Group Project: Cycle A Ice sheets- Atmosphere Group Jennifer Booher, Ty Long, and Jennifer Haren
1. A>E Warming atmosphere – melting ice.
As air temperatures warm, due to global warming, the melting of ice, which is occurring in both Greenland and Antarctica, causes a decrease in sheet ice. If air temperatures continue to rise over Greenland and Antarctica, increased surface melt will play a large role in ice-sheet mass loss. The rising of air temperatures due to carbon dioxide is warming the Earth’s atmosphere by preventing the release of heat. The heat is trapped within the Earth’s atmosphere by greenhouse gases creating a blanket around the Earth. Some argue that the increase in global temperature is cyclic in nature and the cause of the increase in temperature is because the Earth is in between glaciations. These scientists state that we have experienced glacial melting similar to this in the past.
According to the U.S. Global Change Research Program, “U.S. average temperature has risen more than 2 degrees Fahrenheit over the past 50 years and is projected to rise more in the future; how much more depends primarily on the amount of heat trapping gases emitted globally and how sensitive the climate is to those emissions.” Although National temperatures vary more than global temperatures, (partly because of the moderating influence of the ocean) the global temperature is also above average compared to the recent past.
In fact, according to Geoffrey Mohan from the Las Angeles Times, average air temperatures above Greenland’s ice sheets have risen 4 degrees Fahrenheit since 1991. There is much debate and speculation in the scientific community about the amount and the causes of the increase in global and specific area warming. That being said there are studies that shows that this increase in temperature, however much it may be, is having an impact on the rate of ice sheet melting, especially in Greenland.
The IPCC (Intergovernmental Panel on Climate Change) projects that ice mass loss from melting of the Greenland ice sheet will continue to outpace accumulation of snowfall, which means the Greenland Ice Sheet is getting smaller, in part because of the increase in temperature that is causing melting. Natural variations in atmospheric pressure and wind patterns also can add to the record low amounts of Arctic Sea Ice. In addition to these natural causes for decline, there are clear links between rising greenhouse gas concentrations and declines in Arctic sea ice in studies as far back as the early 1990’s.
According to these studies, the extreme loss of ice in 2007 would not have been possible without the long-term reductions that have been occurring at the same time as the sustained increase in atmospheric concentration of carbon dioxide leading to the rapid rise in global temperatures reported since the mid-1970’s (U.S. Global Change Research Program). Overall, there seems to be study after study showing that global temperature, more specifically the atmospheric temperature over Greenland, is rising. Although there are also studies that refute these claims, there is evidence that this rise in temperature is caused from an increase of carbon dioxide in the atmosphere. These rises in temperature have shown, and have been predicted to further show, a decline in the amount of Arctic sea ice.
According to a study from the Journal of Glaciology, using data collected through a daily time series of 'clear-sky' surface temperatures, which has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006 and mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006, large scale surface melt was followed rapidly by mass loss of Greenland’s ice sheet.
A separate study by Abdalati and Konrad Steffen of the University of Colorado showed that the melting of the ice sheet surface has been increasing at a rate of nearly 20% over the last 21 years, while summer temperatures in that same period have increased by one quarter of a degree Celsius (.45º Fahrenheit). The link between ice sheet melting and ice flow suggest that the increasing melt may be more significant than previously believed.
Studies of long-term climate change have discovered a connection between the concentrations of carbon dioxide in the atmosphere and mean global temperature. Carbon dioxide has increased from 280 parts per million to 380 parts per million in 2005. Many scientists believe that higher concentrations of carbon dioxide in the atmosphere will enhance the greenhouse effect making the planet warmer. Most computer climate models suggest that the globe will warm up by 1.5 - 4.5° Celsius if carbon dioxide reaches the predicted level of 600 parts per million by the year 2050.
The findings, recently reported by scientists from the British Antarctic Survey (BAS), the Open University and University of Bristol in the journal Nature could help us understand more about rapid Antarctic climate changes. Previous analysis of ice cores has shown that the climate consists of ice ages and warmer interglacial periods roughly every 100,000 years. This suggests Antarctic temperature shows a high level of sensitivity to greenhouse gases at levels similar to those found today.
According to NCAR scientists Bette Otto-Bliesner, University of Arizona professor Jonathan Overpeck, University of Calgary professor Shawn Marshall, and University of Colorado professor Giff Miller, blending computer modeling with paleoclimate records helps us to understand this past interglacial (a warm period between colder glacial periods) period and to project what future Arctic warmth will mean for the Greenland and Antarctic ice sheets and sea level. From ice cores we also know that the Greenland ice sheet shrunk during the Last Interglaciation and our calculations with the University of Calgary ice sheet model show that the substantial melting of this ice sheet and the complete melting of the nearby eastern Canadian ice fields added up to 3.5 meters (11 feet) of sea level rise. Ancient corals tell us that sea level rise for the Last Interglaciation may have been as high as 6 meters (20 feet) suggesting that some sea level rise may have come from Antarctica. These records and other considerations also suggest that sea level may have risen at rates up to 1 meter per century.
