Plaque years or not, the rate of longevity in centuries past relied on the vagaries of climate. Mortality during the potato famine climbed, due to the lack of nourishment. The famine was created by the long cold rainy weather. When the Vikings colonized Greenland and were able to raise sheep, things went well. When the climate turned, so did their longevity. Ironically, "global warming" would do what it has done every time in the past - increase the available arable land for the production of food. Of course, then we'll burn it as alcohol...but that's a different thread. Then, during the next normal, natural downturn in temperatures the excess human crop that results from the increase in food supply would be eliminated. We are currently well past late in the next ice age cycle; not that they keep a tight schedule. People's peaceful attitudes tend to wander when they or their children are starving. I doubt that we will see this in the US...but in less agricultural areas things could get grim.