Earth Gauge » Ice

Climate Number: 2200 Cubic Miles

kraus — Mon, 01 Mar 2010 14:54:42 +0000

Glaciers have a mass balance. Glaciers lose mass by melting during the warm season (primarily the summer months) and gain mass by accumulating snow during the cold season (centered around the winter months). If a glacier accumulates more mass during the cold season than it loses during the warm season, it is said to have a positive mass balance. If it loses more mass than it gains, it is said to have a negative mass balance. Since 1960, it has become more common for glaciers to have negative mass balance years than positive mass balance years, leading to an overall global trend of glacial retreat. It is estimated that since 1960, the world’s glaciers (this does not include the ice sheets on Greenland and Antarctica) have lost about 2200 cubic miles of ice. Because melt water from these glaciers feeds the creeks and rivers that ultimately flow into the ocean, more glacier melt means higher sea levels. About one-third of the recent 3.1 mm average annual sea level rise is due to glacial melt.

For Comparison: An equivalent to 2200 cubic miles of volume is about 36 million Great Pyramids of Giza, or about six million Sears Towers.

Seasons: Winter, Spring, Summer, Fall

Sources: Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson,(eds.). Cambridge University Press, 2009 and Meier, MF et al. “Glaciers Dominate Eustatic Sea-Level Rise in the 21st Century.” Science Express 19 July 2007 / Page 1 / 10.1126/science.1143906.

Climate Number: 73 Terawatts

kraus — Mon, 01 Mar 2010 14:45:37 +0000

The energy moving in both weather systems and through the wires that power your home can be measured in watts. The Sun heats the Earth causing the fluids of the atmosphere and the oceans to move, creating the winds and currents of Earth’s climate. The vast majority of the energy in the climate system moves through the oceans, where currents of warm and cold waters that dwarf even the largest of Earth’s land rivers transport heat and salt to and from the different ocean basins. Compared to other waters in the Arctic, the Barents Sea, which lies to the north of Scandinavia, has a relatively low amount of seasonal sea ice cover. While the northern portion of the sea freezes over with several feet of ice, the southern portion of the sea remains ice free. A current of water from the North Atlantic brings the basin a sufficient amount of warm water to ward off the Arctic ice’s southerly advance. This current moves about 86 terawatts worth of heat into the Barents Sea, and about 13 terawatts leave the sea through other currents. The remaining 73 terawatts is lost into the atmosphere, making what is known as the Barents Sea Opening a major exit, or release point, for the ocean’s heat storage.

For Comparison: It would take about 61,000 1200 megawatt nuclear power plants – about 140 times the number that exist around the world today – to generate 73 terawatts worth of power. This amount of power is almost 30 times the world’s current electrical generation capacity.

Seasons: Winter, Spring

Sources: Smedsrud, LH et al. “Heat in the Barents Sea: transport, storage, and surface fluxes.” Ocean Science 6 (2010): 219-234 and World Nuclear Association. “Nuclear Power in the World Today.” Accessed Online 28 February 2010

Climate Fact: North American and Eurasian Snow

kraus — Mon, 22 Feb 2010 15:13:48 +0000

Snow is both a product of the weather and a weather maker. It has long been recognized that snow exhibits a cooling effect on local and regional scales. Snow reflects more sunlight than bare ground, meaning that it absorbs less energy. More snow cover also means soils stay moist for longer following the spring melting than they otherwise would. More soil moisture means that more of the sun’s energy that would have been spent heating the ground is instead spent evaporating water. In North America, lots of snow over the continent affects the storm track, or the latitudinal band where travelling cyclonic high and low pressure systems are most common. More specifically, the cold temperatures the snow cover induces eventually force the storm track over North America to veer south. As it does this, the storm track downstream in Eurasia veers north, allowing warmer air masses to penetrate further into the continent than they otherwise would. The presence of these warmer air masses generally means less snow there. Thus, years of above average snow cover in North America tend to be years of below average snow cover in Eurasia.

Seasons: Winter, Spring

Source: Sobolowski, S et al. “Modeled Climate State and Dynamic Responses to Anomalous North American Snow Cover.” Journal of Climate 23 (2010): 785-799.

Snow in a Warming World

kraus — Fri, 19 Feb 2010 21:09:51 +0000

Snowfall and snow cover have direct effects on transportation, soil freeze/thaw cycles, water availability, flood frequency, water quality, wildlife, forest fires and more.

Far from being just a passive product of prevailing climatic conditions, snow cover also influences climate by changing the surface albedo, the amount of solar radiation a surface reflects. The presence of snow, because snow cover reflects more sunlight than bare ground, changes the surface conditions that influence how the atmosphere around us moves – which affects the weather responsible for the snow itself.

Because of snow’s influence on our daily activities and weather, it is important to understand the mechanics behind this phenomenon, as well as why snowfall and snow cover vary from region to region and from year to year.

Where Does it Snow and Why?

How do Changes in Climate Affect Snowfall and Snow Cover?

Where is More Snow Falling?

Where is Less Snow Falling?

What Causes Snowfall to Vary from Year to Year?

