Volcanic aerosols reduce global mean precipitation in the years after
major eruptions, yet the mechanisms that produce this response have not
been rigorously identified. Volcanic aerosols alter the atmosphere's
energy balance, with precipitation changes being one pathway by which
the atmosphere acts to return towards equilibrium. By assessing the
atmosphere's energy budget in climate model simulations, we here show
that global precipitation reduction is largely a consequence of Earth's
surface cooling in response to volcanic aerosols reflecting incoming
sunlight. In addition, these aerosols also directly add energy to the
atmosphere by absorbing outgoing longwave radiation, and this is a major
cause of precipitation decline in the first post-eruption year. We also
identify mechanisms that oppose the post-eruption precipitation decline,
and provide evidence that our results are robust across climate models.