Earths Albedo ELF Activity: Energy 1D
http://andrill.org/education/elf_activities_1D.html As part of NOAA
Environmental Literacy Grant #NA09SEC490009 to the University of
NebraskaLincoln's, ANDRILL Science Management Office. This material
is based on work supported by an Environmental Literacy Grant from
the National Oceanic and Atmospheric Administration's Office of
Education (NA0909SEC4690009) and prior work supported by the
National Science Foundation under Grants ANT-0342484 and
ESI-0632175. Any opinions, findings, and conclusions or
recommendations expressed in these materials are those of the
authors and do not necessarily reflect the views of the NOAA or the
NSF. Slide 2 A continuous stream of sunlight bathes the Earths
surface. Annually, averaged across the top of the Earths
atmosphere, the incoming solar radiation is equal to 342 watts of
energy per square meter. This sunlight provides the energy needed
to warm the Earth to a habitable temperature, support life, power
our weather, and drive ocean currents. This solar energy makes our
planet the just right temperature for life as we know it. Slide 3
Fortunately, not all the incoming sunlight is absorbed by the Earth
system, or our just right planet would be too hot for life.
Globally, approximately 30% of the incoming radiation is reflected
back into space, by clouds and the Earths surface, without altering
the Earths temperature. This is important because the reflection of
a portion of the incoming radiation helps to keep the planet in
energy equilibrium, keeping the planet at a stable temperature of
approximately 15 C. Slide 4 Clouds, dust, and other particles in
the atmosphere reflect about 23.2% of the incoming radiation. 6.7%
is reflected by the Earths surface. Slide 5 Albedo is defined as
the amount a surface reflects. Albedo is derived from the Latin
word "albus" for white. All visible objects reflect some amount of
light. The amount of light reflected depends on the color and
texture of the object. The albedo of an object is a measure of how
much energy it reflects. The number is expressed as an index on a
scale of 0 to 1, with 0 being the lowest albedo and 1.0 the
highest. A pure black substance will have an albedo of 0 (absorbing
most of the radiation and reflecting very little) and a highly
reflective material will have an albedo of 1. If you have ever
walked barefoot on a black driveway in the summer, you know which
surface absorbs the most solar energy. Albedo 0.0 Albed o 1.0 Slide
6 In the albedo image above, white shows areas where the highest
percentage of the solar radiation is reflected by the Earth. Dark
blue shows areas where the lowest percentage of solar radiation is
reflected by the Earth. Notice how the highest albedo values are in
regions where Earth is mostly covered by snow and ice, or clouds,
or both. The lowest albedo values occur in forest- covered
landscapes or open ocean. Earths Average Albedo Slide 7 Grasslands,
forests, oceans, deserts, snow, ice, and even cities all reflect,
absorb, and radiate solar energy. The range of albedos on Earth can
be as low as 0.3 (3%) for water (when the sun is directly overhead)
and as high as 0.9 (95%) for fresh snow cover. Slide 8 Land Surface
TypeColorAlbedo (percent reflected) Taiga & Boreal Forest20%
Deserts and Shrubland30% Inland Water10% Coniferous Forest10%
Deciduous Forest20% Grassland20% Ocean10% Tundra20% Ice and Snow80%
Slide 9 Map of Generalized Land Surface Types Slide 10 Snow- and
Ice-Covered Regions of Earth Slide 11 Snow and ice have a high
albedo. They reflect incoming sunlight, keeping the planet cool.
Slide 12 SOURCE: University of Idaho, College of Sciences Slide 13
The Arctic is warming at almost twice the rate of the rest of the
world. In many areas, the mountains are warming faster than the
lowlands. How will warming temperatures affect snow and ice?
Difference in 2001-2005 average temperature distribution compared
with the 1951-1980 mean temperature distribution. Climate Change
Impacts on Snow and Ice Slide 14 Artis Rams/iStock Snow influences
climate because of its insulating properties and because it
reflects sunlight. Warming temperatures are causing melting of snow
and ice in the Northern Hemisphere, especially in the Arctic.
Similar impacts are observed in parts of the Southern Hemisphere,
especially the Antarctic Peninsula. (See previous slide.) SNOW
Slide 15 Decreasing Snow Cover Snow cover has declined in the
Northern Hemisphere, especially in spring and summer. Mean monthly
snow cover is decreasing by about 1.3% per decade. Northern
Hemisphere Spring Snow Slide 16 Snow is also melting earlier in the
spring, increasing the snow-free period in the Arctic regions. As
the length of the snow-free seasons increase, there is also a
longer period when the boreal forest (taiga) is exposed, thereby
changing (decreasing) its average albedo. This change may
significantly alter the overall planetary albedo, causing even
further warming (positive feedback effect). Slide 17 Snow Outlook
for the Future Yellow to red is less snow Blue is increased snow
The snow line (minimum elevation for snow cover in the mountains)
is projected to rise in many mountain areas. Major reductions in
snow cover are projected for mid- latitudes by the end of the this
century (2100). Slide 18 In this activity, students will calculate
the average albedo of Earth surfaces (land surface types, see
slides 8 and 9). After the experiment, have students discuss what
would happen to the temperature of the planet if there were less
snow and ice. How would this affect the climates of different
regions of our planet? Slide 19 This material is based on work
supported by an Environmental Literacy Grant from the National
Oceanic and Atmospheric Administrations Office of Education
(NA09SEC4690009) and prior work supported by the National Science
Foundation under Grants ANT-0342484 and ESI-0632175. Any opinions,
findings, and conclusions or recommendations expressed in these
materials are those of the authors and do not necessarily reflect
the views of the National Oceanic and Atmospheric Administration or
the National Science Foundation.
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