Query: Methane plays a minor role in global warming but could get much worse if permafrost starts to melt.

Relevant passages:
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 .

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 .

Global warming <=SEP=> Global warming , also referred to as climate change , is the observed century-scale rise in the average temperature of the Earth 's climate system and its related effects . Multiple lines of scientific evidence show that the climate system is warming . Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid 19th century , and in paleoclimate proxy records over thousands of years .   In 2013 , the Intergovernmental Panel on Climate Change ( IPCC ) Fifth Assessment Report concluded that `` It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century . '' The largest human influence has been emission of greenhouse gases such as carbon dioxide , methane and nitrous oxide . Climate model projections summarized in the report indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to for their lowest emissions scenario and 2.6 to for the highest emissions scenario . These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing .   Future climate change and associated impacts will differ from region to region around the globe . Anticipated effects include warming global temperature , rising sea levels , changing precipitation , and expansion of deserts in the subtropics . Warming is expected to be greater over land than over the oceans and greatest in the Arctic , with the continuing retreat of glaciers , permafrost and sea ice . Other likely changes include more frequent extreme weather events including heat waves , droughts , heavy rainfall with floods and heavy snowfall ; ocean acidification ; and species extinctions due to shifting temperature regimes . Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels . Because the climate system has a large `` inertia '' and greenhouse gases will stay in the atmosphere for a long time , many of these effects will not only exist for decades or centuries , but will persist for tens of thousands of years .   Possible societal responses to global warming include mitigation by emissions reduction , adaptation to its effects , building systems resilient to its effects , and possible future climate engineering . Most countries are parties to the United Nations Framework Convention on Climate Change ( UNFCCC ) ,  whose ultimate objective is to prevent dangerous anthropogenic climate change . Parties to the UNFCCC have agreed that deep cuts in emissions are required and that global warming should be limited to well below 2.0 C-change relative to pre-industrial levels , with efforts made to limit warming to 1.5 C-change .   Public reactions to global warming and concern about its effects are also increasing . A global 2015 Pew Research Center report showed a median of 54 % consider it `` a very serious problem '' . There are significant regional differences , with Americans and Chinese ( whose economies are responsible for the greatest annual CO2 emissions ) among the least concerned .