Conclusion

Where Does it Snow and Why?

Two “ingredients” are necessary for snowfall to occur:
• Temperatures between the cloud base and the ground must be around or below freezing;
• A sufficient amount of moisture must be present in the air.

When one of these ingredients is lacking, it becomes the limiting factor for snowfall. How much of each ingredient is present will vary from region to region and from month to month.

Left: Temperatures below or near freezing throughout the lower part of the atmosphere are a necessary condition for snowfall.

Image Courtesy of NOAA.

For example, in the Pacific Northwest, with a prevailing jet stream and surface winds blowing in from the relatively warm Pacific Ocean, winters generally have lots of moisture but not the cold Arctic air that pushes temperatures below freezing. Only the higher elevations (around 2,500 feet and higher) consistently receive snowfall. As result, the region’s mountains hold some of the world’s largest snow accumulations, while in the valleys, which may be only a few dozen miles away, snow is rare. Every ten years or so, a north wind from Canada will pump cold air into the region, giving sea-level cities like Seattle significant snow.

The opposite situation is prevalent in the upper Midwest, which during the winter generally receives a flow of cold air from Canada that keeps temperatures well below freezing. Because this flow originates from land and not the ocean, there is often not enough moisture in the air for snow to occur. Intrusions of warm air from the Gulf of Mexico as well as moisture picked up from the Great Lakes occasionally provide the humidity necessary for snow to form there.

How Do Changes in Climate Affect Snowfall and Snow Cover?

Changes in the frequency and intensity of snowfall occurred over the last century as the world warmed. Because snow’s limiting factors differ from region to region, discussions on the effects a warming trend will have on snowfall are most appropriately conducted with a regional focus. Warming trends do not necessarily mean the whole U.S., a geographic unit with many distinct climate zones, should expect either more or less snowfall.

Where is More Snow Falling?

The Great Lakes Region: As the cold late fall and early winter winds from Canada blow through the Great Lakes region, they pick up moisture from the Great Lakes and deposit it downwind as snow in places like Marquette, Mich. (which gets an average or 180 inches per year) and Syracuse, N.Y. (which gets an average of 120 inches per year) – two of the snowiest places in the U.S. Until the latter part of the 20th century, this lake effect snow would stop around mid-winter in most years when the ice cover had grown across the lake surfaces, thus cutting off the snow’s source of moisture. Today, surface waters in Lake Michigan-Huron are 3.6 degrees Fahrenheit warmer than they were in the late 1970’s and Lake Superior’s surface is 5.3 degrees warmer. The average annual extent and duration of ice cover on these lakes has declined. Lake Superior’s average winter ice cover has fallen from 25 to 15 percent over the last 30 years. Snowfall trends for areas downwind from the lakes climbed during this period when open water during the winter became more prevalent. Syracuse, N.Y., for example, gets an average of 50 percent more snow each winter than it did in the early 20th century.

Left: Trend in the average annual extent of Lake Superior’s ice cover.

Image Courtesy of Austin, JA and Colman, SM, 2008.

The East (Lee) Side of the Rocky Mountains: A combination of more upslope events (i.e. an increase in the number of frontal systems moving across and dumping precipitation over the Rocky Mountain region) and the general increase the region’s cold season humidity have both been correlated with an observed increase in snowfall. This increase is most pronounced in the eastern parts of Colorado and New Mexico.

Above: Snowfall trends for 1930-31 to 2006-07, with dotted areas indicating negative trends and white areas positive trends. Numbers are the magnitude of the respective trends, or the per year percentage departures from the 1930-31 to 2006-07 mean.

Image Courtesy of Kunkel, et al., 2009

Where is Less Snow Falling?

The Southern Snowfall Margin: Oklahoma, Arkansas, Tennessee and North Carolina are considered to be at the southern margin of where wintertime temperatures are cold enough for snow to form. Areas near this southern margin experienced declines in snowfall over the 20th century.

The West: Most of the West’s water supply originates from snowpack. How much snow falls during the winter, when the snow melts and how quickly that melt happens are vital factors for the region’s water resources. Warm, northern-moving currents off the Pacific Coast bring ample moisture to the West during winter. Warming temperatures have corresponded to a decrease in the proportion of annual precipitation falling as snow, decreases in mountain snowpack accumulation and an increase in the elevation of the snowline (the elevation where conditions become cold enough for rainfall to turn to snowfall). Snowfall trends have been particularly pronounced in the Pacific Northwest (PNW), with some mountain stations now reporting snowfall totals less than half of what was reported in the 1930’s. The proportion of annual precipitation falling as snow in the PNW has been declining at a rate of almost nine percent per decade since the 1950’s. Warmer temperatures and less late season snowfall are causing snow cover to melt earlier in the year. In the PNW, the date when snow starts to melt now happens an average of 16 days earlier in the year; in California and Nevada it is happening about nine days earlier. As a result, for the West as a whole, the average date when the spring “pulse” of meltwater is first observed in streams is happening about 20 days earlier than it did in the 1950’s. Earlier snowmelt and peak-annual river flows pose challenges for water managers in the West.

