Warm ocean water stands physically higher than cold water
Satellite radar can detect a looming climate shift by measuring the microscopic expansion of Pacific waves as they absorb immense quantities of solar heat.
When the Pacific Ocean begins to warm during an El Niño event, the water does more than change temperature; it physically grows. Because liquid water expands as it gains heat, a warmer column of sea will stand several centimeters higher than a cold one, even if the amount of water remains exactly the same. NASA and European satellites now track these subtle bulges from space by timing radar pulses that bounce off the surface with centimeter-level precision. This effectively turns the entire ocean into a giant, liquid thermometer that reveals where heat is moving before the weather even begins to change.