Sea levels have risen 10 meters above present levels during the last warm period of Earth 125,000 years ago, according to new research that offers a look at what might happen under our current climate change trajectory.
Our book published today in Nature Communications shows that melting ice from Antarctica has been the main driver of sea level rise in the last inter-glacial period, which lasted about 10,000 years.
Sea level rise is one of the greatest challenges facing humanity caused by climate change, and sound forecasts are crucial if we are to adapt.
This study shows that Antarctica, thought to be the "sleeping giant" of sea-level rise, is actually a key player. Its ice sheets can change rapidly in ways that could have huge impacts on coastal communities and infrastructure in the future. Past Warning
Earth cycles consist of cold ice periods ̵
] Earth is currently in the interglacial period, which began about 10,000 years ago. But greenhouse gas emissions over the last 200 years have caused climate change, which is faster and more extreme than that experienced in the last inter-chapter.
This means that past rates of sea level rise provide only low estimates of what may happen in the future.
We have looked at data from the last intercollegiate occurrence 125,000 to 118,000 years ago. Temperatures were up to 1 ℃ higher than today – similar to those forecast for the near future.
Our study reveals that the melting of ice during the last interglacial period has led to the rise of global seas by about 10 meters above the present level. The ice melted first in Antarctica, then several thousand years later in Greenland.
Sea levels have risen to 3 meters a century, far exceeding the approximately 0.3-meter rise observed over the past 150 years.
The loss of ice in Antarctica occurred when the Southern Ocean warmed early in the interglacial period. This melted water changed the way the oceans of the Earth circulate, causing warming in the northern polar region and triggering the ice melt in Greenland.
Understanding the data
Currently, the average global maritime level is increasing at more than 3 millimeters per year, this rate is projected to increase and the overall sea level rise to 2100 (compared to 2000) is expected to reach 70- 100 centimeters, depending on which path of greenhouse gas emissions we follow.
Such forecasts generally rely on data collected during this century from tide instruments and from the 1990s on satellite data.
Most of these projections do not represent a fundamental natural process – the instability of an ice rock that is not observed in the short instrumental record. That is why geological observations are vital.
When the ice reaches the ocean, it becomes a floating ice shelf that ends in an ice rock. When these rocks become very large, they become unstable and can quickly collapse.
This collapse increases the release of land ice into the ocean. The end result is a rise in sea level worldwide. Several models have tried to include instability on ice rocks, but the results are controversial.
The results of these models, however, predict rates of sea level rise that are intriguingly similar to our recently observed starvation data.  Our work examines records of a general change in sea level, which by definition includes all relevant natural processes.
We have studied the chemical changes in plankton fossil shells in marine sediments from the Red Sea that are reliably associated with changes in sea level. Together with evidence of the meltwater input around Antarctica and Greenland, this record reveals how quickly sea levels rise and differentiates between different ice sheet contributions.
Looking to the future
What is striking about the recent inter-ice record is how high and fast the sea level has risen above current levels. Temperatures over the last inter-ice period were similar to those predicted for the near future, which means that the melting of polar ice sheets is likely to affect future sea levels far more dramatically than previously expected.
The Last Interlinear is not a perfect scenario for the future. The incoming solar radiation was higher than today's due to differences in the position of the Earth relative to the sun.
Carbon dioxide levels were only 280 parts per million, compared to over 410 parts per million today.
Most importantly, the warming between the two poles in the last interglacial did not occur simultaneously. But with today's climate change driven by greenhouse gases, warming and ice loss occur in both regions at the same time.
This means that if climate change continues to change, the past dramatic rise in Earth's sea level could be a small taste of this coming.
Fiona Hibbert, PhD, Australian National University; Eelco Rohling, Professor of Oceanic and Climate Change, Australian National University, and Katharine Grant, ARC DECRA PhD, Australian National University.
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