Above: Linear 1950-1997 trends for snow water equivalent, or the amount of snow remaining on the ground, on
April 1 when the melt season across most of the West is underway.

Image Courtesy of Mote, et al. , 2005.

What Causes Snowfall to Vary from Year to Year?

Weather variability is controlled by a variety of cycles: the daily cycle, the annual cycle and the millennial orbital cycles that are believed to largely drive the ice ages. Multi-annual cycles, during which concentrations of heat in the oceans and atmosphere “move around,” occur on periods between the annual cycle and the millennial cycles and are possibly influenced by cycles in solar output occurring on periods of around 11 years and 80 years. A few multi-annual cycles have been identified as particularly important for understanding America’s year-to-year snowfall variability.

The El Niño-Southern Oscillation: Probably the strongest and most ubiquitous single source of interannual variability, the El Niño-Southern Oscillation (ENSO) is a change in the heat distribution in the tropical Pacific Ocean. The eastern tropical Pacific cools and warms over a period of three to seven years. When it is cool, it is considered to be in a La Niña phase; when it is in a warm, it is considered to be in an El Niño phase.

This cooling and warming affect the circulation in the upper atmosphere and the strength and position of the Northern Hemisphere storm tracks that bring winter storms to the U.S. La Niña phases tend to push the storm tracks north, bringing more winter storms to the northern U.S. El Niño events mean a more southern storm track and more wintertime moisture for the southern U.S. These variations in the position of the storm tracks mean variations in the regional frequency of the winter storms that often accompany snowfall.

El Niño phases correspond to more frequent East Coast Winter Storms, or Nor’easters, which form around Cape Hatteras and travel north along the East coast, bringing high winds and snowfall.

The Arctic Oscillation: In the Northern Hemisphere, how much atmospheric mass is (or how many air molecules are) concentrated at the mid-latitudes and the poles varies from day to day and from year to year. This is reflected in changes in the difference in atmospheric pressure between the mid- and high latitudes, which influences weather in the U.S. Specifically, a greater difference in atmospheric pressure means a stronger jet stream. A stronger jet stream works to “block” the Arctic air masses that would otherwise descend into mid-latitudes and the U.S. A weaker jet stream weakens the blocking, allowing the frigid air to penetrate further south.

When the pressure difference between mid and high latitudes is large, the Arctic Oscillation (AO, the term for this shifting of atmospheric mass) is considered positive and the high latitudes are cooler than normal and the mid-latitudes warmer than normal. When the pressure difference is small, the AO is negative and the higher latitudes are warmer than normal and the mid-latitudes cooler than normal. Another way to remember this is a positive AO relates to positive temperature anomalies in the U.S. and a negative AO relates to negative temperature anomalies in the U.S.

Cities like Chicago and Boston have many more extremely cold days during negative AO phases. The recent late-December to early-January cold snap occurred when the AO was strongly negative. Because it controls how much cold Arctic air reaches the mid-latitudes, where this air mixes with warm and wet air masses, the state of the AO has implications for snowfall in America. In generally snow-deprived Atlanta, there are five times as many days when trace snowfall occurs during negative phase winters versus positive phase winters.

The Pacific Decadal Oscillation: The Pacific Decadal Oscillation (PDO) describes changes in the distribution of sea surface temperatures in the North Pacific on a period of 50-60 years. Like ENSO, this sea surface temperature shift affects atmospheric circulation. The effects of this shift are most pronounced on weather in the western U.S.

Warm phases of the PDO generally shift the storm track northward, giving areas like Alaska more wintertime precipitation and areas like the Pacific Northwest less. Cool phases do roughly the opposite. Warm phases also mean warmer temperatures in the Pacific Northwest, so more of the already reduced precipitation falls as rain instead of snow. Reduced snowpack during warm years results.

Above: North Pacific surface temperature anomalies during positive and negative phases of the Pacific Decadal Oscillation.

Image Courtesy of NOAA.

Oscillation Interaction: How snowfall in the U.S. varies from year to year depends largely on how the different phases of these oscillations interact. For example, a winter with an El Niño driven southerly storm track and strong intrusions of Arctic air driven by a negative AO is likely to have above normal snowfall in the mid-Atlantic and southern snowfall margins. On the other hand, these same regions are not likely to receive much snow during a winter with a La Niña driven northerly storm track and a positive AO.

Conclusion

The specific factors that bring together the conditions necessary for snow vary from region to region. Understanding these regional differences is necessary to understand how snowfall can vary as the global climate changes. Some regions have experienced more snowfall during the recent warming trend while other regions are now receiving less. Multi-annual oscillations and the interactions between these oscillations are key variables in regional snowfall occurrence.

Special thanks to Joe Witte and Steve Tracton for their contributions to this paper.

Sources

Austin, JA and Colman, SM. “A century of temperature variability in Lake Superior.” Limnology and Oceanography 53 (2008): 2724-2730.

Austin, JA and Colman, SM. “Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback.” Geophysical Research Letters 34 (2007): L06604.

