Look, it is not like adding 6°C on all temperatures and that's it. Weather is getting extreme and the environment changes then. There is a book called 6 degrees by Mark Lynas. It is a good read. He spend some time in the archives and collected what might change by comparing to past times. Rainforests will probably die or at least move, sea level will raise by ~70 meters.
On top millions or billions of people start moving around because their homes and their jobs no longer exist. Food will get a problem because the oceans go acid. Did you ever chose jellyfish as a diet? Social friction will increase. After Sandy NY run short on gas supply, remember the guarded gas stations? The western economy relies on weather behaving within a reasonable range, imagine cities without food, because the just in time transport system stucks in 2m snow for weeks. I can continue the list even more, but the point is basically everything will change: culture, economy, cities, agriculture, food, friends, borders, countries, and so on.
The last thing I can imagine is 7 billion people moving orderly to Russia or Canada to begin a new live in peace.
Many areas already deal with extreme temperature variance, the only change will be which areas need to do so.
And exactly how fast do you think the overall temperature is going to change? All the predictions I've seen have been single digit degrees per century.
What's changing is the total energy within the biosphere. That's going to have profound effects throughout the ecosystem. Modeling just what those will be is very difficult.
One trend that's already emerged has been an increasing variability and range to the jet stream, especially in how it increasingly "wanders" north to south. This means that regions might see very rapid and wide temperature swings from summer to winter or back over the course of a few hours to a day. For crops and ecosystems which rely on more predictable and stable conditions, this could prove deadly.
Glacial melting and rising seawaters don't just mean floods, but salt-water intrusion, disturbances of ocean current systems (themselves responsible for transporting vast quantities of heat around the globe, etc.
Some breakdowns in systems seem to have been very rapid. During and toward the end of the last glaciation period, vast ice dams and lakes would form, some over what's now Utah (historic Lake Bonneville, of which the Great Salt Lake is among the last remnants), as well as in eastern Canada. The formation and bursting of ice dams in the pacific northwest lead to the formation of what are now known as the Washington Badlands by way of the Missoula Floods -- as many as 25 major inundation events which created waterfalls, gravel banks, sandbars, and other features, over what's now dry land. Flow speeds exceeded 80 MPH and consisted of cubic _miles_ of water.
https://en.wikipedia.org/wiki/Missoula_Floods
Both circumstances involved warming, though from lower temperatures than today's baseline. The point is that secondary and tertiary climate change effects can be difficult to predict, but also exhibit very great nonlinearity. That is: we don't know what might happen, and it could happen very quickly, even in hours, or days. Certainly massive changes in less than a year's time are possible.
On top millions or billions of people start moving around because their homes and their jobs no longer exist. Food will get a problem because the oceans go acid. Did you ever chose jellyfish as a diet? Social friction will increase. After Sandy NY run short on gas supply, remember the guarded gas stations? The western economy relies on weather behaving within a reasonable range, imagine cities without food, because the just in time transport system stucks in 2m snow for weeks. I can continue the list even more, but the point is basically everything will change: culture, economy, cities, agriculture, food, friends, borders, countries, and so on.
The last thing I can imagine is 7 billion people moving orderly to Russia or Canada to begin a new live in peace.