New research on ancient Antarctic ice reveals Earth's climate cooled significantly over the past three million years, while atmospheric greenhouse gas levels changed only modestly. Scientists analyzed tiny air pockets and rare gases trapped in ice from Allan Hills, Antarctica. This site provides climate snapshots, extending the ice core record further back in time than previously possible.
Two studies published in *Nature* indicate that global ocean temperatures dropped by approximately two to two and a half degrees Celsius over this period. This cooling occurred despite relatively stable levels of carbon dioxide and methane. Carbon dioxide levels generally remained below 300 parts per million, decreasing by about 20 parts per million between 2.7 million and one million years ago. Methane levels stayed around 500 parts per billion.
These findings challenge the assumption that greenhouse gas fluctuations were the sole drivers of long-term climate change during this era. Other factors likely played significant roles. These include changes in Earth's reflectivity, shifts in vegetation and ice coverage, and variations in ocean circulation patterns.
The research was conducted by the National Science Foundation (NSF) Center for Oldest Ice Exploration (COLDEX). Julia Marks-Peterson, a doctoral student at Oregon State University, and Sarah Shackleton, a former postdoctoral researcher at Princeton University, led the studies. Their work provides direct measurements of past atmospheric conditions.
Scientists continue to seek even older ice to expand the climate record further. They have identified ice potentially six million years old and are developing new drilling techniques. This ongoing research aims to refine understanding of past warm climates and the interactions within Earth's climate system.
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