The Earth is constantly hit by solar radiation.
That radiation is the driving force for life on Earth.
However, not all of the radiation that reaches the Earth is absorbed.
In fact, the Earth's ability to reflect a portion of the solar radiation is vital
to sustain the balance that allows life as we know it to thrive.
The fraction of solar radiation a surface reflects
is called its "albedo." An albedo of 1 means that
100% of incoming radiation is reflected. An albedo of 0
means that 0% of incoming radiation is reflected and all of it
is absorbed. On sunny days, you may have noticed that if you walk
barefoot on dark asphalt, it burns your feet more than the lighter concrete.
This is because the dark surface of the black asphalt has a lower albedo
than the lighter-colored concrete. It absorbs more of the incoming radiation and
is much warmer as a result.
Surfaces throughout the Earth have different albedos. NASA is able to measure these differences
with many instruments, including those on the Aqua satellite. These measurements
can tell scientists essential information about the Earth's environment.
Snow-covered ice in the polar regions has a high albedo.
It reflects the majority of incoming radiation, which helps to cool the Earth.
As the Earth's temperature rises with the increase in greenhouse gases,
sea ice in the polar regions can be expected to retreat.
This replaces an ice surface with a water surface, which has a much lower
albedo. This causes more energy to be absorbed, and accelerates the warming
process. The low albedo of dark
green vegetation allows it to absorb sunlight and use it in photosynthesis,
a fundamental process necessary to bring energy into the biosphere.
Satellite imagery helps scientists to see how the albedo of these areas
changes over time, through both natural processes and human alteration.
As we move from rural to urban areas, many factors change,
including the albedo. This causes urban areas to generally be
warmer than their surroundings, a phenomenon known as the "urban heat island effect."
Understanding albedo can lead to suggestions to help reduce
this effect. One possibility would be to paint roofs white in hot regions,
thereby reflecting solar radiation. Though it may not
feel like it's affecting you directly, abledo is critical to the climate of the
entire planet. By measuring and understanding albedo, we can see how our environment
is changing in response to our alterations and how it may impact the
relationship between solar radiation and the Earth.