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[[quoteright:350:[[Film/StarTrekFirstContact http://static.tvtropes.org/pmwiki/pub/images/rsz_earth_assimilated.png]]]]
[[caption-width-right:350:"The atmosphere contains high concentrations of methane, carbon monoxide, and fluorine. [...] Population approximately nine billion...all Borg."]]

->''"There is a notion called 'terraforming' that has held popular theoretical cachet for some time. It holds that given the correct level of technology, the potential is there to change the environment of another planet into one like our own. This is nothing the human race has yet been able to put into practice. It's ''never'' been considered that someone might do it to ''us''. These central positions look less and less like someplace a human could survive. They have been ''un-terraformed''."
-->-- [[Creator/TomBaker Narration]] of the "'''''[[http://www.youtube.com/watch?v=ZDn-oYLBWGg Terraform]]'''''" cinematic for ''VideoGame/HostileWatersAntaeusRising''

Imagine you are a leader of an alien race currently at war with another race, and your natural habitats are drastically different. How would you perform a hostile takeover of a planet?

By making it so the planet is now inhabitable by you and not by the natives, of course! Convert the atmosphere, reshape the land and sea, overrun the native ecosystem with one more suitable -- whatever is necessary to make the very ground your enemies tread on no longer their ally.
A specific context for {{Terraforming}}, and if it's an Earth-like world being changed to another ecosphere, the term would be "xenoforming". Often overlaps with AtmosphereAbuse, though the latter doesn't have to occur specifically for terraforming purposes. Depending on methodology, it can involve GreyGoo, GaiasVengeance, AlienKudzu, or MeatMoss. Due to the destruction, this is an ApocalypseHow of the Planetary Species or Total Extinction variety, depending on how much of the planet's multicellular life is replaced.



[[folder:Anime & Manga]]
* Lord Slug wanted to freeze the Earth because of this in ''Anime/DragonBallZLordSlug''. "Deterraforming" was discussed in the ''WebVideo/DragonBallAbridged'' movie version.
* ''Anime/SpaceBattleshipYamato'':
** In both the original anime and [[Film/SpaceBattleshipYamato the live-action film]], the Gamilas have reduced Earth into a radioactive wasteland by [[ColonyDrop meteor bombing]], and the main characters discover that this would leave a world more suitable for Gamilan life.
** The 2012 reboot, ''Anime/SpaceBattleshipYamato2199'', puts more focus on this aspect of the Gamilas attacks on earth, describing the effects as "pollution" instead of explicit radiation like the original series and live-action movie. The Planet Bombs also seeded poisonous AlienKudzu that's shown penetrating the underground cities, [[spoiler:which is discovered as identical to the plant life on the Floating Continent. However, that ecosystem is not suitable for Gamilan life in this version; the Hostile Terraforming is strictly a way to SaltTheEarth]].
* ''Anime/TekkamanBlade'': The Radam Invasion seeds the earth with strange fungus-like plants while they decimate the Earth Military. [[spoiler: However, the plants aren't there to terraform Earth, they're there to forcibly terraform ''us'' into the best possible Hosts.]]
* This is the alien robot Mazin Garon's modus operandi in ''Manga/AstroBoy''. After he's activated by one of the scientists who found him he goes about remolding the rocks, air and even ''gravity'' of the island he crashed on, killing everything for miles around with the poison gas meant to be the planet's new atmosphere. Although in Garon's case it's not really hostile, as he was only doing what he was programmed to do before the space mail order package he was in crashed on Earth by accident instead of the planet he was supposed to help his owners colonize.
* In ''Anime/NeonGenesisEvangelion'', Adam and Lilith are revealed in supplementary materials to be alien terraforming biotechnology called Seeds of Life created by a long dead {{precursor}} race. The problem is, if one Seed lands on a planet that already has an Seed (in this case, Lilith landing on Earth after Adam has already done so), it would risk a "forbidden union" between the two Seeds' respective offspring that would give rise to a race of godlike entities rivalling the aforementioned precursors. The precursors were aware of the possibility of this happening, and added control rods (the Lances of Longinus) to each Seed's vessel that would automatically seal one of the Seeds in such a situation. This is what happened to Adam, as Lilith's Lance was apparently destroyed in the process of her arrival to Earth. Then a bunch of humans removed the Lance...

[[folder:Comic Books]]
* The first issue of ''ComicBook/{{Sillage}}/Wake'' involves an alien who intends to terraform a jungle planet to suit his species, although in this case he's unaware that there's one sentient being (the human girl Navis) and lots of semi-sentient animals already living there.
* ComicBook/TheAuthority battles God ("The Outer Dark," issues 9-12). Earth's creator is a moon-sized alien being that created the planet as a retirement home. Since Earth's creation, changes to its orbit and ecosystem led to the rise of life as we know it, instead of somewhere its creator would be comfortable. God immediately sets about "fixing" that. Or as The Engineer calls it, "turdscaping".
* Franchise/{{Superman}}: In various media, villainous Kryptonians often attempt to remake [[DoomedHomeTown Krypton]] on Earth. In ''Comicbook/KryptonNoMore'', he and Comicbook/{{Supergirl}} fight two villains with radiation-fueled powers who intend to turn Earth into a radioactive wasteland to suit them.
* In ''ComicBook/TransformersGeneration2'', the Cybertronian Empire's modus operandi was to kill all the inhabitants of each planet and then mechaform the planet itself to make replicas of Cybertron.
* In the ''Film/MarsAttacks'' comic book the Martian overlords have conquered Earth and are in the process of xenoforming Earth into a more Martian-like planet as so to let them live better at the expense of the largely expendable humans.

