So how do we know anything about anything that happened before computer-assisted sensors! Sorry pdq, you clearly do not know enough about the science to understand proxies, so I will go back to educating young receptive minds, and leave your closed one to read and ponder this:
Crowley, T. J.: Causes of climate change over the past 1000 years, Science, 289, 270–277, 2000.
Which contains TSI anomalies back to the year 1000.
Notice that is the journal Science, not Wikipedia or any other website.