The 
Washington Post article, One of the most troubling ideas about climate change just found new evidence in its favor, summarizes a recent study on the possible impact to the jet stream due to climate change.
The Northern Hemisphere jet stream flows in a wavy pattern from west to east, driven by the rotation of the Earth and the difference in temperature between the equator and the North Pole. The flow is stronger when that temperature difference is large.
But when the Arctic warms up faster than the equator does — which is part of the fundamental definition of global warming, and which is already happening — the jet stream’s flow can become weakened and elongated. That’s when you can get the resultant weather extremes.
The changes in the jet stream’s flow fixes weather patterns for a longer period of time. So, for better or worse, patterns in weather persist longer.
The study, its authors write, “adds to the weight of evidence for a human influence on the occurrence of devastating events such as the 2003 European heat wave, the 2010 Pakistan flood and Russian heat wave, the 2011 Texas heat wave and recent floods in Europe.”
What goes unmentioned in the article is that devastating weather events disproportionately impact the poor. The original paper, Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events, has all the technical details.