[[folder:Fan Fiction]]
* ''FanFic/NobodyDies'': [[spoiler: Ichi]] is accidentally doing this in chapter 109.
* In ''Fanfic/TheConversionBureau'' and many of its {{Recursive Fanfiction}}s, Equestria is surrounded by an [[AdvancingWallOfDoom expanding barrier]] that is spreading magic over the earth, and magic is portrayed as harmful to humans, necessitating the eponymous bureaus and the MutagenicGoo that turns them into ponies. The many {{Deconstruction Fic}}s that arose in response to these stories liken the whole process to [[WouldBeRudeToSayGenocide genocide]].

* ''Film/TheArrival'': Aliens are causing global warming in order to kill off humans and make the planet more comfortable for their kind. When confronted, one of them points out that humans are doing the same exact thing, only much slower. The aliens are simply speeding up the process.
* In ''Film/StarTrekIITheWrathOfKhan'', after viewing the description of the Genesis Device, Dr. [=McCoy=] raises the possibility that it could be used to destroy an existing ecosystem while creating a new one. In ''Film/StarTrekIIITheSearchForSpock'' the Klingons saw the device as a weapon, whether it was used for HostileTerraforming or simply to increase the wealth and power of the Federation. An interesting twist here is that, due to the relatively human-like physiology of most Star Trek aliens, the terraformed planet would still for the most part be habitable to the original inhabitants... it's just that the ones who are actually on the planet when it is terraformed would be used as raw materials for the terraforming transformation.
* In ''Film/StarTrekFirstContact'' (pictured above), the Borg travel back in time and assimilate Earth while it's recovering from World War III. Three centuries later, nine billion Borg are living there, and the planet is poisoned and industrialized almost beyond recognition.
* ''Film/TheyLive'' used a similar premise, with aliens "turning our world into theirs". Although it should be noted that this was only ''[[WildMassGuessing speculation]]'' from one resistance member as to what their motives were, which the audience never actually ''does'' find out. It's also contradictory since they were capable of surviving on Earth ''anyway'', having already infiltrated human society for years.
* ''WesternAnimation/BattleForTerra'': The humans sends a machine that can convert the air on Terra to be human breathable in seven days. This would leave the air unbreathable for the Terrians.
* ''Film/TheTrollenbergTerror'' is about aliens' native air slowly enveloping a mountain and later the surrounding area.
* In ''Film/ManOfSteel'', General Zod and his followers attempt to use a device called the World Engine to convert Earth into a new Krypton. Not only is the process incredibly destructive, but Krypton's atmosphere is toxic to humans. When Jor-El tries to persuade Zod not to do this, appealing to the fact that Earth's environment gives Kryptonians super powers and they can live side-by-side with humanity, Zod says he doesn't care about the humans and he doesn't want to have to adjust to the [[SensoryOverload enhanced senses]].
* In ''Film/PacificRim'', [[spoiler: the {{Kaiju}} creators learned from their first attempt during the age of dinosaurs, that they were incompatible with Earth's atmosphere. However, this trope is inverted, as instead of colonizing and ruining our planet, they waited and went to other worlds for 65 million years. Eventually, [[GreenAesop we destabilized our world enough to their liking in 200 years that they could just walk right in]]]].
* In ''Film/GuardiansOfTheGalaxyVol2'', the "Expansion" combines this with AssimilationPlot. [[spoiler:Ego the Living Planet planted seeds on various worlds across the universe that would expand and convert those worlds into extensions of himself. The process would displace and kill every living thing on those worlds, leaving only Ego. The only problem was that he lacked the power to do it himself...which is why he attempted to create hybrid offspring that he could use as batteries. Enter Peter...]]
* ''Film/JusticeLeague2017'': Steppenwolf seeks the three Mother Boxes in order to conclude the terraforming process that he attempted thousands of years ago. This process summons gigantic crystaline tentacles that tear the ground apart and [[RedSkyTakeWarning turn the skies red]], presumably turning any planet it takes place on into a mini-Apokolips.
* ''Film/MortalKombatAnnihilation'': When Shao Kahn launches his invasion of Earthrealm, Sonya and Jax notice that nature is slowly dying because of the merging process. If completed, Earth would become a {{Mordor}}-like realm just like Outworld.

* In ''Literature/LoneWolf'', the Darklords thrive in toxic environments and [[WeaksauceWeakness cannot stand clean ones]]. Thus, their forces slowly spread out and turn the land into {{Mordor}}.

