A scientist who claims waning solar activity in the next 15 years will trigger what some are calling a mini ice age has revived talk about the effects of man-made versus natural disruptors to Earth’s climate.

Valentina Zharkova, a professor of mathematics at Northumbria University in the United Kingdom, used a new model of the sun’s solar cycle, which is the periodic change in solar radiation, sunspots and other solar activity over a span of 11 years, to predict that “solar activity will fall by 60 percent during the 2030s to conditions last seen during the ‘mini ice age’ that began in 1645,” according to a statement.