Query: The heat extremes were especially pervasive in the Arctic, with temperatures in the fall running 20 to 30 degrees Fahrenheit above normal across large stretches of the Arctic Ocean.

Relevant passages:
Arctic Ocean <=SEP=> The Arctic Ocean is the smallest and shallowest of the world 's five major oceans . The International Hydrographic Organization ( IHO ) recognizes it as an ocean , although some oceanographers call it the Arctic Mediterranean Sea or simply the Arctic Sea , classifying it a mediterranean sea or an estuary of the Atlantic Ocean . Alternatively , the Arctic Ocean can be seen as the northernmost part of the all-encompassing World Ocean .   Located mostly in the Arctic north polar region in the middle of the Northern Hemisphere , the Arctic Ocean is almost completely surrounded by Eurasia and North America . It is partly covered by sea ice throughout the year and almost completely in winter . The Arctic Ocean 's surface temperature and salinity vary seasonally as the ice cover melts and freezes ; its salinity is the lowest on average of the five major oceans , due to low evaporation , heavy fresh water inflow from rivers and streams , and limited connection and outflow to surrounding oceanic waters with higher salinities . The summer shrinking of the ice has been quoted at 50 % . The US National Snow and Ice Data Center ( NSIDC ) uses satellite data to provide a daily record of Arctic sea ice cover and the rate of melting compared to an average period and specific past years .

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 .

Arctic sea ice decline <=SEP=> Arctic sea ice decline is the sea ice loss observed in recent decades in the Arctic Ocean . The Intergovernmental Panel on Climate Change ( IPCC ) Fourth Assessment Report states that greenhouse gas forcing is largely , but not wholly , responsible for the decline in Arctic sea ice extent . A study from 2011 suggested that internal variability enhanced the greenhouse gas forced sea ice decline over the last decades . A study from 2007 found the decline to be `` faster than forecasted '' by model simulations . The IPCC Fifth Assessment Report concluded with high confidence that sea ice continues to decrease in extent , and that there is robust evidence for the downward trend in Arctic summer sea ice extent since 1979 . It has been established that the region is at its warmest for at least 40,000 years and the Arctic-wide melt season has lengthened at a rate of 5 days per decade ( from 1979 to 2013 ) , dominated by a later autumn freezeup . Sea ice changes have been identified as a mechanism for polar amplification .