* In ''Literature/TheWarOfTheWorlds'', Martians use areoforming as a weapon, introducing "[[AlienKudzu red weed]]" that chokes out all other plants and sucks up the planet's water. [[spoiler: Fortunately it's as susceptible to Earth microbes as the other Martians]] Possibly an UrExample.
* The ultimate plan of the alien conquerors in John Christopher's ''[[Literature/TheTripods Tripod]]'' novels is to convert Earth's atmosphere into something they can breathe.
* ''Literature/LastAndFirstMen'', the Fifth Men escape a dying earth by terraforming Venus. Halfway through the process they discover that Venus is inhabited and oxygen is lethal to the natives, they keep at it anyways.
* ''Literature/TheWarAgainstTheChtorr'' features an invasion by an alien ecosystem, almost all of it deadly to man.
* The Yuuzhan Vong in the ''Literature/NewJediOrder'' use OrganicTechnology exclusively and "Vongform" many of the planets they conquer, including Coruscant. In the ''ComicBook/{{Legacy}}'' comics a century later the Jedi and Vong shapers attempt to use their technology to re-terraform several devastated planets in the galaxy, but the Sith sabotage the effort.
* The Alectors of the ''Corean Chronicles'' carried this out against the Ancients when they began colonizing Corus.
* This happens to Earth in Thomas Disch's ''The Genocides''.
* ''Franchise/CthulhuMythos'': Allies of the Mythos are trying to work towards "clearing off the Earth" for the Great Old Ones.
* In ''Literature/StarTrekTheGenesisWave'', the titular Wave is designed to do this, transforming planets into new homes for PlantAliens the Lomarians. Fired from the Lomarians' hidden base, the energy wave transforms worlds in its path into swampy hellholes through use of Genesis technology stolen from Dr. Carol Marcus. The Lomarians even go as far as to program their own genetic profile into the genesis matrix, combining colonization with reproduction by having new Lomarians spontaneously generated on transformed worlds.
* ''Literature/TheCulture'' of Ian M Banks considers ''all'' terraforming hostile for this very reason. Also inefficient. Turning dead rocks into tailor-made Orbitals and Rings is much more desirable, on all points.
* In ''The Kraken Wakes'' by Creator/JohnWyndham it turns out that the alien invaders are triggering global warming to melt the ice caps, presumably to increase the amount of ocean deep enough for them to live in.
* A minor example in Creator/HarryTurtledove's ''[[Literature/{{Worldwar}} Colonization]]'' books: when the [[TheReptilians Race]]'s Colonization fleet finally arrives, they bring with them plants and animals from Home, a [[SingleBiomePlanet desert world]]. The plant life thrives in Earth's desert regions and spreads faster than weeds. Since the Race also happens to control most of Earth's desert regions, this works out for them. However, arid American states are also being taken over by the [[AlienKudzu alien plants]]. Home's animals are even worse. Since they're used to food being scarce, they eat all plants down to the roots, leaving not a blade of grass in their wake. Many characters compare them to goats, only much worse. When the US complains to the Race about their animals crossing into American territory, Fleetlord Atvar simply tells them they're free to destroy any plants and animals in their own territory as they wish. Of course, while a farmer with a rifle may scare off and shoot a coyote, good luck doing that to a brontosaurus or a whole herd of them. Neither the plants nor the animals are likely to move into the colder regions, though.
* Creator/IsaacAsimov's ''In A Good Cause...'' has information on the sulphur-reducing Diaboli terraforming the obscure human colony of Chu Hsi to be fit for Diaboli life falling into the hands of a group of human anti-Diaboli Federalists, who intend to release it to break up a Diaboli-sponsored all-human conference. [[spoiler: Except it turns out the information was a forgery by Earth's government, as part of a long-running scheme to manipulate things so that when the human-Diaboli war comes, no human power is on the Diaboli's side.]]
* This is the purpose of the Mimics in ''Literature/AllYouNeedIsKill''.
* There was a ChooseYourOwnAdventure book that involved alien domes that were polluting the air, apparently in an attempt to make the atmosphere like theirs.
* Creator/BrianWAldiss' ''The Saliva Tree'' has a pair of aliens landing near a farm somewhere in England and spreading a chemical that greatly increases crop yield and starts changing the local animal life, including humans, to better suit the invaders' tastes. It starts when everyone at the market complains of the milk being spoiled, and the farmhand who's selling it tastes it as perfectly fine. The main character barely has time to take his lady friend (later fianceé) before the mutagenic effects of the chemical become irreversible (as is, she spends some time violently ill as her body struggles to resist the chemical). The others who stayed were not so lucky.
* In Creator/GeorgeRRMartin's ''Literature/TufVoyaging'' the Ecological Engineering Corps used 30-km "seedships" to wage ecological warfare on an alien race called the Hrangans. The ships cloning all sort of plagues and flora and fauna to devastate worlds. A couple thousand years later the last known seedship is in the possession of one Haviland Tuf who offers his services for hire, often using the ship for beneficial terraforming but sometimes using it for its intended purpose.
* The villains of ''[[Literature/HumanxCommonwealth The Deluge Drivers]]'' attempt to heat up the [[SingleBiomePlanet ice world]] Tran-ky-ky to make it habitable to humans, even though this will decimate the native Tran. Ironically, such warming would've [[BizarreSeasons happened naturally eventually]], but the culprits don't want to wait ten thousand years for the place to warm up.
* The prehistory of ''Literature/TheSeventhTower'' has a self-inflicted version: after a devastating war with the SpiritWorld Aenir, whose denizens can manifest in the physical world as {{Living Shadow}}s, humans created a Veil of [[CastingAShadow enchanted darkness]] to block off the sun. It made most of the planet lethal to Spiritshadows but turned it into a frozen wasteland. [[spoiler:When the BigBad briefly destabilizes the Veil, it causes a mild ecological disaster for the peoples who had adapted to the Ice.]]
* ''Literature/TheSouthernReachTrilogy'': The Crawler's misguided purpose is to revive the world of its creators by terraforming Earth through returning it to a primeval state even though said creators are long dead.
* In ''[[Literature/TheLongEarth The Long Utopia]]'', this appears to be the aim of the [[spoiler: insectoid "Manipulators" who have managed to step (in a different way than previously seen in the series) from an intersecting universe.]] In this particular instance, standard terraforming is too inefficient to deal with the existing flora and fauna, and so [[spoiler: the creatures devise a way to essentially shake the planet apart to harvest raw materials for terraforming-from-scratch efforts.]]
* In ''The Taking'', a 2004 novel by Creator/DeanKoontz, characters speculate that this may be the goal of whatever has arrived with the storm that sweeps across the West Coast. [[spoiler:After the discovery that the aliens are in fact demons that have (possibly) come into the Universe through a black hole, it becomes clear that their intention was to reverse terraform the world into a literal HellOnEarth]].

