Jack Hall, portrayed by Dennis Quaid, is a dedicated paleoclimatologist leading an expedition in the icy wilderness of Antarctica alongside his colleagues, Frank (Jay O. Sanders) and Jason (Dash Mihok). Their mission involves drilling ice core samples from the Larsen Ice Shelf for the NOAA when disaster strikes: the ice shelf unexpectedly fractures, putting Jack perilously close to falling to his death.
Later, at a United Nations conference in New Delhi, Jack unveils shocking findings about the effects of global warming, showing that a similar climate catastrophe occurred 10,000 years ago — essentially transitioning Earth into an Ice Age. He warns that if humanity continues to pollute our atmosphere, this could happen again in a matter of 100 to 1,000 years. Unfortunately, his dire predictions mostly fall on deaf ears, with many diplomats, including the U.S. Vice President (Kenneth Welsh), remaining skeptical.
During the conference, Jack connects with Professor Terry Rapson (Ian Holm) from the Hedland Climate Research Centre in Scotland, who reveals alarming observations about ocean currents being disrupted due to the melting polar ice caps. Terry informs Jack that this melting has significantly diluted the salt levels in the oceans, causing a drastic drop in the temperature of ocean currents by 13 degrees. Two buoys in the North Atlantic confirm this chilling trend, prompting Terry to reach out to Jack. Together with Janet Tokada (Tamlyn Tomita), a meteorologist from NASA, they collaborate to refine a model predicting further climate chaos using Jack's paleoclimatological data.
Across the globe, the climate crisis escalates dramatically; Tokyo is battered by hail the size of softballs, snow blankets New Delhi, and Los Angeles suffers devastating F5 tornadoes. Amidst rising chaos, the U.S. President (Perry King) takes urgent action by grounding all air traffic in the United States due to dangerous turbulence. Meanwhile, a rescue mission for the British Royal Family ends tragically as three RAF helicopters meet their doom inside a super-storm's eye, encountering frigid temperatures that freeze their fuel lines — resulting in a horrific crash.
In the midst of this turmoil, Jack's son, Sam (played by Jake Gyllenhaal), finds himself in New York City for an academic competition, accompanied by his friends Brian and Laura (Emmy Rossum). As violent weather grips the city, Sam pledges to return home on the next train. However, the storm intensifies, leading to flooding in the subway systems and Grand Central Station’s closure.
Determined to reach his son, Jack informs the President that the timeframe for impending disaster has shrunk to just days. He suggests evacuating southern states toward Mexico, as it’s too late for those in the north. Misunderstanding Jack's urgency, the Vice President dismisses him, prompting Jack to head to New York in search of Sam.
In Manhattan, a massive storm surge floods the city, reaching heights of nearly 40 feet. Sam and his friends take refuge in the New York Public Library. During their harrowing experience, Laura injures her leg but continues to help others escape a sinking taxi. With survivors in the northern regions desperately attempting to flee the relentless weather, Jack’s mission becomes all the more critical.
With Frank and Jason by his side, Jack embarks on an arduous trek toward New York. Their vehicle crashes, compelling them to navigate the snowy landscape on foot. Tragedy strikes when Frank sacrifices himself during a desperate struggle to save his friends. As the situation worsens, the President's helicopter is caught in the ever-growing super-storm, resulting in a catastrophic loss of life and leaving the Vice President in command.
Inside the library, under dire circumstances, Sam encourages his companions to heed his father's advice to stay put. As conditions deteriorate, they begin to burn books for warmth and forage for supplies. Unfortunately, Laura's injury turns septic, pushing Sam, Brian, and J.D. to brave the dangers outside in search of penicillin, confronted by wolves from the zoo and freezing temperatures that grip the city.
Jack and Jason take shelter in an abandoned Wendy's, but the unrelenting cold claims Jason as he collapses under the conditions. Left with no other option, Jack secures Jason in the restaurant's kitchen until they can continue their journey. Eventually, they reach the library, where they reunite with Sam's group, and rescue arrives in the form of U.S. Army helicopters.
As Mexico's new President coordinates search and rescue operations, hope arises following the survival of Sam's group. Further rescue missions uncover more survivors high above Manhattan's buildings. The movie concludes with a view from the International Space Station, revealing most of the northern hemisphere encased in ice — a sobering reminder of the consequences of humanity's neglect, coupled with an unexpected reduction in pollution levels.