Citations:
http://www.gsfc.nasa.gov/topstory/20020606greenland.html
http://www.ingentaconnect.com/content/igsoc/jog/2008/00000054/00000184/art00008
http://www.sciencedaily.com/releases/2009/11/091119141039.htm
http://www.cgd.ucar.edu/research/past/interglaciation.html
http://www.eoearth.org/article/Causes_of_climate_change
“National Climate Change” from the U.S. Global Change Research Program
http://downloads.globalchange.gov/usimpacts/pdfs/National.pdf
American Meteorological Society, Glossary of Meteorology
“Greenspace: Greenland ice sheet meltdown: It’s spreading, study finds” from Los
Angeles Times (March 24, 2010)
http://latimesblogs.latimes.com/greenspace/2010/03/global-warming-melting-greenland
2. A>E Atmospheric currents – Melting ice sheets
The natural process of atmospheric circulation distributes heat from the equator to the poles. Each hemisphere has three linked systems of weather patterns which gradually move heat away from where the sun's rays have most impact (at the equator) towards where it has least impact (the Poles).
Paleoclimatologists have hypothesized that the equator-to-pole surface-temperature gradient is a dominant control on the paleocirculation of the atmosphere. Atmospheric simulations using realistic Cretaceous (100 m.y. ago) geography are used to examine quantitatively the relationships between paleogeography, surface-temperature gradients, and the nature of the atmospheric circulation. These results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation.
According to NASA’s Earth Observatory, three variations in atmospheric circulation contribute to an increase in atmospheric temperatures. The primary variation in atmospheric circulation in the Antarctic is the Antarctic Oscillation, also called the Southern Annular Mode. Changes in the El Niño-Southern Oscillation Index (ENSO), an oscillation of ocean temperatures and surface air pressure in the tropical Pacific, can lead to a delayed response (three to four seasons later) in Antarctic sea ice extent. Antarctic sea ice is the periodic strengthening and weakening of something that meteorologists call “zonal wave three,” or ZW3. This pattern alternately strengthens winds that blow cold air away from Antarctica (toward the equator) and winds that bring warmer air from lower latitudes toward Antarctica.
Citations:
http://geology.gsapubs.org/content/10/12/633.abstract
http://earthobservatory.nasa.gov/Features/SeaIce/page4.php
http://ecology.com/featuresarchive/earthwarms/index.html
3. E>A Melting ice – more exposed dark surface – increased atmospheric temperatures.
As the ice sheets melt, the albedo is reduced and the Earth absorbs the energy that is not reflected. Thus, more heat is retained in the Arctic and Antarctic. Albedo is the amount of sunlight reflected by an object. The Polar Ice Caps themselves reflect sunlight energy (heat) back into space, rather than the heat being absorbed by the Earth. When the heat is reflected off of the polar caps, it is returned to the atmosphere. The melting of the ice sheets creates more open water. The darker water absorbs more sunlight and heat, rather than reflecting the sunlight and heat like the lighter, reflective ice does. Another way to explain this refers to albedo. The albedo of snow-covered ice is about 85%, where the ice-free Arctic Ocean water has an average albedo of about 40%. As sea ice shrinks, the greater area of darker, ice-free water absorbs more solar radiation, temperatures rise and more ice melts.
According to studies performed by the scientists affiliated with the International Polar Foundation, the polar icecaps reflect considerable solar radiation: up to 90% depending on ice conditions, compared with much lower average albedos for other parts of the Earth's surface. This keeps the temperature at the poles lower than it would be without the ice cover. Reports note that Antarctica and Greenland can be considered the northern and southern hemisphere’s air conditioner. The dramatic sea ice loss over the last number of decades combine with widespread glacier retreat, has amplified warming in the Polar Regions through the albedo effect, with less heat being reflected back to space. This amplification in atmospheric warming will likely spread over the northern land masses, increasing the likelihood of further release of methane trapped in the frozen permafrost, further fueling global warming.
Based on an article from Global Greenhouse Warming.com, an important property of snow and ice is its high surface albedo. Because up to 90% of the incident solar radiation is reflected by snow and ice surfaces, while as low as about 10% is reflected by the open ocean or forested lands, changes in snow and ice cover are important feedback mechanisms in climate change. In addition, snow and ice are effective insulators. Seasonally frozen ground is more extensive than snow cover, and its presence is important for energy and moisture fluxes. Therefore, frozen surfaces play important roles in energy and climate processes.
