Albedo, latent heat, insolation and more

NOTE: This page was largely created in 2012 and is preserved here for archival and reference purposes. Some editing of content has taken place since, and a video and more images have been added. For further updates, links have been added to further posts discussing the respective topics


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Albedo

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.

The average overall albedo of Earth is 30 to 35%.

There are two areas where albedo changes are felt most in the Arctic, i.e. decline of the sea ice and decline of the snow and ice cover over Greenland, North America and Eurasia.

Sea ice decline

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 more 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.

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.

Decline of snow and ice cover on land

As the snow and ice cover on land melts, 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)

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)

Latent heat

Latent heat is energy associated with a phase change, such as the energy consumed when solid ice turns into water (i.e. melts). During a phase change, the temperature remains constant. Sea ice acts as a buffer that absorbs heat, while keeping the temperature at zero degrees Celsius. As long as there is sea ice in the water, this sea ice will keep absorbing heat, so the temperature doesn't rise at the sea surface.


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 as much as 150ºC.


The above combination image illustrates how much ocean heat is entering the Arctic Ocean from the Atlantic Ocean, heating up the sea ice from below.

The left panel shows the depth of the Arctic Ocean, with darker blue indicating greater depth.

In the right panel, the light blue, green and yellow colors indicate the thickest ice, located in the shallow waters off the coasts of North America and Greenland. The darker blue colors indicate where much of the sea ice has melted away, from below, as also illustrated by the one-month animation below showing sea ice thickness up to June 22, 2022, with an added 8 days of forecasts. The white color indicates where the sea ice has melted away entirely, e.g. in the Bering Strait and north of Siberia, mainly due to warm water from rivers entering the Arctic Ocean. 


The above navy.mil animation illustrates how much sea ice has melted away in June 2022. Once most of the sea ice that was hanging underneath the surface is gone, further heat will still keep moving underneath the sea ice from the Atlantic Ocean and - to a lesser extent - from the Atlantic Ocean into the Arctic Ocean. Without the latent heat buffer, this heat must go elsewhere, i.e. it will typically raise the temperature of the water. The atmosphere will also warm up faster. More evaporation will occur once the sea ice is gone, further warming up the atmosphere (technically known as latent heat of vaporization). 

The image below shows thickness as measured by the University of Bremen for June 27, 2022. 


As temperatures in the Arctic are rising faster than at the Equator, the Jet Stream will change, making it easier for warm air to enter the Arctic. More clouds will form over the Arctic. The lower clouds will reflect more sunlight into space, while cirrus clouds will trap more heat underneath. Furthermore, clouds will also make that less outward IR radiation can escape into space over the Arctic, with a net warming effect (feedback #23). Overall, more clouds result in more warming. 

One huge danger is that, as the buffer disappears that until now has consumed huge amounts of ocean heat, further heat will reach methane hydrates at the seafloor of the Arctic Ocean, causing them to get destabilized resulting in release of methane from these hydrates and from free gas underneath that was previously sealed by the hydrates. 

[ The Buffer has gone, feedback #14 on the Feedbacks page ]

Variability in insolation over the year

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. Finally, calving of the ice can take place where warmer water can reach it, and such calving can strengthen due to strong winds and waves.

As depicted by the Wikipedia image below, the amount of insolation (or solar irradiance) varies over the year, depending on latitude and on the time of year.

Insolation changes with the seasons and also changes between day and night. In the image below, adapted from Wikipedia, latitude is on vertical axis and time of year is on horizontal axis.



                     The June Solstice in 2021 occurred on June 21, 2021.

Summer Solstice, the longest day on the Northern Hemisphere

In the Arctic, annual insolation is at its highest at the June Solstice, which was on June 21 for both 2021 and 2022. At this time of year, the sunlight has less distance to travel through the atmosphere, so less sunlight gets absorbed or scattered before reaching the surface.

In addition, the high Sun angle produces long days. At this time of year, the Sun does not set above the Arctic Circle, so solar radiation continues all day and night. 

While the amount of sunlight that reaches the surface also depends on weather conditions such as clouds, insolation is higher in the Arctic than anywhere else on Earth during June and July.  

[ FAQ#24. Arctic heating up faster? ]
This partly explains why the temperature rise is strongest in the Arctic, as illustrated by the image on the right, from the FAQ page, which shows anomalies versus 1951-1980 of up to 3.49°C.

On 20 June 2020, a temperature of 38°C (100.4°F) was recorded in the Russian town of Verkhoyansk and this has been recognized as a new Arctic temperature record by the World Meteorological Organization (WMO). 

Verkhoyansk is located within the Arctic Circle and also holds the record for the coldest temperature ever recorded in Asia, −67.8 °C (−90.0 °F). This huge temperature difference is partly caused by huge seasonal insolation differences, while Verkhoyansk is also very much located inland, where seasonal differences are stronger. 


Why is the temperature rising so much in the Arctic?

Driving up the Arctic temperature rise are: 

• High insolation on the Northern Hemisphere in Summer, which can cause heatwaves that extend over the Arctic Ocean and cause melt pools on the sea ice.

• Heatwaves that further drive up the water temperature of rivers ending in the Arctic Ocean.

• Strong winds that can speed up ocean currents and cause high waves and rainfall; each of them on their own can have a dramatic impact on the sea ice—when they combine and interact, their impact can be devastating. 

• melting of sea ice causing loss of the latent heat buffer. 

• snow and ice decline causing albedo loss, a self-reinforcing feedback loop.

• thawing permafrost contributing to very high greenhouse gas levels over the Arctic.  

• more ocean heat entering the Arctic Ocean, causing more melting of the sea ice.

• more transfer of ocean heat to the atmosphere over the Arctic, and more clouds.

• eruption of methane from the seafloor of the Arctic Ocean.

• aerosols settling on snow and ice, and causing albedo loss, thus speeding up the decline.

• jet stream changes causing more extreme weather (including heatwaves, fires causing more aerosols, and storms causing more ocean heat to enter the Arctic ocean).


Radiative forcing associated with loss of snow and ice cover in the Arctic

The Arctic Ocean covers 2.8% of Earth's surface. Earth has a total surface area of 510,072,000 km² (196,888,000 miles²), as the table below shows.


Sea ice extent was well under 4 million km² throughout September 2012, as compared to under 8 million square km in 1980, a difference of about 4 million km². 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 km² 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/m² 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/m². 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/m² in 2007 and 2.29 W/m² in 2013.


Videos

In the video below, Paul Beckwith discusses albedo and insolation.



References

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

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

3. Shift in Northern Forests Could Increase Global Warming, Scientific American, March 28, 2011
https://www.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
https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02417.x/abstract

5. Warming turns tundra to forest
https://www.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
https://www.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
https://www.exeter.ac.uk/news/featurednews/title_214902_en.html

8. WMO recognizes new Arctic temperature record of 38⁰C

9. Verkhoyansk
https://en.wikipedia.org/wiki/Verkhoyansk



• Solstice - Wikipedia
https://en.wikipedia.org/wiki/Solstice

• Insolation, solar irradiance - Wikipedia
https://en.wikipedia.org/wiki/Solar_irradiance

• Frequently Asked Questions
https://arctic-news.blogspot.com/p/faq.html

• Insolation
• Naval Research Laboratory
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/arctic.html

• University of Bremen
https://seaice.uni-bremen.de/databrowser