It has been known for a long time that cities create warmer temperatures due to heat stored in buildings, roads, and other man-made structures. They also add heat from air conditioners, boilers, and other combustion sources. This is known as the urban “heat island”.

What has not been known until now, is that cities also raise temperatures in the areas surrounding them, out thousands of miles. A new study shows the extent to which human activities are influencing the atmosphere, both locally, and at distant locations. Scientists have concluded that the heat generated by everyday activities in metropolitan areas alters the character of the jet stream and other major atmospheric systems. This affects temperatures across thousands of miles, significantly warming some areas and cooling others, according to the study this week in Nature Climate Change.