In 2009, American geologist Adrian Helmsley learns that neutrinos from a massive solar flare are causing the temperature of the Earth's core to increase rapidly. Adrian informs White House Chief of Staff Carl Anheuser and United States President Thomas Wilson that this will trigger a catastrophic chain of natural disasters. In 2010 Wilson, along with other international leaders, begin a massive, secret project intended to ensure humanity survives. Approximately 400,000 people are chosen to board ships called "arks" that are constructed in the Himalayas. Additional funding for the project is raised by selling tickets to the private sector for one billion euros per person. By 2011 they start to move humanity's valuable treasures to the Himalayas, so that their history can survive when the end comes.
In 2012, Jackson Curtis is a science-fiction writer in Los Angeles who works part-time as a limousine driver for Russian billionaire Yuri Karpov. Jackson's ex-wife Kate and their children Noah and Lily live with Kate's boyfriend, plastic surgeon and amateur pilot, Gordon Silberman. Jackson takes Noah and Lily camping in Yellowstone National Park, where they meet Charlie Frost, who hosts a radio show from the park. Charlie references a theory that suggests the Mesoamerican Long Count Calendar predicts that the 2012 phenomenon is going to occur, and claims he has knowledge and a map of the ark project. The family returns home as seismic activity vastly increases along the west coast. Jackson grows suspicious and rents a plane to rescue his family. He collects his family and Gordon as the Earth crust displacement begins, and they narrowly escape the city using a Cessna 340 as Los Angeles sinks into the Pacific Ocean.
As millions die in cataclysmic earthquakes worldwide, the group flies to Yellowstone to retrieve Charlie's map, escaping as the Yellowstone Caldera erupts. Charlie, who stayed behind to broadcast the eruption, is killed in the blast. Learning the arks are in China, the group lands in Las Vegas, where they meet Yuri, his twin sons, girlfriend Tamara and pilot Sasha. The group secures an Antonov 500 aircraft and departs for China. Also heading for the arks aboard Air Force One are Anheuser, Helmsley, and First Daughter Laura Wilson. President Wilson chooses to remain in Washington D.C. and is soon killed by a megatsunami which sends the USS John F. Kennedy crashing into the White House. With the Vice President dead and the Speaker of House missing, Anheuser assumes leadership.
Arriving in China in a crash landing that kills Sasha, the group is then spotted by the Chinese People's Liberation Army. Yuri and his sons, possessing tickets, are taken to the arks. The Curtis family, Gordon, and Tamara, none of whom possess tickets, are picked up by Nima, a Buddhist monk on his way to the arks. They stowaway with the help of Nima's brother, Tenzin, who has been working on the ark project. A megatsunami approaches the site as tens of thousands of people are attempting to board the final ark, when a large impact driver becomes lodged between the gears of the ark's hydraulics chamber, preventing a boarding gate from closing and rendering the ship unable to start its engines. In the ensuing chaos, Gordon, Yuri and Tamara are killed, Tenzin is wounded and the flooding ark is set adrift. Jackson and Noah free the impact driver from the closing mechanism, and the crew regains control of the ark, preventing a fatal collision with Mount Everest.
When the global floodwaters from the tsunamis recede, three arks set sail for the Cape of Good Hope in South Africa, where the Drakensberg mountains have risen in relation to sea level. Jackson reconciles with his family and Adrian starts a relationship with Laura. The Earth is shown from space, revealing a drastically changed Africa as the only continent visible above sea level.