[[folder:Live Action TV]]
* In ''Series/QuatermassII'' an alien vanguard takes over selected humans so they can build a chemical plant to make an atmosphere that will support their kind of life, and kill off all terrestrial life.
* The ''Series/StarTrekTheNextGeneration'' episode [[Recap/StarTrekTheNextGenerationS1E17HomeSoil "Home Soil"]] featured a Federation terraforming project that was doing this by accident. And the locals didn't like the "Ugly Bags of Mostly Water" mucking up their planet.
* ''Series/StarTrekDeepSpaceNine'': Sisko used a specialized warhead to poison the atmosphere in such a manner that it would be uninhabitable for human life, but functional for Cardassian in an attempt to force Eddington to surrender. Though the Maquis did pretty much the same thing (except rendering it uninhabitable to Cardassian life but safe to human) to multiple Cardassian colonies.
* ''Series/StargateSG1'':
** In the episode [[Recap/StargateSG1S4E9ScorchedEarth "Scorched Earth"]], an alien vessel was terraforming a planet recently inhabited by a colony of displaced HumanAliens into something hostile to their form of life (in their defense, the ship started its work before the lost "colonists" arrived; it had just been working on the other side of the planet from the stargate, so neither group had noticed the other until now). Unlike most of the civilizations SG-1 encounters, the HumanAliens need a very specific environment to survive, meaning they can't easily be moved to another world, plus the ship had already expended too many resources to abandon the process, so it couldn't just go somewhere else either. Eventually it's resolved when [[spoiler:it turns out the terraforming ship knows the location of said HumanAliens' home planet, having passed it over while on its search for a suitable world. It even helps them relocate back to their homeworld before it returns to its terraforming job.]]
** By connecting to every Stargate in the Gate network simultaneously, the Dakara Superweapon is capable of seeding life across the entire galaxy (and did, millions of years ago)... or can completely wipe it out.
* ''Series/DoctorWho'':
** [[Recap/DoctorWhoS30E4TheSontaranStratagem "The Sontaran Strategem"]]. Weakened by their eternal war with another race of ScaryDogmaticAliens, the Sontarans hatched an uncharacteristically circuitous plan to bathe the earth in gas which is poisonous to native life but nutritious to themselves, so that they can use it to spawn more soldiers.
** In [[Recap/DoctorWhoS6E5TheSeedsOfDeath "The Seeds of Death"]] the Ice Warriors attempt to xenoform Earth using a fungus that will extract oxygen from the atmosphere.
** And from [[HumansAreTheRealMonsters the other direction]], [[Recap/DoctorWhoS9E4TheMutants "The Mutants"]] has a group of evil human colonists plotting to terraform an inhabited planet in a way that will genocide the indigenous sentient culture.
* The ''Series/{{Andromeda}}'' episode "Point of the Spear", the Pyreans (aliens that live in Venus-like environments) tried to forcibly pyroform a Commonwealth world. A large battle breaks out, and to prove that the Commonwealth is not one to be messed with, Dylan orders the planet's destruction via [[EarthShatteringKaboom Nova Bomb]].
* One episode of ''Series/TheOuterLimits1995'' had this with a new model of car that would poison the atmosphere for infiltrated aliens.
* ''Series/{{Defiance}}'' had a somewhat unintentional example, when the Votan Ark ships were destroyed the terraforming equipment they were carrying fell to Earth and malfunctioned, creating deadly hybrid creatures such as Hellbugs and those bear-spider-armadillo things.
** Towards the end of the second season it turns out that [[spoiler: the Votan sent the ''Kaziri'' ahead of the main fleet to terraform Earth, but the crew aborted the mission and buried the ship when they found that Earth was inhabited. However the AI is determined to complete its task and attempts to destroy both the humans and all but a few Votan it chose to preserve in capsules.]]
* The apparent intention of [[spoiler:the Mind Flayer]] in ''Series/StrangerThings''. It [[spoiler:builds a complex network of tunnels under Hawkins, killing everything above them and infecting even the soil itself with its spores. The adolescent demogorgons (nicknamed demodogs) that follow with it in its arrival on Earth are the first soldiers in a new army that it attempts to build before being shut out of the human world]].

