Related by context. Frequent words. (Click for all words.) 68 ozone layer 55 chlorofluorocarbons 52 polar regions 50 CFCs 50 ozone depletion 49 ozone depleting substances 49 ozone 48 Carbon dioxide 48 tooth enamel 48 carbon dioxide 47 greenhouse warming 47 ocean ecosystems 47 acid rain 47 Greenhouse gases 45 mountain glaciers 45 water vapor 45 permafrost 45 oceans 45 Antarctic ice 44 carbon dioxide CO2 44 boreal forest 44 greenhouse gas concentrations 44 tropical forests 44 Carbon dioxide emissions 44 Montreal Protocol 44 atmospheric carbon dioxide 44 burning fossil fuels 44 Martian atmosphere 44 greenhouse gases 43 glaciers 43 radioactive decay 43 ultraviolet radiation 43 aerosols 43 biosphere 43 Greenland ice 43 ecosystems 43 marine ecosystems 42 absorb carbon dioxide 42 troposphere 42 heat trapping greenhouse gases 42 Amazon rainforest 42 planet 41 cosmic rays 41 heat trapping gases 41 magnetosphere 41 albedo 41 gasses 41 gases 41 Antarctica 41 carbon sinks 41 Saturn rings 41 atmospheric circulation 41 comet 40 tropical rainforests 40 atmospheric CO2 40 sulfur dioxide 40 World Meteorological Organisation 40 outer layers 40 marine ecosystem 40 greenhouse gasses 40 radioactive particles 40 greenhouse gases emitted 40 peat bogs 40 aquatic ecosystems 40 coral reefs 40 cosmic radiation 40 ice melts 40 WMO 40 NASA Cassini spacecraft 40 forest ecosystems 40 heat trapping emissions 39 ionosphere 39 polar ice 39 HCFCs 39 methane 39 ultraviolet rays 39 acidification 39 volcanic eruptions 39 Coral reefs 39 PFOS 39 phytoplankton 39 UV radiation 39 UV rays 39 Earth 39 peatlands 39 pollutants 38 magnetic fields 38 CO2 38 neurotoxin 38 Himalayan glaciers 38 chemical composition 38 Glaciers 38 ocean acidification 38 lichens 38 mercury pollution 38 organic compounds 38 infrared radiation 38 World Meteorological Organization 38 vegetation 38 plankton 38 dust particles