Burnett, AW et al. “Increasing Great Lake-Effect Snowfall during the Twentieth Century: A Regional Response to Global Warming.” Journal of Climate 16 (2003): 3535-3542.

DeGaetana, AT et al. “Statistical Prediction of Seasonal East Coast Winter Storm Frequency.” Journal of Climate 15 (2002): 1101-1117.

Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093.

Global Glacier Retreat Project. Nichols College. Accessed Online 5 July 2007 http://www.nichols.edu/departments/Glacier/glacier_retreat.htm.

Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson,(eds.). Cambridge University Press, 2009.

Groisman, P.Y., P.W. Knight, and T.R. Karl. “Heavy precipitation and high streamflow in the United States: Trends in the 20th Century.” 82 (2001): 219-246.

Hanrahan, JL et al. “Connecting past and present climate variability to the water levels of Lakes Michigan and Huron.” Geophysical Research Letters 37 (2010): L01701.

Hirsch, ME et al. “An East Coast Winter Storm Climatology.” Journal of Climate 14 (2001): 882-899.

Kunkel, KE et al. “Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset.” Journal of Atmospheric and Oceanic Technology 26 (2009): 33-44.

Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. “Declining mountain snowpack in western North America.” Bulletin of the American Meteorological Society. 86 (2005): 39–49.

National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif).

The National Park Sevice. North Cascades National Park Complex: Glacial Monitoring Program. Accessed Online 10 July 2007 http://www.nps.gov/noca/naturescience/glacial-mass-balance1.htm

Thompson, David W.J. “Regional Climate Impacts of the Northern Hemisphere Annular Mode.” Science 293 (2001): 85-89.

United States Geologic Survey. “Fifty-Year Record of Glacier Change Reveals Shifting Climate in the Pacific Northwest and Alaska, USA.” 6 July 2009. Accessed Online 7 August 2009 http://pubs.usgs.gov/fs/2009/3046/

USA Today. “Answers archive: Winter, snow, ice.” http://www.usatoday.com/weather/resources/askjack/wasnow.htm

van Mantgem, PJ et al. “Widespread Increase of Tree Mortality Rates in the Western United States.” Science 323 (2009): 521-524.

Weng, H. “The influence of the 11 yr solar cycle on the interannual-centennial climate variability.” Journal of Atmospheric and Solar – Terrestrial Physics 67 (2005): 793-805.

Climate Number: $16.3 Billion

kraus — Mon, 01 Feb 2010 15:37:37 +0000

When put in 2000 US dollars, freezing rain (ice storm) events in America caused an estimated 16.3 billion dollars in total losses between 1949 and 2000 due to downed power lines, downed trees, agricultural losses, transportation accidents and medical costs from injuries due to slippery conditions. Freezing rain events are most frequent in the Northeast, but are also common across the Midwest and Piedmont regions from North Carolina northward. When freezing rain events hit the Southeast they tend to be accompanied by high dewpoints. This means that while ice storms are rarer in the Southeast, they tend to be heavy and particularly damaging when they do hit. Records kept since the late 1920’s show that ice storms were the least frequent during the 1930’s and rose to a peak in the early 1950’s, showing little or no trend thereafter.

For Comparison: 16.3 billion dollars is around the same amount collectively pledged by all participating parties to fight global poverty following the 2008 U.N. anti-poverty summit. It is also roughly the same amount as NASA’s annual budget.

Seasons: Winter

Source: Houston, TG et al. “Freezing rain events: a major weather hazard in the conterminous United States.” Natural Hazards 40 (2007): 485-494.

Climate Fact: Earth’s Ice and Tipping Points

kraus — Mon, 25 Jan 2010 14:35:59 +0000

Ice masses maintain their own local climate through several mechanisms. One mechanism is known as the ice-albedo feedback mechanism: ice is more reflective than surrounding rock or ocean and the more reflective a surface is, the less sunlight it absorbs and the less it warms. Highly reflective ice surfaces promote the cold conditions that allow the ice to exist in the first place. A second mechanism has to do with a glacier’s height. Higher elevations are cooler and for every 340 feet of elevation gain or loss on a glacier, the temperature at the glacier’s surface will rise or fall by between one and 1.8 degrees Fahrenheit. These two phenomena are types of “positive feedback mechanisms” – an initial loss or gain in an ice mass triggers further losses or further gains. Ice masses are also influenced by what are known as “negative feedback mechanisms” – an initial loss or gain in an ice mass triggers effects that make further losses or further gains less likely. A retreat of the Arctic Sea ice, for example, exposes more ocean water. While this increased exposure allows more sunlight to be absorbed (a positive feedback mechanism) it also means that more heat can leave the ocean, thus cooling the waters (a negative feedback mechanism). Another example of a negative feedback mechanism is glacial retreat causing warming, but that warming leading to increased moisture transport to the glacier, greater snow accumulation and glacial growth. Better understanding of these feedbacks and their interactions with other feedbacks will enable better prediction of future trends in Earth’s ice masses.

Seasons: Winter, Spring, Summer, Fall

Source: Notz, D. “The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss.” Proceedings of the National Academy of Sciences 106 (2009): 20590-20595.