* In the second season of ''Earthsearch'', the Angels force the humans off the planet Paradise and back onto their spaceship by using its terraforming technology to melt the icecaps, causing massive flooding.

[[folder:Tabletop Games]]
* Metagaming's [=MicroGame=] 12 ''Invasion of the Air-Eaters''. An alien race invades and uses Atmosphere Converters to change Earth's air to sulfur dioxide, which they can breathe it but we can't.
* ''TabletopGame/{{Warhammer 40000}}''
** "Tyrantforming" is the first stage of devouring a planet by the Tyranids - the spores dropped onto the surface merge with local plantlife, turning it into HungryJungle - rapidly draining the ground of all nutrients. The Tyranids then devour the plants. By the time they're finished with a planet the lack of a breathable atmosphere and any oceans makes the planet inhospitable without substantial effort, while Tyranid organisms left behind make that prospect extremely unwise.
** Orks are described as "an invasive ecosystem by themselves", and shed spores to generate new creatures, which will grow to be squigs, grots, gretchen or full orks depending on the conditions. With enough orks, they create their own flora and fauna, and the whole ecosystem is "orkoformed".
* In ''TabletopGame/MagicTheGathering'', a single drop of Phyrexian oil can corrupt anything but it has an easier time with metallic objects. Karn the Silver Golem unknowingly spread Phyrexian oil on his travels throughout the planes thanks to the Phyrexian heartstone that Urza used to give him life. Then he created an artificial plane Mirrodin full of metal structures and metal-infused people. The oil he left behind quickly corrupted Mirrodin and turned it into New Phyrexia.

