At two degrees, the melting of the Arctic ice sheets will pass a tipping point of collapse, flooding dozens of the world’s major cities this century — and threatening, over many centuries, to elevate sea level as much as 200 feet. At that amount of warming, it is estimated, global GDP, per capita, will be cut by 13 percent. Four hundred million more people will suffer from water scarcity, and even in the northern latitudes heat waves will kill thousands each summer. It will be worse in the planet’s equatorial band. In India, where many cities now numbering in the many millions would become unliveably hot, there would be 32 times as many extreme heat waves, each lasting five times as long and exposing, in total, 93 times more people. This is two degrees — practically speaking, our absolute best-case climate scenario.

David Wallace-Wells, "UN Says Climate Genocide Is Coming. It’s Actually Worse Than That", New York Magazine. I've read a dozen articles about this, this one most clearly lays out what it means that the new IPCC report, so dramatic and concerning, is still presenting what is effectively a best case scenario. The reality will be even worse.