Flint Lockwood thinks he's a genius. But none of the things he invented are things that make sense or are useful. However, he has the support of his mother but when she dies, he's left alone with his father who thinks he should give it up. When the community that he lives in is in an economic crisis because their primary source of income, a sardine cannery, was shut down, Flint decides to try his latest invention, a machine that can turn water into food. But something goes wrong and the machine ends up in the atmosphere. Later it starts raining food. The shifty mayor tries to use this as a way to help their community, but when Flint senses something wrong with the machine, the mayor convinces him to ignore it. However, as Flint predicts, chaos ensues.

In 2009, Adrian Helmsley, an American geologist, visits astrophysicist Dr. Satnam Tsurutani in India and learns that neutrinos from a massive solar flare are causing the temperature of the Earth's core to rapidly increase. Arriving at a party in Washington D.C., Helmsley presents his info to White House Chief of Staff Carl Anheuser who takes him to meet the President. In 2010, U.S. President Thomas Wilson and other international leaders begin a secret project to ensure humanity's survival. More than 400,000 people are chosen to board enormous "arks" constructed at Cho Ming, Tibet, in the southwest Chinese Himalayas. A Buddhist monk named Nima is evacuated while his brother Tenzin joins the Ark project. Additional funding is raised by selling tickets for €1 billion per person. By 2011, valuable items are moved to the arks with the help of art expert and First Daughter Dr. Laura Wilson. In 2012, Jackson Curtis is a science fiction writer in Los Angeles who works as a limousine driver for Russian billionaire Yuri Karpov. Jackson's ex-wife Kate, and their children Noah and Lilly, live with Kate's boyfriend, plastic surgeon Gordon Silberman. Jackson takes Noah and Lilly camping in Yellowstone National Park. After an encounter with Helmsley, they meet Charlie Frost, who hosts a radio show from the park. Charlie plays a video of Charles Hapgood's theory that polar shifts and the Mesoamerican Long Count Calendar predict that the 2012 phenomenon will occur. Charlie also tells Jackson that those who discovered this and plotted to inform the public were killed in various accidents. After an earthquake hits Los Angeles, the family returns home. Jackson grows suspicious and rents a Cessna 340 to rescue his family. He collects his family and Gordon as Earth crust displacement begins with a magnitude 10.9 earthquake, and they narrowly escape Los Angeles as California collapses into the Pacific Ocean. As millions of people die in earthquakes worldwide, the group flies to Yellowstone to retrieve a map from Charlie, escaping as the Yellowstone Caldera erupts. Charlie stays behind to broadcast the eruption and is killed. Learning that the arks are in China, the group lands in Las Vegas to find a larger plane. They find Yuri, his twin sons Alec and Oleg, girlfriend Tamara and pilot Sasha. Helmsley, Anheuser, and Laura Wilson are aboard Air Force One where they are heading to the arks. President Wilson remains in Washington D.C. to address the nation one last time. With the Vice President dead and the Speaker of the House missing, Anheuser appoints himself Acting Commander in Chief even though he is not in the presidential line of succession. Back in Las Vegas, the group steals an Antonov An-500 aircraft and they depart for China as the Yellowstone ash cloud engulfs the city. President Wilson is later killed by a megatsunami that sends the aircraft carrier USS John F. Kennedy crashing into the White House. When the group arrive in China, the plane runs out of fuel and crashes into a glacier, killing Sasha, while the others make a narrow escape. They are then spotted by helicopters from the Chinese army. Yuri and his sons, possessing tickets, are taken to the arks, leaving the Curtis family and Gordon behind along with Tamara because Yuri knows she had an affair with Sasha. The remaining group are picked up by Nima and taken to the arks with her grandparents. They stow away on Ark 4, where the United States contingent is aboard, with the help of Tenzin. As a megatsunami approaches the site, an impact driver becomes lodged in the gears of the ark's hydraulic doors, preventing a boarding gate from closing, which in turn prevents the ship from starting its engines. In the ensuing chaos, Yuri, Gordon and Tamara are killed, and Ark 4 is set adrift. Jackson and Noah dislodge the impact driver and the crew regains control of the ark before it collides with Mount Everest. Jackson rejoins with his family, and he and Kate reconcile. As flood waters from the tsunamis slowly recede, the arks travel to the Cape of Good Hope in South Africa. Helmsley starts a relationship with Laura.?