Global warming, also called climate change, was environmental damage that resulted in planets becoming hotter.
On Earth Edit
Earth was a notable victim of global warming.
The process of global warming was accelerated by a group of Zygons who sought to transform the Earth's atmosphere, and make it more amenable to Zygon life. They invested in industrial projects around the world, with the express goal of damaging the ozone layer, encouraging the introduction of modified CFCs into the atmosphere. They released products, like hairsprays and gassed-up CDs, that would allow humans to poison the world for them. (AUDIO: The Zygon Who Fell to Earth)
Upon taking Rose Tyler to see the Earth's destruction in the year 5,000,000,000, the Ninth Doctor mentioned global warming as one of the things humanity thought would cause their extinction. (TV: The End of the World)
In 2007, Professor Mallingan and his team of scientists began draining the power of the icy planet of Isqar hoping that it would put an end to global warming on Earth. The Tenth Doctor came across Mallingan's plans and enlisted the help of one of his scientists to destroy his lab, saving Isqar. (COMIC: Cold War)
Global warming existed on Pete's World on 2010, which was exacerbated by the Cybermen coming through the breach leading to N-Space over the course of three years. Pete Tyler noted that the temperature increasing by two degrees over 6 months and the melting of the ice caps wasn't caused "just [by] global warming", but by the breach. (TV: Doomsday)
When she visited the time of the Second Great and Bountiful Human Empire with the Tenth Doctor, 21st century native Donna Noble was fascinated that Earth was still populated, despite all the news articles stating the near end of the world, including global warming and the disappearance of bees. (TV: Planet of the Ood)
Rising sea levels caused by global warming flooded the Netherlands, forcing the Dutch people to become refugees. Later in the century they founded a new homeland on an island in the Atlantic Ocean, which they named the New Dutch Republic. (PROSE: St Anthony's Fire)
As a stop-gap solution to global warming, a device called the Great Solar Shield was designed in the 21st century to stall the effects of global warming by partially blocking off the sun. When the Shield broke apart because of the Tenth Doctor's efforts to stop the Silhouettes from attacking Earth, the Doctor told Martha Jones that humanity became up with a more permanent solution a few years afterwards. (COMIC: Sunscreen)
In the 23rd century, three-quarters of the planet's landmass was drowned by water. Humans built islands and colonised parts of the oceans for research and other uses. London was totally flooded. (GAME: TARDIS) Venice prepared to finally submerge into the waters of the Laguna. (AUDIO: The Stones of Venice)
In one possible timeline, global warming and nuclear warfare had turned Earth into a wasteland inhabited by Dregs, a mutated form of humanity, and the planet was known by the name Orphan 55. (TV: Orphan 55)
On other planets Edit
Global warming on Flydon Maxima led to an increase in water levels, rising above the previous 88% water surface coverage. This led to the renaming of the planet as "Despair" and an evacuation, mainly to Flydon Minima. Others adapted to living in floating cities, surviving on fish, seaweed and rainwater. (PROSE: The Depths of Despair)