[[folder:Video Games]]
* The page quote comes from the [[SugarWiki/NeedsMoreLove woefully underappreciated]] 2001 videogame ''VideoGame/HostileWatersAntaeusRising'', very likely the first piece of media some tropers heard about terraforming in the first place. In it, [[spoiler: the genetically-engineered "alien" Species, after having TurnedAgainstTheirMasters,]] begin to drop the ambient temperatures of the island chicane where they operate, in addition to pumping toxins into the air and increasing ground radiation levels, to bypass their [[spoiler: in-built]] sensitivity to heat [[spoiler:(which in itself was a safety feature to prevent them from spreading too far)]]. The effects become more and more pronounced with every mission, until the final islands come to resemble ''nothing'' on Earth (and, indeed, the very last one was ''not even there'' in the first place):
--> '''Sinclair:''' Sinclair, [[http://www.youtube.com/watch?v=0m705hKiRYI First Officer's log entry two-zero-three-two-kappa]]. The air is changing in composition. Radiation levels are shifting, altering in frequency and power. Something's growing in the rocks. The ground is scabbing over, shuddering with intense fungal infection. Its ''freezing''. Humans couldn't ''live'' in an environment like this. Oh... ''God... That's the point!''
* The ''VideoGame/CommandAndConquerTiberianSeries'' centres around humanity adjustments to a world being transformed by the eponymous [[GreyGoo Technicolour Crystaltech]] - which not only convert the atmosphere and the ecosystem, but also extract useful minerals from the Earth's crust for easy harvesting when the invaders finally arrive in person.
* ''VideoGame/HalfLife2'' in its released form contains hints of this - most notably, the Combine drain the Earth's oceans and use Xen species such as Headcrabs and Leeches as biological weapons. The original beta however went much further - a key location in the game was the "[[http://half-life.wikia.com/wiki/Air_Exchange Air Exchange]]", which replaced the air with noxious gases breathable by the Combine, and which meant that all human characters in the game had to wear gas masks.
* In ''VideoGame/StarControlII'', Mycon Deep Children reshape planets they collide with, stimulating their volcanic activity to the point where it's comfortable for Mycons - obviously, since they enjoy temperatures above 600 Kelvins, it's less than comfortable for pretty much everyone else. Mycons don't seem to care.
* ''VideoGame/{{Resistance}}'' has massive temperature shifts - most obvious in ''Resistance 3'' - due to the Chimera terraforming the planet to be more suitable their own needs.
* In ''VideoGame/{{Spore}}'', you can deterraform planets of an enemy empire to reduce the level of colony that planet can maintain (especially effective against enemy home-worlds, as it reduces them from thriving T-3s with extra settlements, to a basic T-2 with two settlements at best). Empires will regard this as an act of war. More in line with this trope, the Grox, EnemyToAllLivingThings, can be killed by terraforming their planets, and likewise they specialize in deterraforming.
* Phazon from the ''VideoGame/MetroidPrimeTrilogy'' tends to do this. [[spoiler: It turns out to be a SentientPhlebotinum PlanetaryParasite that originates from the planet Phaze, which deliberately seeds the universe with phazon meteors.]]
* The Korath Clan in ''VideoGame/GalacticCivilizations 2'' prefer to eliminate a planet's entire biosphere. They can then colonize the resulted toxic world.
* All K-D Labs RTS games employ combat terraforming to some extent.
** All sides in ''VideoGame/{{Perimeter}}'' and two sides in ''Maelstrom'' can terraform the battlefield to create passages and so on. Both sides in ''Perimeter II'' (Exosus being waterborn, Comeback being landlubbers) and Hai-Genti in ''Maelstrom'' instead make parts of land inhabitable only for themselves.
** In ''Perimeter'', terraforming is out-and-out weaponized. The Exodus' superweapon, the Scum Disruptor, creates a volcano wherever it's targeted, and Scum Splitters create a [[EarthquakesCauseFissures localized earthquake]].
* In ''VideoGame/LostPlanet: Extreme Condition'' [[MegaCorp NEVEC]] is planning to terraform E.D.N. III in a way that would instantly thaw out the planet and kill the native [[BugWar Akrids]] ''and'' the rebelling colonists. Fortunately Wayne discovers an alternative that won't fry the colonists and by ''Lost Planet 2'', ten years later, most of the frozen wastes of E.D.N. III have been replaced by deserts and jungles, and several new Akrid species are coming out of hibernation.
* In ''Stars!'' [[http://wiki.starsautohost.org/wiki/Claim_Adjuster Claim Adjuster]] trait can undo enemy terraforming via Retro Bombs. Claim Adjuster races also can use Orbital Adjuster on a planet without conquering it, and [[http://wiki.starsautohost.org/wiki/Packet_Physics Packet Physics]] races terraform planets they bombard with mineral packets. If environmental requirements of the sides are different (frequently, as it's 3 independent values), it's deterraforming for the target.
* In ''[[VideoGame/HaegemoniaLegionsOfIron Haegemonia]]: The Solon Legacy'', high-level spies can reverse-terraform enemy planets. It's not permanent (the enemy can simply terraform it back if they have the tech) but as planet quality is the primary factor in maximum planet population, killing off a few hundred million colonists or at least inciting revolution due to massive overpopulation with [[LinearWarriorsQuadraticWizards a single spy]] can really wreck someone's day.
* ''VideoGame/Aurora4X'': Terraforming can add or remove any gas into a planet's atmosphere. HilarityEnsues as well.
* ''VideoGame/DeBlob'': Interestingly, neither the Raydians nor the Inkies seem to be able to tolerate the environment that is suitable to the other; A world full of color and lacking ink is downright chaotic for the Inkies [[spoiler:(and deprives them of the ink they need to replicate themselves)]], while the Inky world of black and white is painfully dull and polluted for the Raydians, even more so if they are forced into the suits that impede their movements [[spoiler:and are the only known way that the Inkies can generate new ink]]. So it follows that in the areas that the Inkies take over, they dramatically alter the environment in addition to altering / bleaching buildings. This is often seen in the first console game in the form of massive spills / slicks of ink on the surface of formerly clean water and stunted vegetation. In the second game these effects are much more pronounced - Prisma City has suffered both heavy water and air pollution even before the formal Inky takeover, some buildings / landforms are submerged underground to impede Blob's progress, and perhaps most dramatically of all, the canyon leading to the Inktron Collider (formerly Prisma City's hydroelectric plant) is near-completely submerged in frozen ink. Of course, as Blob makes progress, he alters the landscape in a fashion that is detrimental to the Inkies.
* The planned fate of Earth in ''VideoGame/{{Manhunter}}''.
* The Shroobs do this to the Mushroom Kingdom in ''VideoGame/MarioAndLuigiPartnersInTime''. After raiding Peach's Castle and Toad Town, they proceed to cover it all in their native purple mushrooms -- and also harvest vim from Toads, [[AndIMustScream turning them into those mushrooms as well]].
* ''VideoGame/SidMeiersAlphaCentauri'' plays this trope every possible way, both in terms of mechanics and actual story. Humanity as a whole is trying to survive on alien planet. Said planet is a sentient being, which treats human activity as symptomes of a disease and reacts accordingly, mobilising immune response. With sufficent technology, it's possible to melt polar caps or cool down the planet, directly influencing sea level. This may lead to drowning of numerous cities, most likely belonging to unprepared enemy factions ''or'' render all ports facitilies useless (which can hit really hard pirate faction). There are also tectonic warheads, perfectly capable of causing local tectonic shift. And last, but not least, are fungal payloads, which cause a massive outburst of native lifeforms where they hit - usually with mind worms read to attack everything outside their new habitat.
* In ''VideoGame/CivilizationBeyondEarth'' colonies following the path of Purity intend to replace their new planet's ecosystem with that of Earth's, rather than adapting themselves like [[BioAugmentation Harmony]] and [[CyberneticsEatYourSoul Supremacy]]. In fact, Harmony-leaning factions will demand that Purity and Supremacy factions stop clearing the miasma (a highly-toxic alien gas) near their lands, showing that they view this act as this trope.
** On a tactical level, Harmony factions can engage in some Hostile Un-terraforming by deploying Miasmic Condensors, orbital units that create miasma (which [[GeoEffects heals and powers up]] their units, but damages those of other affinities). Their workers can also do the same to individual hexes as a defensive measure. This can also screw up any non-Harmony faction's trade, as their trade routes can't go through miasma hexes.
* In the ''[[Videogame/{{X}} X-Universe]]'''s distant past, humanity launched fleets of [[RecursiveCreators self-replicating, self-improving]] terraforming starships to make the uninhabited planets of the precursors' PortalNetwork habitable. A [[AIIsACrapshoot glitched software update]] in 2146 caused the Terraformers to return to the Solar System in force, "terraforming" anything they found. New York City was leveled by a redirected [[ColonyDrop comet or asteroid impact]]. In the games, most of the planets found in Terraformer (now "Xenon") territory have been heavily scarred by Xenon experiments.
* Megatron's ultimate plan in ''VideoGame/TransformersDevastation'' is to turn Earth into a second Cybertron. [[spoiler: However, the technology he uses comes from Optimus's assumed heroic predecessor.]]
* In the ''VideoGame/StarCraft'' series the Zerg cover the surfaces of planets with [[MeatMoss Creep]] on which they are able to "build structures" and get a bonus to their healing speed. Other races cannot build on Creep until it clears away after the source of the Creep (Hatcheries, Creep Colonies, Creep Tumors, or Overlords) is destroyed.
** In ''VideoGame/StarcraftIILegacyOfTheVoid'' Amon starts terraforming Aiur with corrupted Void crystals that suck the life out of the surrounding life forms and summon Void entities.
* In ''VideoGame/{{Stellaris}}'', the [[spoiler:Prethyon Scourge]] can do this to worlds. The only solution is OrbitalBombardment; if they're caught mid-process, simply wiping out the terraformers from orbit will suffice, but if the world's been completely altered, [[ItsTheOnlyWayToBeSure the entire biosphere has to be glassed into oblivion]].
** Before update 1.3 it was possible to terraform inhabited planets to an ecosystem the population wasn't suited for, making them uncomfortable. After that patch only uninhabited (or stone age) planets can be terraformed by playable factions, but the process removes all tile blockers including hostile fauna or flora, suggesting that terraforming is an global extinction-level event.
* In ''VideoGame/{{Evolve}}'', this is part of the process of a monster invasion. While the defenders are busy fighting the beasts, they fail to notice the atmosphere becoming toxic and the weather becoming unstable. Once there are no more humans, structures are razed and the planet is practically immolated as the monsters use key positions as nesting grounds.
* ''VideoGame/{{Stars}}'' allows this as a tactic by races with the Claim Adjustor trait.
* ''VideoGame/{{Xcom 2}}'' has this on some maps. It's not a stated goal of the aliens and the effect is pretty patchwork, so it's probably more of a matter of the [[AliensAreBastards Elders being careless or lazy]] than malicous destruction. Nevertheless, the imported plants grow over everything to the near total exclusion of anything from Earth. These spots tended to be isolated out in the wildnerness, usually near [[VichyEarth ADVENT]] facilities the populace was never meant to see.
** What is active policy is the euthnasia of nearly all animals, domesticated or otherwise. It's so bad that finding a pack of wild dogs is a rumor that can take almost a week to follow up upon. It also raises the question where those legendary [[ImpossiblyDeliciousFood ADVENT burgers]] come from.
--> '''Shen:''' Nobody seems to be asking the hard questions, like when was the last time anyone saw a cow?
* In ''VideoGame/JusticeLeagueHeroes'', Darkseid uses the Mother Box to warp reality and converts Earth into a new Apokolips.

