A new study from researchers at The Australian National University (ANU) on
how the world’s largest ice sheet developed also provides vital clues about
climate change tipping points.
Forty million years ago, Antarctica grew massive ice sheets for the first
time. The ANU study shows how these ice sheets stayed low, wet, and
relatively warm for millions of years.
The current Antarctic ice sheet is the largest block of ice on Earth,
covering more than 14 million square kilometers. If it melted, sea levels
would rise by about 60 meters.
But it hasn’t always been that way.
The spectacular ice sheet we’re familiar with today didn’t develop until
around 12 million years ago, according to study co-author Dr. Bradley
Opdyke.
“This had a huge impact on the stability of global sea levels,” Dr. Opdyke
said. “Sea-level is a key indicator of global climate changes, so having
more complete sea-level records will give us clues about climate tipping
points, and what we might expect in the future.”
Once the ice sheets become so high, dry, and dynamic, determining past sea
level and temperature changes becomes less certain.
Scientists study the ratio of isotopes of oxygen in different materials from
the deep sea to look for clues.
“This study could help us tease out some of the causes of the dramatic
changes we saw in the middle Miocene period — around 12 million years ago,”
Dr. Opdyke.
“Around this time in the Miocene we also started seeing pulses to lower CO2
levels that had interesting evolutionary consequences, like the appearance
of grasses that are better adapted to a lower CO2 world.”
“The middle Pliocene period — about three million years ago — is important
as well, because it’s the last time CO2 levels were similar to those of
today.”
Reference:
Sea level and deep-sea temperature reconstructions suggest quasi-stable
states and critical transitions over the past 40 million years
by Eelco J. Rohling, Jimin Yu, David Heslop, Gavin L. Foster, Bradley Opdyke
and Andrew P. Roberts, 25 June 2021, Science Advances.
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Planet and Environment