Query: If there is  a cloud cover, the heat is trapped by water vapour as a greenhouse gas  and the temperature stays quite warm.

Relevant passages:
Water <=SEP=> Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth 's streams , lakes , and oceans , and the fluids of most living organisms . Its chemical formula is H2O , meaning that its molecule contains one oxygen and two hydrogen atoms , that are connected by covalent bonds . Water strictly refers to the liquid state of that substance , that prevails at standard ambient temperature and pressure ; but it often refers also to its solid state ( ice ) or its gaseous state ( steam or water vapor ) . It also occurs in nature as snow , glaciers , ice packs and icebergs , clouds , fog , dew , aquifers , and atmospheric humidity .   Water covers 71 % of the Earth 's surface . It is vital for all known forms of life . On Earth , 96.5 % of the planet 's crust water is found in seas and oceans , 1.7 % in groundwater , 1.7 % in glaciers and the ice caps of Antarctica and Greenland , a small fraction in other large water bodies , and 0.001 % in the air as vapor , clouds ( formed of ice and liquid water suspended in air ) , and precipitation . Only 2.5 % of this water is freshwater , and 98.8 % of that water is in ice ( excepting ice in clouds ) and groundwater . Less than 0.3 % of all freshwater is in rivers , lakes , and the atmosphere , and an even smaller amount of the Earth 's freshwater ( 0.003 % ) is contained within biological bodies and manufactured products . A greater quantity of water is found in the earth 's interior .   Water on Earth moves continually through the water cycle of evaporation and transpiration ( evapotranspiration ) , condensation , precipitation , and runoff , usually reaching the sea . Evaporation and transpiration contribute to the precipitation over land . Large amounts of water are also chemically combined or adsorbed in hydrated minerals .   Safe drinking water is essential to humans and other lifeforms even though it provides no calories or organic nutrients . Access to safe drinking water has improved over the last decades in almost every part of the world , but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation . There is a clear correlation between access to safe water and gross domestic product per capita . However , some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability . A report , issued in November 2009 , suggests that by 2030 , in some developing regions of the world , water demand will exceed supply by 50 % .   Water plays an important role in the world economy . Approximately 70 % of the freshwater used by humans goes to agriculture . Fishing in salt and fresh water bodies is a major source of food for many parts of the world . Much of long-distance trade of commodities ( such as oil and natural gas ) and manufactured products is transported by boats through seas , rivers , lakes , and canals . Large quantities of water , ice , and steam are used for cooling and heating , in industry and homes . Water is an excellent solvent for a wide variety of chemical substances ; as such it is widely used in industrial processes , and in cooking and washing . Water is also central to many sports and other forms of entertainment , such as swimming , pleasure boating , boat racing , surfing , sport fishing , and diving .

Urban heat island <=SEP=> An urban heat island ( UHI ) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities . The temperature difference usually is larger at night than during the day , and is most apparent when winds are weak . UHI is most noticeable during the summer and winter . The main cause of the urban heat island effect is from the modification of land surfaces . Waste heat generated by energy usage is a secondary contributor . As a population center grows , it tends to expand its area and increase its average temperature . The less-used term heat island refers to any area , populated or not , which is consistently hotter than the surrounding area .   Monthly rainfall is greater downwind of cities , partially due to the UHI . Increases in heat within urban centers increases the length of growing seasons , and decreases the occurrence of weak tornadoes . The UHI decreases air quality by increasing the production of pollutants such as ozone , and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems .   Not all cities have a distinct urban heat island . Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-colored surfaces in urban areas , which reflect more sunlight and absorb less heat .   There are concerns raised about possible contribution from urban heat islands to global warming . Research on China and India indicates that urban heat island effect contributes to climate warming by about 30 % . On the other hand , one 1999 comparison between urban and rural areas proposed that the urban heat island effects have little influence on global mean temperature trends . Many studies reveal increases in the severity of the effect with the progress of climate change .

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 .

Atmosphere of Venus <=SEP=> The atmosphere of Venus is the layer of gases surrounding Venus . It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth . The temperature at the surface is 740 K ( 467 ° C , 872 ° F ) , and the pressure is 93 bar ( 9.3 MPa ) , roughly the pressure found 900 m underwater on Earth . The Venusian atmosphere supports opaque clouds made of sulfuric acid , making optical Earth-based and orbital observation of the surface impossible . Information about the topography has been obtained exclusively by radar imaging . Aside from carbon dioxide , the other main component is nitrogen . Other chemical compounds are present only in trace amounts .   Mikhail Lomonosov was the first person to hypothesize the existence of an atmosphere on Venus based on his observation of the transit of Venus of 1761 in a small observatory near his house in Saint Petersburg , Russia .   Aside from the very surface layers , the atmosphere is in a state of vigorous circulation . The upper layer of troposphere exhibits a phenomenon of super-rotation , in which the atmosphere circles the planet in just four Earth days , much faster than the planet 's sidereal day of 243 days . The winds supporting super-rotation blow at a speed of 100 m/s ( ~ 360 km/h or 220 mph ) or more . Winds move at up to 60 times the speed of the planet 's rotation , while Earth 's fastest winds are only 10 % to 20 % rotation speed . On the other hand , the wind speed becomes increasingly slower as the elevation from the surface decreases , with the breeze barely reaching the speed of 10 km/h ( 2.8 m/s ) on the surface . Near the poles are anticyclonic structures called polar vortices . Each vortex is double-eyed and shows a characteristic S-shaped pattern of clouds . Above there is an intermediate layer of mesosphere which separates the troposphere from the thermosphere . The thermosphere is also characterized by strong circulation , but very different in its nature - the gases heated and partially ionized by sunlight in the sunlit hemisphere migrate to the dark hemisphere where they recombine and downwell .   Unlike Earth , Venus lacks a magnetic field . Its ionosphere separates the atmosphere from outer space and the solar wind . This ionised layer excludes the solar magnetic field , giving Venus a distinct magnetic environment . This is considered Venus 's induced magnetosphere . Lighter gases , including water vapour , are continuously blown away by the solar wind through the induced magnetotail . It is speculated that the atmosphere of Venus up to around 4 billion years ago was more like that of the Earth with liquid water on the surface . A runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of the levels of other greenhouse gases .   Despite the harsh conditions on the surface , the atmospheric pressure and temperature at about 50 km to 65 km above the surface of the planet is nearly the same as that of the Earth , making its upper atmosphere the most Earth-like area in the Solar System , even more so than the surface of Mars . Due to the similarity in pressure and temperature and the fact that breathable air ( 21 % oxygen , 78 % nitrogen ) is a lifting gas on Venus in the same way that helium is a lifting gas on Earth , the upper atmosphere has been proposed as a location for both exploration and colonization .   On January 29 , 2013 , ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to `` the ion tail seen streaming from a comet under similar conditions . ''