albedo of about 0.10. This will thus reduce the albedo of a fraction 4/510 of the earth's surface by an amount 0.50. The average albedo of Earth at present is about 0.29. So, the disappearance of summer ice will reduce the global average albedo by 0.0039, which is about 1.35% relative to its present value.

A drop of as little as 1% in Earth’s albedo corresponds with a warming roughly equal to the effect of doubling the amount of carbon dioxide in the atmosphere, which would cause Earth to retain an additional 3.4 watts of energy for every square meter of surface area (NASA, 2005; Flanner et al., 2011). Based on those figures, a global drop in albedo of 0.0039 is equivalent to a 1.3 W/sq m increase in radiative forcing globally. 

A collapse of the sea ice would go hand on hand with dramatic loss of snow and ice cover on land in the Arctic. The albedo change resulting from the snowline retreat on land is similarly large as the retreat of sea ice, so the combined impact could be well over 2 W/sq m. To put this in context, albedo changes in the Arctic alone could more than double the net radiative forcing resulting from the emissions caused by all people of the world, estimated by the IPCC to be 1.6 W/sq m in 2007 and 2.29 W/sq m in 2013. 

References: 

- March 2014 Arctic Sea Ice Volume 2nd lowest on Record

http://arctic-news.blogspot.com/2014/04/march-2014-arctic-sea-ice-volume-2nd-lowest-on-record.html

- Warming of the Arctic Fueling Extreme Weather
http://arctic-news.blogspot.com/2014/06/warming-of-the-arctic-fueling-extreme-weather.html

- Albedo change in the Arctic threatens to cause runaway global warming
http://arctic-news.blogspot.com/2012/10/albedo-change-in-the-arctic-threatens-to-cause-runaway-global-warming.html

- Albedo change in the Arctic

http://arctic-news.blogspot.com/2012/07/albedo-change-in-arctic.html

Post by Sam Carana.

Winter in Southern Greenland

NASA image, acquired December 30, 2012

As the year 2012 drew to a close, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this scene of sea ice, land ice, and fresh snow in southern Greenland. It is a fairly typical wintertime scene, but one that illustrates both seasonal and thousand-year changes.

As its name implies, the East Greenland Current flows along Greenland’s east coast, and it carries ice southward out of the Arctic Ocean via the Fram Strait. Sea ice carried by this cool current typically reaches the southern tip of Greenland at the beginning of winter. In this image, the southward-moving ice forms a series of tendrils and swirls in ghostly gray.

On Greenland itself, a fresh coat of snow blankets most of the land. The brilliant white snow is lighter than the bare ice beneath it, and serves as an excellent reflector of sunlight.

Albedo is the portion of energy an object reflects back into space, indicated by a value between 0 and 1. Fresh snow has an albedo of about 0.9, reflecting nearly all sunlight back into space. Dark ocean water has an albedo of about 0.06, absorbing almost all the light energy it receives. Bare ice falls roughly between these two extremes, with an albedo of about 0.5. So fresh snow sitting on the surface of Greenland’s ice sends most of the energy it receives back into space, serving as an insulator for the ice below. But for the coastal ice of southern Greenland, this situation is temporary.

“Melting of this snow, and then melting of the older ice sheet below, will likely resume in March or April,” says Ted Scambos, lead scientist at the National Snow and Ice Data Center. “In recent decades, the retreat of the ice edge has increased due to ice flow and summer melt. Last year’s melt volume was the highest by far in the past 35 years. This melt exposes bare ice near the edge of the ice sheet.”

“The Greenland ice sheet is far smaller than it was during past ice ages, tens to hundreds of thousands of years ago,” Scambos continues. “As the ice sheet retreated millennia ago, it revealed the craggy landscape of fjords and rugged hills seen along the coast.” Those rugged hills cast long shadows in in the low-angled sunlight.

References

- Winter in Southern Greenland, Earthobservatory.nasa.gov - January 6, 2013

- Cooperative Institute for Marine and Atmospheric Studies. (2008) The East Greenland Current. University of Miami. Accessed January 3, 2013.

- NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response. Caption by Michon Scott, with information from Florence Fetterer, Walt Meier, and Ted Scambos, National Snow and Ice Data Center.

Albedo changes in the Arctic

How global warming and feedbacks are causing huge albedo changes in the Arctic.

Image credit: Rutgers University

Snow cover decline

Decline of the snow cover on land in the northern hemisphere is accelerating, as illustrated by the image on the right. (1)

Fresh snow can have an albedo as high as 0.85, meaning that up to 85% of the sunlight falling on snow can get reflected back into space. As the snow melts, its structure changes making it less reflective, i.e. its albedo will go down, to as low as 40%. (2)

As a result, more sunlight gets absorbed, accelerating the melting process. Eventually, where snow melts away, spots of bare soil become exposed, and dark wet soil has a very low albedo, reflecting only between 5% and 15% of the sunlight. Thus, even more sunlight gets absorbed and the soil's temperature increases, causing more of the remaining snow to melt. (2)

