Oceans – Red alert

Crédit photo : © Getty Images

Covering 70% of the globe, the ocean is the pigment that gives our Blue Planet its name. Yet it is suffering from out-of-control global warming. At the poles, the icy mantle of the cryosphere — which makes up 10% of our planet — is melting and cracking apart. Published on 25 September 2019, the latest IPCC report reviews these two components of our climate system, intimately linked by the water cycle among other factors. With contributions from a hundred or so international authors and compiling over 7,000 scientific papers, the report’s findings are very troubling: the cryosphere and oceans are in great danger, whereas they are vital to life on Earth.

We shall give only a few key figures here — almost all being in the red — that reflect the importance of the ocean, which alone provides 50% of the oxygen we breathe, has been absorbing on average one quarter of total carbon dioxide emissions since the 1980s and currently stores over 90% of the excess heat produced by these emissions. In all, 670 million people living in mountainous regions and 680 million living in low-lying coastal zones are totally dependent on these systems. Four million people live in the Arctic and 65 million in small island developing states (SIDS).
According to the IPCC, “All people on Earth depend directly or indirectly on the ocean and cryosphere”. Both are heading towards a slow death, which will also mean ours unless we act now.
Let us recall at this point how valuable our satellite allies are. The IPCC has in fact used many data from spaceborne altimeters and called upon the expertise of CNES and the French geophysics and oceanography research laboratory, LEGOS.

All the Earth’s ice is melting, whether at the poles or making up glaciers. While this generalised meltdown is accelerating the rise in sea level, the retreat of glaciers is also modifying river flow and affecting not only water resources but also natural hazards such as avalanches and flooding.
Even the permafrost is melting, freeing huge quantities of greenhouse gases into the atmosphere that are adding to global warming.
Water is heating up and marine life is suffocating. The ocean will continue to warm up and experience heat waves that, like on land, will become more frequent and more intense, disrupting both ecosystems (and particularly precious coral reefs) and marine currents. As a consequence, the planet will experience more extreme climate events. Furthermore, while the ocean absorbs one quarter of carbon dioxide emissions, once dissolved, this CO2 is transformed into carbonic acid that affects fish reproduction among others. The combination of heat, acidity and oxygen deficiency — leaving aside fishing — means that the ocean’s desertification is a sad but ongoing reality.
Sea level is rising: swollen by melting ice and the water’s dilatation due to heat, the ocean is eating away land and weakening our coastlines. Devastated by violent events or slowly submerged by salt water, which affects soil and freshwater resources, some coastal areas may become uninhabitable.
Extreme climate events are becoming stronger and more regular. Huge hurricanes feed off warm water. Supported by a higher ocean, this type of event leads to greater devastation when it hits land, not stopping at the coast but advancing further inland. A warmer ocean also means heavy rain, though the slowing down of major marine currents tends to lead to a decrease in rainfall in areas such as the Sahel.
There is an urgent need to limit greenhouse gas emissions. Although the report highlights, as usual, ways of addressing this issue, scientists are calling for urgent decisions. According to Jean-Pierre Gattuso, research director at the CNRS Oceanography Laboratory and co-author of the report, “with ambitious action, the worst can easily be avoided”.

For more information:
Space serving climate, IPCC report exploits extensive record of satellite oceanography data – CNES, 26 September 2019

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