Global cooling was a conjecture during the 1970s of imminent cooling of the Earth's surface and atmosphere along with a posited commencement of glaciation. This hypothesis never had significant scientific support, but gained temporary popular attention due to a combination of press reports that did not accurately reflect the scientific understanding of ice age cycles, and a slight downward trend of temperatures from the 1940s to the early 1970s. General scientific opinion is that the Earth has not durably cooled, but undergone global warming throughout the 20th century