References - Is Global Warming breaking up the Integrity of the Permafrost? http://methane-hydrates.blogspot.com/2013/05/is-global-warming-breaking-up-the-integrity-of-the-permafrost.html - Noctilucent clouds indicate more methane in upper atmosphere http://arctic-news.blogspot.com/2012/09/noctilucent-clouds-indicate-more-methane-in-upper-atmosphere.html - Noctilucent Clouds Get an Early Start http://science.nasa.gov/science-news/science-at-nasa/2013/07jun_nlcs - Aeronomy of Ice in the Mesosphere (AIM) sate