A group of scientists are warning that weather extremes in the future and growing demand could lead to a drop in power supplied from renewable energy. In a new study, researchers considered how 13 extreme weather models would affect cities in Sweden. Their findings were recently published inNature Energy. Many scientists have partly blamed human activities for rising world temperatures and an increase in extreme weather events. The world’s power systems are expected to face pressure as more of the world’s population chooses to live in cities, the study predicts. The United Nations has estimated that 68 percent of people will live in cities by 2050. That compares to about 55 percent who live in cities currently. One of the biggest expected pressures to face power systems will be an increase in the use of air conditioning systems because of rising temperatures.