There is always ice on the Atlantic. If there wasn't, then the Titanic would have reached New York quite safely. But in 1250, this was of a different order entirely.
The Atlantic Ice Pack began to grow, quite rapidly and quite noticeably. This was the first indication of what was to come.
It's known for certain that the glaciers in the North Atlantic and Greenland began coming further south than at any time since the major Ice Ages. But there is also oral history to suggest that this was a worldwide phenomenon.
By 1275, plant life had frozen in Iceland. Some of them are still trapped beneath the ice now.
From then until 1300, summers were uniformly bad across Europe, North America and North Asia. Each year, the average temperatures dropped just that little bit more. After that, nobody even expected a warm summer anymore. Everyone was resigned to the cold.
This was a little more than just putting on a warm coat if you went outside. Crops need sunlight; and they don't need excessive rain. The rains came with a vengeance.
It had been quite wet throughout Northern Europe since 1310, but what happened in 1315 was unprecedented. Only oral and legendary memories of the thawing of the Great Ice Age, around 9,300 years previously, was worse. That had led to the Great Flood of (quite literally) Biblical proportions.
Now heavy rain in Spring washed away the seeds in the ground. It rained heavily and constantly until 1317; and people starved. Seed stores were consumed for sustenance, which made it impossible to plant crops even when the bad weather was over. Famine overtook much of Europe and North Asia until 1322. Average life expectancy averaged just 35 years old.
The stories told of that time are horrific. Cannibalism, elderly people voluntarily starving, children cast out into forests to fend for themselves (the origin of Hansel and Gretel by the way), riots and violence formed just some of the tales.
And still we weren't in what historians call the Little Ice Age.