"Harvey was almost certainly strengthened and intensified by climate change. Unusually warm waters both at the surface and deeper in the Gulf of Mexico allowed the storm to surge from a Category 1 to a Category 4 just off the Gulf Coast, something that is extraordinarily rare. Warming also seems to have disrupted normal wind patterns, which might be why Harvey stalled directly over Houston for days, then wandered back out to sea, only to make landfall again.... is what allowed it to dump over four feet of rain."
"But we must remember that so far the world has only experienced about one degree Celsius of warming. Climate disasters after two degrees of warming will probably be more than twice as bad as they are now, because the relationship between temperature and atmospheric water vapor capacity is nonlinear (that is, one unit of temperature increase means greater than one unit of increase in maximum humidity). More water-saturated air means more powerful storms — and that's leaving aside slower-moving problems like sea level rise, glacial melt, disruptions to agriculture, chronic extreme heat, and so on...."