A little much needed cooling for a few days...

The volcano that recently erupted in Iceland has been spewing swaths of ash and smoke into the sky. The ash is so thick that flights throughout Europe have been cancelled in a uniform grounding of planes of a scale not seen since the September 11, 2001 terrorism attacks. It is unclear how much longer the grounding will last, but one can guess it will last at least a few days. 

The combination of the eruption and the grounding of planes could provide a little bit of global cooling for the next few days. Granted, it will likely be a remarkably minute effect, but it is something. The thick ash and smoke will block the sun for quite a while and cool the land underneath it. Indeed, previous eruptions have had a profound impact. In 1991, a volcanic eruption in the Philippines is believed to have cooled the earth's surface by almost one degree fahrenheit. 

And to add to any cooling from the volcano, the grounding of flights will certainly help. Considering western Europe and Scandinavia is the world's busiest flight corridor and jets are significant contributors to climate change, cancelled flights could at least slow down some warming. Mind you, it will likely be even less influential than the volcano.

The downside, outside of people not getting on their flights, could be acid rain and serious air pollution. The ash will likely make its way towards the ground (though it hadn't yet when I write this) and have significant breathing problems. And ash is extremely acidic, so it could lead to acid rain or very acidic water supplies. Degradation of the ozone layer is also of concern.

The acidification is largely caused by sulfur-dioxide contained in the ash. Throwing sulfur-dioxide into the atmosphere is a solution to climate change being proposed by some that is encapsulated in the term "geo-engineering". But, as the risks around acid rain and the ozone layer are realized, it is very clear that there is no free lunch.