Why is "kernel_task" taking so much CPU?

Sometimes the fans on my Mac will ramp up, and after a minute I'll go into Activity Monitor and see "kernel_task" occupying a large portion of the CPU. What's going on?

Thanks to Howard Oakley, we have an answer.

Long-story-short, the kernel does this when your CPU or GPU gets too hot. It starts pretending to run heavy jobs to keep the fans running high, which cools the machine down.

Let's ignore the fact that-that solution seems weird and is misleading to a lot of users and trust that Apple's engineers chose the best solution they had. (You can't do anything about it anyway.)

The question to ask yourself is, why is my computer running hot if it's not the kernel_task process? Two options:

1. Some other heavy process is running hot (like photoanalysisd, the tool that scans your photos for faces)
2. The ventilation grates on your Mac are covered or plugged, preventing the fans from being able to effectively cool the processor or GPU

My advice: don't download software to limit the fan speed, and don't try to quit the kernel_task (which you won't be able to do anyway). Just clean the ventilation ports with a little bit of compressed air.

If that doesn't work, sleep your computer for awhile to let it cool back down, then wake it back up and watch Activity Monitor to see what processes are running hot while the machine is still cool, and google those process names to see what they are and what you can do about it.

Sometimes a reboot will help at this point for runaway jobs, especially on a new OS release.

HTH.