Climate Fact: Antarctica’s Subglacial Lakes

kraus — Fri, 15 Jan 2010 16:02:11 +0000

Beneath the Antarctic ice sheet lie some of Earth’s final frontiers – networks of subglacial lakes, many of which have been isolated from the atmosphere for as long as 15 million years. Outlet channels allow these lakes to periodically drain into the ocean, refill and drain again. The largest of these lakes, Lake Vostok, lies about 2.5 miles below the surface of the East Antarctic ice sheet and is about the size of Lake Ontario. Recently, subglacial lakes have attracted the attention and imagination of much of the scientific community for two primary reasons:

• Ice Stream Stability: Ice streams are areas of continental ice sheets where inland ice flows rapidly into the ocean – they can be characterized as “rivers of ice.” Subglacial lakes are an important component of ice stream dynamics. A series of large lakes sit at the onset of the Recovery ice stream, which comprises eight percent of the East Antarctic ice sheet, providing the initial “lubricant” for ice destabilization and movement (which occurs at a rate of about 320 feet per year). The periodic drainage of these lakes can lead to periodic accelerations in ice flow as well. Better understanding the relationship between subglacial lakes and the ice that covers them is crucial to predicting future rates of continental ice loss and sea level rise.

• Unique Ecosystems: Because subglacial lakes have been essentially untouched by sunlight, oxygen and other ecosystems for millions of years, the life that does exist in these lakes is unique and potentially analogous to early life on Earth, particularly life that survived in extensive glacial periods of Earth’s distant past (500-1,000 million years ago). Samples taken from outlet water flowing from a subglacial lake 500 yards below Taylor Glacier in West Antarctica reveal that the microorganisms living there use a series of reactions with sulfate and ferric iron to “breathe” and metabolize the limited organic matter in this virtually oxygen-free environment. Similar reactions have been performed in laboratories, but no where else on Earth have such ecosystems been found. The scouring of the iron rich rocks by the massive ice sheets is thought to be the source of the nutrients that feed this life.

To see depictions of Antarctica’s subglacial lake networks and Lake Vostok, visit http://www.earthgauge.net/climate-facts-image-library#4. These images come from the National Science Foundation and are in the public domain.

Seasons: Winter, Spring, Summer, Fall

Sources: Grom, Jack. “Ancient Ecosystem Discovered Beneath Antarctic Glacier.” ScienceNOW Daily News 16 April 2009. Accessed Online 14 January 2010 and Bell, RE et al. “Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams.” Nature 445 (2007): 904-907 and Mikucki, JA et al. “A Contemporary Microbially Maintained Subglacial Ferrous ‘Ocean.’” Science 324 (2009): 397-400 and Christner, BC et al. “Limnological conditions in Subglacial Lake Vostok, Antarctica.” Limnology and Oceanography 51 (2006): 2485-2501.

Climate Fact: Antarctic Sea Ice

kraus — Wed, 13 Jan 2010 14:42:55 +0000

Much attention has been given to the decline of sea ice over the North Pole, which fell to a September minimum of 1.6 million square miles in 2007, about 40 percent below normal levels. On the other side of the world, the sea ice that extends from Antarctica’s continental ice sheets out over the ocean fluctuates between an average summertime (March) minimum extent of about 1.1 million square miles to an average of 6.9 million miles at the end of winter (September). In contrast to the Arctic ice, the average annual extent of the southern hemisphere ice has actually grown since the late 1970s at a rate of around one percent per decade. This trend has been linked to:

•   Ozone Depletion: The most pronounced rates of ozone depletion have occurred over Antarctica, where the ozone hole forms during the spring months. While the strong westerly winds that “trap” frigid air around the continent during winter make the ozone hole possible, the hole itself works as a feedback by accentuating the pressure difference between the continent and the mid-latitudes of the Southern Hemisphere. This works to strengthen the winds responsible for the ozone hole in the first place.
•   Wind Shifts: The accentuation of the pole to mid-latitude pressure difference linked to ozone depletion has deepened several of the continent’s low pressure zones, strengthening some of the winds that blow from the continent over the ocean during the autumn months. This has led to increases in sea ice over several of Antarctica’s coastal regions.
•   Freshwater on the Ocean Surface: Increased precipitation around Antarctica and melting of the glaciers that sit on the land have led to freshening of the ocean surface waters. This promotes ice formation.

Shifts in the winds have also caused decreases in sea ice extent in some areas of the continent – specifically parts of the Southern Ocean adjacent to the Indian Ocean and the Amundsen-Bellingshausen Sea sectors. These losses have been more than compensated for by gains in other areas.

Seasons: Winter, Spring, Summer, Fall

Source: Turner, J et al. “Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase in Antarctic sea ice extent.” Geophysical Research Letters 36 (2009): L08502.

