Human activities, including fossil fuel combustion, farming, and deforestation, are known to increase the levels of carbon dioxide, methane, and nitrous oxides in our atmosphere. Measurable warming of Earth due to these greenhouse gases can alter ecosystem dynamics. In addition to the direct climatic effects on organisms within biomes, warming can lower levels of sea ice and increase precipitation in Arctic areas. Global warming can also melt permafrost in the tundra and increase sea surface temperatures, which could increase the intensity of hurricanes in vulnerable areas. Within communities, climatic change can shift interdependent species "out of sync," potentially causing indirect loss of species. For example, if pollinators and the plants they pollinate become out of synch, the pollinators may not be able to switch to a different food source, and the plants may not be able to reproduce. If the climate warms significantly, tundra permafrost may melt, which may lead to the community.