PLovett
While I’m sure we are both in agreement with this atmospheric pollution debate, contrails and there effect on surface temperature is also a furphy. Contrails tend to be seasonal. They are much more prevalent in the winter months than the summer months. Most contrails are very short lived, i.e. less than 30 seconds. Generally over the US 0f A around early September each year contrails are few and far between and those that do form are very short lived.
It is true that there appeared to be a small increase in average temperature across the US for a few weeks after 911 but most scientists are divided as to its cause. The most plausible reason I have seen is because road transport increased dramatically after 911 because of the hundreds of thousands of people stranded all over the country renting cars to get home. Evidence supporting this is the huge increase in business car rental companies had the days following 911.