Heat // Current TV

Greenland's ice is growing darker

In the past, the bright surface of the Greenland Ice Sheet reflected well over half of the sunlight that fell on it. This reflectiveness helped keep the ice sheet stable, as less absorbed sunlight meant less heating and melting. In the past decade, however, satellites have observed a decrease in Greenland’s reflectiveness. This darker surface now absorbs more sunlight, which accelerates melting.

The map above shows the difference between the amount of sunlight Greenland reflected in the summer of 2011 versus the average percent it reflected between 2000 to 2006. Virtually the entire ice sheet shows some change, with some areas reflecting close to 20 percent less light than a decade ago. The map is based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Terra and Aqua satellites. It was produced as part of the National Oceanic and Atmospheric Administration’s Arctic Report Card.

Climate scientists have long expected that Earth’s polar regions will become less reflective as global temperatures rise. Rising temperatures melt snow and ice, and the uncovered terrain—water, vegetation, bare ground—is darker and absorbs more sunlight. The loss of reflectiveness then amplifies the initial warming.

Most of the patterns on the map fit expectations. Warmer, lower-elevation areas of the ice sheet have darkened more than the colder, higher-altitude interior. Each summer, winter snow retreats from the edge of the ice sheet. Dark pools of melt water form on the surface of the ice, and windblown dust and other particles also collect near the surface, making it even less reflective.

But the darkening in the interior is just as remarkable as the changes at the margins, according to Jason Box of Ohio State University, who analyzed the reflectiveness data. The interior is the high point of the ice sheet, nearly two miles above sea level, and there is no visible melting in the summer. So why is the area becoming darker?

The darkening, says Box, is due to changes in the shape and size of the ice crystals in the snowpack. As temperatures rise, snow grains clump together and reflect less light than the many-faceted, smaller crystals (see lower image from a scanning electron microscope). Additional heat rounds the sharp edges of the crystals, and round particles absorb more sunlight than jagged ones.

More at the linkIn the past, the bright surface of the Greenland Ice Sheet reflected well over half of... more

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Sunless solar cells could make energy from anything hot

Photovoltaic cells that convert heat, not sunlight, to electricity may turn out to be the solution for capturing all the energy we waste through heat.

Photovoltaic cells are best known for turning sunlight into electrical power--and they're big business. But did you know that there's a type of PV cell that eats heat instead of light to make power? It could replace the Li-ion battery in your cell phone, and it may also be used to scavenge waste heat from almost anything that normally dumps it into the environment, from your TV's electronics to your car's engine (even an electrical one).

Thermal PV tech has been around ages, and works the same way as the solar variation: Incoming radiation excites the atoms in its semiconductor structure, which then push electrons out--generating current. And much as is the case for solar PV cells, the advances in the tech have all been about improving their efficiency. Scientists at MIT have recently honed this tech, pushing the efficiency up so far that thermal PV cells are now a viable alternative to all sorts of other tech. MIT's breakthrough was to add a layer of tungsten to the front of a PV cell, with a surface that's been etched on a nanoscopic scale so that when heated it emits infrared light (heat) at wavelengths precisely tuned to the best efficiency of the PV cell behind it.

Right now, MIT is building the tech into tiny silicon micro-reactors. These are tiny furnaces that burn butane to generate heat, and then extract the heat to produce electricity. If that sounds convoluted, then this will impress you: The microreactors are small enough to replace the button cell Li-ion batteries you find in devices like watches, and convert the chemical ingredients that make them tick with three times better efficiency than Li-ion can match. Better yet, when they run out of fuel you simply snap in an extra cartridge of butane to recharge them.

But because MIT's system is so very efficient, and is based on a material that's not too rare or expensive, it could be used to build fuel-less heat-scavenging units that are stuck inside all sorts of devices to recover the wasted heat energy that nearly every machine we've ever made kicks out (thanks to the lovely laws of physics). How about the hot back of your TV? Or the hot chassis of the electric motor in your Nissan Leaf? Let's get fanciful and imagine it would be possible to claw back a few milliwatts of energy from the hot shower water you simply let run down the drain.

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