Here are two quotes. The first is from Trouet et al 2009:
The increased pressure difference between the Azores High (+3 hPa) and the Icelandic Low (–5 hPa) during positive NAO phases results in enhanced zonal flow, with stronger westerlies transporting warm air to the European continent. The axis of maximum moisture transport and the preferred stormtrack extend further to the north and east during positive NAO phases when the Azores High is strengthened, resulting in wetter winters over northwestern Europe (50-to-200–mm positive anomalies per season) and decreased precipitation over southern Europe and northwestern Africa (50-to-100–mm negative anomalies per season).
The next quotation is not:
Judged by the implied shift of the upper westerlies, the main depression tracks and the zone of low pressure associated with them (the “Iceland low”) should have had, in the period 1000-1300, an average position 1-3 ° north of the modern normal (1900-1939 average) position– a displacement that probably implies less ice on the Arctic seas, because a northward progression by almost this amount between 1800 and 1940 went hand in hand with a roughly equal retreat of the ice…
The [MCA] appears as one of dry summers, i.e., an oceanic, summer anticyclonic type of regime. In the subsequent cold epoch,… the summers have contributed a more than proportionate share of the year’s rain, whereas the winters became relatively dry.
The exercise for today is 1) to identify the source of the second quotation [PLEASE DO NOT GOOGLE as anyone can google things and you immediately encounter a PPT that reveals the source] and 2) explain exactly how the Trouet et al 2009 explanation overturns (or even differs) from the explanation in the other article.