If I understand the question right, it's based on the assumption that a shortage of food or arable land in Scandinavia is part of what led to viking raids across northern Europe. This is an old assumption.

Thomas Malthus famously postulated that the world could only sustain so many people, after which there would be violence and famine until the population settled down to whatever was sustainable. In the mid-1800s, early scholars of the Viking Age made what was then the reasonable assumption that this was indeed a causal factor, whereas proponents of Social Darwinism and other groups that drew on Malthus's thought used the Viking Age as proof of Malthus's (and their own) theories.

All this research is now over a hundred years old, which means that it's well out of copyright and a lot of it has entered the public domain through Google Books. In short, these long-forgotten but recently digitized texts now constitute cutting-edge information for desktop researchers and Wikipedia aficionados. And so, for anyone not specializing in 9th-century northern European history, it's still very reasonable to still think these old assumptions are the way scholars think. But in this case, it's not.

We've gotten a lot better at understanding the past than did historians in the 1800s. It's not because we're smarter or less biased—neither of which is inherently true—but rather because we've developed and learned to appreciate more techniques for exploring the past than just reading the same old dusty sets of books. Archaeology in particular has professionalized, dramatically diversifying the knowledge of the past accessible to researchers today.

One of the most important new fields opened by archaeology, in my opinion, is landscape archaeology. This is an umbrella term that describes many perspectives and methods of research, but in particular, it's let us see that settlement across Scandinavia actually increased during the Viking Age. That is to say, Scandinavians started going abroad on viking raids even though Scandinavia had lots more arable space to offer. And, in fact, large scale studies of phosphate samples and archaeological pollen indicate that arable land increased while forests decreased in proportion during these centuries.

Admittedly, this evidence can cut both ways. An analysis of this evidence could lead to the conclusion that Viking Age Scandinavians were desperate to increase food production and they just couldn't keep up, leading to two centuries of overflowing violence. But this rests on an assumption about how we should interpret the evidence rather than the evidence itself. And some things that we would expect to see in the kind of scenario—like competition for land, violent local raids for food, and the impoverishment of land-based aristocracies—simply don't appear to have happened. Meanwhile, studies of Viking Age graves in Scandinavia have offered no dramatic indicators of malnutrition that aren't broadly evident across many premodern (and even some modern) societies.

So I'm of the opinion that famine didn't cause the Viking Age. And I don't really see famine as a major factor in the other major structural changes of the early middle ages, including the devolution of Western Roman power and the rise of an Islamic caliphate. In some cases, famine certainly was a factor in violence (for example, much of the violent feuding of Viking Age Iceland, where you risked taking an axe for eating another person's spoiled whale meat). But I'm always hesitant to point to a single cause for any major event. If you'd like to know more about current opinions about causes for the Viking Age, I'd recommend glancing at my comments on What caused the Viking Age of the 8th-10th century? I know that might not be what you were initially look for, but I still hope it's an all right answer to your question!