Cirrus clouds play a key role in Earth’s climate by trapping heat. Using satellite observations and radiative transfer modeling, we examined how thinning these clouds might help cool the planet. We find that natural homogeneous and heterogeneous cirrus have distinct radiative effects, and that the instantaneous impact of cirrus cloud thinning can lead to either cooling or warming, depending on atmospheric dynamics. These insights help guide future studies of cirrus clouds using climate models.