Query: “Arctic land stores about twice as much carbon as the atmosphere.

Relevant passages:
Mars <=SEP=> Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System , after Mercury . Named after the Roman god of war , it is often referred to as the `` Red Planet '' because the iron oxide prevalent on its surface gives it a reddish appearance . Mars is a terrestrial planet with a thin atmosphere , having surface features reminiscent both of the impact craters of the Moon and the valleys , deserts , and polar ice caps of Earth .   The rotational period and seasonal cycles of Mars are likewise similar to those of Earth , as is the tilt that produces the seasons . Mars is the site of Olympus Mons , the largest volcano and second-highest known mountain in the Solar System , and of Valles Marineris , one of the largest canyons in the Solar System . The smooth Borealis basin in the northern hemisphere covers 40 % of the planet and may be a giant impact feature . Mars has two moons , Phobos and Deimos , which are small and irregularly shaped . These may be captured asteroids , similar to 5261 Eureka , a Mars trojan .   There are ongoing investigations assessing the past habitability potential of Mars , as well as the possibility of extant life . Future astrobiology missions are planned , including the Mars 2020 and ExoMars rovers . Liquid water can not exist on the surface of Mars due to low atmospheric pressure , which is about that of the Earth 's , except at the lowest elevations for short periods . The two polar ice caps appear to be made largely of water . The volume of water ice in the south polar ice cap , if melted , would be sufficient to cover the entire planetary surface to a depth of 11 m . In November 2016 , NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars . The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior .   Mars can easily be seen from Earth with the naked eye , as can its reddish coloring . Its apparent magnitude reaches − 2.91 , which is surpassed only by Jupiter , Venus , the Moon , and the Sun . Optical ground-based telescopes are typically limited to resolving features about 300 km across when Earth and Mars are closest because of Earth 's atmosphere .

Sperm whale <=SEP=> The sperm whale ( Physeter macrocephalus ) , or cachalot , is the largest of the toothed whales and the largest toothed predator . It is the only living member of genus Physeter , and one of three extant species in the sperm whale family , along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia .   The sperm whale is a pelagic mammal with a worldwide range , and will migrate seasonally for feeding and breeding . Females and young males live together in groups while mature males live solitary lives outside of the mating season . The females cooperate to protect and nurse their young . Females give birth every four to twenty years , and care for the calves for more than a decade . A mature sperm whale has few natural predators , although calves and weakened adults are sometimes killed by pods of orcas .   Mature males average 16 m in length but some may reach 20.5 m , with the head representing up to one-third of the animal 's length . Plunging to 2250 m , it is the second deepest diving mammal , following only the Cuvier 's beaked whale .   The sperm whale is a prominent user of echolocation and communication , with vocalization as loud as 230 decibels ( re 1 µPa at 1 m ) underwater . It has the largest brain of any animal on Earth , more than five times heavier than a human 's . Sperm whales can live for more than 60 years .   The spermaceti oil from which the whale derives its name was a prime target of the whaling industry , and was dominant for use in oil lamps , lubricants , and candles . Ambergris is a solid waxy waste product from its digestive system . It is still highly valued as a fixative in perfumes and other uses . It remains as flotsam from deceased whales , and is sought by beachcombers . The species is now protected by a whaling moratorium , and is currently listed as vulnerable by the International Union for the Conservation of Nature and Natural Resources ( IUCN ) .

Permafrost <=SEP=> In geology , permafrost is ground , including rock or ( cryotic ) soil , at or below the freezing point of water 0 C for two or more years . Most permafrost is located in high latitudes ( in and around the Arctic and Antarctic regions ) , but alpine permafrost may exist at high altitudes in much lower latitudes . Ground ice is not always present , as may be in the case of nonporous bedrock , but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material . Permafrost accounts for 0.022 % of total water on earth and exists in 24 % of exposed land in the Northern Hemisphere . It also occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean , portions of which were exposed during the last glacial period , with global weather implications .   A global temperature rise of 1.5 C-change above current levels would be enough to start the thawing of permafrost in Siberia , according to one group of scientists .

Climate change feedback <=SEP=> Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing , and so play an important part in determining the climate sensitivity and future climate state . Feedback in general is the process in which changing one quantity changes a second quantity , and the change in the second quantity in turn changes the first . Positive feedback amplifies the change in the first quantity while negative feedback reduces it .   The term `` forcing '' means a change which may `` push '' the climate system in the direction of warming or cooling . An example of a climate forcing is increased atmospheric concentrations of greenhouse gases . By definition , forcings are external to the climate system while feedbacks are internal ; in essence , feedbacks represent the internal processes of the system . Some feedbacks may act in relative isolation to the rest of the climate system ; others may be tightly coupled ; hence it may be difficult to tell just how much a particular process contributes . Forcings , feedbacks and the dynamics of the climate system determine how much and how fast the climate changes . The main positive feedback in global warming is the tendency of warming to increase the amount of water vapor in the atmosphere , which in turn leads to further warming . The main negative feedback comes from the Stefan -- Boltzmann law , the amount of heat radiated from the Earth into space changes with the fourth power of the temperature of Earth 's surface and atmosphere .   Some observed and potential effects of global warming are positive feedbacks , which contribute directly to further global warming . The Intergovernmental Panel on Climate Change 's ( IPCC ) Fourth Assessment Report states that `` Anthropogenic warming could lead to some effects that are abrupt or irreversible , depending upon the rate and magnitude of the climate change . ''

Atmospheric methane <=SEP=> Atmospheric methane is the methane present in Earth 's atmosphere . Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth 's atmosphere . The 100-year global warming potential of methane is 28 . That is , over a 100-year period , it traps 28 times more heat per mass unit than carbon dioxide and 32 times the effect when accounted for aerosol interactions . Global methane levels , had risen to 1800 parts per billion ( ppb ) by 2011 , an increase by a factor of 2.5 since pre-industrial times , from 722 ppb , the highest value in at least 800,000 years . Its concentration is higher in the Northern Hemisphere since most sources ( both natural and human ) are located on land and the Northern Hemisphere has more land mass . The concentrations vary seasonally , with , for example , a minimum in the northern tropics during April − May mainly due to removal by the hydroxyl radical .   Early in the Earth 's history carbon dioxide and methane likely produced a greenhouse effect . The carbon dioxide would have been produced by volcanoes and the methane by early microbes . During this time , Earth 's earliest life appeared . These first , ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water . Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth 's history . With no oxygen , methane stayed in the atmosphere longer and at higher concentrations than it does today .   Methane is created near the surface , and it is carried into the stratosphere by rising air in the tropics . Uncontrolled build-up of methane in Earth 's atmosphere is naturally checked -- although human influence can upset this natural regulation -- by methane 's reaction with hydroxyl radicals formed from singlet oxygen atoms and with water vapor .