Albedo, from Wikipedia

Changes in vegetation can further accelerate this process. Russia's boreal forest - the largest continuous expanse of forest in the world - has seen a transformation in recent years from larch to conifer trees. Larch trees drop their needles in the fall, allowing the vast, snow-covered ground in winter to reflect sunlight and heat back into space and helping to keep temperatures in the region very cold. But conifers such as spruce and fir retain their needles, which absorb sunlight and increase the forest's ground-level heat retention. (3)

A conversion from larch to evergreen stands in low-diversity regions of southern Siberia would generate a local positive radiative forcing of 5.1±2.6 W m−2. This radiative heating would reinforce the warming projected to occur in the area under climate change. (4)

Tundra in the Arctic used to be covered by a white blanket of snow most of the year. However, as the landscape is warming up, more trees and shrubs appear. Scientists who studied part of the Eurasian Arctic, found that willow and alder shrubs, once stunted by harsh weather, have been growing upward to the height of trees in recent decades. They now rise above the snowfall, presenting a dark, light-absorbing surface. This increased absorption of the Sun's radiation, combined with microclimates created by forested areas, adds to global warming, making an already-warming climate warm even more rapidly. (5 & 6)

Furthermore, encroachment of trees onto Arctic tundra caused by the warming may cause large release of carbon to the atmosphere, concludes a recent study. This is because tundra soil contains a lot of stored organic matter, due to slow decomposition, but the trees stimulate the decomposition of this material. (7)


Sea ice decline

In the Arctic, sea ice volume has fallen dramatically over the years, as illustrated by the image on the right. The trend points at 2014 as the year when Arctic sea ice will first reach zero volume for some time during that year. (8)

The Arctic Ocean looks set to be ice-free for a period of at least three months in 2015 (August, September and October), and for a period of at least 6 months from the year 2020 (June through to November). (9)

Decline of the Arctic sea ice is accelerating, due to numerous feedbacks. As the Arctic atmosphere warms up, any snow cover on top of the ice will melt away ever quickly, decreasing the surface albedo and thus reinforcing the warm-up. As melt ponds appear on top of the ice, the albedo will drop even further.

Sam Carana's Diagram of Doom pictures ten feedbacks that jointly work to accelerate sea ice decline. (10)

The image below shows the three areas where albedo change will be felt most in the Arctic, i.e. sea ice loss, decline of albedo in Greenland and more early and extensive retreat of snow and ice cover in other areas in the Arctic. (8)

Big changes in the Arctic within years, by Sam Carana

References

1. Northern Hemisphere Snow Cover Anomalies 1967-2012 June, Rutgers University
http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6

2. Albedo, Albedo Change blog
albedochange.blogspot.com/2009/02/albedo-change.html

3. Shift in Northern Forests Could Increase Global Warming, Scientific American, March 28, 2011
scientificamerican.com/article.cfm?id=shift-northern-forests-increase-global-warming

4. Sensitivity of Siberian larch forests to climate change, Shuman et al., April 5, 2011, Wiley.com
onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02417.x/abstract

5. Warming turns tundra to forest
ox.ac.uk/media/news_stories/2012/120604.html

6. Eurasian Arctic greening reveals teleconnections and the potential for structurally novel ecosystems, Macias-Fauria et al., 2012
nature.com/nclimate/journal/v2/n8/full/nclimate1558.html

7. Expansion of forests in the European Arctic could result in the release of carbon dioxide, University of Exeter news, June 18, 2012
http://www.exeter.ac.uk/news/featurednews/title_214902_en.html

8. Big changes in the Arctic within years, Sam Carana, October 26, 2012, Arctic-News blog
arctic-news.blogspot.com/2012/10/big-changes-in-arctic-within-years.html

9. Getting the Picture, Sam Carana, August 2012, Arctic-News blog
http://arctic-news.blogspot.com/2012/08/getting-the-picture.html

10. Diagram of Doom, Sam Carana, August 2012, Arctic-News blog
http://arctic-news.blogspot.com/2012/08/diagram-of-doom.html


Further reading

- Albedo change in the Arctic
arctic-news.blogspot.com/2012/07/albedo-change-in-arctic.html

- Greenland is melting at incredible rate
arctic-news.blogspot.com/2012/07/greenland-is-melting-at-incredible-rate.html

- Albedo change in the Arctic threatens to cause runaway global warming
arctic-news.blogspot.com/2012/10/albedo-change-in-the-arctic-threatens-to-cause-runaway-global-warming.html

Albedo

Albedo

Albedo, from Wikipedia

The word albedo is derived from the Latin word "albus" (white). The range of possible values of albedo (whiteness) goes from 0 (darkest) to 1 (brightest).

Albedo change occurs when a surface changes in color, e.g. if a snow-covered area warms and the snow melts, the albedo decreases.

Fresh snow can have an albedo as high as 85%, but as the snow melts more, its albedo will go down, to as low as 40%. The albedo of ice is typically between 30% and 40%. As sea ice melts away, the albedo goes down dramatically, firstly because melt pools start to appear on top of the ice, and finally because it becomes open water, which has an albedo of only about 7% or 8%.

The average overall albedo of Earth is 30 to 35%. These figures are from Wikipedia.