The elevation of the level of the oceans is no longer a suspense subject; Year after year, the statements confirm the inexorable progression of water on land, driven by the melting of ice and global warming. NASA, which monitors the phenomenon closely thanks to several satellites, has just reported a figure that has enough to challenge us. In 2024, the sea rose 0.59 cm, while projections tabled on 0.43 cm, ie a difference of more than 37 % !
How to explain such a difference? Because if in your pool or bathtub, such a difference is not even seen, on a planetary scale, it is considerable. The most confusing, these are the reasons that caused this leap, since they are not to be found on the side of a potential acceleration of the melting of polar caps. What’s going on, is that our oceans expand ; Explanations.
Thermal dilation: the new engine of the rose of waters
Water rises due to two main factors. The most important, the melting of glaciers, and the other, the expansion of water under the effect of heat. For decades, this expansion weighed heavier in the scale than the melting. Nevertheless, in 2024, the opposite happened: thermal expansion has become the main cause of the rise of waters.
What exactly do we mean by Thermal expansion in this context? It is a fairly simple physical phenomenon to understand: when water warms up, its molecules are growing more, which increases its volume. As the oceans absorb more than 90 % of the excess heat accumulated on the planet, this dilation is now more importantly.
Usually, this heat remained concentrated in the superficial layers of the waters, more easily ventilated by the winds. In 2024, the intensity of cyclones and the recurrence of storms stirred the water column to unusual depths, diffusing the heat down, which caused a more generalized expansion. It is not because there is more water on the planet that the levels of the ocean rose faster, it is that This is warmer and therefore takes up more space.
As this heat diffuses more vertically than before, it modifies the thermal structure of the oceans and complicates the task of scientists. Forecast models were based on a relatively stable distribution of temperatures; However, this brewing turns everything upside down; The evolution of the level of the oceans is therefore much more difficult to anticipate.
When the ocean overflows, it distinguishes everything
As salt water is larger and warmer, it tends to infiltrate more in large estuaries : Ganges (India), Mississippi (United States), Yangtsé (China) or Mekong (Southeast Asia). Very sensitive areas, which see their irrigation threatened as well as their availability of fresh water.
This more accentuated heat also promotes Waves of extreme temperatures at seathat one could almost call “ocean heat waves”. They wreak havoc by killing plankton, the basis of the entire oceanic food chain, and end up disturbing the local economy of certain countries, centered exclusively around fishing.
These upheavals also threaten to disrupt major currents, such as Amoc, this vast system which redistributes the heat between the tropics and the North Atlantic. If this ocean engine was weakening, it could deregulate our seasons, make certain ribs more vulnerable to storms and aggravate the rise of waters. A real vicious circle of which it is today extremely difficult to get out.
Behind these few millimeters more are played out the lives of millions of peoplethe good health of our ecosystems and the robustness of our resilience capacities in the face of A phenomenon impossible to brake. Thermal dilation is no longer A secondary actress of climate changeand NASA climate models will now have to integrate it as a priority variable to monitor.
- In 2024, the ocean climb was much faster than expected, according to NASA measurements.
- The heat accumulated in the ocean, brewed in depth by more frequent storms, caused an unprecedented expansion of its volume.
- This thermal dilation accentuates saline intrusions, threatens marine biodiversity and complicates the forecast of future floods.
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