Related by context. Frequent words. (Click for all words.) 62 atmospheric methane 61 extinctions 61 vertebrate species 60 species extinctions 59 mass extinctions 59 megafauna 58 mammal species 58 terrestrial ecosystems 58 interglacial period 56 amphibian species 56 temperate forests 56 Cambrian explosion 56 amphibian populations 55 temperate zones 55 species 55 mass extinction 55 mountain glaciers 55 overhunting 55 mammals 55 greenhouse gas concentrations 55 atmospheric carbon dioxide 54 glacial retreat 54 penguin species 54 atmospheric CO2 54 gigatonnes 53 CO2 concentrations 53 mammal 53 glacial melt 53 Antarctic ozone 53 Younger Dryas 53 ocean acidity 52 temperate regions 52 subtropical regions 52 greenhouse warming 52 Ocean acidification 52 biosphere 52 atmospheric concentrations 52 Cretaceous Period 51 Beringia 51 avian species 51 glacial melting 51 Volcanic eruptions 51 retreating glaciers 51 mammalian species 51 biodiversity hotspots 51 multicellular organisms 51 volcanism 51 frog species 51 humans 51 atmospheric CO 50 primate species 50 H. erectus 50 Homo sapiens 50 tropics 50 bee populations 50 glaciers 50 marine sediments 50 drylands 50 icecap 50 Little Ice Age 50 glaciers melt 50 feathered dinosaurs 50 western lowland gorillas 50 oceans 49 driest continent 49 solar irradiance 49 glaciation 49 Arctic permafrost 49 chytrid fungus 49 anthropogenic climate 49 interglacial 49 coral species 49 prolonged droughts 49 mid latitudes 49 stratospheric ozone 49 El Ninos 49 Sumatran rhinos 49 vertebrates 49 Polar Regions 49 prokaryotes 49 continental drift 48 baleen whales 48 icecaps 48 supercontinent 48 hydrological cycle 48 influenza pandemics 48 Anthropocene 48 boreal forests 48 Medieval Warm Period 48 landmass 48 honeybee population 48 poleward 48 Yellowstone ecosystem 48 arid regions 48 radiative forcing 48 Late Cretaceous 48 clouded leopards 48 gigatons 48 nitrogen fixation 48 hotter summers 48 extinct