[[folder: Visual Novels]]
* In ''VisualNovel/SayaNoUta'', the [[spoiler:ultimate goal of the villain deuteragonist, Saya, is to convert all life on Earth into the sort of creature that she is. This inevitably creates a world that would be completely uninhabitable for unconverted human beings, populated by grossly mutated mockeries of normal life, and by twisted people likely driven insane by the pain of their transformation]].

* ''Webcomic/WhiteNoise'' had this happen in the backstory. The aliens who [[ApocalypseHow killed off everyone on Earth's surface]] then attempted to terraform the planet to suit them, resulting in a clouds of toxic Murk that roam the surface.
* In ''Webcomic/{{Homestuck}}'', the Troll Queen aka Betty Crocker's attempts to recreate Alternia on Earth lead to mass flooding and the extinction of humanity. Among other things, she tried to force humans to adopt troll culture and romance which was impossible due to basic biological differences. Humans don't mix their genetic material in buckets to make new larva, for example.

[[folder:Web Original]]
* In ''WebVideo/NatOneProductions'''s story-line ''Denazra'', the machine fleets that are slowly [[RobotWar cleansing the galaxy of organic life]] do this to every suitable planet they come across. They usually start work as soon as they arrive, regardless of anybody still living there.
* ''WebOriginal/OrionsArm'': Happened on occasion due to many early colonists preferring to [[HumanSubspecies adapt]] to new environments rather than terraform, putting them into conflict with later waves who would rather change the planet than themselves.
** Most notably when the original Martian Tweaks were forced to leave their homeworld when the atmospheric pressure and oxygen content were raised to intolerable (for them) levels. However, the terraforming of Mars took long enough that a second clade of Martian tweaks emerged, and managed to halt the process at a level they are comfortable at.
** A similar thing happened on Venus, despite the extremophile tweaks wiping out the baseline colonists (the former were then banished from the solar system).
** When Zarathustra, one of the first exosolar colonies, was settled there was minimal terraforming and the tweaked colonists [[LostColony went feral]]. A couple centuries later [[MegaCorp Jupiter Transsystems]] arrived, enslaved the natives, and set up terraforming stations that would have killed off the tweak population if they hadn't also awakened and pissed off the [[DeusEstMachina original colony AI]].