Climate Fact: Antarctica’s Moisture Sources

kraus — Tue, 05 Jan 2010 21:35:41 +0000

Once water is evaporated from the ocean or a moist land surface, it may spend days traveling through the air. Complicated systems of winds at different levels of the atmosphere can transport moisture (as well as other gases and dust) from the point of origin to remote locations thousands of miles away. While about 30 percent of the moisture that rains or snows over Antarctica originates in the Southern Ocean close to the continent, the rest comes from latitudes north of 50 degrees South (about the same latitude as the southern tip of New Zealand). Ten percent comes from north of 30 degrees South (about the same latitude as Durban, South Africa). The higher elevations closer to the center of Antarctica have mean moisture origin sources north of 44 degrees South. During the summer, when there is less sea ice, more of Antarctica’s precipitation originates from the waters around the continent.

Seasons: Winter, Spring, Summer, Fall

Source: Sodemann, H and Stohl, A. “Asymmetries in the moisture origin of Antarctic precipitation.” Geophysical Research Letters 36 (2009): L22803.

Antarctica Climate Number: 300,000 Years

kraus — Tue, 05 Jan 2010 21:33:17 +0000

For the first half of the Cenozoic (the era spanning 65 million years ago to today), Earth was too warm to support ice sheets and sea levels were much higher than today. Then, about 34 million years ago, the Earth crossed a threshold. Over a period of about 300,000 years, the temperature dropped and ice sheets began to form on Antarctica. While most of the ice formed in the highlands of East Antarctica, some ice probably formed in West Antarctica, which is much closer to sea-level. The amount of ice on Antarctica has both grown and shrunk significantly over the past 34 million years, but the ice sheet covering East Antarctica has been relatively stable for about the past three million. The water in both ice sheets came from the ocean; as the ice sheets formed during this 300,000 year period, sea level fell by 220 feet, creating much more land area.

Seasons: Winter, Spring, Summer, Fall

Wilson, DS and Luyendyk, BP. “West Antarctic paleotopography estimated at the Eocene-Oligocene climate transition.” Geophysical Research Letters 36 (2009): L16302 and Katz, ME et al. “Stepwise transition from the Eocene greenhouse to the Oligocene icehouse.” Nature Geoscience 1 (2008): 329-334.

Antarctica Climate Number: 7.2 million cubic miles

kraus — Mon, 04 Jan 2010 15:11:48 +0000

Ninety (90) percent of Earth’s ice sits on top of Antarctica, a 5.4 million square mile continent. Virtually all of this area is covered by an ice sheet that can be three miles high with an average thickness of 1.24 miles, giving it an approximate total volume of 7.2 million cubic miles.

For Comparison: The amount of water in just one cubic mile of ice is equivalent to three days worth of discharge from the Mississippi River Delta. If all 7.2 million cubic miles of ice melted, enough water would flow into the oceans to raise sea levels by 275 feet!

Seasons: Winter, Spring, Summer, Fall

Source: ScienceDaily: Science Reference. “Antarctic Ice Sheet.” Accessed Online 4 January 2010

Climate Fact: Regional Snow Trends

espinoza — Mon, 21 Dec 2009 11:49:21 +0000

In Brief: Higher temperatures are reducing America’s snowfall, with a few regional exceptions.

Snow is not just an inhibitor of holiday travelers, nor is it just a passive product of prevailing weather conditions. Snow is a weather maker in and of itself. Snow-covered ground reflects far more of the sun’s radiation than it otherwise would and more reflection means lower temperatures at the surface. Because surface temperatures influence atmospheric circulation, understanding trends in snow and ice cover are crucial for effectively modeling weather and climate. Records indicate that as temperatures have risen, the southern margin where snow falls has moved north. This means that less snow is falling/accumulating in the mountains of the Western U.S., the Mid-Atlantic and the Kansas-Missouri regions. In the Western U.S., where 75 percent of year-round water sources originate from snow melt in the mountains, the trends have been particularly pronounced. Parts of the Northwest are receiving about half of the snowfall they received in the 1930’s. New England’s snowfall trends have been relatively flat. On the other hand, higher temperatures mean more moisture in the air. Regions such as the eastern side of the Rocky Mountains, particularly the eastern parts of Colorado and New Mexico, are now getting more snowfall as it is still cold enough for snow and there is more water in the air. The Great Lakes/northern Ohio Valley regions are also getting more snow, which is probably due to less ice cover on the Great Lakes. Less ice cover makes more lake effect snow possible.

(Source: Kunkel, KE et al. “Trends in Twentieth-Century U.S. Snowfall Using a Quality-Controlled Dataset.” Journal of Atmospheric and Oceanic Technology 26 (2009): 33-44.)

Climate Fact: Lake Effect Snow on the Upswing

espinoza — Mon, 21 Dec 2009 11:31:10 +0000

In Brief: Less ice cover on the Great Lakes is contributing to more snow regional lake effect snow.

Over much of the U.S., the 20th century warming trend means less snow and more rain. In most areas, the lack of cold limits snowfall, but this is not true in the Great Lakes region. Here, temperatures are below freezing throughout much of the year and it is lack of moisture that limits snowfall. Much of the moisture that makes up the region’s snow comes from the Great Lakes. As frigid winds from the Canadian interior pass over the relatively warmer waters of the Great Lakes, the cold air picks up moisture which is deposited as snow in areas downwind – a phenomenon termed “lake effect snow.” Two of these downwind areas rank as the third and fourth snowiest areas in the United States – Marquette, Michigan (180 inches annually) and Syracuse, NY (120 inches annually). Once the lakes freeze, however, there is no more exposed water and the moisture source disappears.

