Earth’s AlbedoELF Activity: Energy 1D

http://andrill.org/education/elf_activities_1D.html

As part of NOAA Environmental Literacy Grant #NA09SEC490009 to the University of Nebraska–Lincoln'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.

A continuous stream of sunlight bathes the Earth’s surface. Annually, averaged across the top of the Earth’s 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.

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 Earth’s surface, without altering the Earth’s 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.

Clouds, dust, and other particles in the atmosphere reflect about 23.2% of the incoming radiation.

6.7% is reflected by the Earth’s surface.

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

Albedo 1.0

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.

Earth’s Average Albedo

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.

Land Surface Type

Color Albedo(percent reflected)

Taiga & Boreal Forest 20%

Deserts and Shrubland

30%

Inland Water 10%

Coniferous Forest 10%

Deciduous Forest 20%

Grassland 20%

Ocean 10%

Tundra 20%

Ice and Snow 80%

Map of Generalized Land Surface Types

Snow- and Ice-Covered Regions of Earth

Snow and ice have a high albedo. They reflect incoming sunlight, keeping the planet cool.

Source: University of Idaho, College of Sciences

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

Artis Rams/iStockSnow 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

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

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).

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).

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?

This material is based on work supported by an Environmental Literacy Grant from the National Oceanic and Atmospheric

Administration’s 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.http://andrill.org/education/elf/activities