Cryosphere Part 1: The Arctic

1. Cryosphere Part 1: The Arctic Global Environmental Change – Lecture 5 Spring 2014

2. What is the Cryosphere? • The National Snow & Ice Data Center explains that some places on Earth are so cold that water is a solid—ice or snow • Scientists call these frozen places of our planet the "cryosphere" • The word "cryosphere" comes from the Greek word for cold, "kryos“ • This is important because the cryosphere influences the climate of the entire world, and it is home to people, plants and animals

3. Regions of the Cryosphere • Arctic • Greenland • Antarctica • Third Pole • Frozen Ground • Glaciers • Sea Ice • Ice Shelves and Icebergs

4. Tour of the Cryosphere

5. Basic Scientific Background • Before examining the cryosphere in more detail, it will be useful to examine some basic concepts • Feedback • Albedo

6. Feedback Mechanism • Any process that acts to oppose or amplify changes to a system that is in a steady state • Feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input • The response is often proportional • That is, as the system deviates more from the steady state position, the faster the process works to counteract it

7. Homeostasis • Property of an open system, especially living organisms, to regulate its internal environment so as to maintain a stable condition, by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms • Term was coined in 1932 by Walter Cannon from the Greek roots homo- (same, like) and sta- (to stand or stay)

8. Negative Feedback • A type of feedback, during which a system responds so as to reverse the direction of change • Since this process tends to keep things constant, it is stabilizing and attempts to maintain homeostasis

9. Negative Feedback Example – A Ball Rolling Inside a Curved Bowl • Initially, the ball oscillated from side-to-side, rising far up the sides of the bowl • With time, the amplitude of the motion decreases until the ball comes to rest at the bottom of the bowl • Once stationary, the ball has reached a position of stability

10. Positive Feedback – Microphone Screech • Small sounds picked up by the microphone are amplified by the nearby speaker, where the microphone once again picks up the amplified sound and rebroadcasts it through the speakers • This looping continues until the initially tiny sound is re-amplified repeatedly to a piercing squeal

11. Audio Feedback • An example of microphone-speaker feedback

12. Nuclear Chain Reaction

13. Cybernetic Systems • From the Greek kubernetes, meaning a steersman • Cybernetics means the branch of study concerned with self-regulating systems using communication and control in either mechanical devices or living biological organisms

14. Cybernetic System Components • Sensor • Amplifier • Controller

15. Instrument vs. Man • Cybernetic control by electrical system • Cybernetic control by human brain

16. Albedo • Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space • It is a measure of the reflectivity of the earth's surface

17. Effect of Albedo Change • Ice, especially with snow on top of it, has a high albedo: most sunlight hitting the surface bounces back towards space • Water is much more absorbent and less reflective • So, if there is a lot of water, more solar radiation is absorbed by the ocean than when ice dominates

18. Seasonal Importance of Albedo • Albedo is not important at high latitudes in winter: there is hardly any incoming sunlight to worry about • It becomes important in spring and summer when the radiation entering through leads can greatly increase the melt rate of the sea ice

19. Ice Albedo Feedback • Ice with snow cover has a high albedo of about 0.9, meaning that 90% of incident radiation is reflected into space – there is little heating of the ground • Bare ice absorbs about 50% of the incident radiation • Open ocean absorbs 94% • As ice melts, more and more heat is retained, creating a positive feedback

20. Ice-Albedo Feedback Summary • The Ice-Albedo feedback can work in reverse • If climate starts to cool, snow accumulates, turns to ice, and reflects more light back into space • This further cools the surface and the air above it • Either in forward or reverse, ice-albedo is a positive feedback, amplifying the input perturbation

21. High-Latitude Climate Sensitivity • The high latitudes, particularly the Arctic, are predicted by all the Global Circulation Models to be much more sensitive to climate change then the temperate and tropical regions • This is currently observed • It is largely a result of the ice-albedo feedback • It is estimated that the Arctic will see 2-4 times the as much warming as the global average • Sea ice changes have a very obvious effect on the large changes climate changes seen in the Greenland ice cores

22. 2012 Temperature Data

23. Arctic Feedbacks • Feedback mechanisms in the Arctic are of growing concern • In 2009, the World Wildlife Federation published a well written report entitled “Arctic Climate Feedbacks: Global Implications” edited by Martin Sommerkorn & Susan Joy Hassol – a link to the PDF version of the second edition is on the Activity Sheet • While WWF is an advocacy group, this report was written by research scientists (see pp. 93-96 of the report), and was mentioned by Professor Ricky Rood of the University of Michigan in a blog dated October 1, 2009