Throughout the region, lake effect snow levels have been increasing, a trend linked to warmer lakes with less ice. Since at least the 1970’s, ice cover on the Great Lakes has been declining.
Ice cover on Lake Superior, which has been warming by 1.2 degrees Fahrenheit per decade since 1985, used to cover on average 25 percent of the lake area but now covers less than 15 percent. Water temperatures in all of the lakes have been rising. October-April temperatures averaged over all the Lakes rose by one degree Fahrenheit between 1995 and 2000.
In Syracuse, NY, snowfall levels increased by 50 percent between 1913 and 2000.

(Source: Burnett, AW et al. “Increasing Great Lake-Effect Snowfall during the Twentieth Century: A Regional Response to Global Warming.” Journal of Climate 16 (2003): 3535-3542.)

Climate Trivia: Ice Melt and H-Bombs

kraus — Mon, 07 Dec 2009 15:47:36 +0000

Since at least 1960, more of Earth’s land glaciers have been shrinking than growing. As these glaciers shrink, they absorb heat from the atmosphere. To release the amount of energy that the glaciers have absorbed over the last 50 years, how many one-megaton hydrogen bombs would you need to detonate?

a)   200
b)   1000
c)   50,000
d)   200,000
e)   2,000,000

The correct answer is e. Two million hydrogen bombs worth of energy has melted ice that used to sit on our land surfaces. Today, that ice is in the oceans in liquid form.

Seasons: Winter, Spring, Summer, Fall

Source: Levitus, et al. “Anthropogenic Warming of Earth’s Climate System.” Science 292 (2001): 267-270.

Climate Number: 20 Teragrams

kraus — Mon, 30 Nov 2009 16:26:28 +0000

On average, about 20 trillion grams (20 teragrams) of dust are suspended in Earth’s atmosphere, where the dust particles stay for an average of 21 days. Dust is an important part of Earth’s climate – dust affects how clouds develop and how much sunlight reaches the Earth, which affects rainfall. The Dust Bowl of the 1930’s, which began due to lack of rainfall, was made worse by farming practices that released lots of dust into the air. Also, when dust lands on ice such as snow and glaciers, it makes these masses darker and more vulnerable to melting. On the other hand, dust deposits fertilize both land plants and ocean algae.

For Comparison: 20 teragrams weighs about as much as two million Boeing 757-200’s.

Seasons: Winter, Spring, Summer, Fall

Sources: Grini, A et al. “Model simulations of dust sources and transport in the global atmosphere: Effects of soil erodibility and wind speed variability.” Journal of Geophysical Research 110 (2005): D02205 and Painter, TH. “Where Deserts and Mountains Collide: The Implications of Accelerated Snowmelt by Disturbed Desert Dust.” U.S. National
Academy of Sciences, Washington, DC. 24 June 2009 and Hoerling, M et al. “Distinct causes for two principal U.S. droughts of the 20th century.” Geophysical Research Letters 36 (2009): L19708.

Climate Fact: Ice Mass Update

kraus — Mon, 09 Nov 2009 16:29:46 +0000

Two of the biggest ice masses on Earth are the Greenland and Antarctic ice sheets, which together hold more than 90 percent of Earth’s ice. These ice sheets, particularly the Antarctic ice sheet, help to keep the planet cool by reflecting the sun’s energy. As the Earth begins to warm, the ice melts, which works to exacerbate warming as bare rock and soil absorb more solar energy than ice does. The melting of these ice sheets has accelerated in recent years. Greenland’s ice sheet lost about 137 gigatons (one gigaton is one billion tons) of ice each year during the 2002 and 2003 melt seasons and lost 286 gigatons each year between 2007 and 2009. This accounts for about 0.09 mm of the 3.1 mm annual rise in global sea level. Antarctica’s ice sheet lost about 104 gigatons each year between 2002 and 2006, while it lost 246 gigatons each year between 2006 and 2009. This accounts for about 0.08 mm of the annual rise in global sea level.

Seasons: Spring, Summer, Fall

Source: Velicogna, I. “Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE.” Geophysical Research Letters 36 (2009): L19503.

Climate Fact: SST Changes with Latitude

kraus — Fri, 06 Nov 2009 16:18:01 +0000

In today’s modern Holocene climate, warm surface waters in the tropical oceans gradually transition into the near-freezing surface waters near the poles. During warmer periods of Earth’s distant past, this temperature gradient was far less pronounced. In the early Eocene epoch (56-53 million years ago), average annual temperatures in Siberia and Canada were about 65 degrees Fahrenheit (compared to 32 degrees today) and Earth had no permanent polar ice caps. During this time, there was little temperature difference between waters in the tropics and waters in the mid-latitudes and sub-polar regions. Waters in the sub-polar regions of the southern hemisphere were even warmer than the tropical waters of today – as high as 93 degrees Fahrenheit. Cooler waters could only be found at the poles, with the average annual surface temperature at the North Pole being around 73 degrees Fahrenheit. These high temperatures did not last and over the course of the next 20 million years the mid- and high latitudes cooled. By around 35 million years ago, permanent ice sheets had grown on Antarctica. Temperatures in the tropics, however, remained largely the same, giving us the latitudinal temperature contrasts that characterize today’s climate.

