What's your predicted scenario?

Mass migration from South America, Africa and Asia north toward the arctic.

From South America, people will be moving through a devastated Amazon that's been clear-cut and burned away almost completely to make room for farming and ranching.

America will resist the oncoming millions of people with tent cities popping up at the border. Military will deploy with occasional shootings and violence. For awhile there is a stalemate. But as temperatures climb and cities flood, Americans in the south will pack up, heading north to states bordering Canada that have become more temperate. Military units will pull up to higher latitudes, staying just ahead of the refugees until they've reached a point that they can survive just the weather.

Eventually the United States asks Canada to open their borders and allow Americans in. Canada politely declines and America decides to force the issue and invades, securing cropland, fresh water and land for its citizens, then proceeds to shore up this new border to repel the south American refugees.

This situation is repeated across Europe in various forms with southern peoples racing north and northern peoples closing borders and deploying militaries to stop them. Death tolls are in the billions as China and India and most African governments collapse and food becomes impossible to find.

Once able, new alliances form across the north and the remaining populations are set to saving what they can, building new infrastructure, growing food and doing what it takes to survive. All citizens are mobilized to work and art is a luxury that cannot be afforded. All resources are put toward sustaining society and sustainable energy. Technologies are developed only in regards to drawdown, terraforming or green energy projects. A harsher society forms with little use for useless mouths.

Just a thought. But seems reasonable.