Which leaves one wondering why anyone would ever build a computer model, if at best it could only tell you what you told it to tell you, right? I think words like "big" and "major" are too open-ended. To use an aphorism from journalism, 1000 deaths in Asia equals 100 deaths in Europe equals 10 deaths in West Virginia, equals one death next door. How big is "big"? If the Black Sea should double in size over the next 100 years, and displace tens of thousands of people, it would STILL be just a local event, probably under my radar.
It does in relation to the almost simultaneous rise of two, seemingly unconnected civilizations. The earliest contact we can find is during the first intermediate period of the Egyptians, by then both civilizations were heading for their second millennium of existence.
Unconnected? How so? I see many connections, from the specific (there was a LOT of interaction between these particular two, since they were only a few weeks travel distance apart, and coexisted in connecting territory for a long time), to the general (after the last ice age, civilizations of equal sophistication arise in India and China). Globally, at the inception of the Holocene, groups of humans independently developed agriculture, and division of labor, and permanent cities, and language both oral and written, and religions, and civilization generally. The end of the last ice age enabled this - and it MIGHT have happened between previous ice ages, only to be lost with the glaciers. Even today, "scientific breakthroughs" tend to happen in two or more places simultaneously, because the existing theoretical basis is in place.
