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Albedo - 0 views

  • When an object reflects most of the light that hits it, it looks bright and it has a high albedo.
    • zacmah
      snow has these qualities.
  • When an object absorbs most of the light that hits it, it looks dark.
    • zacmah
      water (melting snow) has these qualities

Albedo - Wikipedia, the free encyclopedia - 0 views

  • The albedo of an object is the extent to which it reflects light, defined as the ratio of reflected to incident electromagnetic radiation.
    • ttelesnicki3
      this is a good definition for albedo...
  • In climatology it is sometimes expressed as a percentage
  • Albedos of typical materials in visible light range from up to 90% for fresh snow, to about 4% for charcoal, one of the darkest substances.
  • ...4 more annotations...
    • zacmah
      ocean absorbs heat; when ice caps melt they increase the ocean's volume and warm the Earth.
  • a distance, the ocean surface has a low albedo, as do most forests,
  • The classic example of albedo effect is the snow-temperature feedback. If a snow covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase.
    • zacmah
      happening in the Arctic
  • Human activities have changed the albedo
    this is a good definition

Albedo of the Earth - 0 views

  • For example, the albedo of the Earth is 0.39

Albedo - Encyclopedia of Earth - 0 views

  • Albedo is known as surface reflectivity of sun’s radiation. The term has its origins from a Latin word albus, meaning “white”. It is quantified as the proportion, or percentage of solar radiation of all wavelengths reflected by a body or surface to the amount incident upon it. An ideal white body has an albedo of 100% and an ideal black body, 0%. The typical amounts of solar radiation reflected from various objects are shown in Table 1. Albedo values can range between 3% for water at small zenith angles to over 95% for fresh snow. On average the Earth and its atmosphere typically reflect about 4% and 26%, respectively, of the sun’s incoming radiation back to space over the course of one year. As a result, the earth-atmosphere system has a combined albedo of about 30%, a number highly dependent on the local surface makeup, cover, and cloud distribution.
    • ttelesnicki3
      albedo: a percent that shows how much of the sunds radiation is reflected off an object
      white: 100%
      black: 0%

Global Warming - Crystalinks - 0 views

  • Greenhouse gases in the atmosphere

    The atmospheric concentrations of carbon dioxide and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that carbon dioxide values this high were last attained 40 million years ago. About three-quarters of the anthropogenic emissions of carbon dioxide to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation.

    The longest continuous instrumental measurement of carbon dioxide mixing ratios began in 1958 at Mauna Loa. Since then, the annually averaged value has increased monotonically from 315 ppmv as shown by the Keeling Curve. The concentration reached 376 ppmv in 2003. South Pole records show similar growth. The monthly measurements display small seasonal oscillations.

    Methane is produced biologically and released from gas pipelines. Some biological sources are "natural" such as termites and others are attributable to human activity such as agriculture, e.g., rice paddies. Recent evidence suggests that forests may also be a source (RC; BBC). Note that this is a contribution to the natural greenhouse effect, and not to the anthropogenic greenhouse effect (Ealert).

  • Adding carbon dioxide (CO2) or methane (CH4) to an atmosphere, with no other changes, will tend to make a planet's surface warmer; greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 30 °C lower, and the Earth uninhabitable.
    Talks about Greenhouse gases and how they affect the atmosphere (carbon dioxide and methane)

Greenhouse Effect - Crystalinks - 0 views

  • The Natural Greenhouse Effect

    The earth receives an enormous amount of solar radiation. Just above the atmosphere, the solar power flux density averages about 1366 watts per square meter, or 1.740×1017 W over the entire Earth. This figure greatly exceeds the power generated by human activities. The difference between the natural greenhouse effect and global warming is that- global warming is anthropogenic whereas greenhouse effect is not.

    The solar power hitting Earth is balanced over time by an equal amount of power radiating from the Earth (as the amount of energy from the Sun that is stored is small). Almost all radiation leaving the Earth takes two forms: reflected solar radiation and thermal black body radiation.

    Reflected solar radiation accounts for 30% of the Earth's total radiation: on average, 6% of the incoming solar radiation is reflected by the atmosphere, 20% is reflected by clouds, and 4% is reflected by the surface.

