I wish I had the source data - but I was watching a report that was done on atmosperic temperatures in the aftermath of 9/11 - when there were no planes in the sky other than a few military aircraft. If I remember correctly, there was a measurable amount of cooling when the airplanes weren't contributing to atmospheric pollution - which then went "back to normal" when the planes started flying again.

So, again, there are even more factors to consider and we DON'T have all the answers.