24. Impact on Northern Hemisphere • Amplification of global warming in the Arctic will have fundamental impacts on Northern Hemisphere weather and climate • Due to the sun’s rays striking the Earth’s surface more directly at the equator than at the poles, there is an inequality in the amount of solar radiation received at the poles and the equator, which gives rise to a gradient in atmospheric temperatures, driving circulation of air in the atmosphere • This transports heat from regions of low-latitude warmth to the cooler poles, heat which is then radiated to space • Because of this transport, poleward of about 38º in each hemisphere, the Earth emits more radiation to space (as longwave radiation) than it receives from the sun as shortwave radiation

25. Heat Transport • Much of the atmospheric heat transport is accomplished by weather systems travelling along the wavy jet streams of the middle and higher latitudes in each hemisphere (red arrows)

26. Sea-Ice Modification • Arctic sea-ice cover modifies the basic temperature gradients from the equator to the poles and hence the manner in which the atmosphere transports heat • Sea ice influences temperature gradients because of its high reflectivity and its role as an insulating layer atop the Arctic Ocean • At its maximum seasonal extent in spring, when it covers an area roughly twice the size of the continental United States, the albedo of the freshly snow covered ice surface may exceed 80 per cent, meaning that it reflects more than 80 per cent of the sun’s energy back to space and absorbs less than 20 per cent • By September, the ice cover shrinks to about half of its spring size • While summer melting causes the albedo of the ice pack to decrease to about 50 per cent through exposing the bare ice and the formation of melt ponds, this is still much higher than that of the ocean and land areas, which may have albedos of less than 10 per cent

27. Climate Stabilization • When arctic sea-ice melts, it absorbs a lot of energy, and keeps the air temperature from rising • Sea-ice is also a good insulator – from October through April, it covers much of the Arctic ocean, greatly slowing the rate of heat loss to the atmosphere • As ice cover diminishes, the insulating effect is also diminished, allowing the Arctic atmosphere to warm in winter • This has important climate implications

28. Ice Margin • As the figure shows, the ice margin is characterized by particularly strong temperature gradients during winter • This favors the development of low pressure systems along the edge of the ice

29. Polar Vortex • A persistent, large-scale cyclone located near either of a planet's geographical poles is called a polar vortex • On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere • They surround the polar highs and lie in the wake of the polar front • These cold-core low-pressure areas strengthen in the winter and weaken in the summer due to their reliance upon the temperature differential between the equator and the poles • The term is not new, dating back at least as far as 1853 • When the polar vortex is strong, the Westerlies increase in strength • When the polar cyclone is weak, the general flow pattern across mid-latitudes buckles and significant cold outbreaks occur • Ozone depletion occurs within the polar vortex, particularly over the Southern Hemisphere, and reaches a maximum in the spring

30. Arctic Amplification • Depictions from the NCAR CCSM3 global climate model of: (a) near surface (2 meter) temperature deviations by month and year over the Arctic Ocean • Deviations are relative to 1979-2007 average • The simulation uses the IPCC A1B emissions scenario for this century and observed greenhouse gas concentrations for the 1990s

31. Arctic Atmospheric Temperature • Latitude by height plot of October-March temperature deviations for 2050-2059 • Deviations are relative to 1979-2007 average • The simulation uses the IPCC A1B emissions scenario for this century and observed greenhouse gas concentrations for the 1990s

32. Future Warming

33. Static Stability and Atmospheric Thickness • Atmospheric heating over the Arctic Ocean through a considerable depth will alter both the change in temperature with elevation (known as the atmosphere’s static stability) and the gradient of atmospheric thickness from the equator to the poles • Atmospheric thickness is the separation, in meters, between two adjacent pressure levels in the atmosphere, and it increases with increasing atmospheric temperature

34. Weather Changes • A weak thickness gradient toward the poles, will weaken the vertical change in wind speed, called the wind shear • Warming the Arctic atmosphere will decrease the thickness gradient between the poles and the equator • Changes in the static stability and atmospheric thickness gradient will affect the development, tracks and strengths of weather systems, and the precipitation that they generate

35. North Atlantic Oscillation • The NAO describes a correlation in the strengths of the Icelandic Low (the semipermanent low pressure cell centered near Iceland) and the Azores High (the semipermanent high pressure cell centered near the Azores) — the major atmospheric “centers of action” in the North Atlantic. • When both centers are strong (a deep low and a strong high), the NAO is in its positive phase • When both centers are weak (a shallow low and a weak high), the NAO is in its negative phase

36. NAO Diagram

37. NAO Variation

38. Polar Vortex Breakdown Figure 1. Arctic Atmospheric Pressure: normal 850 mb geopotential height values which were observed for December from 1968-1996 (left) and unusual 850 geopotential height values that were observed for December 2009 (middle) and for February 2010 (right). Figures from NOAA/ESRL Physical Sciences Division.

