The link in the post is to a History channel clip discussing how the Medieval Warm Period led to the Little Ice Age. That's right; we've now gotten to the point that the alleged "science" in The Day After Tomorrow is the prediction of warmistas: we're going to cause the next ice age by overwarming the Earth.
The basic thought seems to be that the warm climate of the Medieval Warm Period caused changes in ocean currents, thus resulting in a sudden chill: warm air melted the polar ice caps, changing the salinity of the ocean, thus stopping the "conveyor" that brought warm water to the north Atlantic, making temps in the north more mild.
First off, present-day--even with "record" reductions in arctic ice--there has been no sign of any change to the velocity or direction of ocean currents.
Second, this theory fails to explain what caused the warming of the Medieval Warm period. It's not due to SUVs and coal-fired power plants; so what made it so warm? It certainly wasn't due to human activity. Whatever carbon dioxide was in the atmosphere then--we're repeatedly told that it was around 280 ppm--was from natural sources...so how the hell could "global warming" have taken place?
Mann et al, authors of the "Hockey Stick", eliminated the Medieval Warm Period from the climate record via fraudulent means because, as other warmistas have said, "We have to get rid of the Medieval Warm Period." Now that we've entered an anomalously long solar minimum and temps appear to be dropping, suddenly the MWP actually happened and caused the LIA. WTF?
We're told that solar variability can't cause climate change because the sun's output only varies by 0.07%...yet what other mechanism can explain the MWP and the LIA?
Need I explain how much energy 0.07% of the sun's output is? Need I explain how much energy that represents at the Earth's surface?
Okay: the Earth absorbs 1.32x1019 watts. That is energy from the sun at the Earth's surface, okay?. 0.07% of that is 9.25x1015 watts.
9.25 million gigawatts.
The United States uses 3.34 terawatts of energy every year. 0.07% of the Earth's total solar inundation is enough to run the US for about three thousand years.
(Note please that I am talking total solar irradiance, not the amount of power which can be extracted from sunlight using solar cells.)
0.07% may not be a large variation in the sun's output, and that's good, because a truly large variation would probably have made it impossible for life to exist on Earth in the first place.
But it for damn sure is enough to cause climate variability.