[[folder:Western Animation]]
* Oglethorpe and Emory of ''WesternAnimation/AquaTeenHungerForce'' tried to do this in the episode "Bad Replicant". Except they have no idea how to do.
* ''Franchise/DCAnimatedUniverse'':
** The Imperiex in the series premier of ''WesternAnimation/JusticeLeague'' are WeakenedByTheLight, and so make machines that blanket the Earth's sky in [[TheNightThatNeverEnds perpetual darkness]].
** In ''WesternAnimation/SupermanTheAnimatedSeries'', the forces of Apokolips attempt to cause a volcanic reaction that will turn Earth into a [[LethalLavaLand lava-spewing]] {{Mordor}} like their own planet. They try it again during the invasion in the finale of ''Justice League Unlimited''. Neither one serves much of a practical purpose; Darkseid basically just wanted to mark Earth as his own.
* ''WesternAnimation/SuperFriends'' (1973-74):
** The inhabitants of the planet Solar Terrarium are moving the Earth closer to the Sun so it will become hotter and more comfortable for them. They are too desperate for their own survival that they couldn't worry that the increased heat and resulting climate change will kill most of the humans living here. Being the benevolent heroes that they are, the Super Friends agreed to repair their planet if they stopped trying to mess with Earth's climate.
** In an episode of ''Challenge of the Super Friends'', beings from the planet Venus agree to help the Legion of Doom destroy the Super Friends in exchange for increasing the Greenhouse Effect on Earth so that the Venusians will be comfortable there.
* In ''WesternAnimation/TransformersPrime'', [[spoiler: the Decepticons intend to use the Omega Lock to convert Earth into a second Cybertron.]]
** This idea was used earlier, in the ''WesternAnimation/TheTransformers'', episode "The Key to Vector Sigma."
** On a smaller scale, Decepticon pirate, Hammerstrike of ''WesternAnimation/TransformersRobotsInDisguise2015'' causes oil spills to try to recreate the Cybertronian seas that he's accustomed to.
* ''WesternAnimation/TeenageMutantNinjaTurtles2012'': Episode [[Recap/TeenageMutantNinjaTurtles2012S1E17TCRI "TCRI"]]. The Kraang plan to alter earth's atmosphere to one that they prefer, and that earth natives can't breathe in.
* In ''WesternAnimation/Ben10Omniverse'', the Kraaho attempted to detonate a nuclear device on Earth to heat it up and make it more comfortable for them, not caring that this would kill off the humans.
* ''Young Samson & Goliath'' episode "Cold Wind From Venus". Two robots from Venus plan to impose "environmental control" over the entire Earth by reducing the temperature to -200 degrees Fahrenheit (turning it into an [[SingleBiomePlanet Ice Planet]]) so Venusians can settle here.
* In ''WesternAnimation/StevenUniverse,'' it is revealed that had Earth become a Gem colony as planned, it would have been completely gutted to serve the Gem home world's purposes. The [[StoryboardingTheApocalypse graphic simulation]] shows us a world that is nearly hollowed out, to the point that it can only charitably be called a planet at all, with Gem technology covering what's left. We don't know how many inhabited worlds have met this end. While the Crystal Gems managed to save the Earth, in-universe maps show that the Earth's geography was still drastically altered--most prominently, Siberia has largely sunk.
* The Irken Empire from ''WesternAnimation/InvaderZim'' employs a procedure dubbed "Organic Sweep" to terraform an already conquered planet. This consist of the entire Irken Armada bombarding the planet's surface with all their artillery, eradicating all the organic life and structures that might have survived the previous conquering.

[[folder:Real Life]]
* Our Sun, full stop. When Venus was formed, it had water oceans as Earth has now but the Sun evaporated them, converting Venus into the DeathWorld that is now[[note]]But not before being for a time a world with conditions even more extreme than current ones[[/note]]. Conversely, as the Sun's luminosity is increasing as it ages, in around a billion years from now it's expected the Earth will be unhabitable too.
* Invasive species, migrants introduce new species of plants or animals to an ecosystem for their own benefit and the results on the native ecology are frequently disastrous.
* The American Acclimatization Society's attempt to introduce [[https://en.wikipedia.org/wiki/American_Acclimatization_Society#Shakespeare.27s_birds European birds]] mentioned in the works of Creator/WilliamShakespeare to North America.
* Going back in time, [[https://en.wikipedia.org/wiki/Great_Oxygenation_Event the oxygen crisis]]. Free oxygen like we know today was not around much at first, and most early life was unable to survive its introduction. Any air-breathing life since then (such as us) needed to be able to survive in an atmosphere with abundant oxygen. This was among the greatest extinction events in Earth's history.