1. Sea ice and clouds: albedo and climate change. Professor Simon K. Haslett Centre for Excellence in Learning and Teaching Simon.haslett@newport.ac.uk 7 th April 2010

2. Introduction Albedo refers to the reflectivity of a land or ocean surface. Surface albedo is important for understanding climate as it influences the amount of solar radiation absorbed. High albedo surfaces are light-coloured, such as snow, ice, bare sand, and clouds, and reflect up to 80% of solar radiation back out into space, whereas low albedo surfaces are dark-coloured, such as oceans and forests, and absorb up to 95% of incoming solar radiation. Therefore, high albedo surfaces have a cooling affect, whereas low albedo surfaces have a warming effect on the climate system. In this presentation, the formation and albedo-climate- impacts of sea ice and then clouds are examined.

3. Sea Ice Sea ice is formed when the sea freezes over in high latitude regions, but is not restricted to the Arctic and Antarctic. There are two main categories of sea ice: –Drift Ice that is carried on ocean currents, but can converge and build up to produce significant ice floes and ridges. –Landfast or Fast Ice that forms attached to land, which is important for coastal communities for hunting and fishing. Within these categories there are different types of sea ice classified according to their age.

4. Drift Ice

5. Landfast or Fast Ice

6. Types of Sea Ice New Ice – this is sea ice comprising a layer of poorly- bound ice crystals up to about 10cm thick that has recently formed. Grey Ice – slightly older ice that is greyish in colour and forming a surface layer 10-15cm thick. Grey-white Ice – slightly thicker (15-30cm) and older ice that is grey-white in colour. First Year Ice – greenish-white coloured sea ice that has accumulated over one winter, ranging in thickness from 30cm to 2m. Old Ice – any ice that survives through a summer to begin accumulating again in a subsequent winter, often pale blue in colour.

7. Sea Ice Extent The extent of sea ice cover over the ocean can vary regardless of the type of sea ice present. Extent of coverage is usually assigned in one of four ranges: –Low cover: ranging between 1-25% of sea surface. –Moderate cover: ranging between 26-50% of sea surface. –High cover: ranging between 51-75% of sea surface. –Very high cover: ranging between 76-99% of sea surface. Often the extent of sea ice cover varies with distance from the coast, but in polar oceans, like the Arctic, cover is 100%.

8. Sea ice cover Low (1-25%)Moderate (26-50%) High (51-75%)Very High (76-99%)

9. Sea Ice and Climate Sea ice formation requires cold atmospheric and oceanic temperatures and so is sensitive to climate change. Sea ice albedo affects climate, with its extent being perhaps the most important factor as this determines the size of the albedo surface. Extensive sea ice raises ocean albedo, reflecting up to 80% of incoming solar radiation and contributing to atmospheric cooling. Decreases in the extent of sea ice lowers oceanic albedo, absorbing more (up to 95%) radiation and contributes to global warming.

10. Sea ice and Climate Areas of open water, known as ‘leads’ are significant as they play a major role in ocean-atmosphere heat exchange because: –The lower albedo absorbs solar radiation and raises the water temperature (most significant in summer). –Upwelling waters from lower in the water column allows heat to escape into the atmosphere (most significant in winter). Most ‘leads’ are transient, but permanent ‘polynyas’ can become established. Sea ice formation is also important for thermohaline circulation of the North Atlantic, as freshwater is extracted to form the sea ice, leaving the saltier and denser brine to sink, drawing in surface water from the south as a conveyor system.

11. Measuring Sea Ice Sea ice has historically been measured by ships at sea and in coastal ports. Since the 1970’s, satellites have been measuring sea ice extent and thickness, mainly using passive microwave data. Between 1978 and 2005, as global temperatures increased, such measurements have recorded a decrease in total sea ice extent of -2.7% per decade (Solomon et al., 2007). However, in the same period, the extent of sea ice surviving through the summer has been decreasing more rapidly at -7.4% per decade (Solomon et al., 2007).

12. Future Sea Ice and Climate One model predicts an abrupt reduction of sea ice cover after 2024 with the melting of 4 million km 2 over 10 years and complete absence of summer sea ice by 2040 (Holland et al., 2007). This is of concern as more extensive low albedo ocean surface water is being uncovered each summer that is absorbing increasing amounts of solar radiation and may be contributing to global warming. Also, increasing ‘leads’ in winter allows more heat to escape from the ocean into the atmosphere, which in the Arctic will affect weather patterns that could, for example, lead to a 30% reduction in rainfall in western North America (Sewall and Sloan, 2004).

13. Clouds and Climate Clouds have a similar albedo effect as sea ice; however, their relationship to climate change is more complex. It is difficult to measure the extent and thickness of clouds using any single technique. Satellites tend to measure the upper clouds only. Ground-based surveys tend to measure the lower clouds only. Stratus cloud (high albedo)Cumulus cloud (lower albedo)

14. Cloud Dynamics Cloud dynamics under climate change are uncertain and it is not understood if global warming will either reduce or increase atmospheric moisture and clouds. If atmospheric moisture and cloud formation increases under climate change, through enhanced evapotranspiration, then the cloud albedo effect will increase and help to moderate global warming and contribute to cooling.

15. Summary Albedo is an important contributor to climate change. Sea ice has a high albedo and may be drift or landfast ice. There are varying types of sea ice, classified depending on age and thickness. The extent of sea ice cover is important, as dark ocean water has a low albedo compared with light-coloured sea ice. Satellite measurements record a decrease of total sea ice cover and a larger decrease of sea ice that survives summer melting. Cloud coverage is similar, but more difficult to measure and has more complex relationship to climate change.

16. Summary Video

17. Further Reading Comiso, J. C., 2006. Abrupt decline in the Arctic winter sea ice cover. Geophysical Research Letters, 33, L18504.Abrupt decline in the Arctic winter sea ice cover Holland, M. M., Bitz, C. M. and Tremblay, B., 2006. Future abrupt reductions in the summer Arctic sea ice. Geophysical Research Letters, 33, L23503.Future abrupt reductions in the summer Arctic sea ice. Natural Resources Canada, 2009. The Atlas of Canada: Sea Ice. NRC Website: www.nrcan.gc.ca.The Atlas of Canada: Sea Ice Serreze, M. C., Holland, M. M. and Stroeve, J., 2007. Perspectives on the Arctic’s shrinking sea-ice cover. Science, 315, 1533-1536.Perspectives on the Arctic’s shrinking sea-ice cover. Sewall, J. O. and Sloan, L. C., 2004. Disappearing Arctic sea ice reduces available water in the American west. Geophysical Research Letters, 31, L06209.Disappearing Arctic sea ice reduces available water in the American west. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds), 2007. Climate Change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007. Cambridge University Press, Cambridge and New York (see Chapters 3 and 4).Climate Change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007.

18. This resource was created by the University of Wales, Newport and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).http://creativecommons.org/licenses/by-nc-sa/2.0/uk/ All images courtesy of Professor Simon Haslett. However the resource, where specified below, contains other 3 rd party materials under their own licenses. The licenses and attributions are outlined below: 1.The name of the University of Wales, Newport and its logos are unregistered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. 2.The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license. AuthorProfessor Simon K. Haslett Research AssistantJonathan Wallen Institute - OwnerUniversity of Wales, Newport TitleSea ice and clouds: albedo and climate change DescriptionThe effect that reflective land and ocean surfaces have on climate Date Created2010 Educational LevelHigher KeywordsUKOER, GEESOER, albedo, sea ice, clouds Creative Commons LicenseAttribution-Non-Commercial-Share Alike 2.0 UK: England & Wales