Climate warnings from the distant past

  Last updated November 29, 2019 at 9:06 am

Topics:  

By studying sea levels from the last inter-glacial period, scientists have revealed what may happen on our current temperature trajectory.


sea level_melting ice_climate change

A polar bear wandering on melting pack ice in Canada, north of the Arctic Circle, during the summer 2017. Scientists say the last interglacial offers lessons for future sea level rise. Credit: Florian Ledoux/The Nature Conservancy




Why This Matters: Clock’s ticking.




Sea levels rose 10 metres above present levels during Earth’s last warm period 125,000 years ago, according to new research that offers a glimpse of what may happen under our current climate change trajectory.


Our paper, published in Nature Communications, shows that melting ice from Antarctica was the main driver of sea level rise in the last interglacial period, which lasted about 10,000 years.


Rising sea levels are one of the biggest challenges to humanity posed by climate change, and sound predictions are crucial if we are to adapt.


This research shows that Antarctica, long thought to be the “sleeping giant” of sea level rise, is actually a key player. Its ice sheets can change quickly, and in ways that could have huge implications for coastal communities and infrastructure in future.


A warning from the past


Earth’s cycles consist of both cold glacial periods – or ice ages – when large parts of the world are covered in large ice sheets, and warmer interglacial periods when the ice thaws and sea levels rise.


The Earth is presently in an interglacial period which began about 10,000 years ago. But greenhouse gas emissions over the past 200 years have caused climate changes that are faster and more extreme than experienced during the last interglacial. This means past rates of sea level rise provide only low-end predictions of what might happen in future.




Deeper: Sea level rise is accelerating




We examined data from the last interglacial, which occurred 125,000 to 118,000 years ago. Temperatures were up to 1℃ higher than today – similar to those projected for the near future.


Our research reveals that ice melt in the last interglacial period caused global seas to rise about 10 metres above the present level. The ice melted first in Antarctica, then a few thousand years later in Greenland.


Sea levels rose at up to 3 metres per century, far exceeding the roughly 0.3-metre rise observed over the past 150 years.


The early ice loss in Antarctica occurred when the Southern Ocean warmed at the start of the interglacial. This meltwater changed the way Earth’s oceans circulated, which caused warming in the northern polar region and triggered ice melt in Greenland.


sea level_melting ice_climate change

Dogs hauling a sled through meltwater on coastal sea ice during an expedition in northwest Greenland, June 2019. Credit: STEFFEN M. OLSEN/DANISH METEOROLOGICAL INSTITUTE


Understanding the data


Global average sea level is currently estimated to be rising at more than 3 millimetres a year. This rate is projected to increase and total sea-level rise by 2100 (relative to 2000) is projected to reach 70-100 centimetres, depending on which greenhouse gas emissions pathway we follow.


Such projections usually rely on records gathered this century from tide gauges, and since the 1990s from satellite data.




Deeper: New satellites show worrying view of droughts and ice loss




Most of these projections do not account for a key natural process – ice-cliff instability – which is not observed in the short instrumental record. This is why geological observations are vital.


When ice reaches the ocean, it becomes a floating ice-shelf which ends in an ice-cliff. When these cliffs get very large, they become unstable and can rapidly collapse.


sea level_melting ice_climate change

Antactica was long thought to be the sleeping giant of sea level rise, but is now considered a key driver. Credit: Australian Antarctic Division


This collapse increases the discharge of land ice into the ocean. The end result is global sea-level rise. A few models have attempted to include ice-cliff instability, but the results are contentious. Outputs from these models do, however, predict rates of sea-level rise that are intriguingly similar to our newly observed last interglacial data.


Our work examines records of total sea-level change, which by definition includes all relevant natural processes.


We examined chemical changes in fossil plankton shells in marine sediments from the Red Sea, which reliably relate to changes in sea level. Together with evidence of meltwater input around Antarctica and Greenland, this record reveals how rapidly sea level rose, and distinguishes between different ice sheet contributions.


Looking to future sea level rise


What is striking about the last interglacial record is how high and quickly sea level rose above present levels. Temperatures during the last interglacial were similar to those projected for the near future, which means melting polar ice sheets will likely affect future sea levels far more dramatically than anticipated to date.


The last interglacial is not a perfect scenario for the future. Incoming solar radiation was higher than today because of differences in Earth’s position relative to the Sun. Carbon dioxide levels were only 280 parts per million, compared with more than 410 parts per million today.


Crucially, warming between the two poles in the last interglacial did not happen simultaneously. But under today’s greenhouse-gas-driven climate change, warming and ice loss are happening in both regions at the same time. This means that if climate change continues unabated, Earth’s past dramatic sea level rise could be a small taste of what’s to come.


This article was co-authored by Eelco Rohling and Katharine Grant from the Australian National University. 


This article was republished from The Conversation under a Creative Commons license. Read the original article here


More Like This


Aussie coasts are at risk if we don’t limit climate change


Persecute, protect or ignore? Dilemma as species move due to climate change




About the Author

Fiona Hibbert
Fiona Hibbert is a Post-doctoral Research Fellow at the Australian National University. Her current research focuses on the contribution of former ice-sheets to global sea-level budgets.

Published By

Featured Videos

Placeholder
Space technology predicts droughts several months in advance
Placeholder
ANU Science On Location: Booderee National Park
Placeholder
ANU Science On Location: Ningaloo Reef
Placeholder
A mix of science and sourdough
Placeholder
How does the crested pigeon make their mysterious alarm sound?
Placeholder
Why do magpies swoop?
Placeholder
Critically endangered swift parrot needs your help!
Placeholder
ANU Science On Location: Siding Spring Observatory
Placeholder
ANU Science On Location: Mountain Ash forests
Placeholder
ANU Science On Location: Warramunga Station
Placeholder
Secret life may thrive in warm caves under Antarctica’s glaciers
Placeholder
Scientists help solve mystery of what causes exploding stars
Placeholder
Case Closed: Mystery of How First Animals Appeared on Earth Has Been Solved
Placeholder
Palm cockatoos beat drum like Ringo Starr
Placeholder
Butterfly wings inspire new solar technologies
Placeholder
From window to mirror, on demand
Placeholder
The search for exploding stars
Placeholder
Coral bleaching on the Great Barrier Reef
Placeholder
Join The Search For Planet 9