Luiz Rocha
Salty Dog
You can't rule it out either, it's not like we've been keeping temp readings for the past 500 years, or more.
We have not, but things like ice cores, tree rings and (yes) coral colonies have been keeping temp records for the past 2,000 years, or more.
Don't believe it? Just set up two tanks with different temperatures and compare how the coral grows on both...