On Tuesday 23 May 2023, data collected by the Climate Change Institute at the University of Maine showed that the Earth’s surface temperature and that of the surface of the oceans reached an all-time high for that date of the year.
This worrying triple climate record, with air and ocean temperatures at their highest and the level of the ice surface at its lowest, is only the beginning.
Yet the ocean is essential for regulating the climate. It provides us with half the oxygen we breathe. In addition, it absorbs 93% of the heat due to the greenhouse effect, thereby limiting the rise in atmospheric temperature. However, global warming caused by the additional greenhouse effect (due to human activities) is disrupting its regulatory role. This leads to problems such as acidification, oxygen deficiency and rising sea levels. These consequences are extremely dangerous, both for humans and for marine ecosystems.
The ocean is gradually warming up and it’s only the beginning
The ocean will continue to warm. By 2100, its upper layer (up to 2,000 m deep) is expected to warm two to four times faster than the already high rate observed since the 1970s in a low-GHG emissions scenario, and 5 to 7 times faster in a high emissions scenario. Maritime heatwaves will become increasingly frequent, intense and long-lasting.
Annual variations in global ocean surface temperature from 1880 to 2022, as a function of temperature variation
At the heart of ocean warming: Identifying the sources of the phenomenon
The ocean has absorbed 90% of the excess heat from the Earth’s system caused by human activity during the industrial era. According to the IPCC, human influence is the main factor in the increase in ocean temperature observed since the 1970s.
Since the start of the industrial revolution a few centuries ago, mankind has consumed huge quantities of fossil fuels, deforested vast tracts of land and engaged in various other activities that have led to a significant injection of greenhouse gases into the Earth’s atmosphere.
This phenomenon has led to global warming.
The impact of global warming on coral reefs and marine ecosystems
Rising temperatures increase the risk of irreversible extinction of marine and coastal ecosystems.
According to the latest UNESCO estimates, more than half of all marine species could be in danger of extinction by 2100. At present, with a temperature rise of 1.1°C, around 60% of the world’s marine ecosystems have already been altered or dealt with unsustainably. If the temperature rises by 1.5°C, between 70% and 90% of coral reefs could be destroyed, and a rise of 2°C could lead to the disappearance of almost all reefs. This situation highlights the urgent need to act to preserve our marine ecosystems. Seagrass beds and mangroves are also under threat, even though they store carbon much better than terrestrial ecosystems.
Read: Blue carbon ecosytems: key instruments to fight climate change?
How can we tackle the climate crisis?
It is crucial that we act now to preserve the ocean and counter global warming: the ocean is a prime ally in limiting the impact of atmospheric warming.
So we need to start mitigating the effects of climate change now, by drastically reducing our greenhouse gas emissions. For example, by adopting a sober approach to everything we consume (goods, plastics, energy, etc.), and by favouring the transition to renewable energies, we can further slow the devastating effects of global warming on the ocean.
Read: the energy transition: an integral answer to the climate emergency
In addition, the creation of vast protected areas and the preservation and restoration of fragile coastal habitats are essential to safeguarding marine biodiversity, making it more resilient and enabling it to adapt to temperature changes. Limiting destructive activities such as offshore drilling to preserve biodiversity is also a solution.
All this requires solid international cooperation and concrete agreements for truly effective measures.
