Nowhere is global warming having as obvious an impact as in the Arctic, and people living in Alaska, northern Canada, northern Scandinavia and Siberia have front-row seats. Some experts say that temperatures in these regions have risen by 3˚ to 5˚F over the past 30 years. And the temperature in the Arctic has warmed at twice the global average rate in the past century, according to the 2007 Intergovernmental Panel on Climate Change (IPCC) report. Permafrost is ground that maintains a temperature below freezing for at least two years. In some areas, that frozen layer is thawing, causing roads to collapse, runways to crack, and homes to sink, split apart, or even fall into the sea. But inside that icy ground is a threat more dangerous than crumbling infrastructure: massive amounts of greenhouse gases that, if released into the atmosphere, have the potential to quickly intensify climate change.