November 20 2015

Reflecting on Reflection: Suomi NPP Instruments Aid Monitoring of Earth's Albedo

monthly map from VIIRS
Global Monthly Albedo Map of July 2015, derived from JPSS VIIRS granule albedo product.
Albedo—it’s more than just a fancy word to describe the reflectivity of the Earth. It’s an important, albeit complex, factor affecting our climate—and the NOAA/NASA Suomi NPP satellite is helping scientists monitor it.

Reflecting on Reflection

As part of their work to understand why global temperatures are rising and how carbon dioxide and other greenhouse gases affect are changing the climate system, scientists regularly monitor Earth’s energy budget to determine how much of the sun’s energy is absorbed by the earth and how much is lost to space.

Approximately one-third of the sun’s energy that reaches Earth is reflected back into space by clouds and the atmosphere. The remaining two-thirds is absorbed by the land, ocean, and atmosphere. But how much energy these surfaces absorb varies.

albedo rise and fall
As noted above, global albedo rose and fell in different years, but did not necessarily head in either direction for long.
Light-colored surfaces, such as the Arctic and deserts, reflect more solar energy, whereas darker surfaces, such as the deep ocean and forested areas, reflect less. These varying rates of absorption and reflection can affect temperature.

Scientists measure the albedo of Earth’s various surfaces on a scale of 0 to 1, with 0 being a completely non-reflective black surface and 1 being a completely non-absorbing white surface.

Satellite measurements across the various surfaces have been accumulated since the late 1970’s. Based on this data, scientists say Earth’s albedo is about .3, but it varies throughout the year, as a variety of natural and human-caused phenomena can cause Earth’s albedo to fluctuate.

ice sheet in greenland
In this satellite image of southern Greenland, the ice sheet is more reflective than either the land exposed along the coast line. Credit: NOAA
For example, ice has a higher albedo than vegetation, soil or water. This means that as the ice expands, more solar radiation is reflected to space and less is absorbed by the surface causing temperatures to decrease. Cooler temperatures lead to increased ice formation, more reflection of solar radiation back to space, and even cooler temperatures (thereby creating what’s known as a positive feedback).

But this can work in the opposite direction, too. Once ice begins to melt and uncover land or water, more solar radiation will be absorbed by the surface, raising temperatures and causing even more ice to melt.

Other phenomena, including cloud cover, human activity (e.g. afforestation and deforestation), and airborne particles (such as those from pollution, volcanoes, and dust storms), can alter albedo as well, often on timescales ranging from days to years.

Nevertheless, despite these periodic fluctuations, scientists say no sustained shifts, either up or down, have occurred—yet.

Instruments Provide Insight

How will scientists know if a change in Earth’s albedo is something more than short-term fluctuation? By having access to long-term environmental data records, which is precisely what the instruments on Suomi NPP and future Joint Polar Satellite System satellites will provide.

The satellite’s CERES instrument provides data on Earth’s Radiation Budget to help scientists study the effect clouds have on the planet’s energy balance. CERES data also helps assess the radiative effects and climatic impact of natural disasters like volcanic eruptions, major floods and droughts.

“How this [balance] changes over time is critical because in a climate system that’s in equilibrium, [absorption and reflection] should balance and, if they do, then temperatures will remain relatively constant with time,” said Norman Loeb, Cloud and Earth Radiant Energy System (CERES) principal investigator at NASA’s Langley Research Center, in a video about tracking Earth’s heat balance. “When you add greenhouse gasses such as carbon dioxide and methane, you change that radiation balance at the top of the atmosphere; you reduce the amount of outgoing radiation, so that imbalance means that more energy is in the system. Part of it is stored in the oceans and part of it goes into warming the earth.”

This CERES data can be combined with the satellite’s Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, which provides high-resolution imagery across all wavelengths of light, to produce a better understanding of how the land, oceans, and atmosphere influence Earth’s albedo.

The long term data record provided by these instruments will provide a basis for scientific understanding of climate variations and trends.

"Earth’s albedo fluctuates markedly over short time periods due to natural variations in the climate system,” said the Langley Research Center’s Loeb. "To confidently detect changes in Earth’s albedo above natural variability, a much longer record is needed. It is paramount that we continue … observations as long as possible.”

NOAA's JPSS-1, the second spacecraft within NOAA's next generation of polar-orbiting satellites, will contribute to continuity of these measurements following its launch in early 2017.

To see recent Global Land Surface Albedo data from Suomi NPP, visit the NOAA website at http://www.star.nesdis.noaa.gov/jpss/EDRs/products_Albedo.php. To learn more about the Suomi NPP satellite, visit www.jpss.noaa.gov.