The Intergovernmental Panel on Climate Change (IPCC) has just published its special report on oceans and the cryosphere on 25 September. One hundred and four scientists from thirty-six countries have referenced and deciphered seventy thousand publications; their 900-page report provides an implacable diagnosis of the state of the oceans and ice-covered areas. Climate change caused by greenhouse gas emissions has profoundly altered the oceans; and it is not over yet. Projections are alarming and reveal major consequences not only on human activities but on the survival of hundreds of millions of people exposed.
Readers of UP' Magazine sometimes reproach us for being too alarmist about the climate. But the information that scientists who study the state of our planet are constantly producing is not overly optimistic. Far from it. The latest report of the IPCC is, as such, particularly salty... and icy.
The ocean is out of control
The experts mandated by the United Nations have focused on what represents 71 % of the surface of our planet and forms 90 % of the living environment: the oceans. Whether Atlantic, Arctic or Pacific... from the surface to the abyss, offshore or near the coast, the ocean is out of control. Yet it produces almost half of our oxygen and redistributes huge masses of energy in the form of heat in its currents. It captures up to a third of the carbon dioxide produced by human activities. This ocean is sick. It has a fever, it is overheating and it is suffocating from lack of oxygen. When it is not polluted, it is flooded with these chemical compounds that are dumped along the coasts, producing huge "dead zones", marine deserts where life disappears.
When the ocean goes bad, the whole planet, including humans, is impacted. The ocean has seen its rate of warming double in the last twenty-five years. Scientists clearly detected the first signs of warming in the 1970s. But the pace accelerated from 1993 onwards. The oceans are warming at an average rate of 0.11°C per decade. It may not seem like a huge figure, but it reflects a change in the very nature of the oceans. What's more, measurements show that warming is most noticeable in the deep layers between 700 and 2000 metres. At these depths, the rate of warming has tripled. Not all oceans are affected in the same way. The Arctic is warming twice as much as the global average.
The IPCC report even speaks of "ocean heat waves", those heat waves that have doubled in number since the early 1980s. These heat waves are burning entire ecosystems of algae forests, which provide shelter and food for a large number of marine species. The increase in water temperature causes changes in salinity and consequently the circulation of water in ocean currents, on the one hand, but also between the surface and the depths.
This circulation is the driving force behind the feeding of many species. Nutrients on the sea floor no longer rise to the surface, causing a significant proportion of the marine biomass to disappear. As a direct consequence for humans, fishing is declining and will continue to decline. Yet it is the main, if not exclusive, source of food for hundreds of millions of people on all the world's coasts.
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The impact of climate change on the oceans can also be measured by rising water levels. This is the factor that generates the most imagination and has fuelled many successful films. But today it's not cinema.
The most obvious cause of sea level rise is the warming of ocean water, which causes the oceans to expand. When the water in the pot boils, it sometimes rises and overflows. The other major contributor to the phenomenon is the melting of ice all over the planet. Not a day goes by without announcing the break-up of entire sections of ice pack, the disappearance of a mountain glacier or the accelerated melting of permafrost, the ground that has been frozen since the dawn of time. The IPCC report states that the accelerated melting in recent years of the world's two ice caps, Antarctica and Greenland, alone has released 430 billion tonnes of fresh water into the oceans. Extreme, rapid and violent events that combine to contribute to sea level rise.
Sea levels are rising and are beginning to put at risk 680 million people living in areas where the altitude above sea level is no more than ten metres. The IPCC has revised all forecasts upwards in this respect. By the end of the century, the rise in sea level is expected to be between 0.59 m and 1.10 m . It all depends on the quantities of greenhouse gases we release into the atmosphere and the global rise in temperatures. If we manage to contain warming to 1.5°C, we would be at the lower end of the range. But the ocean system is highly inertial and sea level rise has already begun. There seems to be no turning back.
Sea level rise should not be considered in terms of centimetres alone. Indeed, a rise of fifty centimetres seems insignificant for ordinary people; are not some French coastal regions used to tides of more than six metres? What must be understood is that all the factors are intertwined. Ocean warming will produce more water vapour and the formation of extreme weather phenomena: cyclones, submersive waves, storms and floods. According to IPCC projections, these phenomena are expected to multiply and intensify. Exceptional events that until now have occurred only once every century could occur every year. These phenomena, combined with rising sea levels, will be devastating. Storms such as Katrina, for example, would have multiplying effects, with floods sinking considerably higher and farther inland.
Megacities as small villages
Megacities as well as small villages, if they are near the sea, will be affected by these phenomena. The IPCC now counts 680 million people potentially exposed. They will exceed one billion in 2050. IPCC experts also note that variations in the intensity of sea level rise could reach more than 30 % depending on the region. Urbanized islands and atolls are the most threatened, but giant cities, because of their population density, such as Shanghai or New York, are in the front line. The deltas and mouths of large rivers such as the Ganges, with their immense agricultural areas, are in serious danger and the construction of dykes and works to force the waters to rise seem necessary solutions in certain well circumscribed cases but inaccessible on a larger scale. On the world's coasts, building defences could reduce the risk of flooding by 100 to 1 000 times, the report says. But on one condition: invest "tens to hundreds of billions of dollars a year". This is not easy everywhere.
The IPCC advocates the restoration of natural environments such as mangroves or coral reefs, but the most radical and certainly the most effective solution to save the most human lives would be to leave. To retreat in front of the rising sea and settle elsewhere, higher up. But we still need to be able to do so and to have the land to receive these new climate migrants that the IPCC scientists are telling us about.
Do not despair
Despite this alarming information, we should not despair. That is what the authors of the report are trying to tell us, obviously without really believing in it. Many phenomena are irreversible. Climate change is on its way and there is no turning back. The oceans have absorbed 90% of the additional heat generated by man-made CO2. The consequences are already clearly identifiable and measurable. But the IPCC predicts that the oceans will still be sucking in 2 to 4 times as much heat by 2100 in an optimistic scenario. « Because of this stored heat, we can no longer go back, whatever we do with our emissions, climate change is irreversible. "Climate scientist Valérie Masson-Delmotte, who participated in the drafting of the IPCC document, told the AFP.
On the other hand, we can try to avoid making things worse by reducing our greenhouse gas emissions in order to slow down the warming of the oceans and save us some time. « The changes in the ocean will not stop suddenly by lowering emissions, but their pace should slow down. That would save time... " promises Valérie Masson-Delmotte. Gaining time to prepare for rising waters and the extreme weather events associated with them (submergence waves, storms): by building dykes around large coastal megacities or by anticipating the inevitable displacement of certain populations currently living on territories that could become uninhabitable by the end of the century.
"Save time," as a plea in the face of urgency.
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This article is published as part of Covering Climate Now, a global collaboration of 300 selected media outlets to strengthen coverage of climate issues.