    The remaining 70% of the incoming solar radiation is absorbed: 16% by the atmosphere (including the almost complete absorption of shortwave ultraviolet over most areas by the stratospheric ozone layer); 3% by clouds; and 51% by the land and oceans.

    This absorbed energy heats the atmosphere, oceans, and land and powers life on the planet. It should be noted that the surface of the Earth is in constant flux with daily, yearly and age long cycles and trends in temperature and other variables for a variety of causes; thus these percentages apply on average only.

    Like the Sun, the Earth is a thermal radiator. Because the Earth's surface is much cooler than the Sun (287 K vs 5780 K), Wien's displacement law dictates that Earth radiates its thermal energy at longer wavelengths than the Sun. While the Sun's radiation peaks at a visible wavelength of 500 nanometers, Earth's radiation peak is in the longwave (far) infrared at about 10 micrometres.

    The Earth's atmosphere is largely transparent at visible and near-infrared wavelengths, but not at 10 micrometres (this is, probably, not entirely coincidental: the transparency to "visible" wavelengths makes eyes adapted to seeing these wavelengths useful; and eye that could see in a strongly-absorbed wavelength would not be so useful).

    Only about 6% of the Earth's total radiation to space is direct thermal radiation from the surface. The atmosphere absorbs 71% of the surface thermal radiation before it can escape. The atmosphere itself behaves as a radiator in the far infrared, so it re-radiates this energy.

    The Earth's atmosphere and clouds therefore account for 91.4% of its longwave infrared radiation and 64% of Earth's total emissions at all wavelengths. The atmosphere and clouds get this energy from the solar energy they directly absorb; thermal radiation from the surface; and from heat brought up by convection and the condensation of water vapor.

    Because the atmosphere is such a good absorber of longwave infrared, it effectively forms a one-way blanket over Earth's surface. Visible and near-visible radiation from the Sun easily gets through, but thermal radiation from the surface can't easily get back out. In response, Earth's surface warms up.

    The power of the surface radiation increases by the Stefan-Boltzmann law until it (over time) compensates for the atmospheric absorption. Another, simpler, but essentially equivalent way of looking at this is that the surface is heated by two sources: direct solar radiation, and thermal radiation from the atmosphere; it is thus warmer than if heated by solar radiation alone.

    The result of the greenhouse effect is that average surface temperatures are considerably higher than they would otherwise be if the Earth's surface temperature were determined solely by the albedo and blackbody properties of the surface.

  • The greenhouse gases

    Water vapor (H2O) causes about 60% of Earth's naturally-occurring greenhouse effect. Other gases influencing the effect include carbon dioxide (CO2) (about 26%), methane (CH4), nitrous oxide (N2O) and ozone (O3) (about 8%). Collectively, these gases are known as greenhouse gases. The greenhouse effect due to carbon dioxide is specifically known as the Callendar effect.

  • There has been an observed global average temperature increase of about 0.5oC since 1960 (Science 308, 1431, 2005). There is still some public controversy about the role of human activities and that of CO2 and other greenhouse gas increases for global warming.
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  • The average surface temperature would be "-18ƒC if the atmosphere played no role. In reality this temperature is closer to 15ƒC above zero due to the combination of the greenhouse effect and the convective flow of heat energy within the atmosphere.
    This page explains the natural Greenhouse effect and talks about radiation from Earth. It also includes the term albedo.

Latitude - Wikipedia, the free encyclopedia - 0 views

shared by sulaiman on 23 Nov 07 - Cached
  • Latitude, usually denoted symbolically by the Greek letter phi, \phi\,\!, gives the location of a place on Earth north or south of the equator.
  • Lines of Latitude are the horizontal lines shown running east-to-west on maps.
sulaiman - 0 views


Longitude - Wikipedia, the free encyclopedia - 0 views

shared by sulaiman on 23 Nov 07 - Cached
  • Longitude is the east-west geographic coordinate measurement most commonly used in cartography and global navigation.

  • A line of longitude is a meridian and half of a great circle.

  • Unlike latitude, which has the equator as a natural starting position, there is no natural starting position for longitude.
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