The disaster will not be for thirty or fifty years from now. It won't be in a century. No, it's for 2030, which is tomorrow.
A shocking study has just been published in Nature, conducted by Australian researchers who have been analysing for several years a geological period of intense upheaval, the Pliocene. During this period, the Earth experienced almost exactly the same climatic configuration as we have today. Same level of CO2 in the atmosphere, rise in temperatures of the same magnitude. The result at the time was the melting of a third of Antarctica, which caused the sea level to rise by 25 metres. The same situation could happen again in 2030. A general repetition of a catastrophe that awaits us if we do not take the right measures to tackle the climate crisis.
If the oceans rose 25 metres, the Netherlands would be finished, Normandy would lose its Cotentin, no more islands in Brittany, Nantes and Bordeaux under the sea, the Camargue scratched off the map, the Promenade des Anglais and Vieux-Nice drowned, not to mention the Nile Delta, Bangladesh, New York and the East Coast of the United States, the list goes on and on. 1 billion people would be affected and forced to leave their homes. As many as migrants climate scenarios already predicted by the United Nations scenarios.
This grim prospect could become a reality if we continue to release greenhouse gases into the atmosphere and abandon any desire to reduce global warming below 1.5°C. This limit, set by the Paris Agreement, already seems obsolete, with IPCC experts predicting, depending on the current state of affairs, a temperature increase of around 4°C.
Scientists and the media are constantly alerting us to the risks we are running, but a new study published on October 3 in the journal Nature sheds new light on the urgency of our need to act. An Australian team from Victoria University in Wellington has been working for several years on the Pliocene, a period that took place about three million years ago. This era is particularly interesting because its climatic configuration is not very far from the one we are experiencing today. It can therefore be used as a predictive model. During this period, the concentration of CO2 in the atmosphere reached levels comparable to those we are experiencing today: more than 400 parts per million.
Three million years ago, a period of intense temperature warming began. They reached levels equivalent to an increase of 2°C compared to pre-industrial times. Let us recall that we are currently at almost 1.5°C. According to the IPCC's forecasts, we should reach, or even exceed the 2°C provided for in the Paris Agreement as early as 2030 if we do not drastically reduce our greenhouse gas emissions today.
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What happened in the Pliocene?
Rising temperatures have melted the ice, particularly in Antarctica, which has lost a third of its ice surface. This melted ice poured into the oceans, causing them to rise 25 metres.
Australian researchers explain have drilled cores of sediments deposited during the Pliocene and preserved beneath the rugged hills of the Whanganui Basin in New Zealand. One of the researchers, Professor Timothy Naish, who has been working in this field for nearly 30 years, has identified more than 50 fluctuations in global sea level over the 3.5 million years of Earth's history. Sea levels have risen and fallen in response to natural climate cycles, known as the Milankovitch cycles, which are caused by long-term changes in the Earth's solar orbit every 20,000, 40,000 and 100,000 years. These changes in turn cause the polar ice caps to grow or melt.
While it was thought that sea level had fluctuated by several tens of metres, efforts to reconstruct the exact amplitude had so far been thwarted by difficulties due to the Earth's deformation processes and the incompleteness of many cycles.
Researchers therefore used a well-established theoretical relationship between the size of particles carried by waves on the continental shelf and the depth of the sea floor. They then applied this method to 800 metres of drill cores and outcrops, representing continuous sedimentary sequences covering a period ranging from 2.5 to 3.3 million years.
They showed that during the Pliocene, the global sea level fluctuated regularly between 5 and 25 metres. By taking into account local tectonic land movements and regional sea-level changes caused by gravitational and crustal changes to determine sea-level estimates, they obtained an approximation of the global mean sea-level change.
Twenty-five meters is a lot...
Australian researchers have concluded that most of the sea-level rise during the Pliocene came from the Antarctic ice caps. During the warm Pliocene, the geography of the Earth's continents and oceans and the size of the polar ice sheets were similar to those of today, with only a small ice sheet over Greenland during the warmest period. The melting of the Greenland ice sheet would have contributed up to five metres to the maximum 25-metre rise in global sea level recorded in the Whanganui Basin.
Twenty-five metres is much more than climate experts predict. According to the recent report The Intergovernmental Panel on Climate Change (IPCC) Ad Hoc Panel on Oceans and Cryosphere, glaciers and polar ice caps continue to lose mass at an accelerated rate. Until now, the increase has been expected to be in the range of 0.60 to 1.1 metres by 2100. But the new study is formal: we will be in Pliocene conditions as early as 2030, in eleven years' time!
" At the current rate of global emissions, we could be back in the Pliocene by 2030 and we will have exceeded the 2°C target set in Paris. One of the most critical questions facing humanity is how much and how fast sea levels will rise. "
Georgia Rose Grant, Researcher, Victoria University of Wellington
Researchers are therefore pushing the logic of the results of their experiments to the limit: it is quite possible that Antarctica will melt and lose a third of its surface area, which would potentially cause, according to their hypotheses, a rise in the level of the world's seas of around 20-25 metres.
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It is true that not a day goes by without information coming to us from the Antarctic or the Arctic on the fracture of this or that glacier or the melting of millions of cubic metres of ice. A study published last January 30 warned of the fate of the Thwaites glacier in West Antarctica; a 100 km wide, 600 km long, 3 km thick glacier, the size of a quarter of the size of France, which is melting and disintegrating at an accelerated rate under the distraught eyes of scientists.
This gigantic mass of ice, which rested on a rocky mantle, flows or breaks directly into the sea, mechanically raising its level.
Tipping point about to be crossed
For Australian researchers, " The fact that more than 90 % of the heat from global warming has been dumped into the ocean so far is of great concern. Much of the water has flowed into the Southern Ocean, which bathes the margins of the Antarctic ice sheet.. "They... continue : " Already today, we are seeing warm circumpolar deep water upwellings entering the ice shelf cavities in several locations around Antarctica. Along the Amundsen Sea coast of West Antarctica, where the ocean has warmed the most, the ice sheet (polar ice resting on a rocky mantle - Ed.) tapers and pulls out the fastest"
One third of the Antarctic ice sheet - the equivalent of 20 metres of sea level rise - is anchored below sea level and vulnerable to widespread collapse due to warming oceans. The process is not the same in the Arctic where the melting of sea ice, not resting on rocky ground, has a lesser impact on sea level rise. This is why Australian scientists estimate that out of the 25 metres of predicted rise in sea level, most of it, 20 metres, is due to the Antarctic.
" Our study supports the idea that a tipping point in the Antarctic ice sheet could be crossed if global temperatures are allowed to rise by more than 2℃. "
Such a scenario could lead to the melting of a large portion of the ice cap, which would reshape shorelines around the world. Indeed, if such a scenario were to occur, it would dramatically change our geography and lead to disasters that are difficult to conceive of.
All the more so as the effects of climate change being cumulativeThe rise of the oceans would aggravate the impact of storms and other extreme events that climatologists predict as a result of rising temperatures, particularly those of the ocean. A higher sea would cause damage farther inland if submerged by submerged waves. The impact of a cyclone like Katrina would be multiplied.
This study by Nature develops a hypothesis in the form of an alert. An alert that is added to others and should prompt us to act without delay. It is still possible to stabilize the climate mechanism by reducing our greenhouse gas emissions. This implies courageous political choices and complete changes in our models of society. The state of the world in recent years does not give us much cause for optimism, but on the other hand, pressure from the people could have an effect on leaders if they are still unable to make the right decisions.
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