Query: Dr. Gutzler said spring temperatures have an impact, too, with warmer air causing more snow to turn to vapor and essentially disappear.

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Precipitation <=SEP=> In meteorology , precipitation is any product of the condensation of atmospheric water vapor that falls under gravity . The main forms of precipitation include drizzle , rain , sleet , snow , graupel and hail . Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor , so that the water condenses and `` precipitates '' . Thus , fog and mist are not precipitation but suspensions , because the water vapor does not condense sufficiently to precipitate . Two processes , possibly acting together , can lead to air becoming saturated : cooling the air or adding water vapor to the air . Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud . Short , intense periods of rain in scattered locations are called `` showers . ''   Moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain . This process is typically active when freezing rain is occurring . A stationary front is often present near the area of freezing rain and serves as the foci for forcing and rising air . Provided necessary and sufficient atmospheric moisture content , the moisture within the rising air will condense into clouds , namely stratus and cumulonimbus . Eventually , the cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects . Where relatively warm water bodies are present , for example due to water evaporation from lakes , lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones . Lake-effect snowfall can be locally heavy . Thundersnow is possible within a cyclone 's comma head and within lake effect precipitation bands . In mountainous areas , heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation . On the leeward side of mountains , desert climates can exist due to the dry air caused by compressional heating . The movement of the monsoon trough , or intertropical convergence zone , brings rainy seasons to savannah climes .   Precipitation is a major component of the water cycle , and is responsible for depositing the fresh water on the planet . Approximately 505000 km3 of water falls as precipitation each year ; 398000 km3 of it over the oceans and 107000 km3 over land . Given the Earth 's surface area , that means the globally averaged annual precipitation is 990 mm , but over land it is only 715 mm . Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes .   Precipitation may occur on other celestial bodies , e.g. when it gets cold , Mars has precipitation which most likely takes the form of frost , rather than rain or snow .

Snow <=SEP=> Snow pertains to frozen crystalline water throughout its life cycle , starting when it precipitates from clouds and accumulates on surfaces , then metamorphoses in place , and ultimately melts , slides or sublimates away . Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air . Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets , which freeze in hexagonal-shaped crystals . Snowflakes take on a variety of shapes , basic among these are platelets , needles , columns and rime . As snow accumulates into a snowpack , it may blow into drifts . Over time , accumulated snow metamorphoses , by sintering , sublimation and freeze-thaw . Where the climate is cold enough for year-to-year accumulation , a glacier may form . Otherwise , snow typically melts seasonally , causing runoff into streams and rivers and recharging groundwater .   Major snow-prone areas include the polar regions , the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures . In the Southern Hemisphere , snow is confined primarily to mountainous areas , apart from Antarctica .   Snow affects such human activities as transportation : creating the need for keeping roadways , wings , and windows clear ; agriculture : providing water to crops and safeguarding livestock ; such sports as skiing , snowboarding , snowmachine travel ; and warfare : impairing target acquisition , degrading the performance of combatants and materiel , and impeding mobility . Snow affects ecosystems , as well , by providing an insulating layer during winter under which plants and animals are able to survive the cold .

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 .

Effects of global warming <=SEP=> The effects of global warming are the environmental and social changes caused ( directly or indirectly ) by human emissions of greenhouse gases . There is a scientific consensus that climate change is occurring , and that human activities are the primary driver . Many impacts of climate change have already been observed , including glacier retreat , changes in the timing of seasonal events ( e.g. , earlier flowering of plants ) , and changes in agricultural productivity .   Future effects of climate change will vary depending on climate change policies and social development . The two main policies to address climate change are reducing human greenhouse gas emissions ( climate change mitigation ) and adapting to the impacts of climate change . Geoengineering is another policy option .   Near-term climate change policies could significantly affect long-term climate change impacts . Stringent mitigation policies might be able to limit global warming ( in 2100 ) to around 2 ° C or below , relative to pre-industrial levels . Without mitigation , increased energy demand and extensive use of fossil fuels might lead to global warming of around 4 ° C. Higher magnitudes of global warming would be more difficult to adapt to , and would increase the risk of negative impacts .

Thunderstorm <=SEP=> A thunderstorm , also known as an electrical storm , lightning storm , or thundershower , is a storm characterized by the presence of lightning and its acoustic effect on the Earth 's atmosphere , known as thunder . Thunderstorms occur in association with a type of cloud known as a cumulonimbus . They are usually accompanied by strong winds , heavy rain , and sometimes snow , sleet , hail , or , in contrast , no precipitation at all . Thunderstorms may line up in a series or become a rainband , known as a squall line . Strong or severe thunderstorms , known as supercells , rotate as do cyclones . While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy , vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction .   Thunderstorms result from the rapid upward movement of warm , moist air , sometimes along a front . As the warm , moist air moves upward , it cools , condenses , and forms a cumulonimbus cloud that can reach heights of over 20 km . As the rising air reaches its dew point temperature , water vapor condenses into water droplets or ice , reducing pressure locally within the thunderstorm cell . Any precipitation falls the long distance through the clouds towards the Earth 's surface . As the droplets fall , they collide with other droplets and become larger . The falling droplets create a downdraft as it pulls cold air with it , and this cold air spreads out at the Earth 's surface , occasionally causing strong winds that are commonly associated with thunderstorms .   Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude , where warm , moist air from tropical latitudes collides with cooler air from polar latitudes . Thunderstorms are responsible for the development and formation of many severe weather phenomena . Thunderstorms , and the phenomena that occur along with them , pose great hazards . Damage that results from thunderstorms is mainly inflicted by downburst winds , large hailstones , and flash flooding caused by heavy precipitation . Stronger thunderstorm cells are capable of producing tornadoes and waterspouts .   There are four types of thunderstorms : single-cell , multi-cell cluster , multi-cell lines , and supercells . Supercell thunderstorms are the strongest and the most associated with severe weather phenomena . Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes . Dry thunderstorms , with no precipitation , can cause the outbreak of wildfires from the heat generated from the cloud-to-ground lightning that accompanies them . Several means are used to study thunderstorms : weather radar , weather stations , and video photography . Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century . Beyond the Earth 's atmosphere , thunderstorms have also been observed on the planets of Jupiter , Saturn , Neptune , and , probably , Venus .