Query: Surface measurements find more downward infrared radiation warming the planet's surface.

Relevant passages:
Earth <=SEP=> Earth ( from Eorðe -LSB- Γαῖα , Gaia -RSB- Terra ) , otherwise known as the World or the Globe , is the third planet from the Sun and the only object in the Universe known to harbor life . It is the densest planet in the Solar System and the largest of the four terrestrial planets .   According to radiometric dating and other sources of evidence , Earth formed about 4.54 billion years ago . Earth 's gravity interacts with other objects in space , especially the Sun and the Moon , Earth 's only natural satellite . During one orbit around the Sun , Earth rotates about its axis over 365 times ; thus , an Earth year is about 365.26 days long . Earth 's axis of rotation is tilted , producing seasonal variations on the planet 's surface . The gravitational interaction between the Earth and Moon causes ocean tides , stabilizes the Earth 's orientation on its axis , and gradually slows its rotation .   Earth 's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years . About 71 % of Earth 's surface is covered with water , mostly by its oceans . The remaining 29 % is land consisting of continents and islands that together have many lakes , rivers and other sources of water that contribute to the hydrosphere . The majority of Earth 's polar regions are covered in ice , including the Antarctic ice sheet and the sea ice of the Arctic ice pack . Earth 's interior remains active with a solid iron inner core , a liquid outer core that generates the Earth 's magnetic field , and a convecting mantle that drives plate tectonics .   Within the first billion years of Earth 's history , life appeared in the oceans and began to affect the Earth 's atmosphere and surface , leading to the proliferation of aerobic and anaerobic organisms . Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago . Since then , the combination of Earth 's distance from the Sun , physical properties , and geological history have allowed life to evolve and thrive . In the history of the Earth , biodiversity has gone through long periods of expansion , occasionally punctuated by mass extinction events . Over 99 % of all species that ever lived on Earth are extinct . Estimates of the number of species on Earth today vary widely ; most species have not been described . Over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival . Humans have developed diverse societies and cultures ; politically , the world has about 200 sovereign states .

Cloud <=SEP=> In meteorology , a cloud is an aerosol comprising a visible mass of minute liquid droplets , frozen crystals , or particles suspended in the atmosphere above the surface of a planetary body . The droplets and crystals may be made of water or various chemicals . On Earth , clouds are formed as a result of saturation of the air when it is cooled to its dew point , or when it gains sufficient moisture ( usually in the form of water vapor ) from an adjacent source to raise the dew point to the ambient temperature . They are seen in the Earth 's homosphere ( which includes the troposphere , stratosphere , and mesosphere ) . Nephology is the science of clouds which is undertaken in the cloud physics branch of meteorology .   There are two systems of naming clouds in their respective layers of the atmosphere ; Latin in the troposphere and mostly alpha-numeric above the troposphere . Cloud types in the troposphere , the atmospheric layer closest to Earth 's surface , have Latin names due to the universal adaptation of Luke Howard 's nomenclature . Formally proposed in 1802 , it became the basis of a modern international system that classifies clouds into five physical forms and three altitude levels ( formerly known as étages ) . These physical types , in approximate ascending order of convective activity , include stratiform sheets , cirriform wisps and patches , stratocumuliform layers ( mainly structured as rolls , ripples , and patches ) , cumuliform heaps , and very large cumulonimbiform heaps that often show complex structure . The physical forms are cross-classified by the altitude levels to produce ten basic genus-types , most of which can be divided into species , and subdivided into varieties .   Two cirriform clouds that form higher up in the stratosphere and mesosphere have common names for their main types , but are sub-classified alpha-numerically . They are relatively uncommon and are mostly seen in the polar regions of Earth . Clouds have been observed in the atmospheres of other planets and moons in the Solar System and beyond . However , due to their different temperature characteristics , they are often composed of other substances such as methane , ammonia , and sulfuric acid as well as water .   Homospheric types determined by cross-classification of forms and levels .   '' Homospheric types include the ten tropospheric genera and two additional major types above the troposphere . The cumulus genus includes three variants as defined by vertical size .

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 .