All species exist within ecosystems, and those ecosystems are full of limiting factors. Limiting factors are things that limit population growth or size, and limiting factors can be abiotic or biotic factors. Abiotic factors are non-living factors like water, temperature, oxygen levels, soil acidity, and so on. Biotic factors are living factors and would include things like predator and prey relationships and availability of organic food. While I can't possibly include every limiting factor there is, I can simplify things by saying that all living organisms need food, water, and shelter. Shelter will include weather-related abiotic factors.

Organisms have tolerance levels within those limiting factors. For example, a tree might grow best at a particular temperature; however, it is capable of growing in colder or warmer temperatures. With that said, there are temperatures that exist outside of the tree's tolerance range. This is true of many species, and those species are then forced to seek environments that return them to conditions within their tolerance ranges. The United States Forest has been tracking species distribution for quite some time, and a recent study of 764 species showed that there is an average "poleward migration" of nearly 17 km per decade. There is data that shows the same kind of poleward migration for black spruce trees, white spruce trees, and Siberian pine trees; however, the migration speeds are much slower for trees.

How these kinds of migrations will affect humans is still largely unknown, so go ahead and make a hypothesis and discuss your reasons.