New Delhi, May 17
Scientists say the simultaneous events of an exceptionally warm and moist period ushered in by a “warm ice age” approximately 7,00,000 years ago and the expansion of polar glaciers played a critical role in permanently altering the climate cycles on Earth.
A European research team including Earth scientists from Heidelberg University, Germany, used recently acquired geological data in combination with computer simulations to identify this seemingly paradoxical connection. They have published their results in the journal Nature Communications.
The researchers said that it was only in the past 7,00,000 years that phases shifted between distinct glacial and warm periods about every 1,00,000 years. Before then, they said, the Earth’s climate was governed by 40,000-year cycles with shorter and weaker glacial periods.
Glacial periods, or geological ice ages, are characterised by the development of large ice sheets in the Northern Hemisphere.
The change in the climate cycles occurred in the Middle Pleistocene Transition period, which began approximately 1.2 million years ago and ended about 670,000 years ago.
“The mechanisms responsible for this critical change in the global climate rhythm remain largely unknown. They cannot be attributed to variations in the orbital parameters governing the Earth’s climate,” explained Associate Professor Andre Bahr, Heidelberg University.
“But the recently identified ‘warm ice age’, which caused the accumulation of excess continental ice, did play a critical role,” said Bahr.
For their investigations, the researchers used new climate records from a drill core off Portugal and loess records from the Chinese Plateau, the data from which was then fed into computer simulations.
The models showed a long-term warming and wetting trend in both subtropical regions for the past 800,000 to 670,000 years.
Contemporaneous with this last ice age in the Middle Pleistocene Transition period, the sea surface temperatures in the North Atlantic and tropical North Pacific were warmer than in the preceding interglacial, the phase between the two ice ages, or glacial periods.
This led to higher moisture production and rainfall in Southwest Europe, the expansion of Mediterranean forests, and an enhanced summer monsoon in East Asia.
The moisture also reached the polar regions where it contributed to the expansion of the Northern Eurasian ice sheets.
“They persisted for some time and heralded in the phase of sustained and far-reaching ice-age glaciation that lasted until the late Pleistocene.
“Such expansion of the continental glaciers was necessary to trigger the shift from the 40,000-year cycles to the 100,000-year cycles we experience today, which was critical for the Earth’s later climate evolution,” said Bahr.
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