Seasons: Winter, Spring, Summer, Fall

Sources: Bijl, PK et al. “Early Palaeogene temperature evolution of the southwest Pacific Ocean.” Nature 461 (2009): 776-779 and Baez, J. “Temperature.” Department of Mathematics: University of California Riverside. 1 October 2006. Accessed Online 6 November 2009

Climate Fact: Lake Superior Stratification

kraus — Mon, 28 Sep 2009 15:36:03 +0000

During winter, Lake Superior’s cold water is on the surface and warm water is on the bottom; during summer, the opposite is the case. The “switchover” happens in the late spring or early summer and is an important event, as it “stirs” the water. This stirring brings nutrients (which feed the lake’s wildlife) from the depths of the lake to the surface. After the switchover, summertime stratification season begins. This period, when a layer of warm and relatively nutrient poor water covers the lake surface, occurs until another switchover happens in the fall. Over the past 30 years, the temperature around Lake Superior has increased by 2.4 degrees Fahrenheit and the water temperature in Lake Superior has risen by 5.3 degrees Fahrenheit. The relatively higher rate of temperature rise in the water is thought to be due to declining average winter ice cover, which fell by 11.3 percent over the same 30-year period. Open water absorbs more sunlight than ice does, resulting in greater warming. This creates a positive feedback cycle where warming leads to less ice and more warming. This warming has been linked to a longer summer stratification season – now 25 days (17 percent) longer than it was in the early 20th century.

Seasons: Winter, Spring, Summer, Fall

Source: Austin, JA and Colman, SM. “Lake Superior summer water temperatures are increasing more rapidly thanregional air temperatures: A positive ice-albedo feedback.” Geophysical Research Letters 34 (2007): L06604 and Austin, JA and Colman, SM. “A century of temperature variability in Lake Superior.” Limnology and Oceanography 53 (2008): 2724-2730.

Climate Fact: Pacific Brants and Climate Shifts

kraus — Fri, 11 Sep 2009 15:56:03 +0000

The rich waters in Alaska’s Arctic and sub-Arctic estuaries provide the Pacific Brant, a small goose that travels in flocks of as many as 500 birds, with a steady supply of eelgrass (its principle food source) during the summer months. Traditionally (before the late 1970’s), almost 90 percent of the population would spend their summers in Alaska, retreating south to Mexico during the fall and winter months. Since the North Pacific “regime shift” of 1976-1977, a phenomenon that featured noticeable changes in ocean circulation and species distributions/concentrations, the waters in the North Pacific and Bering Sea have been warming. In Alaska, this warming has corresponded to more eelgrass and more favorable conditions for the birds. The regime shift has also corresponded to weakening of the Aleutian Low, the low pressure center that lies near the Aleutian Islands. As the low has weakened, the number of days each autumn when there are favorable tail winds for the migration has decreased. These trends may account for the increase in the number of Pacific Brants spotted in Alaska during the winter. Counts before 1977 would rarely detect more than 3,000 birds. In recent years, the counts have found as many as 40,000 birds.

To view and download a public domain image of a Pacific Brant family, visit the United States Geological; Survey: http://gallery.usgs.gov/photos/09_09_2009_hlc5Fsq11Y_09_09_2009_0.

Seasons: Fall, Winter

Source: U.S Department of Interior, U.S. Geological Survey. “Opting Out of Migration: As Climate Warms, Arctic-Nesting Geese Elect to Winter in Alaska Instead of Mexico.” 9 September 2009. Accessed Online 11 September 2009

Climate Fact: Spring Snowmelt in the West

kraus — Wed, 26 Aug 2009 16:19:07 +0000

About 75 percent of the West’s water resources originate in snowpack. Most precipitation in the region occurs during the winter, the period of the year when the reservoirs are replenished after the dry summer and early fall months. The reservoirs are at their high points in the spring. Traditionally, snowpack would last into the late spring and summer months, and not overwhelm the already full reservoirs in the early to mid-spring. Since the 1950’s however, there has been a steady trend of earlier snowmelt across the West, causing the rivers to start their spring snowmelt “pulse” sooner. If the rivers peak too soon, in order to keep the dams from breaking water from the reservoirs must be discharged instead of being conserved for the summer months. In some parts of the West, the average date of the start of the spring streamflow “pulse” is now happening over 20 days earlier than it did in the 1950’s.

To see how spring snowmelt timing has changed in your local area since the 1950’s, visit http://www.earthgauge.net/climate-facts-image-library#9. This image is featured in the “Global Climate Change Impacts in the United States” report recently published by the U.S. Global Change Research Program. The image is in the public domain.

Seasons: Spring

Source: Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson,(eds.). Cambridge University Press, 2009