Jan. 16, 2019: Pick up your cell phone and look at it. That rectangular marvel of modern technology contains thousands of lines of code. Among them is the World Magnetic Model (WMM)–a program that helps your phone navigate. And it’s in a bit of trouble. Researchers have announced that the WMM needs an emergency update because Earth’s magnetic field is changing.

Savvy backcountry hikers have long known that compass needles don’t really point north. The magnetic north pole is displaced hundreds of miles from the true north pole and, to make matters worse, it wanders unpredictably from year to year. To find true north in the continental USA, you have to correct compass directions by as much as 20 degrees using a special “declination table.”

The World Magnetic Model is a computer program that makes this correction for you. It improves the navigation of devices ranging from nuclear submarines to common smartphones.

“The WMM is the standard magnetic model used for navigation by organizations such as NATO, the Ministry of Defence, and the US Department of Defense, and also by smartphone operating systems such as Android and iOS,” explains Will Brown of the British Geological Survey’s Geomagnetism Team, which produces the model in collaboration with NOAA of the USA.

“When you open your smartphone’s map app, you may see an arrow pointing which way you’re facing, and there’s something quite clever going on underneath,” he continues. “Your phone contains a magnetometer that is measuring the Earth’s magnetic field. In order to make sense of this information, Android and iOS operating systems use the WMM to correct the measurements to true north.”

Normally the World Magnetic Model is updated every 5 years. For decades that’s been often enough to track natural changes in our planet’s magnetism caused by fluctuations in Earth’s molten core. But suddenly things are changing faster than before.

“Since late 2014, Earth’s core field has varied in an unpredicted, and currently unpredictable, manner [including a sudden change in declinaton called a ‘geomagnetic jerk‘ in 2014/2015],” says Brown. “The aim of the WMM is to be globally accurate within 1 degree of declination, but we were going to exceed that limit in only 3 years.” That’s why, for the first time, they are issuing an update to the WMM before the usual 5 year mark in 2020.

The new model is based data from a global network of 160 surface observatories and satellites in low-Earth orbit such as ESA’s Swarm mission. It was supposed to be released on Jan. 15th but has been delayed until Jan. 30th because of the partial shutdown of the US government.