You can use Intel's power gadget to see the status of your CPU's temperature, power usage and clock frequency (i.e. if it's boosting, or if it's being throttled) https://software.intel.com/en-us/articles/intel-power-gadget...

e.g., if I start an h264 encode, first my CPU boosts, reaching 3.3 GHz (it's a 2.7 GHz i7), but after a minute, it's dropped to 2.4 GHz due to the thermals. Wouldn't surprise me if I stuck it in a freezer it would stay at a higher frequency.

Depending on laptop, quite possibly.

If it's thermal throttling, then cooling is going to help.

https://www.gizmodo.com.au/2015/06/if-you-water-cool-the-new...

During the heat wave last summer, my mac book pro became very noticeably slower.

Heat dissipation is a real issue for many devices.

When we switched to laptops from desktops at work, a full build including tests took quite a bit longer and a lot more variable in time; thermal limiting appeared to be the reason for the variance.

You can get laptop trays that are supposed to improve heat dissipation.