39. January, 2014 • Regions of light blue color show the "wavy" counter-clockwise path of the jet stream for January 6, 2014. U.S. is near bottom center • Regions of light blue color show a more circular flow for the jet stream during the period December 15-17, 2013.

40. February 26, 2014 Great Lake ice cover as seen on February 19, 2014, by the MODIS instrument on NASA's Aqua satellite. Ice cover on North America’s Great Lakes reached 88 percent in mid-February 2014—levels not observed since 1994. The average maximum ice extent since 1973 is just over 50 percent. It has surpassed 80 percent just five times in four decades. The lowest average ice extent occurred in 2002, when only 9.5 percent of the lakes froze. Image credit: NASA Earth Observatory. Winds at a height where the pressure is 250 mb show the axis of the jet stream, seen here at 00 UTC February 26, 2014. A sharp trough of low pressure was present over the Eastern U.S., and unusually strong ridges of high pressure were over the Western U.S. and the North Atlantic.

41. Arctic Oscillation (AO) Index • The Arctic Oscillation refers to an opposing pattern of pressure between the Arctic and the northern middle latitudes • Overall, if the atmospheric pressure is high in the Arctic, it tends to be low in the northern middle latitudes, such as northern Europe and North America • When pressure is high in the Arctic and low in mid-latitudes, the Arctic Oscillation is in its negative phase • In the positive phase, the pattern is reversed

42. Arctic OscillationDiagrams

43. Snowmageddon

44. Heavy Snowfall = No Climate Warming? • Global warming skeptics regularly have a field day whenever a record snow storm pounds the U.S., claiming that such events are inconsistent with a globe that is warming • If the globe is warming, there should, on average, be fewer days when it snows, and thus fewer snow storms • However, it is possible that if climate change is simultaneously causing an increase in ratio of snowstorms with very heavy snow to storms with ordinary amounts of snow, we could actually see an increase in very heavy snowstorms in some portions of the world • There is evidence that this is happening for winter storms in the Northeast U.S.--the mighty Nor'easters like the "Snowmageddon" storm of February 5-6 and "Snowpocalypse" of December 19, 2009.

45. Evidence • There are two requirements for a record snow storm: • 1) A near-record amount of moisture in the air (or a very slow moving storm). • 2) Temperatures cold enough for snow.

46. Groisman Study • Groisman et al. (2004) found a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events in the U.S. over the past 100 years, though mainly in spring and summer • They did find a significant increase in winter heavy precipitation events have occurred in the Northeast U.S.

47. Changnon Study • Changnon et al. (2006) found, "The temporal distribution of snowstorms exhibited wide fluctuations during 1901-2000, with downward 100-yr trends in the lower Midwest, South, and West Coast. Upward trends occurred in the upper Midwest, East, and Northeast, and the national trend for 1901-2000 was upward, corresponding to trends in strong cyclonic activity."

48. 2009-2010

49. Lake Effect Snow • A study by Kunkel et al. (2008) noted that we should expect an increase in lake-effect snowstorms over the next few decades • Lake-effect snow is produced by the strong flow of cold air across large areas of relatively warmer ice-free water

50. Kunkel Study • The report says, "As the climate has warmed, ice coverage on the Great Lakes has fallen. The maximum seasonal coverage of Great Lakes ice decreased at a rate of 8.4 percent per decade from 1973 through 2008, amounting to a roughly 30 percent decrease in ice coverage. This has created conditions conducive to greater evaporation of moisture and thus heavier snowstorms. Among recent extreme lake-effect snow events was a February 2007 10-day storm total of over 10 feet of snow in western New York state. Climate models suggest that lake-effect snowfalls are likely to increase over the next few decades. In the longer term, lake-effect snows are likely to decrease as temperatures continue to rise, with the precipitation then falling as rain".