By Sid Perkins
Glaciers along the southeastern rim of the Tibetan Plateau temporarily defied a warming climate around 9,000 years ago. Now a new model helps explain how they accumulated ice even though other glaciers in the region waned, scientists say.
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Cyclical variations in the Earth’s orbit cause long-term fluctuations in the amount of sunlight reaching the top of the atmosphere, also known as insolation, in the Northern Hemisphere during summer months. Just after the most recent ice age ended, about 10,000 years ago, the Northern Hemisphere’s insolation was on the rise and the climate was warmer than it is today, says Summer Rupper, a climatologist at Brigham Young University in Provo, Utah. Field data indicate that most glaciers in the region were retreating around 9,000 years ago, but in one area — the high mountains that stretch from the central Himalayas eastward into southern China — the ice masses inexplicably grew. Now, analyses by Rupper and her colleagues reported in an upcoming Quaternary Research suggest how those glaciers amassed ice in a warming climate.
The researchers looked at previous studies that had used 18 different models to compare global climate about 6,000 years ago with today’s climate. Few studies have focused on the period about 9,000 years ago, but the team’s analyses show that the climate at that time was comparable to conditions around 6,000 years ago, Rupper says.