"The view of Earth from space is famously familiarbright blue ocean, swirling gyres of white clouds, touches of terrestrial green. The luminosity of this image is the result of the sun's rays shining on the planet, where they're either reflected or absorbed by materials on Earth's surface and in our atmosphere. But a new study that examined Earth's overall brightness reveals that something eerie is happening to that familiar picture."
"Scientists measure the planet's brightness by factoring in how much light reaches earth and how much is reflected back out to space (as measured by orbiting satellites). This reflectivity is known as albedo, and Earth's overall albedo has been decreasing for decades. But according to a new study published recently in Proceedings of the National Academy of Sciences USA, that change isn't uniform: the Northern Hemisphere is getting even darker than its southern counterpart."
Measurements of incoming sunlight and outgoing longwave radiation over a 24-year period indicate that Earth's reflectivity (albedo) has declined overall, with the Northern Hemisphere darkening more than the Southern. Multiple satellite datasets were combined with high-resolution spectral imagers, snow and cloud maps, and climate models to assess spatial and temporal changes. Reduced polar ice, changes in surface properties, and cloud cover contribute to decreased reflectivity. The uneven loss of brightness in the Northern Hemisphere may amplify regional warming and disrupt atmospheric circulation, potentially throwing weather systems out of balance.
Read at www.scientificamerican.com
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