I agree it's much of a muchness. There are more daytime than night-time flights, which probably redresses the balance. I was really calling out Classified's wild pomposity as too much, which it was.
I defer to Classified's reference:
http://journals.ametsoc.org/doi/pdf/10.1175/JAM2325.1"Although most investigators favor the finding that contrail cirrus produce atmospheric warming on regional scales in the United States and Europe, the impact on global warming is still in the noise. Should aircraft activity increase as projected, the global effects
would become significant by 2050."
Although that's 2005, and things might seem to have clarified since then.