Nuclear bombs suck a lot of dust and rocky debris into the atmosphere.
Most of this rock and dust falls back down to the Earth, but some of the finer dust can stay in the atmosphere for weeks or even months. One result of this is red sunsets as the dust scatters light from the Sun, but a much more subtle effect is that of Global Cooling. The dust high up in the atmosphere reflects a lot of the light from the Sun so that it never reaches the Earth's surface. This causes the Earth to cool down. Volcanoes also cause these problems as they throw up dust into the atmosphere too.