Sun may affect global warming and cooling

The brightening and dimming of the sun may account for a 1,500-year cycle of cooling and warming on parts of the Earth, a study of ice in the North Atlantic suggests.

Researchers found that a very slight difference in the amount of solar energy reaching the Earth can have a powerful chilling effect on the climate: ice builds up in lands bordering the North Atlantic, the average temperature drops in Europe and North America.

‘‘Whether the whole Earth is affected, we don’t know for sure yet, but it is certainly implied,’’ said Gerard C. Bond, a researcher at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, New York.