If the Earth, for some reason, became tidally locked

How hot would it get on the side facing the sun and how cold would it get on the darkside?

Scientists conducted simulations to explore climate dynamics of tidally locked Earth-like exoplanets and to illustrate how the climate would adjust if Earth abruptly entered a tidally locked state. The experiments were made as if Earth were to have one hemisphere facing its star the Sun (only day), and the other always facing away (only night), or in other words being tidally locked. The findings were that tidal heating could yield a surface heat flux about three times greater. The surface temperature changes rapidly over land masses to day-side values of about 290 K and to night-side values of about 240 K. The ocean surface temperature changes more slowly; the night-side ocean remains near the freezing point for the length of the simulation.

The simulations started from a typical January 1 initial condition in the present-day climate, setting the planetary rotation rate to 1/365th of the present value (so that 1 day is equal to 1 current Earth year). The insolation was fixed so that there is a perpetual subsolar point on the equator at 88°W (near the coast of Ecuador). The simulation was run for 50 years.

You can use the moon as a reference. The moon isn't tidally locked to the sun (it is tidally locked to the Earth). BUT, because its period of daylight cycle is substantially greater, there is negligible thermal lag from day to night that keeps it warm. Additionally, a lack of atmosphere and a lack of a water ocean helps the moon respond quickly to temperature changes.

Besides, if this does happen, it is very likely that Earth would loose its oceans. Maybe even atmosphere.


The result is that the side facing the sun could get as hot as 390 Kelvin, and the dark side could get as cold as 100 Kelvin.

Compare this to Earth's ordinary temperature range from 184 Kelvin to 331 Kelvin.