As permafrost thaws, the land, atmosphere, water resources, ecosystems, and human communities are affected. Coastal areas and hillsides are vulnerable to erosion by thawing of permafrost.  Thawing permafrost also causes a positive feedback to global warming, as carbon trapped within the once-frozen soils is released as <a href="/physical_science/chemistry/methane.html&edu=elem">methane</a>, a powerful <a href="/earth/climate/cli_greengas.html&edu=elem">greenhouse gas</a>.
Watch the NBC Learn video - <a href="/earth/changing_planet/permafrost_methane_intro.html&edu=elem">Thawing Permafrost and Methane</a> to find out more.<p><small><em>Image courtesy of the    USGS</em></small></p>Anti-crepuscular rays are beams of sunlight that appear to converge on a point opposite the sun. They are similar to crepuscular rays, but are seen opposite the sun in the sky. Anti-crepuscular rays are most frequently visible near sunrise or sunset. This photo of anti-crepuscular rays was taken at sunset in Boulder, Colorado. Crepuscular rays are usually much brighter than anti-crepuscular rays.<p><small><em> Image Courtesy of Carlye Calvin</em></small></p>A near-Earth <a href="/our_solar_system/asteroids.html&edu=elem">asteroid</a> - named 2012 DA14 by astronomers - passed within 17,200 miles from Earth on February 15, 2013. On closest approach at about 1:25 p.m. CST on February 15, although it was within the orbit of the <a href="/earth/moons_and_rings.html&edu=elem">Moon</a> and even geosynchronous <a href="/space_missions/satellites.html&edu=elem">satellites</a>, it didn't strike Earth!  Find out more from <a href="">NASA</a>! Fragments of a meteorite hit Chelyabinsk, Russia on 2/15/2013 <a href="">injuring over 500</a>. Learn about <a href="">meteors and meteorites</a>.<p><small><em>NASA/JPL-CalTech</em></small></p>Greenland's <a href="">ice sheet</a> saw a record <a href="">melt</a> in July 2012.  Scientists studying this event have found that this melting event was triggered by an influx of unusually warm air and amplified by the presence of a blanket of thin low-level <a href="">clouds</a> which pushed temperatures up above freezing.  For more information see the <a href="">press release</a> from the University of Wisconsin Madison.<p><small><em>Image courtesy of University of Wisconsin-Madison</em></small></p>This historic image is the first ever taken from a spacecraft in orbit about <a href="/mercury/mercury.html&edu=elem">Mercury</a>, the innermost planet of the solar system.  Taken on 3/29/2011 by <a href="/space_missions/robotic/messenger/messenger.html&edu=elem">MESSENGER</a>, it shows numerous craters across the <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=elem">surface</a> of the planet.  Temperatures there can reach over 800F because Mercury is so close to the Sun and rotates so slowly.  MESSENGER entered orbit around Mercury earlier in March 2011.<p><small><em>NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington</em></small></p>A <a href="">study</a> of over 40,000 written entries in Irish Annals and ice core measurements shows a strong correlation between <a href="">volcanic eruptions</a> and extreme cold weather in Ireland over a 1200 year period, from 431 to 1649.  During this time up to 48 volcanic eruptions were identified in Greenland ice core records through deposition of volcanic sulfate in annual layers of ice. Find out more about <a href="">volcanoes and climate</a>.<p><small><em>Image Courtesy of Marco Fulle</em></small></p>

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