ST. PETERSBURG, February 6 (RIA Novosti) - Low solar activity could trigger a global freeze in the middle of the 21st century, a Russian astronomer said Monday.

Khabibullo Abdusamatov of the Pulkovo Astronomic Observatory said temperatures would begin falling six or seven years from now, when global warming caused by increased solar activity in the 20th century reached its peak, and that the coldest period would occur 15-20 years after a major solar output decline in 2035-2045.

Abdusamatov said dramatic changes in the earth's surface temperatures were an ordinary phenomenon, not an anomaly, and resulted from variations in the Sun's energy output and ultraviolet radiation.

The Northern Hemisphere's most recent cool-down period of 1645-1705, known as the Little Ice Age, left canals in Holland frozen solid and forced people in Greenland to abandon their houses to glaciers, the scientist said.

Images (Russian frost)