A recent paper by Francis & Hunter provides an interesting discussion about reasons for the recent decline in the Arctic sea-ice extent, based on new satellite observations. One common proposition about sea ice is that it involves a positive feed-back because the ice affects the planetary albedo (how the planet reflects the sunlight back to space before the energy enters the ‘climate system’).
Citations
http://www.sciencepoles.org/articles/article_detail/climate_change_the_essentials/
http://www.global-greenhouse-warming.com/melting-greenland.html
http://www.realclimate.org/index.php/archives/2006/12/not-just-ice-albedo/
http://www.suite101.com/content/global-environmental-impacts-of-a-warming-arctic-a160748
“Chapter 11:Natural Causes of Climate Change” from Climate Studies: Introduction to
Climate Science (2010) from the American Meteorological Society
“Quick Facts on Ice Sheets” from the National Snow and Ice Data Center
http://nsidc.org/quickfacts/icesheets.html
http://www.carbon-info.org/carboninfo_029.htm
4. E>A Reduce sea ice and ice sheets – Increase atmospheric temperatures
In response to reduced sea ice cover, increases in atmospheric water vapor content, partly may have enhanced warming in the lower part of the atmosphere during summer and early autumn. It can be concluded that diminishing sea ice has had a leading role in recent Arctic temperature amplification. Cloud coverage over ice sheets acts as a blanket insulating the atmosphere, which is able to maintain warmer temperatures. The melting of sea ice over the Arctic Ocean is likely to increase the humidity of the overlying air, which creates more clouds. Clouds can cause both cooling and warming. Clouds cause cooling by reflecting sunlight to space, and they cause warming by absorbing and emitting to Earth’s surface outgoing infrared radiation. In the dark winter, the clouds would have a warming effect, and in the summer, the clouds could have a cooling effect, especially with low cloud cover.
According to Kerry Emanuel the author of What We Know about Climate Change, the basic theory and models show another consequential result of a few degrees of warming. The amount of water vapor in the air rises exponentially with temperature: a seven-degree increase in temperature increases water vapor by 25 percent. One might at first suppose that since the amount of water ascending into clouds increases, the amount of rain that falls out of them must increase in proportion. But condensing water vapor heats the atmosphere. Because the air is warmer, the relative humidity can be higher (in essence, the air is able to 'hold' more water when its warmer), leading to more water vapor in the atmosphere, says the NCDC. There is much scientific uncertainty as to the degree this feedback loop causes increased warming, inasmuch as the water vapor also causes increased cloud formation, which in turn reflects heat back out into space.
Citations:
http://www.nature.com/nature/journal/v464/n7293/full/nature09051.html
http://bostonreview.net/BR32.1/emanuel.php
http://www.ecobridge.org/climate_roulette.html
“Chapter 11:Natural Causes of Climate Change” from Climate Studies: Introduction to
Climate Science (2010) from the American Meteorological Society
5. B>A>E>H>L Human interference has caused influx of green house gases – increase atmospheric temperatures – Melting of ice sheets - Rise in sea level – Shoreline retreat
According to the researchers at NASA, the leading contributor of global warming is the burning of fossil fuels. Historically, the burning of fossil fuels is the main source of energy for most countries. The main human activities that contribute to global warming are the burning of fossil fuels (coal, oil, and natural gas) and the clearing of land. Most of the burning occurs in automobiles, in factories, and in electric power plants that provide energy for houses and office buildings. The burning of fossil fuels creates carbon dioxide, whose chemical formula is CO2. CO2 is a greenhouse gas that slows the escape of heat into space. As global warming causes the atmosphere to increase in temperature, the polar ice sheets that are found in Antarctica will begin to melt at a drastically increased rate. As the rate of melting increases because of warmer temperatures, the massive ice sheets will begin to move and spread out faster on the Antarctic continent. An increased spreading rate will cause more ice shelves to form as the glacier moves out onto the water quicker and more water will become displaced. “Around the world, glaciers, including the ice sheets of Greenland and Antarctica are melting at alarming rates.” The increase in glacial melting will lead to the rise in sea level. As atmospheric conditions warm ice forms are melting leading to rise in sea level causing the retreat of shorelines. As a result, the sea level would rise throughout the world. Many coastal areas would experience flooding, erosion, a loss of wetlands, and an entry of seawater into freshwater areas. High sea levels would submerge some coastal cities, small island nations, and other inhabited regions.