ST. PETERSBURG, Russia - A Russian astronomer has predicted that Earth will experience a "mini Ice Age" in the middle of this century, caused by low solar activity.

Khabibullo Abdusamatov of the Pulkovo Astronomic Observatory in St. Petersburg said Monday that temperatures will begin falling six or seven years from now, when global warming caused by increased solar activity in the 20th century reaches its peak, RIA Novosti reported.

The coldest period will occur 15 to 20 years after a major solar output decline between 2035 and 2045, Abdusamatov said.

Dramatic changes in the earth's surface temperatures are an ordinary phenomenon, not an anomaly, he said, and result from variations in the sun's energy output and ultraviolet radiation.

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