Set the World on Fire

Fire is actually a potential biosignature, since it means something is filling the atmosphere with an unstable gas like oxygen. If we find a planet covered in flames, it might be an indicator that it supports life. Or used to, anyway, before the fire.

—Randall Munroe, xkcd, "Earth-Like Exoplanet" mouseover text

Sometimes the Villain is so bad that he scorches the earth beneath his feet (see also Walking Wasteland). Sometimes his evil diffuses around the world and literally sets the world on fire. Sometimes the world is set on fire by some mishap.

Examples of Set the World on Fire include:

Anime and Manga

in the anime version of Black Butler, the villain's plan involves cleansing the world by setting it on fire. He only manages London before being stopped.

Film

Reign of Fire has dragons emerging from the depths of the Earth and burning the world.
In the film version of Irwin Allen's Voyage To The Bottom Of The Sea, the major plot is that the Earth's Van Allen belts are on fire and slowly roasting the planet.
The 1980s Scare'Em Straight documentary The Nuclear Holocaust: a Scientific Forecast shows how a full-scale nuclear exchange would set fire to almost every bit of combustible material on Earth that wasn't vaporized. "The whole world is burning," says the show's surprisingly cheerful host.

Literature

In the short story/novel Nightfall, people set their cities aflame when darkness comes (about every 2,000 years), since they panic (having never seen actual darkness).

Live-Action TV

On Smallville an old psychic had a heart attack and died when she saw Lex Luthor's future: standing in the Oval Office as the world burns.
An entire alternate Earth is destroyed by fire and lava in classic Doctor Who serial Inferno.
Babylon 5: on the eve of defeat, President Clark programmed the Earth's network of defense satellites to turn on his own planet. If he couldn't rule, no one could.

Music

In Jonathan Coulton's "Skullcrusher Mountain", the singer's plan involves being in a submarine while igniting the atmosphere.
Ian Campbell's "The Sun is Burning" (later Covered Up by Simon and Garfunkel).

Now the sun has come to Earth
Shrouded in a mushroom cloud of death
Death comes in a blinding flash
Of hellish heat and leaves a smear of ash
And the sun has come to Earth

Defied in The Ink Spots' song "I Don't Want to Set the World on Fire". "...I just want to start a flame in your heart".
A repeated image in "Daze" by Poets of the Fall:

And you can give me everything I need this way
We'll be loving 'til the first light of the day
Set the world on fire with bitter sweet desire
To chase away the night, let the whole world burn
Set the world on fire for bliss in sweet denial,
Oblivion and peace. Will you let me burn?

Mythology

According to the Norse mythology, during the Ragnarök the fire giant Surtr will set the world on fire.
In Islam, the end of the world will involve Allah setting the world on fire.
According to some accounts, the Christian end of the world will also involve the world being set on fire.

Tabletop Games

The end result of Exterminatus by virus bombs in Warhammer 40,000 is this. The virus eats every organic thing on the planet and turns them into organic sludge, high in oxygen content. Then an orbital strike engulfs the world in a firestorm.

Video Games

Mass Effect 3: "Earth is burning."

Web Comics

On of the planets in Homestuck was set entirely on fire. The main character blew the fire out anyway
Happens in the Dresden Codak strip Caveman Science Fiction

Western Animation

Trigon from Teen Titans, when he emerged on earth his presence caused the earth to look like a volcanic wasteland complete with people frozen as statues. They got better.
In the season 1 finale of Beast Wars, the Vok decide that "the project" has been contaminated by our stranded heroes and villains. Cue one of the two moons turning into a giant laser gun of fiery death. Hey! One moon! That means we're on Earth, after all!
While not a planet per se, Ben 10's alien form Heat Blast has its species originating from a star, meaning that there home 'planet' is constantly on fire.
Attempted in the finale of Avatar: The Last Airbender by Firelord Ozai.
On one Christmas Episode of Futurama, the oxygen content of Earth's atmosphere is elevated by mutant Christmas trees. Then Bender lights a cigar...

Real Life

Setting the entire atmosphere on fire was one of concerns about exploding the atomic bomb. Luckily it wasn't true - if you're reading this, it didn't happen.