Related by context. Frequent words. (Click for all words.) 68 permafrost 58 methane hydrates 58 methane hydrate 57 Permafrost 57 marine sediments 57 icecaps 56 gas hydrates 55 peat bogs 53 polar caps 53 melting permafrost 53 Greenland Ice 52 Weddell Sea 52 glacial ice 51 Antarctic ice 51 icecap 50 sedimentary rock 50 polar regions 50 geological formations 50 glaciers 50 meltwater 50 Arctic tundra 50 Melting ice 49 peat bog 49 lake sediments 49 retreating glaciers 49 glaciation 49 Arctic Ocean 49 Arctic 49 polar ice 49 terrestrial ecosystems 49 Sediments 49 melting ice 49 mountain glaciers 48 hydrological cycle 48 boreal forests 48 greenhouse warming 48 Greenland ice 48 glacier melt 48 seabed 48 Earth crust 48 Greenland glaciers 48 arctic 48 Quaternary 48 boreal forest 48 glacier 48 oceanic crust 48 methane 48 oceans 48 boreal 48 sediment cores 48 glacial 47 melting glaciers 47 geologic formations 47 Microorganisms 47 sediments 47 protective ozone layer 47 Antarctica 47 Seed Vault 47 atmospheric CO2 47 underground caverns 47 landmasses 46 volcanism 46 glacial lakes 46 ocean acidity 46 stratospheric ozone 46 gigatons 46 shrinking glaciers 46 glacial melt 46 lithosphere 46 atmospheric carbon dioxide 46 glacial till 46 biodiversity hotspots 46 ozone depletion 45 middens 45 species extinctions 45 seafloor 45 crustal 45 atmospheric concentrations 45 glaciologists 45 Greenland 45 peatlands 45 equatorial regions 45 icebound 45 biosphere 45 regolith 45 earth crust 45 moon Europa 44 tundra 44 melting 44 Antarctic 44 subtropical regions 44 geologic 44 Spitsbergen 44 Saturn moon Enceladus 44 Glaciers 44 subsurface 44 Antarctic Ice 44 Little Ice Age 44 interglacial 44 peridotite 44 Arctic seabed