Paris Soir - Study reveals how Earth's orbit controls ice ages

That's according to a new study published Thursday in Science, which analyzed how subtle shifts in Earth's orbit around the Sun have historically triggered massive climate changes.

A research team examined a million-year record of climate change, focusing on land-based ice sheets across the Northern Hemisphere and deep ocean temperatures.

They then paired this data with small but cyclical variations in Earth's orbital patterns.

"For many years, the difficulty in answering how small changes in Earth's orbit around the Sun translate to large shifts between glacial and interglacial states has been a central theme in paleoclimate research," lead author Stephen Barker, a professor at Cardiff University, told AFP.

Earth has long alternated between ice ages and warmer interglacial periods, with the last glaciation ending approximately 11,700 years ago. This transition marked the beginning of the Holocene epoch, an era of relative climate stability that enabled early human societies to shift from nomadic hunting and gathering to settled agriculture.

Scientists have long recognized a connection between Earth's orbit and ice ages. However, due to challenges in accurately dating climate changes that occurred so far in the past, they struggled to pinpoint which orbital parameters were responsible for starting and ending these glacial cycles.

According to Barker, the key breakthrough came from analyzing the "shape" of the ancient climate record -- the curves showing how temperatures rose and fell over time -- rather than just the timing of ice age transitions.

This approach allowed the team to determine how the three orbital factors -- tilt, wobble, and the shape of Earth's orbit around the Sun -- interact to drive ice age cycles over the past 900,000 years.

Barker said that without the Industrial Revolution, assuming fossil fuels had never been burned, "we would expect a glaciation to occur within the next 11,000 years, and it would end in 66,000 years' time."

Co-author Lorraine Lisiecki, a professor at the University of California, Santa Barbara, emphasized the significance of the study, stating that it "confirms the natural climate change cycles we observe on Earth over tens of thousands of years are largely predictable and not random or chaotic."

However, Barker strongly cautioned against interpreting the findings to suggest that human-caused climate change is beneficial.

Carbon dioxide levels have nearly doubled since the Industrial Revolution, and if emissions remain unchecked, "then in around 8,000 years' time, Antarctica would have melted, leading to around 70 meters of sea-level rise," said Barker.

"Instead of there being glaciers, you'll be underwater," he warned.

Looking ahead, the research team aims to expand on their findings by investigating the long-term impact of human-driven climate change and how it may reshape the planet's natural climate cycles.

I.Moreau--PS